Response of Structures Under Extreme Loading (PROTECT 2015)
Behaviour of Concrete under Biaxial Dynamic Loading
It is well known that both the compressive and tensile strength of concrete are rising with increasing strain rate. It is further known that a biaxial compression stress state also leads to a higher compressive strength. So the question arises: do these two effects superimpose in the case of a dynamic biaxial loading? This kind of load can arise in accidents like vehicle or airplane crash, rock fall or landslide on concrete structures. To investigate this topic, a biaxial Split-HOPKINSON-Bar (SHB) has been developed and constructed at the Technische Universität Dresden. With this new test setup cubic concrete specimens can be loaded with two compressive impulses perpendicular to each other with a time delay of less than 20 μs. First results have been achieved. These show that there is an interaction of the strength increasing effect because of the dynamic loading and that of biaxial state of stress. So the biaxial dynamic compressive strength of concrete is significant higher than the uniaxial dynamic strength and the biaxial static strength.
Behaviour of High-strength and Normal-strength Strain-hardening Cement-based Composites (SHCC) Subjected to Impact Loading
The article at hand presents the results of a series of high-speed dynamic experiments on two different types of strain-hardening cement-based composites (SHCC): a high-strength mixture and a normal-strength one. Spallation tests are performed using a Hopkinson bar at strain rates between 150 and 180 s-1. Additionally, high-speed pullout tests on single fibers are carried out. The results of these tests are compared to the results of corresponding quasi-static uniaxial tension tests and fiber pullout tests. Furthermore, the mechanical performance of the SHCC under different loading rates is related to the conditions of fracture surfaces and of the pulled out fibers as observed in the electron microscope. Finally, the findings on the high-strength SHCC are compared to the related features of the normal-strength SHCC.
Effect of Crumb Rubber on Pull Out Response of FRP Rebar in Fiber-reinforced Lightweight Concrete
Use of crumb rubber from scrap tire in the reinforced concrete along with Fibre Reinforced Polymer (FRP) bar is a novel way of recycling tire and providing durable and sustainable concrete structure. The performance of reinforced concrete structures depends on the proper transfer of forces between concrete and reinforcement. And this proper transfer of forces depends of the quality of bond between concrete and reinforcement bar. In this study, the bond characteristics of sand coated Glass Fibre Reinforced Polymer (GFRP) bar embedded in lightweight concrete with crumb rubber as partial or full replacement of sand has been evaluated. Quasi static bond pullout tests were performed on 60 cylindrical test specimens to determine the effects of crumb rubber percentage, FRP bar diameter and short steel fibre presence on bond performance. Two different bar sizes (10mm and 16 mm diameters) were used while keeping the constant embedment length of five times the bar diameter. The study showed that increase in crumb rubber content reduces the bond strength. Presence of short steel fibre disrupts the bond with FRP bar. The research also showed that bond strength is higher with 16 mm bar compare to 10mm bar due to prominent surface roughness
A Study on Shock Absorbing Properties of Rubber Pieces for Bridge Seismic Restrainers
Japanese specifications for highway bridges require installing unseating prevention seismic restrainer on bridges with high potential of large girder and substructures’ relative movement during an earthquake. Although the devices are required to resist impact and rubber pieces are commonly used as shock absorbers, no standard design and evaluation methods of shock-absorbing rubbers have been established. Thus, their designs depend on designers’ discretion. In general, rubber pieces with various sizes and hardness are installed in small spaces within the device, and their surfaces are constrained by surrounding steel members. However, the effect of surrounding confinement on their shock absorbing capacity is not clearly determined in the past. So in order to establish the dynamic design method of seismic restrainers with rubber pieces in the future, it is important that we comprehend the effects of various parameter such as dimensions, hardness, loading rate and confinement on shock absorbing properties of rubber pieces. Based on the above background, in our study, at first we conducted impact tests on square chloroprene rubber pieces with various dimensions, and impact velocities by using falling weight impact machine. Next, confined rubber pieces were also tested because their surfaces are usually confined by surrounding steel members of brackets. For confinement, their side faces are constrained such that rubber cannot deform in the directions normal to the constrained faces. A confining factor is defined as constrained area divided by total area of all four sides, and experimental cases included this factor of 0 to 1. Finally, based on many experimental results, correlations between shape and confining factor and reduction rate of impact load were clarified. In addition, the empirical equations were provided to determine dynamic stiffness using stress-strain relationship
Evaluation of Rheological Models within Lattice-based Simulations of Concrete under Dynamic Loading
Concrete is a highly rate dependent material. Its mechanical properties (e.g. strength, elasticity, ultimate strain) depend on the loading rate. For example, tensile strength increases with the loading rate. For intermediate loading rates the strength enhancement is related to the viscosity of free water within micro-/nano-pores in concrete, the so-called Stefan effect, whereas the strengthening effect at higher loading rates is dominated by micro-/meso-inertia of the material within the fracture process zone (FPZ). These rate dependent mechanisms should be included in the formulation for physically realistic modeling of concrete materials. In this study rheological material models are used to represent rate effects, where viscous components (e.g. dashpots) are connected to local spring elements within Rigid-Body-Spring Networks. Three types of constitutive relationships are considered: 1) visco-elastic, 2) visco-plastic, and 3) visco-elasto-plastic damage models. Direct tensile tests are simulated and characteristics of the three different rheological models are compared through their stress-strain responses
On the Mechanical Characterization of Materials for Protection of Infrastructure Elements from the Effects of IEDs and Blast Charges
The need to protect infrastructure elements from the effects of Improvised Explosive Devices requires a deep knowledge of the mechanical behaviour of the protective structure component materials under high strain rates and under different loading modes (tension, compression and shear). Several sandwich slab systems, based on a combination of reinforced concrete and Ultra High Performance Fibre Reinforced Concrete (UHPFRC) layers, were tested under blast, by a series of contact and near-contact charge tests, in order to analyse the improvement of the performance of existing structure by retrofitting. This paper presents the experimental techniques, used to study UHPC and UHPFRCs behaviour at high strain rate, and results in direct tension, compression and shear
Low, Medium and High Strain Rate Characteristics of Cenosphere Aluminum Syntactic Foam for Blast and Impact Applications
Syntactic foams are commonly used as a core of sandwich structures in the mitigation of blast and impact. With the advancement of foaming technology, new classes of aluminum syntactic foams are being developed and explored for their potential applications in blast and impact mitigation. In the present investigation, cenosphere filled aluminum syntactic foams developed using liquid metallurgy route are studied for their compression behavior under low (0.001 /s - 0.01 /s), medium (1 /s - 10 /s), and high strain rates (> 500 /s). Low and medium strain rate tests are conducted using servo-hydraulic machine whereas, split-Hopkinson pressure bar (SHPB) is used for high strain rate investigation. The foam exhibits peak stress at a strain of about 5%, and this stress is used to examine strain rate sensitivity and to determine sensitivity parameter at three different strain rate regimes considered in the present investigation. Based on this investigation, it is observed that there is considerable improvement in the compressive strength and energy absorption of foam at higher strain rates. Deformation phenomena are explained in terms of microstructural behavior under these strain rates.
Potential Use of Drilling Resistance Test as a Non-destructive Testing Tool in Failure Forensics
High Performance Concrete (HPC) is being extensively used in a wide and varied range of structural applications to meet specific needs. Stipulated performance levels of HPC are accomplished by carefully selecting high quality ingredients and adopting judicious mix design. Nevertheless, High Performance Concretes at elevated temperatures undergo changes in their physical structure and chemical composition that affect their strength characteristics adversely. Need for quick assessment of fire damaged concrete for strength characteristics, has motivated this work, which explores the potential of drilling resistance test on concrete as a Non Destructive Testing (NDT) tool. Drilling times, penetration depths and sound level measurement while drilling have been recorded and analysed to provide monograms that are handy as reckoners in failure forensics.
Characteristics of Recycled Asphalt Pavement Self-consolidating Concrete
Self-consolidating concrete (SCC) is used nowadays in many of concrete construction projects. It has superior characteristics such as a low yield, considerable viscosity, and does not segregate, which makes it very attractive to contractors. Also, SCC is used when there is no access to vibrators or when it is difficult to vibrate to consolidate the concrete in the event of having heaving and complex reinforcements. The SCC can consolidate itself under the effect of its self-weight without the need for mechanical compaction. The aggregates are used as fillers in the concrete mixture to provide the needed volume and it is also a cheap material, but it is not renewable material. Therefore, the use of waste materials such as Recycled Asphalt Pavement (RAP) to replace a percent of the conventional aggregates can result in a more costeffective and sustainable concrete. The objective of this study is to investigate the fresh and hardened properties of SCC that contains Recycled Asphalt Pavement (RAP). A conventional control PCC SCC mixture with targeted properties is developed and its properties is altered later to produce the remaining RAP concrete mixtures. The concrete mixtures will have similar properties to the control concrete mixtures, but the percent of coarse aggregates that will be replaced by RAP will vary between 10% – 40%. After the fresh and hardened properties of SCC are measured, a set of recommendations will be presented to assist engineers to determine the suitable percentage by which coarse aggregates can be replaced with RAP, and determine the applicability of the use of SCCRAP in different engineering applications
Self-consolidating Concrete Prepared with Recycled Concrete Aggregate and Recycled Asphalt Pavement
This paper investigates the fresh, mechanical, and durability characteristics of Self-Consolidating Concrete incorporating Recycled Concrete Aggregate and Recycled Asphalt pavement (SCC-RCA-RAP). Mixtures were divided into different groups, with constant water to cementitious materials ratio of 0.4, based on the recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP) content: 0, 25, 50, and 75% of coarse aggregate (CA) replaced by equal percentages of RCA and RAP. All mixtures were designed with a target slump flow higher than 500 mm. The control mixture for each group was prepared with 100% Portland cement while all other mixtures were designed with different percentages of Portland cement replaced by a combination of Supplementary Cementitious Materials (SCMs) such as class C fly ash, and granulated blast furnace slag. Fresh concrete properties such as: flow ability, deformability; filling capacity, and resistance to segregation were investigated. Moreover, hardened characteristics such as, the compressive strength at different ages, and the split tensile strength were studied. The use of Supplementary Cementitious materials instead of cement has resulted in smaller 28-days-compressive strength compared to those of the control mixes. The use of RCA and RAP as a replacement of CA had an adverse effect on the hardened properties of SCC mixtures
Numerical Predictions of Laboratory Tsunami Waves
The paper aims at development of a numerical approach to simulate tsunami waves that are produced with different techniques in laboratory experiments. The present study also examines the interaction of a tsunami wave with a rigid wall and estimates the dynamic pressures acting on the wall surface. It should be emphasized that this research aims at simulating the tsunami waves but there is no intention to examine the correspondence of the different lab waves that are produced by different experimental devices with a tsunami real wave. Comparison of the numerical prediction of a tsunami wave shapes with the experimental measurement of the wave shapes shows good correspondence. Four types of laboratory techniques to create laboratory tsunami waves were examined: a sudden release of a water column, horizontal or vertical motion of a piston and rotation of a rigid plate. Comparison of waves of the same height that are formed by these four methods shows that the horizontal piston motion device produces the shortest wave, and the vertical piston motion device produces the longest wave. The wave that is produced by plate rotation is similar to the wave produced by "water column release", but it is slightly longer. The peak pressure on the rigid wall produced by the horizontal piston, is of the lowest magnitude (among the waves of the same height, caused by these four techniques), while the pressure due to a rotational plate has the largest magnitude. It was found that different techniques produce different wave characteristics; therefore selection of the proper laboratory technique requires some consideration and comparison to the required real tsunami wave that should be simulated
High Strain Rate Response of Rocks under Dynamic Loading Using Split Hopkinson Pressure Bar
In the present work, dynamic stress-strain response of two rocks from different regions in India, e.g. Kota sandstone and Dholpur sandstone have been investigated through split Hopkinson pressure bar (SHPB) test at different strain rates for the first time in the literature. The dry and saturated density, specific gravity, static compressive strength and tensile strength values of the rocks have also been determined. Petrological study of the rocks has been carried out through scanning electron microscope test. It is observed from the stress-strain response of the rocks that the peak stress increases with increasing strain rate. Dynamic strength increase factors for these rocks have been determined by comparing the dynamic and the static peak compressive stress values. A correlation equation has been proposed herein for the dynamic strength increase factor of sandstone rocks
Material Characteristics of Glass Fibre Reinforced Polymer (GFRP) Bars at High Temperature
The lack of adequate information on glass fibre reinforced polymer (GFRP) material characteristics at high temperatures lowers the accuracy of analytical and design models developed to predict the behaviour of GFRP reinforced concrete members. This paper presents experimental results of a series of tensile tests on GFRP bars at elevated temperatures. These results are a part of ongoing comprehensive material tests on various GFRP products from different manufacturers. Up until now, material tests conducted on GFRP bars have been limited to bars of up to 12 mm in diameter. To represent real fire situations in typical FRP reinforced concrete structures, two novel features have been implemented in the experimental program: large and commonly used GFRP reinforcements (#5 with nominal diameter of 16 mm), and tensile tests under transient temperature. Temperature ranges from 25 to 400ËšC have been considered for steady state temperature tests. In transient condition tests, specimens are loaded before heat exposure. For the transient temperature tests, bars loaded to service levels (75 kN) failed at temperatures above 500ËšC.
Effect of Temperature on Porosity, PSD and Hence, Performance of Concrete
The porosity and pore size distribution (PSD), tortuosity, degree of interconnectivity and nature of pore etc., govern most of the important properties of cement based materials. The mechanical properties, namely, strength, elastic modulus etc. are governed by porosity and pore sizes. The durability performance on the other hand is governed by tortuosity, degree of interconnectivity. Thermal conductivity is governed by nature of the pores and moisture content. Concrete and other cement based materials, when subjected to elevated temperatures, under goes nearly irreversible physical and chemical changes. Such physical and chemical changes results in change in porosity and pore size distribution leading to changes in properties and performances. Porosity and pore size distribution can be measured through Mercury Intrusion Porosimetry (MIP), Back Scattered Electron (BSE) microscopy and some other techniques. In spite of some of drawbacks and disadvantages MIP is a popular method for investigation of PSD. Thus effect of elevated temperature on PSD of concrete had been studied using MIP and outcomes are presented in this paper. A general equation for pore size distribution (PSD) of cement based materials including concrete is considered. The equation relates cumulative pore fraction volume to pore size. The constant parameters of the equation are porosity, mean distribution radius and a dispersion coefficient. The relationship of these pore size distribution parameters with temperature of exposure is presented and discussed. Hence effect of elevated temperature on PSD is presented. The strength, and durability related material properties of concrete can be related to pore-size distribution parameters and other features of microstructure of concrete. Thus effect of exposure temperature on variation of strength and other performance parameter can be better understood through the relationship and discussion presented.
Assessment of Fire Damaged Concrete Elements Using Colour Identification Technique
In this study, an effort is made to describe how the change in colour of fire exposed concrete indicates the temperature attained during fire exposure in quantitative terms/digital values. The experiments were carried out by exposing M 30 grade concrete cube specimens to definite temperatures for different time durations. Concrete samples were collected from fire exposed cubes and analysed for change in colour using graphic card technology of computer. The tests for the determination of percentage voids and ultrasonic pulse velocity (UPV) were also carried out on fire exposed concrete cubes. The data generated for the variation in UPV values and percentage voids will further help in estimation of temperature attained in fire exposed concrete in real fire conditions
Performance of Polypropylene Concrete Subjected to Heating and Different Cooling Regimes
Fire is one of the most destructive powers to which a building structure can be subjected, often exposing concrete elements to elevated temperatures. The relative properties of concrete after such an exposure are of significant importance in terms of the serviceability of buildings. Unraveling the heating history of concrete and different cooling regimes is important for forensic research or to determine whether a fire-exposed concrete structure and its components are still structurally sound or not. Assessment of fire-damaged concrete structures usually starts with visual observation of colour change, cracking and spalling. Thus, it is important to know the effect of elevated temperatures on normal strength retention properties of concrete. This study reports the effect of elevated temperature on the mechanical properties of the 100mm concrete cube specimen with polypropylene fibres and cooled differently under various regimes. In the heating cycle, the specimen were subjected to elevated temperatures ranging from 2000C to 8000C, in steps of 2000C with a rest period of 1 hour at the reference thermal levels.. Then they were cooled to room temperature differently. The cooling regimes studied include, furnace cooling, air cooling and sudden cooling. After exposure to elevated temperatures and cooled differently, the weight loss, and residual compressive strength retention characteristics were studied. Test results indicated that weight and compressive strengths significantly reduce, with an increase in temperature and are strongly dependent on cooling regimes adopted
Mathematical Model of Compressive and Flexural Strength of Concrete Subjected to Elevated Temperature Using Dimensional Analysis—Buckingham’s Pi Theorem
The effect of elevated temperature, its duration and cooling condition on compressive and flexural strength of concrete is a complex phenomenon and its characterization is governed by several other parameters related to concrete. The destructive testing of concrete subjected to elevated temperature for evaluating its compressive and flexural strength consumes time and put constraints on field schedules and hence there is need to develop the mathematical model which can provide an accurate range of results based on previous data. This paper presents the capability and application of dimensional analysis using Buckingham’s ðœ‹ theorem approach for predicting compressive and flexural strength of M-20 and M-40 grade concrete subjected to elevated temperature. A mathematical model is developed using Buckingham’s ðœ‹ theorem. The functional relationship of variables of concrete is expressed in the form of an exponential equation which is dimensionally homogeneous. A dimensional constant is determined from the physical characteristics such as grade of cement, initial setting time, final setting time, fineness of fly ash, consistency of cement, room temperature, elevated temperature and the dimensionless parameters are then, formed by grouping together the variables of like parameters. Concrete of M-20 and M-40 grade was cast and subjected to temperature 600 and 8000C for different durations .The natural cooling and cooling by water jet was achieved. The performance of the concrete was, and then tested for compression and flexure. The validation of mathematical model is done with experimental results and the correlation coefficient (φ) is developed which indicates the best fitting of model results with experimental results
Sugarcane Bagasse Ash as a Pozzolanic Admixture in Concrete for Resistance to Sustained Elevated Temperatures
In the present investigation, a feasibility study is made to utilize the sugar cane bagasse ash (SCBA) as an admixture in concrete and examine its role in imparting resistance under elevated temperatures. The ash was obtained from a sugar mill in India where the bagasse was recycled as fuel for the mill. This ash was characterized for its physical properties and chemical composition. Incorporated as a supplementary cementing admixture, SCBA replaced Portland cement from 0 to 25% by mass fraction at 5% increments. The resulting concrete was subjected to elevated temperatures of 300ºC, 400ºC and 500ºC, exposed for 2 hours in each case. A reference series was examined at room temperature. Compressive and flexural strength were evaluated and compared with the reference performance at room temperature and reported as residual properties. The results show that the SCBA sample had a grain size distribution very similar to that of the Type GU Portland cement used in this study. X-ray florescence showed that this ash was chiefly composed of SiO2 (>70%). The compressive strength of concrete cubes increases up to 10% SCBA incorporation. Even at 15% cement substitution, it matches that of the reference mix containing Portland cement alone. While there was a consistent drop in the compressive strength at higher temperatures, inclusion of SCBA marginally slows down this deterioration. The flexural strength of concrete containing SCBA was always lower than that seen with Portland cement alone. Once again, the drop was seen to be less significant up to 10% cement substitutions. The findings strongly endorse that bagasse ash imparts resistance to concrete against elevated temperatures and may be used as a supplementary cementing admixture
Effect of Elevated Temperatures on the Performance of Concrete Using Manufactured Sand
The huge quantity of concrete is consumed by construction industry all over the world. In India, the conventional concrete is produced by using natural sand obtained from riverbeds as fine aggregate. Dwindling sand resources poses the environmental problem and hence government restrictions on sand quarrying has resulted in scarcity and significant increase in its cost. This study presents the effect of the use of manufactured sand as fine aggregate in concrete. The experimental work is mainly concerned with the study of mechanical properties like compressive strength and residual compressive strength of manufactured sand concrete at elevated temperature for various percentage replacement of natural sand by manufactured sand. Concrete cube specimen were tested at ambient, 2000C, 4000C, 6000C and at 8000C with 2 hours of retention for their residual compressive strengths. The change in weight loss of concrete at these temperatures is also measured and discussed. Test results have shown increase in compressive strength at any level of replacement of natural sand by manufactured sand. The study has also shown no adverse effect on residual strengths at elevated temperatures
Assessment of Residual Strength in Steel Fiber Reinforced Concrete at Various Elevated Temperature
This experimental investigation was focused on the study of compressive behavior of steel fiber reinforced concrete (SFRC) subjected to different sustained elevated temperature ranging from 1000 C to 4000 C. In order to evaluate the effect of elevated temperature on M40 grade SFRC steel fibers of length 30 mm were used. Specimens were casted by using 0%, 1%, and 2% volume fractions. Data obtained from laboratory test results showed that residual strength varied inversely with the quantity of fibers at all levels of sustained elevated temperatures. The compressive toughness of SFRC was also evaluated to investigate the mechanical properties of SFRC at sustained elevated temperatures of 1000 C, 2000 C 3000 C and 4000 C. Test results showed that increase in the volume of steel fibers does not have significant variation in compressive strength at room temperature whereas it is observed that there is a decreasing trend in the residual compressive strength of SFRC up to sustained elevated temperature of 4000 C.
Behaviour of Binary, Ternary and Tertiary Blended Concrete Exposed to High Temperature and Moisture by Steam
This project is especially carried out for “Dyeing Millsâ€. Dyeing mills are important part of Gujarat’s textile industry and in particular Surat. The major problem faced by these industries structure, is degradation of concrete at a pretty early age. Average life expectancy of structure is only around 15-20 years which is very less compared to other structures. To control the permeability and porosity of concrete a mix design of M30 (according to IS 10262:2009) was made. Cement was replaced by flyash, metakaolin and silica fume to make for different blended concrete and corrosion resistance, strength characteristic and durability was found.
Influence of Polypropylene and Steel Fibers in Concretes Subjected to High Temperature
The aim of the study is to improve the understanding of the influence of formulation parameters, such as type and geometry of polypropylene (PP) and steel (S) fibers, type of aggregate, cure conditions, on the behaviour of high strength concretes subjected to high temperature. Firstly different concrete compositions with various amounts of polypropylene and/or steel fibers were subjected to ISO 834 fire test. Secondly, two selected formulations were exposed to characterisation test at a heating of 0.5°C/min. The initial and residual mechanical properties, concrete mass loss and porosity were investigated. Results showed the changes in porosity, compressive and splitting tensile strength which could be due to the adding of PP and S fibers
Concrete’s Characteristic Temperature under Combined Heating and Loading
Due to the complex behavior of concrete at high temperatures, the traditional design assumption that concrete has full strength if the maximum temperature is below 500°C and that it has no strength beyond 500°C may be insufficient. High stress levels have the capability to induce failure well before the concrete core reaches this threshold temperature. This suggests that other indicators are needed to predict concrete failure at high temperatures. Therefore, a new concept, Characteristic Temperature, was defined—it signifies the temperature where the concrete strains caused by sustained loads experiences a transition to rapid contraction
Fire Performance of Concrete: Effect of Temperature Gradients?
This paper first presents analytical and numerical solutions for the temperature within a φ100mm×200mm cylinder subject to a uniform heat flux boundary condition. The concrete temperature and its gradients are shown to be strongly dependent on the heat flux, which unfortunately can hardly be controlled accurately and consistently in conventional furnace/oven tests. As a result, the effect of temperature gradients within concrete on its fire performance has not been properly addressed and included in currently available constitutive models; neither has the influence of critical processes linked with temperature gradients, including thermal stresses, moisture transport, and pore pressures. Through addressing major shortcomings of current “standardizedâ€ tests by establishing heat flux as a parameter of study, an ongoing research at The University of Queensland aims to develop more realistic constitutive models for concrete at elevated temperatures. Key features of this research are also briefly outlined
To Stress-strain Behaviour of Steel Fibre Reinforced Concrete at Elevated Temperature
Research of load-bearing systems exposed to fire conditions is an actual topic in civil engineering. Real-size experiments are simulated using various software and computational models in order to predict the structural behaviour, whilst the experiment results serve as an input for appertaining software models and their further application. In the frame of this paper a finite element modelling is described in details together with the gained results and outputs
High Temperature Properties of Calcium Aluminate Cement Concrete
In this research work, material properties of calcium aluminate cement concrete (CACC) was investigated at elevated temperatures. For material properties, compressive strength, splitting tensile strength, elastic modulus and stress-strain response were measured at 24, 200, 400, 600 and 800°C and compared to normal strength concrete (NSC). Scanning electron microscopy (SEM) was also used to study the microstructure of CACC and NSC at different temperatures up to 600°C. Test data for CACC revealed that the presence of alumina as a binding agent exhibited considerable enhancement in the mechanical performance compared to NSC. At elevated temperatures, reduction in the stress-strain response was observed in both CACC and NSC; however, axial strain is higher in case of CACC. Conversion of hydrates within the microstructure of CACC plays vital role in the reduction of strength with the increase in temperature up to 400°C. Visual investigations after high temperature exposure revealed that CACC exhibits low cracking with less color changes as compared to that of NSC.
Mechanical Properties of Geopolymer Mortar after Exposure to Elevated Temperatures
This paper presents experimental results on mechanical properties of geopolymer mortar specimens, prepared by alkaline solution activating metakaolin and fly ash blend. Bending, compressive, tensile and bond strength tests were conducted on large sets of geopolymer mortar specimens at ambient temperature and after exposure to elevated temperatures, to evaluate the residual strength of geopolymer mortar at elevated temperatures. Comparative strength tests were also conducted on Portland cement mortar. Results from these tests show that bending, compressive, tensile and bond strength of geopolymer mortar increases at 100oC, and then decreases in 300- 700oC range. Geopolymer mortar exhibits a slightly lower bending strength, but higher compressive, tensile and bond strength, than ordinary Portland cement mortar at ambient temperature and after exposure to elevated temperatures. Thus MK-FA based geopolymer mortar can provide similar or higher level of fire resistance than Portland cement mortar in buildings, in addition to numerous environmental benefits, such as lower energy consumption and lower carbon dioxide emissions during production
Influence of the Cooling Process and Load Level on the Residual Mechanical Properties of Ordinary Concretes After Fire
This paper presents the results of an experimental research on the assessment of the effect of the load level and cooling process on residual mechanical properties of ordinary concretes after fire. The concretes tested were made of granite or calcareous aggregates since they are the most used in civil construction in general. For each concrete was determined the residual compressive; direct and splitting tensile and flexural tensile strengths and modulus of elasticity. The influence of the loading level (0.3 and 0.7fcd), cooling process (cooling in the air and cooling by water jet) and temperature (20, 300, 500 and 700ºC) on the mentioned mechanical properties was determined. The high temperatures attained and the rapid cooling down process on the concrete showed a negative effect on its residual mechanical properties. The load level showed a favorable effect on the residual compressive strength of the concrete cooled slowly in the air but the opposite was observed in the case of sudden cooling down by water jet.
Protection Methods against the Explosive Spalling of Concrete
To study the mechanism and to minimize the risk of the explosive spalling of concrete at high temperatures, a series of tests has been performed at ETH Zurich. As protection methods, polypropylene fibers (PP-fibers) and protective coatings are demonstrated to be efficient at preventing explosive spalling in these tests. To evaluate PP-fibers and protective coatings, an explosive spalling criterion has been developed using a thermal-hydro-mechanical model. This criterion considers the influences from the pore pressure and thermal stresses. To validate this criterion, test results are used to predict the spalling, and have shown that the proposed explosive spalling criterion is feasible and can evaluate the performance of protection methods.
Mechanical Properties of High Strength Q460 Structural Steel After Being Exposed to Fire
An experimental study was undertaken to investigate the post-fire mechanical properties of high strength Q460 steel. Tensile coupons taken from high strength Q460 steel sheets were exposed to different elevated temperatures up to 900℃, and were then allowed to cool down to ambient temperature before they were tested to failure. Two cooling methods were considered, namely natural cooling and water cooling. Tensile tests were conducted to obtain their post-fire stress-strain curves and associated mechanical properties (yield strength, elastic modulus, ultimate strength and elongation). It was found that the post-fire mechanical properties of high strength Q460 steel are significantly reduced below the original ambient temperature mechanical properties when they are exposed to temperatures exceeding 600℃.
Modeling Fracture of Steel at Elevated Temperature
This paper summarizes recent research on modeling steel fracture at elevated temperature. Modeling fracture is important for simulating the behavior of steel connections in fire, where fracture of bolts or other connection elements is often the failure mode that controls overall strength and deformation capacity of the connection. In this study, true stress-strain curves for structural steel at ambient and elevated temperatures are first developed that extend beyond necking. Then two widely used fracture criteria (ductile fracture and shear fracture criterion) are studied in order to model steel fracture at ambient and elevated temperatures. Calibration of fracture parameters for these criteria is performed by using finite element analysis together with experimental data. To verify the accuracy of the calibrated fracture parameters, comparisons are presented between the results of elevated temperature connection tests and simulation results.
High Strain Rate Behaviour in Tension of Different Reinforcing Steels
In their lifetime reinforced concrete structures can be exposed to severe dynamic loadings such as blast and impact. In this case concrete and reinforcing bars are subjected to high strain-rates. Although the dynamic behaviour of the reinforcing steel is of crucial importance in the structural assessment under the aforementioned conditions, only few researchers analysed this issue. The tensile high strain rate behaviour of the B500A, B500B, B450C and AISI304 reinforcing steels was studied by means of experiments carried out at 250, 500 and 1000s-1 using a Split Hopkinson Tensile Bar (SHTB). In the case of B500A steel, the specimens were coming from four different rebar having diameter of 6, 8, 10 and 12mm. For the B450C steel, considered as a composite bar made of a hardened outer layer, an intermediate hardened layer and a soft inner core, the effects of the strain rate on the mechanical properties in tension of these three layers were evaluated. Reinforcing steel specimens (coming from a rebar having a diameter of 12mm) of the B500B and AISI304 types were finally investigated at the same high strain rates. With the obtained data the parameters of the most common material constitutive relationships were determined.
Composite Corrosion Protection System in Rehabilitation of Steel Structures in Corrosive Environment—A Case Study
India loses USD 33 billion every year due to corrosion of infrastructure, industrial equipment and other vital installations, according to latest estimates from Corrosion Management Committee of Confederation of Indian Industry[1]. This paper addresses corrosion management and prevention using Galvanic Systems, through a case study of a structural steel bridge in Goa, a coastal and corrosive zone of West India. The bridge was found to be in advanced stage of corrosion damage merely one year after its construction, and was treated with a composite treatment of galvanic corrosion protection using custom designed sacrificial anodes, and systematic protective coating system of acyclic, polyisocyanate reticulant based polyurethane. The performance against atmospheric corrosion of this system was observed through of periodic visual observations and physical measurements since early 2012; electrochemical readings were taken at the end of 30 months of treatment. It is seen that the composite system exhibits satisfactory protective behaviour, and may be considered for treatment of similar structures in corrosive environments.
Estimation of Equivalent Diagonal Strut and Shear Strength of URM Wall Infilled RC Frame
In this study, RC frames with URM wall for typical school buildings in Korea are experimentally investigated to evaluate their seismic capacity. For this purpose, onebay, one-fourth scale specimens with URM walls are tested under in-plain loading. In this paper, the diagonal strut mechanism of URM wall is discussed using principal compressive strains on URM wall. The lateral strength carried by URM wall and RC frame are also explained based on the compressive stress acting on URM wall and the curvature distribution along both columns during the test.
Evaluation of Dynamic Shear Resistance of RC Beams Under Rapid Loadings Based on Modified Field Compression Theory
The aim of this study was to develop an analytical model to estimate the dynamic shear capacity of RC beams which may exhibit diagonal tension failure under impact and blast loadings. Thus, the modified compression field theory has been extended to dynamic loading in this study. The developed analytical model has been applied to the experimental results obtained from rapid loading tests of RC beams. As a result, the developed analytical model has been in good agreement with the experimental results.
The Need for Enhanced Resiliency in Building Design and Construction
Enhanced resiliency is crucial for improved community recovery and continuity following disasters. Community continuity often has regional, national, or even international impacts. Data is presented to demonstrate the need for enhanced resiliency in building design and construction due to dramatic increases property losses over the last five decades. A variety of possibilities causing this dilemma are investigated. Programs, strategies, and trends as well as the pros and cons of voluntary and mandatory efforts intended to result in more resilient communities are highlighted. Activities and research necessary to support the integration of enhanced resiliency in building design and construction are identified.
Evaluating the Robustness of Precast Concrete Framing Enhancements for Progressive Collapse Resistance
The ability of a structure to resist a disproportionate collapse due to localized damage has become a topic of increasing concern within the building community in the wake of structural collapses worldwide over the last half century. According to current criteria, progressive collapse resistant design is typically implemented by removing columns one at a time in one-story lengths from the structural frame at several prescribed locations to simulate the local damage. The structure must then redistribute its loads to prevent collapse. This paper describes a modified approach to quantifying the robustness of building frame systems subjected to a single column loss damage scenario. This robustness procedure incorporates both ultimate strength limits of the system and measurements of consequence (i.e., the severity of collapse at overload) in describing the overall collapse resistance of the structure. This procedure is applied to a 10-story precast/prestressed concrete prototype building system. A parametric study is conducted on the assumed collapse-resistant properties of typical discrete beam-tocolumn connections. These results will be utilized to inform the development, and testing, of an improved connection detail
Validation of Dynamic Increase Factors in Structural Design Codes
In the design of structural concrete for impact loading, design or model codes often employ a dynamic increase factor (DIF) to impose dynamic effect on static response. Dynamic increase factors that are obtained from laboratory material test results and that are commonly given as a function of strain rate only are quite different from each other depending on the design concept of design codes like ACI 349M-06 , fib Model Code 2010 and ACI 370R-14. Because the dynamic increase factors currently adopted in the codes are too simple and limited to consider a variety of strength of materials, their application in practical design is questionable. In this study, the dynamic increase factors used in the three codes were validated through the finite element analysis of reinforced concrete slab elements which were tested and reported by other researcher. The test was intended to simulate a wall element of the containment building in nuclear power plants that is assumed to be subject to impact scenario that the Pentagon experienced on September 11, 2001. The finite element analysis was performed using the ABAQAUS 6.10 and the plasticity models were employed for the concrete, reinforcement. The dynamic increase factors given in the three codes were applied to the stress-strain curves of the materials. To estimate the dynamic increase factors, strain rate was adopted as a parameter. Comparison of the test and analysis was done with regard to perforation depth, maximum deflection, and surface crack area of the slab. Consequently, it was found that DIF has so great an effect on the behavior of the reinforced concrete structures that selection of DIF should be very careful. The result implies that DIF should be provided in design codes in more delicate format considering various influence factors.
Robustness of Floor Systems Due to Post-Drilled Holes
Most of our attention is focused on serious hazards with rather spectacular consequences, like fire, explosions, earthquakes, and so on. However, this type of event is fortunately infrequent and well-covered by regulations, codes, scientific work, and engineering practice. In practice, we’ve seen a much higher frequency of uncontrolled drilled holes with lower consequences until now. Floor systems are rarely or inadvertently designed to withstand this kind of action; there is a lack of knowledge of which system is the most appropriate in an ultimate limit state or an accidental situation. In this paper, a robustness factor R is defined which reflects the same philosophy as a safety factor and is equal to the ratio of the total reinforcement demand with a certain kind of opening to avoid collapse, and the reinforcement requested without openings. When this factor is equal to 1, the system is very robust and needs no additional reinforcement; however, if it becomes higher than 1, your system becomes sensitive for post-drilled holes at a random location
Cyclic Performance of Shape Memory Alloy Reinforced Concrete Walls
Concrete walls are commonly used to resist lateral loads. Their relatively high stiffness limits the inter-story drifts and minimizes damage to other structural and nonstructural elements. However, significant structural damage to the walls is expected during seismic events. This study investigates numerically the effectiveness of using Superelastic (SE) Shape Memory Alloy (SMA) bars to improve the seismic performance of moderate and squat concrete walls. The used analytical model was validated using experimental results by others. It was then utilized to investigate the cyclic load-displacement response of one-intermediate and two-squat walls while incorporating SMA bars. Results of this study led to identifying the location of SMA bars that result in best seismic performance
Retrofitting of Ancient Masonry: Experimental Tests and Numerical Simulations
The paper presents the experimental study carried out on stone masonry specimens prepared in the laboratory: the preparation of the specimen was made according to L'Aquila traditional techniques, using original stone elements of "Palazzo Camponeschi" (an historical building situated in the old city center) and typical poor lime mortar. The panels were then injected and some of them also reinforced with steel fiber net applied on the external surfaces. Shear-compression tests were carried out to evaluate the shear strength and the failure modes of the specimen. Moreover, a non-linear finite element model (FEM) has been created in order to reproduce experimental tests and to better understand the damage phenomena. Peak responses and premature delamination of the external reinforcement were predicted with good approximation. A better prediction in terms of stiffness and post-peak behavior of the wall specimens would be possible assuming different hypothesis about external constrains and contact lows in the FEM
Strengthening and Repair of Las Vegas Distribution Center after a Severe Fire
The Distribution Center Las Vegas (Medellin – Colombia) is the principal storage and distribution center of the big retail company in Colombia. The project has an area of 646.000,0 ft2 and was built in year 2005 (Figure 1). Some years ago, in 4 hours, a conflagration destroyed 430.000,0 ft2 of the warehouse (Figure 2). Being centralized the distribution; all activities of the retail company were severely affected and were necessary, after three months of investigations and redesigns, to begin the reconstruction work. The whole building was divided in 3 blocks (Figure 1 and Figures 3 and 4). The dimensions are indicated in the figures. The height of the columns and walls was variable between 33 ft and 46 ft. For the reconstruction was necessary to consider the most severe specifications to protect the new building against fire. So it was necessary to build new fire walls, 40 ft height supported in the old and new additional frames using the existing deep pier foundations and much of these were unable to resist additional loads. Many of the piers become new loads that were twice the initial loads and for this reason were necessary to strengthen 61 piers (Piers excavated by hand and cast in place).
FRP Shear Strengthening of Thin-Walled Plate Girder Web Panels Subjected to Cyclic Loading
This paper examines a novel FRP strengthening methodology intended to improve the shear capacity and shear buckling of thin plate girder webs. Slender plates are used in a variety of structural engineering applications because of their high strength-to-weight ratio and, in certain configurations, their postbuckling reserve capacity. However, out-of-plane displacements may be induced by in-plane loads close to or exceeding the buckling load, which in turn induces secondary bending stresses at welded plate boundaries. Under cyclic loads, as in the case of bridges with repeated axle loads, this phenomenon is referred to as breathing, and may cause cumulative fatigue damage to plate girders, which may influence the limit state of the girder. This may contribute to overall deterioration of bridges, which is a topic of critical importance in Europe, North America and Japan. The effectiveness of the novel FRP strengthening technique under static loading has already been demonstrated through tests by the authors. The optimum strengthening technique; which involves bonding a preformed, corrugated FRP panel to one side of the steel plate girder web; was adopted for the second series of tests, which examine cyclic loading to simulate repeated axle loads in real bridges. The variables considered in this work are the type of the strengthening material (CFRP and GFRP) and the load intensity. Six specimens were manufactured to simulate the end panel of a plate girder with potential length of 15m. Test results along with non-linear finite element modelling proved the efficiency of the strengthening technique in reducing the critical stresses and consequently increased the fatigue life of the tested plate girders.
Strengthening and Repair of Reinforced Concrete Beams Using Concrete Jackets
The necessity to rehabilitate a Reinforced Concrete (RC) structure emerges from several reasons such as new safety requirements, change of structure occupancy, incorrect design calculations and/or degradation of materials with time. One of the most commonly used mitigation practices to strengthen and repair RC beams is the application of RC jackets at either one side or three sides of the beams. The use of these jackets to improve the flexural performance of RC beams is investigated in this study. An iterative incremental algorithm that takes into account the influence of slip along the interface between the old and new concrete layers is developed. In addition, the distribution of interfacial strain gradient, slip and shear stresses along the interface are predicted. A very good agreement is shown between the current proposed analytical model and the published experimental data on RC jacketed beams. Based on an extensive parametric study, effective flexural modification factors of these beams are developed and verified.
External Strengthening of Shear Deficient Reinforced Concrete Beams with Flexural CFRP Laminates
This paper presents an experimental investigation of reinforced concrete (RC) beams strengthened in shear with externally bonded flexural carbon-fiber reinforced polymer (CFRP) sheets attached to the soffit of the beam via epoxy adhesives. The current state-of-the-art technology of shear strengthening of RC beams is by externally bonding CFRP sheets or plates to the vertical sides of the beam’s web with different orientations and configurations using epoxy adhesives. However, in certain applications, the sides of the beam might not be accessible for shear strengthening or might be too shallow to develop the strength of the CFRP laminates without anchors. Therefore, the objective of this study is to investigate the contribution of external flexural longitudinal CFRP laminates on the shear strength of RC beams casted without internal stirrups. The beam specimens were simply supported and tested under four point bending and the load versus mid-span displacement responses were recorded until failure. As expected, all beams failed in shear as a result of a diagonaltension crack. The strengthened specimens showed an increase in the load-carrying capacity of 49%-61% over the control unstrengthened specimen. It could be concluded that external flexural CFRP reinforcement has a significant effect on the concrete shear strength of beams and could be used as a valid alternative when the vertical sides of RC beams are not accessible
Introduction to Shape Memory Alloys for Concrete Confinement Applications
Recent structures struck by earthquakes revealed the deficiencies of their reinforced concrete (RC) column members to avoid progressive failure scenarios. Therefore, strengthening RC column is paramount to ensure the structural integrity and public safety in future events of earthquakes disasters. The critical need to replace traditional strengthening materials and techniques with more efficient and effective ones had led to the evolvement of smarter and innovative class of materials termed Shape Memory Alloys (SMA). The SMA possesses unique characteristic properties that lie in their ability to undergo large deformations and return to their undeformed shape through stress removal or heating. Limited research studies conducted using SMA have shown high potential for building industry applications. Thus, the main objective of this paper is to introduce Civil Engineers to the unique thermomechanical characteristics of SMA, along with a brief review on some of the confinement applications using SMA.
Thermo-Mechanical Training of Iron-Based Shape Memory Alloys Used to Strengthen RC Beams
The Shape Memory Alloys (SMAs) are rarely used in structural engineering applications due to the high cost of constitutive materials and production schemes. Recently, the Iron-Based SMA (Fe-SAM) is being developed. The inexpensive constitutive materials of the Fe-SMA and the availability of mass production facilities of steel products makes this material suitable for large structural engineering applications than the most common shape memory alloys (i.e. NiTi). SMAs are mainly characterized by the Shape Memory Effect (SME) phenomenon. The SME represents the ability of the SMA to recover its original shape after being deformed beyond the elastic limits through heating. The SME for some SMAs can be further improved by the thermo-mechanical training. This paper reports on the effect of thermo-mechanical training of Fe-SMA bars used for flexural strengthening of Reinforced Concrete (RC) beam using the Near-Surface Mounted (NSM) strengthening technique. The pre-strained Fe-SMA bar was anchored inside a groove in the tension face of the RC beam and then heated up to 350oC where the activation of the bar occurred causing a prestressing force to be developed in the Fe-SMA bar that counteracts the applied loads. The results were compared with another beam strengthened with Fe-SMA without thermo-mechanical training of the bar. The results revealed a better performance at service loads in the case of the beam strengthened with trained NSM Fe-SMA bar.
Evaluation of Member Contributions in Concrete Connections using the Digital Image Correlation Technique
The Digital Image Correlation Technique (DICT) was recently proposed as an alternative instrumentation to conventional Linear Strain Conversion devices due to the superior characteristics of the former in accurately capturing the deformation in structures. In this research, the DICT was used to calculate the member contributions of slotted-beam column connections tested under quasi-static loading. The slottedbeam system is primarily used in the design of concrete structures prone to highmagnitude earthquake motions. It possesses exceptional minimal beam elongation and non-tearing action to the concrete slabs, and thus, maintains a rigid diaphragm of building floors. The detailed procedure of calculating the member contributions using the DICT method is outlined in this paper. Analysis results indicate the domination of beam flexural bending to the total drift with smaller contribution of the joint distortion and column bending.
Effect of Soil Type on Pile-Soil Interaction
This paper investigates the effect of changing the type of soil on pile-soil interaction. The pile-soil interaction was investigated in soft and stiff soils. Also, the analysis pile-soil interaction was conducted under the effect of lateral loads. The analysis of the pile-soil interaction was performed using the finite difference (FD) software LPILE, finite element (FE) modeling of pile- soil interaction using Abaqus/Cae, and FE modeling using SAP2000. A lateral displacement of 0.787 in. was applied to the top of the pile while maintaining a zero slope in a guided fixation. The bending moment and lateral displacement along the depth of the pile was reported. A good agreement was found between the results of the FE models and the FD solution. The results indicated that embedding piles in stiffer soils leads to larger moments and smaller displacements.
Assessment of Impulse and Pressure Wave Distribution on Realistic City Models
As the level of threat in urban settings regarding terrorist incidents increase, it becomes a necessity to develop advanced methodologies to enhance the security level. A bombing attack, which is a widely used method by the terrorists, creates extreme loading conditions on the surrounding buildings. Therefore, to be able to design more resilient and durable structures, it’s necessary to estimate these loading conditions that occur as the result of a bombing attack. “MAPEXâ€ is the acronym for the European Union CIPS Project that stands for “Probabilistic damage-mapping development tools for urban critical infrastructures against terrorist attacksâ€, and its general aim is to generate probabilistic damage-mapping methodologies for the estimation, investigation and the optimization of the security level of urban critical infrastructures against explosive attacks. These methodologies will have important functions such as, estimating risks to the facilities, investigating explosive attacks and providing help for the planning of crisis management and evacuation protocols [1]. As a part of the “MAPEXâ€ Project, five urban scenarios using five city models which are parts of city of Munich, Germany have first been modeled on a computer environment, and then using various amounts of TNT and stand-off distances, explosion simulations have been conducted and the results have been post-processed. For the modeling, Ansys- DesignModeler®; and for the simulations, Ansys-Autodyn® hypercode have been used. After conducting the simulations, the pressure vs time and the impulse vs time data have been obtained for the previously defined gauge points.
A Parametric Study of Live Load Distribution Factors for Steel Girder Integral Abutment Bridge: Camera-Ready Guidelines
This research examines the relativity of both AASHTO Standard Specification and AASHTO LRFD girder distribution factors (GDF) for use with designing integral abutment bridges. To evaluate the GDFs, the Scotch Road integral abutment bridge was modeled in the finite element software Abaqus/Cae. The model was verified using temperature-displacement data recorded from April, 2003 to May, 2006. Following the validation of the finite element model (FEM), three loading cases including one, two, and three lanes, were run in Abaqus. The stress data obtained from each case was used to calculate the GDF for each girder. Lane one loading provided the most reasonable results for AASHTO LRFD, while the AASHTO standard equation was overly conservative in all cases. The GDF calculated using the finite element model was only about 30% lower than the AASHTO LRFD value for one lane loaded, while being 50% lower than the AASHTO standard specifications. Both AASHTO GDF equations were overly conservative for both two and three lanes loaded. The finite element calculated GDF was approximately 50% and 60% lower for two and three lanes loaded compared to AASHTO LRFD. A limited parametric study was conducted to investigate the effect of number of piles, girder spacing, and boundary conditions on the GDF ratios. The GDF ratios decreased in accuracy as the girder spacing decreased for one lane loaded. A simply supported bridge was compared with an equivalent IAB. It was found that IABs are less conservative than simply supported bridges for interior GDFs in all loading cases
High Strength Concrete (HSC): Concrete Solution for Emerging High Rise Concrete Structures
Today, the challenge to the construction industry is to construct tall structures with thin sections, which are economically viable and having good quality concrete finish. This necessitates the need to develop High Strength Concrete with expertise and available resources. Ambuja method of Concrete mix design method which is combination of IS and DOE method is used to design M80 concrete grade. In this project an attempt is made to study the behaviour of silica fume and Alccofine (3%, 5%, and 7% replacement by weight of cement) along with Fly Ash (20%) on fresh & hardened property of concrete. For fresh property of concrete, workability test were performed and results were compared with respect to dosage variations of minerals (3%, 5%, 7%) and also with each other. Test results include Initial Slump, Slump after 30min and Slump after 60min. For hardened concrete the development of compressive strength of concrete using SCM’s at the age of 1, 3, 7 and 28 days were investigated and compared with respect to SCM’s dosage variations and also with each other and for durability, the Penetration of Chloride Ion into Concrete by Ponding test was performed. This paper broadly covers the concept, need, advantages, materials, and mix design approach and strength characteristics of high strength concrete based on the learning from conducting the trials at our Concrete Labs and also on construction sites
Numerical Simulation of Wind-Induced Noise Using Wind Turbulence Information
In this study, wind-induced noise is simulated as time-histories of fluctuating sound pressure by Auto-Regressive (AR) model. The coefficient matrices associated with the model are determined according to the prescribed spectral density of sound pressure in the frequency domain. In order to verify the validity as well as reliability of the approach, various checks on the simulated results have been carried out. The results show that wind-induced sound can be simulated well by the AR model with low order and small sampling time step. The AR method is thus potential for timedomain solutions of noise mitigation in wind environmental problems
A Fundamental Study on the Ultimate Pull-Out Strength of an Anchor Bolt in Concrete Structures using SPH
The anchorage zone of the concrete structure under pull-out loading is usually designed by the assumption that there are three possible failure modes such as the rupture of anchor bolt, cone failure of concrete, and bond failure between anchor bolts. In general, the design load is considered the smallest load of these failure mode assumptions. However, unexpected failure often occurs in the anchorage zone due to the complex failure or the change of failure condition. Therefore, it is important to develop the accurate evaluation method of load bearing capacity of the anchor bolt. In this study, we conducted an analytical study using Adaptive Smoothed Particle Hydrodynamics (ASPH) to simulate the failure process of the anchorage zone and discussed the effect of embedment depth of anchor bolts on the ultimate strength
Finite Element Simulation of Newly Developed Beam-Column Connection System Subjected to Seismic Loading
Slotted beam-column connection was developed recently as an alternative system for the seismic design of connections in concrete structures. The system includes a vertical slot made into the beam member at the column face, while its main feature is that the bottom reinforcement yields under both positive and negative bending, and thus, the top reinforcement remains elastic during the seismic motion. Therefore, the elongation of the beam member, which is an important parameter in the performance of beam-column connections, is maintained insignificant. The elastic response of the top fiber will also provide a non-tearing action to the attached concrete slab. In this research, nonlinear 3D Finite Element Method (FEM) models were developed and validated against experimental test results of large scale slotted beamcolumn connections. The results of the models are analyzed in terms of loaddisplacement relationships, beam rotation, strain profiles, and cracking pattern. It is concluded that further research into the effect of relocating the vertical slots, away from the column face, on the accuracy of the models in predicting the response of the system is needed before being able to conduct parametric studies using the FEM models
Seismic Performance Evaluation and Retrofit of an R/C Frame with Brittle Beam-Column Joint Damaged by the 2013 Bohol, Philippines Earthquake
A magnitude 7.1 earthquake attacked Bohol Island, Philippines on October/15/2013 (local time) and damaged a number of reinforced concrete (R/C) buildings. This paper focuses on one of moderately damaged R/C buildings where severe damage was observed to exterior beam-column joints, because no lateral reinforcement was provided at the joints. There is no realistic method to evaluate and/or upgrade the seismic performance of such substandard R/C beam-column joints. Therefore, a series of laboratory tests was conducted to experimentally evaluate the seismic behavior and performance of a 1/2.5 scale partial frame representing the damaged structure. As a result, the specimen exhibited a lower seismic resistance compared to that from design calculations. Moreover, in this experimental study, R/C wing walls were applied to the other specimen to prevent join failure and to upgrade the seismic performance. Effectiveness of the seismic retrofit by wing walls was verified through comparing the experimental results between both specimens with/without retrofit
Variation of Maximum Inter-Storey Drift for Steel Moment Resisting Frames Considering the Horizontal and Vertical Seismic Components
Steel Moment Resisting Frames (SMRFs) are widely used to resist seismic loads. Different response parameters such as maximum roof drift, Maximum Interstorey Drift (MID), and local plastic rotations are used to assess their seismic performance. This study investigates the variability of MID at collapse, evaluates the effect of vertical seismic component and identifies the critical floors. A ten storey SMRF was considered as a case study. Incremental dynamic analysis (IDA) was conducted using five different ground motions considering both the horizontal and vertical components. It was observed that the storey experiencing the MID is not always the severely damaged storey. The vertical seismic component significantly increased the column axial forces and the vertical deformations of the beams, and, thus increased the state of seismic damage in the frame. The effect of the vertical seismic component on the MID was also investigated.
Numerical Modeling of the Shaking Table Tests of a Bridge Column
A blind prediction contest was organized by PEER and NEES to predict the behaviour of a full-scale reinforced concrete bridge column subjected to unidirectional seismic excitation on the NEES-UCSD shaking table. Designed consistent with the modern design guidelines, the column had a 1.2 m-diameter cross section, cantilevered 7.3 m, and supported a 229-Mg concrete block at the top. The column was subjected to six historical ground motions with the peak ground acceleration values ranging from 0.20 to 0.53 g. The objective of this study is to numerically model the behaviour of this specimen under six consecutive ground motions while considering the damage accumulation, and gauge the accuracy of a recently developed nonlinear analysis procedure. This procedure uses distributedplasticity, displacement-based, frame elements with a fiber section discretization. Shear effects are captured through the 2D implementation of the Disturbed Stress Field Model. Suitable for modeling large-scale concrete frames found in practice, the procedure uses default material models and analysis options, and thus does not require the ‘tweaking’ of parameters. This paper provides a brief overview of the analysis procedure, summarizes the experimental program, and presents the numerical modeling details. The comparisons of the experimental and numerical responses are then discussed. Influences of critical modeling aspects, such as the time step length, the use of supplementary viscous damping, and the strain rate effects, are also examined
Seismic Performance of Frame-Shear Wall Structure with Innovative Replaceable Coupling Beams
This paper introduces the theory and design method of replaceable coupling beams. A real engineering project of the high-rise frame-shear structure with replaceable low-yield-strength steel shear panels was analyzed and full-scale cyclic tests of the replaceable devices were introduced. Finite element models were created and both experimental and analysis results show excellent energy dissipation capacity of the replaceable devices whereas the seismic performance of the structure with replaceable coupling beams was demonstrated through the comparison with traditional structure. It indicates that replaceable coupling beam has the desirable seismic performance by concentrating damage in the replaceable devices, whereas the global response of the structure can meet the required service levels
Numerical Modelling and Seismic Retrofit Design for Historical Vazir House
Heritage structures are of immense value and pride to any nation. The importance of protection of these structures can hardly be understated. The Vazir House in Swat, Pakistan is a historical building which was constructed in 1936. The structural system of the building consists of load bearing walls which have been constructed using double leaf random rubble stone masonry. Mud mortar has been used to bond the stone units. The survey of the building indicated that seismic vulnerabilities existed in the building. This paper presents the details of seismic analysis of Vazir House and its retrofit design. The retrofit scheme was designed with a view to keep the structural intervention to a minimum level. The scheme is based on the basic concepts of strengthening of weak areas and links of a structure. A 3D finite element modelling of the building has been carried out and the performance of the original and retrofitted models of the building was studied. The stress level and deformation characteristics of the retrofitted building were found to be satisfactory; the retrofitting scheme was subsequently implemented in the building.
Seismic Performance of Post-heated Reinforced Concrete Frame Joints
An experimental study was carried out to investigate the seismic performance of post-heated reinforced concrete frame joints. Three full-scale joints that are part of reinforced concrete frames, and exposed to fire, were tested under a combined axial loading and cyclic lateral displacement history, to simulate earthquake loading. The joints were tested in two groups, namely in the unheated and post-heated states. In terms of seismic performance, test results indicate that the frame joints did not sustain much damage with 60 min fire exposure time, since the concrete did not lose much of its mechanical properties and steel rebars recovered much of temperature induced strength loss. Hence the energy dissipation capacity in joints of the frame that exposed to 60 min of fire remained mostly in fact. However, the damage to joints was more serious in frame with 90 min fire exposure time, due to loss of mechanical properties in concrete and steel rebars, leading to lower seismic performance of joints after fire exposure. All three fire exposed joints failed in shear failure mode under seismic loading
Near-field Explosion Effects on Reinforced Concrete Columns
Explosion effects on critical infrastructures have been an area of intense research over the last few decades; especially after the Oklahoma City bombing. The increase in research activities is attributable to the increasing number of terrorists’ attacks and incidence of accidental explosions around the world. The consequences of terrorists’ attacks using explosives and accidental explosions can be widespread and lead to damage to infrastructures and fatality to occupants of buildings. Thus building owners, government departments as well as professionals are seeking to better understand the response of structural systems, especially reinforced concrete columns, to blast loading. A significant amount of research work has been conducted to study the response of structural and nonstructural building elements to blast loading. Most of this research has concentrated on elements of the façade of buildings such as infill walls and window glass. The research investigating the behaviour of structural elements such as columns and beams are limited to their behaviour under far-range explosions. There is a lack of research data on the behaviour of reinforced concrete columns subjected to near-field explosions. The research reported in this paper was designed to investigate the effects of nearfield explosions on reinforced concrete columns with different transverse reinforcement detailing and at scaled distances less than 1.0 m/kg1/3. The results of the live explosion testing show that the effect of transverse reinforcement detailing is not significant at the high scaled distances. At smaller scaled distances, however, columns with close transverse reinforcement spacing performed better than companion columns with conventional transverse reinforcement spacing. Thus, reinforced concrete columns designed and detailed for areas of high seismicity have an inherently higher blast resistance in comparison with columns designed for areas of low seismicity or for gravity load resistance only
Influence of Lateral Load Resisting System on Collapse Performance of Reinforced Concrete Structures Exposed to Blasts
The objective of this study is to examine the influence of the type of lateral load resisting system on the progressive collapse behavior of reinforced concrete structures exposed to extreme blast loads. In this study, three 10-story hypothetical reinforced concrete structures were modeled with shear wall systems and corresponding moment resisting frame systems. The structures consisted of 3, 4, and 5-bay plans, and designed according to American Concrete Institute (ACI 318- 11) Code Standards to resist gravity and wind loads. The structures were exposed to a charge at the ground floor level and close to the middle exterior columns. The blast was of sufficient magnitude to severely damage at least one of the exterior columns in all of the structures. The collapse behavior was modeled with the Applied Element Method, which captured the nonlinear, transient dynamic response of the structures. In this approach, elements are initially connected with spring elements between element surfaces, and once material failure occurs, elements may separate and collide to replicate material disintegration and debris propagation. Concrete failure behavior is simulated with a Maekawa compression model, where cracking initiates when principal stress equals the material tensile strength. Reinforcement is modeled with spring elements, and the steel nonlinear stress-strain curve is described by Ristic’s model. Models ranged in size from approximately 75,000-117,000 elements and were solved with a time step increment of 0.0001 s to capture realistic blast response. It was found that the reinforced concrete frames that contained shear wall systems generally resisted a progressive collapse more successfully than moment resisting frames, where the collapse progression was halted once it reached the shear walls. On the other hand, moment-resisting frame buildings usually resulted in a complete progressive collapse.
Damage and Loss of Capacity of RC Columns Subjected to Close-In Detonations: An Experimental and Numerical Program
The assessment of dynamic response and residual capacity of reinforced concrete (RC) columns to blast load is decisive for protection of buildings, especially regarding progressive collapse risk. In the case of explosive devices placed next to a critical structural element, complex and extreme loading is applied on the nearby system and the material response is characterized by high non-linearities. In this study, small-scale experimental tests have been performed at CEA-Gramat to investigate RC columns response for near-field detonations. By modifying the stand-off distance, different damage levels of RC column due to blast loadings have been obtained for a given charge weight. These results give information on the dynamic response of RC structure. The numerical simulation of reinforced concrete structures subjected to high velocity impacts and explosions remains a difficult task today. These difficulties are related to numerical aspects (convergence problems of the nonlinear stress strain relation in 3D problem, efficiency of the numerical procedure and robustness), but also to the ability of the material model to simulate the correct behavior of a very complex and heterogeneous material like concrete. Those works have led to the elaboration of PRM (Pontiroli, Rouquand & Mazars [1], [2], [3]) concrete model now routinely used to simulate the concrete response under a large range of dynamic loadings. The capabilities of the PRM model are illustrated by a restitution of RC columns response due to the blast effect. Numerical results are compared to experimental tests so as to evaluate simulation tools. In future works, residual load-carrying capacity of undamaged and blast damaged RC columns will be measured by axial compressive tests, and the loss of loading resistance will be analyzed.
Finite Element Analysis and Modeling of Steel Beams under Blast Loading
Terrorist attacks such as the bombings of U.S. embassies in Nairobi, Kenya and Dar El-Salaam, Tanzania have encouraged researchers around the world to study the behavior of potentially vulnerable structures when subject to blast loads. Also, none of the existing steel design codes have any provision related to designing against blast loads. Therefore, steel buildings designed based on the provisions of current codes may be unable to maintain their structural integrity under the influence of these events. Experiments involving wide-flange steel beams being subjected to live explosives (up to 250 kg of ammonium nitrate-fuel oil (ANFO) mixture) were carried out by other researchers at McMaster University and the experimental results obtained therefrom were used as a quantitative basis to validate the finite element model in this paper. The displacement response results, recorded during the tests, were used to verify the results obtained from the model. ABAQUS FEA software, a commercially-available finite element analysis program, was used to model the steel beams. Results obtained from ABAQUS were compared with the experimental test results.
Protection Using SC Composite Structures: Overview of Blast and Impact Resistance
Steel-plate composite concrete (SC) structures consist of external steel-plates acting compositely with a concrete core. These steel plates provide reinforcement and serve as formwork decreasing construction time when compared to conventional reinforced concrete (RC). SC structures have recently been used for nuclear power plant (NPP) construction in the United States, Japan, and Korea. The structural behavior of SC structures has been extensively studied and design standards have recently been published as AISC N690 Appendix N9. This standard provides specific guidance for design basis loads and general guidance for impulsive and impact loads. While the use of SC structures in the United States has been almost exclusively in NPPs, there are important benefits for engineers of other protection needs to be aware of. For example, it has been demonstrated that the same level of projectile protection can be achieved from an SC wall which is 30% thinner than an RC wall. Similar protective benefits are provided by SC walls against explosive loads. This paper includes an explanation of design philosophy and recommended design methods for impulsive and impact loads
Factors Governing the Dynamic Response of Reinforced Reactive Powder Concrete Slabs under Explosive Loads
A set of numerical studies on the influence of critical factors on the dynamic response of reinforced reactive powder concrete (RPC) two-way slabs under explosive loads is presented using the software LS-DYNA. The finite element model used in the analysis accounts for realistic explosive loads, reinforcement ratio and restraint conditions, as well as dynamic properties of constitutive materials. Empirical relations of dynamic increase factor (DIF) -strain rate for RPC are proposed based on compressive and tensile SHPB impact test results. The validity of the model is established by comparing predictions from numerical analysis with relative test results. Results from parametric studies indicate that restraint conditions, depth of slabs and compressive strength of RPC have significant influence on dynamic response of RPC slabs, while load level and reinforcement ratio have minor influence on dynamic response of RPC slabs. The dynamic response of slabs is reduced significantly by considering the strain rate effect
Sensitivity Analysis of Progressive Collapse of Steel Moment Frames Subjected to Blast Loading
It is becoming increasingly important to mitigate the effects of blasts by accidents or terrorist-campaigns on the structures. The explosive loading may result in large deformation of structural components thus endangering overall safety of the structure. Sometimes local failure of column(s) may cause disproportionate or progressive collapse of the structure if the beams and slab system in the affected zone does not offer sufficient tie strength to redistribute the loads. In the present paper, steel moment frames (SMF) of different plan shapes such as square, T and L are subjected to blast loading. The frames have been designed to resist gravity and seismic loads, but not blast loads or vehicle-bomb impacts. The blast loading with different parameters viz. charge weight and standoff distance, and position relative to the structure is considered. The blast loads are computed using empirical relations and charts available in the literature for determining coefficient of reflection. The blast loads are applied on the frames followed by conducting nonlinear static analysis. The probabilities of failure of SMFs due to the blast loading are investigated and the effect of uncertainties in blast parameters is assessed by plotting blast fragility curves. Sensitivity of fragility curves is also studied. Probabilistic analysis is carried out using Monte Carlo (MC) simulations. Few remedies to protect steel frames vulnerable to progressive collapse are discussed.
Numerical Calculation of a Blast Load on the Example of a Slab and Wall Structure of any Geometry
Nowadays, due to increasingly common acts of terrorism, particular attention should be paid to ensuring safety of a structure in an accidental design situation, such as for example an interior explosion. When designing a blast-resistant structure, designer has to possess knowledge about the phenomenon of explosion. At the moment of detonation of an explosive charge shock wave radiates inside the existing structure. A process of reflection starts when it reaches a wall or a slab. This problem has been solved for a single wall isolated from the structure and many tests have been carried out. Currently researchers investigate how the shock wave propagates across the entire structural system, where reflected from one of the walls (or the floor) it reaches other elements. The paper presents a numerical solution to a partially confined explosion within vented slab and wall structure of any geometry. A computer program that establishes reflected shock overpressure was developed and will help designers to check the load-bearing capacity of the structure in an accidental situation (an explosion
Mineral-Phenolic Foam for Blast Mitigation
The present work studies the dynamic response of mineral-phenolic foam as well as its energy absorption capacity when subjected to shock loading by means of experimental tests. The experimental tests are carried out by a shock tube equipment available at Politecnico di Milano with a proper modification of the test set-up. The shock wave generated by the shock tube impinges a steel plate diffuser that is directly in contact with two prismatic foam specimens. Behind the specimens, a steel rigid flange is placed as a contrast. The pressure history applied to the plate diffuser is characterized by a maximum pressure value of about 0.46 MPa and a positive phase duration of about 20 ms.
Development of Simplified Analytical Tools for Impact and Impulsive Loading Analysis of Reinforced Concrete Slabs
This paper presents a simplified method to analyze reinforced concrete structures subjected to missile impacts. The method, a nonlinear finite element analysis (NLFEA) procedure employing a smeared rotating crack macro-modeling approach, represents a middle ground between simplified methods based on single degree of freedom (SDOF) systems and complex meso- or micro-element hydrocodes. A soft missile impact test and a hard missile impact test from IRIS_2010 workshop were modeled and the results were compared with experimental results in terms of time-displacement response, damage shape, and residual velocity
Residual Velocity of Rigid Projectiles Perforating Concrete Barriers
The residual velocity of a projectile, in case of perforation, is an important parameter in designing a protective structure. The residual velocity is a measure of the resistance level provided by the barrier when it is breached. It is also an important parameter in studying the response and resistance of barriers. The current work presents a formula to estimate the residual velocity of a perforating nondeformable projectile. It is based on an energy balance that includes physical assumptions related to the damaged barrier, and it requires knowledge of the perforation velocity. Subsequently, an expression for the residual velocity is formulated. The model parameters have been calibrated according to a set of published experimental data and it shows good agreement with other published experimental measurements
Impact Response Analysis of RC Beams by Means of Fiber Element Approach
In this study, in order to establish a simple and engineered analysis method for appropriately evaluating the dynamic response characteristics of RC beams under impact loading, impact response analysis method based on a fiber element approach was proposed. An applicability of the method was discussed comparing with the experimental results of a total of eleven small-scale RC beams having different dimensions and impact velocities of impact striker. From this study, the following results were obtained: 1) applying the proposed method, the deflection behavior of the beams can be appropriately predicted; and then 2) the method may be able to use as a tool for evaluation of the dynamic response characteristics of the RC beams and/or frames under the impact loading
Damage Analysis of a Bridge Deck under the Impact of Massive Falling Cargo from Passing Truck
The falling massive cargos impact can cause severe damage on bridge decks. However, such kind of researches and studies have been reported. In this paper, an accident of a falling massive cargo onto bridge deck from passing truck is investigated, which happened to a cable-stayed bridge with twin pylons, twin cable planes, composite deck and main span of 590m. The falling cargos are three 20-ton steel coils in a truck traffic accident, leading to serious damage to bridge deck. A series dynamic numerical simulation using a nonlinear finite element analysis program is conducted to investigate the bearing behavior and response of the RC bridge deck subject to massive cargos impact. The simulation result indicates that the main failure mechanism of the bridge deck is flexural-punching mode, and that both the local and global response are dominating during the collision. Furthermore, the punching strength of RC deck is evaluated by a dynamic loading analysis. The capacity analysis result shows that mixed mode will always govern the behavior of RC bridge deck within the impact energy range of massive cargos. The RC deck is not more robust than we expected when subject to large cargos impact. It is necessary to take measures to avoid such accident
Analysis of a Bridge Substructure Subject to Falling Rock Impact
As a critical failure mode of the precipitous slopes, rockfall is one of the frequent geological hazards in mountainous area. Meanwhile, bridges are absolutely necessary in the mountainous transport networks due to the challenging topography and geological conditions. In recent years, the rockfall has posed serious threat to safety of bridges while such kind of researches and studies have nearly been reported. In this paper, a series of static and dynamic numerical simulations is conducted to investigate the behavior of the bridge substructure subject to a falling rock impact. Based on the analysis results, the damage degree of the RC columns are categorized into four levels with increasing impact intensity. The effects of impact direction, striking location and impact energy on the behaviors of the bridge piers are examined through a parametric study. The research result shows that the damage of RC piers caused by falling rocks impact has local characteristic and that the main failure mode of the bridge piers is shear mechanism. Even the maximum impact load induced by a 20-tons rock at a velocity of 5m/s is twice higher than the bearing capacity of piers. Thus, some active protection measures should be taken to protect bridges from falling rock impact
Analytical Study of Reinforced Concrete Beams Tested under Impact Loading
During dynamic events such as impact, structures experience high rates of loading and the materials experience elevated strain-rates. During such events, a large amount of energy is also suddenly imparted to the structure. If the structure fails to absorb the incoming energy, a sudden, catastrophic collapse may occur. In spite of our continued efforts to understand the impact resistance of reinforced concrete elements, our comprehension in this area remains severely limited. Impact tests were carried out on simply supported reinforced concrete beams using a fully instrumented drop-weight impact machine. The drop height was varied to change the rate of loading, and a companion test was carried out at a slow, quasi-static rate of loading. ABAQUS FEA software, a commercially available finite-element analysis program, was used to model the reinforced concrete beams. It was shown that the ultimate load-carrying capacity of reinforced concrete beams increases with an increase in the rates of loading, but after a certain loading-rate, a plateau in the load capacity is attained. Also, results obtained from the software analyses were in good agreement with the laboratory test results
Vehicle Collision with Reinforced Concrete Bridge Columns
This paper evaluates the peak dynamic force (PDF) and the equivalent static force (ESF) of the vehicle collision with reinforced concrete bridge columns through an extensive finite element (FE) analyses. An extensive parametric study of thirteen parameters was conducted. Three approaches were considered during the course of this research to investigate the ESF. In the first approach, stiffness based, the ESF was defined as the static force producing the same maximum displacement which is produced by a vehicle collision at the point of impact. In the second approach, the ESF was calculated following the Eurocode. In the third approach, PTMSA, the ESF was defined as the peak of the 25 millisecond moving average. The different ESFs were compared to the ESF of American Association of State Highway and Transportation Officials-Load and Resistance Factor Design (AASHTO-LRFD; 2,670 kN (600 kips)). In general, the ESF calculated following the Eurocode presented the lower bound while those from the stiffness based approach presented the upper bound. The recommended ESF of the AASHTO-LRFD was found to be non-conservative for some cases and too conservative for others. This research proposed an equation to calculate a design impact force which is function of the vehicle’s mass and velocity. This paper proposed a simplified equation based on the Eurocode equation of the ESF. However, the proposed equations do not need cumbersome FE analyses
Falling-Weight Impact Tests of Flexural Strengthened RC Beams with AFRP Sheet
In this study, in order to investigate the impact resistant behavior of the flexural strengthened Reinforced Concrete (RC) beams with Aramid Fiber Reinforced Polymer (AFRP) sheet, falling-weight impact tests were conducted taking with/without bonding AFRP sheet and a height of the falling weight as variables. From this study, the following results were obtained: 1) impact resistant capacity of the RC beams can be upgraded up to 1.2 times by flexural strengthening with AFRP sheet; and 2) at the ultimate state, the AFRP sheet tends to be ruptured right under the loading point rather than being debonded.
Design of Structures for the Effects of Falling Objects
Many times, design engineers come across situations when the effects of the impact of falling objects are considered of significance to the safety of a structure. Some of the situations may include rock fall protection structures, accidental fall of elevator counterweights, design of protective structures around construction sites or existing buildings where building components are reported to fall off the building, moving of heavy loads suspended from gantry cranes, and any other objects falling at high speed. A simple method suitable for design office practice using the principles of conservation of energy will be presented. The derivation of the Energy Equation will be presented based on widely recognized principles of motion of objects. It is assumed that the striking body is rigid such as a steel object, and the struck object is a flexural member such as a structural steel beam or a reinforced concrete slab or beam. The design objective is to provide strength and ductility so that the kinetic energy delivered by the falling object may be resisted by the strain energy developed by the structural elements. A design example will be provided to demonstrate the use of the procedure
Modeling of Reinforced Concrete Slabs under High-Mass Low-Velocity Impact
There is a growing need for analytical tools that can accurately model the behavior of reinforced concrete (RC) structures under extreme loads, particularly with respect to blast and impact. Current capabilities are almost entirely confined to hydrocodes (e.g., LS-DYNA) and such procedures have often met with limited success as they typically require complex micro-modeling representations of the structure, which is expensive in preparation and computation, and many of the commercial programs have shown deficiencies in their abilities to adequately capture cracked concrete response, particularly with regard to brittle shear-critical behavior. This paper presents the application of an alternative modeling procedure for RC slabs and shells subjected to blast and impact loads. The nonlinear finite element program employed uses a layered thick-shell element with RC constitutive modeling done in accordance with the formulations of the Disturbed Stress Field Model, a smeared rotating crack procedure shown to be capable of accurately capturing the behavior of shear-critical elements under conventional static loads. The smeared modeling approach differs from that typically employed by hydrocodes and results in simple model construction and reduced computation cost. The program is used to model the response of intermediate-scale RC and steel fiber-reinforced concrete slabs tested under repeated high-mass low-velocity impacts. Using simple finite element meshing techniques and material behavioral models requiring only basic user input, good correlation between the observed and modeled slab response was attained. The analyses provided high accuracy estimates of peak and residual displacements and successfully captured the punching shear failure modes observed experimentally.
Dynamic Delamination of Fire Insulation Applied on Steel Structures under High Strain Rate Loading
This paper presents an experimental-numerical approach for evaluating dynamic fracture and delamination of fire insulation from steel structures during impulsive loading. The experiments encompass drop mass impact tests on steel beams insulated with three types of spray applied fire resistive material (SFRM), namely Portland cement-based, gypsum-based and mineral fiber-based, commonly utilized in steel construction. The impact tests are conducted on steel beams at two kinetic energy levels to evaluate the strain rate-dependency of fracture energy and the extent of delamination at steel-SFRM interface. Results from experiments show that the cracking and delamination of SFRM is mainly localized on the bottom flange with slight extension into lower part of web of beam at the mid span. A fracture mechanics-based numerical approach is subsequently employed to simulate the conducted experiments using LS-DYNA finite element code. In the explicit numerical model, cohesive zone approach is adopted to model fracture process zone at the interface of steel and SFRM. By quantifying and calibrating the extent of delamination on the bottom flange, the dynamic increase factor of fracture energy and stress-displacement relationships, determined through previous static fracture tests, is estimated. Results from numerical simulations infer that the extent of delamination in mineral fiber-based SFRM is not dependent on strain rate; however, in the case of gypsum-based and Portland cement-based SFRM, the extent of delamination is a function of strain rate
Impact and Residual Capacities of Ultra-High-Performance Fiber-Reinforced Concrete Beams with Steel Rebars
This study aims to investigate the structural impact and residual performances of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams. To this end, eight large-sized steel bar-reinforced UHPFRC beams were fabricated and tested under quasi-static and impact loads. Impact load was applied using a drop-weight impact test machine, where the incident kinetic energy and impact velocity were 4.5 kJ and 4.2 m/s, respectively. Residual flexural performance after impact damage was evaluated by comparing the flexural performances of undamaged beams. Results demonstrated that the impact and residual capacities were significantly improved by including 2 vol.% of steel fibers. The beams with longer steel fibers (Lf = 19.5 and 30 mm) exhibited better impact and residual performances including a lower maximum mid-span deflection and a higher residual moment capacity than those with shorter fiber (Lf = 13 mm). Finally, the residual capacity of UHPFRC beams was closely related to the maximum mid-span deflection under impact and the quasi-static flexural behavior of the undamaged beams
Structural Failure of Reinforced Concrete Bearing Walls under Fire: A Full-Scale Experimental Investigation
This paper describes the structural damage and failure observed during a full-scale experimental investigation on the out-of-plane behavior of seven planar reinforced concrete (RC) bearing walls under fire. The specimens were heated on one surface over half of the wall height through the ASTM E119 standard fire time-temperature curve, while simultaneously being subjected to a constant axial load at the top. The walls were fixed at the base and free to displace vertically and rotate at the top. In the out-of-plane lateral direction, the top of four specimens was restrained (representing a rigid floor slab), the top of one specimen was free (representing a compromised floor slab), and the top of two specimens was subjected to a step-wise increasing lateral load (to investigate the change in wall lateral stiffness during the fire). Catastrophic out-ofplane buckling failures of two walls occurred at fire durations much shorter than the resistance rating per Section 2.1 of ACI 216. The walls that did not fail during fire were subjected to slow-rate reversed-cyclic out-of-plane lateral displacements immediately after fire and after natural cooling. There were significant losses in the out-of-plane lateral strength of the walls during the fire, with additional losses occurring during natural cooling as well. It was also observed that through-thickness diagonal cracking from fire can result in shear-dominated out-of-plane lateral behavior and failure of otherwise slender walls. Implications of these results for current RC building design codes are discussed
Modeling Shear Failure in Precast Prestressed Concrete Hollowcore Slabs under Fire Conditions
Prestressed concrete hollowcore slabs are susceptible to shear failure under fire conditions. However, current approaches do not consider shear limit state in evaluating failure of hollowcore slabs under fire conditions. This paper presents an approach for modeling the fire response of PC hollowcore slabs by taking into consideration shear limit state. A three dimensional finite element model is developed for evaluating failure of fire exposed prestressed concrete (PC) hollowcore slabs under various limiting states, including shear. This nonlinear finite element model, developed in ANSYS, utilizes a transient thermo-structural analysis to trace the response of typical hollowcore slabs under fire condition. The validity of the model is established by comparing temperatures, deflections and failure modes from the numerical model with data obtained from fire tests. This model can be utilized to study the effect of critical parameters on shear response of PC hollowcore slabs
Practical Reliability-Based Calculation Tool for the Post-Fire Assessment of Concrete Beams
If a structure has been able to maintain stability during fire exposure, the residual load-bearing capacity of the structural elements after fire should be determined when deciding upon the further use of the structure. Since adequate safety is a primary requirement for all structures and since many uncertainties are associated with the post-fire assessment, only a reliability-based assessment can be acceptable for real-life applications. In this contribution an easy-to-use reliability-based tool is presented for the post-fire assessment of the load-bearing capacity of concrete beams
The Punching Shear Mechanism in Reinforced-Concrete Slabs under Fire Conditions
Punching shear transfer at ambient temperature is a complex phenomenon and continues to be the subject of research. The addition of elevated temperature makes the problem of punching shear even more challenging. The shear behavior of reinforced-concrete in fire is dependent upon the degradation of the individual material properties with temperature, their interaction, and the effects of restrained thermal expansion. This paper reports the experimental findings of fifteen 1400×1400mm slabcolumn specimens, tested in punching shear at elevated temperatures. A purpose built reaction frame allowed the support conditions to be either restrained or unrestrained. Load was applied to the column stub and the slabs were heated from above using a 960×990mm array of propane gas radiant panels. Instrumentation included strain gauges, thermocouples, displacement transducers and digital cameras for displacement measurement using digital image correlation (DIC). Clear differences between the behavior of slabs with different support conditions were observed. Unrestrained slabs failed soon after the heating started, whereas the equivalent restrained slabs endured up to two hours of heating. One of the restrained slabs (the most heavily reinforced) went on to fail during cooling. The tests indicated that the diameter of the shear cone does not depend upon the restraint condition, and DIC allowed the crack locations and slab rotation angles to be visualized throughout testing
Effect of Temperature Induced Bond Degradation on Fire Response of Reinforced Concrete Beams
Reinforced concrete structures, when exposed to elevated temperatures lose load carrying capacity due to degradation in mechanical properties as well as deterioration in the interfacial bond between concrete and rebars. The extent of bond deterioration influences stress transfer between concrete and causes a reduction in load carrying capacity of reinforced concrete members. In this paper, the influence of temperature induced bond degradation on response of reinforced concrete beams exposed to fire is investigated. A finite element based numerical model is developed in ABAQUS for tracing the response of reinforced concrete beams exposed to fire. The interfacial bond between concrete and reinforcing steel is taken into account using zero thickness bond-link elements consisting of two orthogonal springs to transfer shear and normal forces in the transition zone between rebar and concrete. The non-linear behavior of the bond-link element is defined using temperature dependent interfacial bond stress-slip models proposed in literature. Predictions from the model are compared against measured response parameters during fire tests. It is illustrated that interfacial bond between reinforcing steel and concrete can significantly influence response of RC beams exposed to fire, and thus needs to be accounted for in evaluating fire resistance of RC members
Blast and Fire Design of Precast Layered FRC Tunnel Segments
multi–layered tunnel segment made of fiber–reinforced concrete is proposed to improve blast and fire resistance. Shock tube tests on 2-layers circular plates have pointed out that no delamination takes place when exposed to blast waves. The tunnel dynamic response under internal blast loads, in the form of pressure–impulse diagrams, is presented in this paper. The layered precast tunnel segment solution made of different fiber–reinforced cementitious composites is compared with a traditional solution where the lining section is made of reinforced concrete. The results presented show the better performance of the layered solution compared to the traditional one if subjected to internal explosion and in case of pre–explosion fire actions
Influence of Curing Regimes on Flexural Behaviour of Ultra-High Performance Concrete Beams
Mechanical properties of concrete are greatly influenced by curing modes. Hot cured beams often exhibit higher compressive strengths compared to those cured at room temperature. This study sought to investigate and compare the effect of different curing modes on the flexural and shear behaviour of Ultra-high performance fibre reinforced beams (UHPFRC). The research further explores the effect of varying fibre proportions has on beam’s flexural capacity. In this study, a total of nine UHPFRC beams, comprising 7 singly reinforced beams and two beams without longitudinal reinforcements. A compressive strength of up to 170 MPa was achieved in this study. The beams had steel fibre content per volume of 1%, 2% and 4%. The test data of beam deflection, strain, fracture energy and moment capacity are presented in the paper. The results show minor difference in the flexural and deformation behaviour of beams with fibre volumetric ratio of 1% and 2%. The beams with 4% volumetric ratio exhibited higher flexural capacity and in all cases, no shear related failure was recorded. The beams with 2% fibres rom both curing regimes recorded the highest fracture energy
Experimental Study on Fire Performance of Loaded Reinforced Concrete Beams
The performance of reinforced concrete (RC) beams under simultaneous fire and structure loading conditions is presented in this paper. Four RC beams were tested under different configurations viz. two control beams and two beams under fire conditions. The test program includes a series of four experiments on normal and high strength concrete beams. To study the flexural behaviour of RC beams, two reference specimens of different grades (M30 and M60) were tested under four point loading test. In the tests, observations for first cracking load, ultimate load, deflections and fire resistance were monitored. Data from test is utilized to compute performance of normal and high strength concrete beams. Measured temperature and deflection were compared as a function of fire exposure time. Results from the test infer that concrete beams made of normal strength concrete possess higher fire resistance as compared to high strength concrete beams
Post-Fire Investigations of Prestressed Concrete Structures
Concrete structures reinforced with prestressing steel, referred to as prestressed concrete (PSC) structures, are commonly used in bridge and tall building construction as they can easily be optimized. However, prestressing steel is well known to have complex behavior when exposed to high temperatures. To date, this structure’s high temperature behavior is not fully understood and can potentially complicate post-fire structural investigations of PSC structures. After a fire, it is often difficult to guarantee stability or specify necessary repairs for this type of structure. The study herein aims to help develop guidance for investigating and assessing PSC structures (with emphasis on bridge beams) post-fire. Investigations of specific and real PSC structures after fire exposure are reviewed as case studies herein. Characteristic damage indicators and test methods for assessment are discussed. The authors characterize the residual condition of a lab-scale PSC structure previously exposed to severe temperature. Nondestructive strength analyses of prestressing steel using a calibrated hardness test procedure were carried out. Results were compared to those from destructive methods and showed satisfactory correlation. The high temperature exposed concrete was also inspected. The paper concludes with recommendations of future research required to better identify the condition of PSC structures after fires
Tensile Membrane Action and the Performance of Composite Slabs in Fire
A common strategy for reducing passive fire protection on composite floor slabs is to specify protection only to primary and secondary beams on the column grid. While unprotected secondary steel beams lose much of their strength at high temperatures, large deflection of the central zone of the slab causes tensile membrane action (TMA), which enhances its load capacity compared with that of the small-deflection yield-line mechanism, and compensates for this loss of strength. Various simplified models of TMA, starting with the optimal small-deflection yield-line mechanism, have been developed as design methods for fire resistance, based mainly on research published in the 1960s. These methods have been published as design guides in the UK, the European Union and New Zealand, and have been implemented in public-domain design software. A critical appraisal of the original research, and the design methods developed from it, suggests that it is in need of re-development from the first principles of structural mechanics. Disparities exist in the logical approach, both in the treatment of enhancement of yield-line capacity with deflection, and in the limiting deflection corresponding to the “Integrityâ€ limit of fire resistance. While the basic simplification of TMA is justifiable, the re-development needs to follow the sequence of behaviour as a composite slab with unprotected downstand beams is heated in fire. Initial studies of the yield-line behaviour of non-composite slabs and the enhancement of their capacity produced by TMA at finite deflections removed logical flaws from the existing treatments, and allowed the sequence of fracture of concrete and reinforcement to be tracked as deflections increase. However, since the compression zones of a concrete slab heat slowly in a fire and concrete tension cannot be considered in a design analysis, the effects of fire were not directly addressed. In this paper unprotected composite steel beams are included in a composite slab panel, and are heated as fire progresses. The initial yield-line mechanism differs from that of a non-composite slab, and varies with load intensity and beam temperature. This mechanism is fixed, but the slab deflects further as the beam temperatures rise. The formulation allows plasticity and fracture of the reinforcement, and the compressive strength of the concrete. Stresses around the yield lines can be monitored from negligible deflection to structural failure, and provides a rational way of predicting when integrity failure via a through-depth tensile crack will occur
New Design of Beam FRP Reinforcement for Fire Performance
More widespread use of fiber reinforced polymer (FRP) as reinforcement for concrete is hampered by a lack of proven performance in fire. The performance of the FRP reinforcement at elevated temperatures is dominated by the polymer resin that is used as the FRP’s matrix and forms its outer surface. The resin softens at relatively low temperatures – the glass transition temperature of the polymer is typically in the range 60-180°C – and whilst this depends on the resin and cure conditions used, these temperatures will almost certainly be exceeded within a concrete element during a fire. As a consequence, bond will be lost between the reinforcement and the concrete. This paper investigates a new arrangement of internal FRP reinforcement that does not rely only upon bond for load transfer. Instead of using straight, separate, FRP bars as reinforcement, closed FRP loops are used as the longitudinal reinforcement. When the interlock, adhesive, and friction mechanisms of bond force transfer are lost due to softening of the resin, tensile forces in the reinforcement (FRP fibers) can still be carried by the loops. The paper describes the results from an initial series of 4-point bending tests on beams subjected to heating using gas radiant panels under sustained applied load. The tests demonstrate the initial potential of the FRP loop reinforcement system compared to similar FRP-reinforced specimens containing straight bars; however, the performance of the loop-reinforced system was limited by concrete shear failure in the lap area, indicating that a better understanding of the lap length requirements is needed
Elevated Temperature Performance of Concrete Beams Reinforced with FRP Bars
There is a strong case for fibre reinforced polymer (FRP) bars to be used in reinforced concrete (RC) construction, owing to numerous important benefits such as corrosion resistance and high tensile strength. However the limiting temperature for FRP reinforcement in case of fire is typically assumed to be defined by the FRP’s glass transition temperature (Tg); this can prevent FRP from being efficiently used in many structures that require fire resistance ratings. Tensile tests performed at the University of Edinburgh have demonstrated that FRP bars can retain considerable (>50%) tensile strength at temperatures above Tg, and due to their high ambient temperature strength the absolute strength values at a given temperature may be higher than for mild steel reinforcement in many cases. In certain applications it may therefore be reasonable to assume that the critical temperature for FRP bars is greater than Tg, provided that “coolâ€ anchorage zones are maintained. To investigate these ideas, 32 small-scale RC beams were tested with either continuous or spliced FRP or steel reinforcement, at ambient temperature or under transient localised heating. The results confirm that cool anchorage is necessary for fire-safe use of FRP bars as internal reinforcement for concrete; the only alternative is to provide considerably larger concrete covers as compared with steel reinforcing bars. The performance of cool anchored FRP bars is demonstrated to be satisfactory under full service load with midspan bar temperatures typically exceeding 400°C. Residual tests on beams that did not fail during heating showed considerable strength retention in some cases.
Practical Strategies for Enhancing Fire Resistance of FRP-strengthened Reinforced Concrete Beams
macroscopic finite element based computer model is developed and verified that accounts for constitutive material properties at elevated temperatures, temperature induced bond degradation (slip) at the interface of FRP and concrete, and realistic load and restraint conditions. This model is used to conduct a set of parametric studies to establish and quantify influence of different parameters such as fire scenario, insulation scheme, anchorages, bond degradation, axial restraint force and load level on the fire response of FRP-RC beams. In addition, comprehensive experimental studies are conducted on insulated FRP-strengthened RC beams under standard and realistic fires. Five different supplemental fire insulation schemes, four insulation thicknesses and different configuration of end zone anchorages of FRP are examined. Based on test results, as well as the parametric studies, practical strategies including different insulation schemes/configurations, its thicknesses and end anchorages (to reduce debonding mechanism) are presented in this paper to enhance fire response of FRPstrengthened RC beams. Results demonstrate that beyond an optimum insulation thickness, fire resistance does not increase considerably. Moreover, appropriate insulation scheme and effective anchorage towards the end of FRP zone (at terminating points) significantly enhances fire resistance of FRP-RC beam under fire
Fire Protection of CFRP-strengthened RC Structures
The work within describes the test method for determining the contribution to the fire resistance of CFRP-strengthened reinforced concrete structural members, developed in the Fire Testing Laboratory of Building Research Institute (ITB). The first test results have shown that the required thickness of fire protection material is larger than had been expected and calculated numerically. For example, in order to protect the CFRP strips glued onto the beam’s concrete surface, without any mechanical fixing, for 120 minutes of standard fire conditions (ISO 834), which is to maintain temperature on the contact surface between the CFRP strip and concrete lower surface at 62°C (143.6°F), 125 mm of a fire protection is needed. The same insulation material, at only 30 mm thick, can fire proof the same cross-section size RC beam without CFRP-strengthening for 240 minutes
Numerical Analysis of Composite Beams with Shear-tab Connections Subjected to Fire
This paper focuses on the development of detailed numerical models to predict the behavior and failure modes of composite beams with shear-tab connections subjected to combined thermal and gravity loads. The models simulate the behavior of shear-tab connections by incorporating temperature dependent material behavior, surface contact definition in the connection region, and detailed modeling of all connection components. The results of these models include connection rotation histories and composite beam displacement histories which demonstrate the effect of fire protection and fire duration on the composite beam. These models gain insight into the effect of fire protection on the composite beam behavior and axial forces in the connections. Detailed modeling techniques were benchmarked against large-scale experiments of composite beams with simple connections subjected to mechanical and thermal loads (including heating and cooling
Behavior and Design of Composite Beams for Fire Loading
Current U.S. design methods for structures in fire rely upon prescriptive approaches that focus on providing fire protection to keep material temperatures below a given threshold. While these methods are typically conservative, they do not take into consideration the structural performance of such members. In order to move towards a performance-based design approach for fire, it is necessary to quantify not only the thermal response but also the mechanical performance of structural components at elevated temperatures. A numerical model was developed and benchmarked to calculate the flexural capacity of partially composite beams at elevated temperatures. The model accounts for the failure modes associated with composite beam strength including: full yielding of the steel beam, failure of the concrete slab in compression, or shear stud fracture. An extensive parametric study was conducted to determine the influence of variations in cross-section geometry, level of composite action, and temperature distribution. A simple design method for determining the nominal moment capacity of a composite beam at elevated temperatures was developed based upon the parametric study results. This method uses a temperature-dependent retention factor along with the ambient nominal moment capacity to calculate the moment capacity of the composite beam at elevated temperatures
Modelling Thermal Profiles in Fire-Exposed Concrete Filled Hollow Steel Sections Protected with Intumescent Paint
Concrete filled hollow steel (CFS) sections are increasingly used in multi-storey buildings and can, in some cases, provide adequate fire resistance without the need for supplemental fire protection. When calculations show that unprotected CFS sections have inadequate structural capacity at the required fire resistance period (FR), these sections require applied fire protection. For plain steel sections (i.e. unfilled hollow steel sections) the design structural capacity at the required FR is typically assumed to depend only on the limiting steel temperature, and is assumed to be the same for both unprotected and protected sections; however, for CFS sections this assumption does not apply. Heated CFS sections develop thermal gradients within their concrete cores. The cross-sectional thermal gradients, upon which the material properties and structural capacities of CFS sections depend, are influenced by many factors such as: the limiting steel tube temperature assumed in design; the required fire resistance period; and the cross-sectional dimensions. This paper presents a parametric analysis on the effect of these three key parameters on the thermal gradients within CFS sections exposed to an assumed steel temperaturetime history. This is performed using ABAQUS finite element (FE) modelling. This is used to develop a simplified design equation to predict the thermal gradients within CFS columns based on these parameters, supporting a rational, simplified approach for fire resistance prediction of protected CFS columns
Structural Fire Design for Composite Steel Deck Construction in Canada
In Canada, there has been a dearth of research and design attention given to developing innovative fire design solutions for composite steel deck construction. This is despite the increasing number of these constructions in densely populated metropolitan centers in Canada. These structures are currently treated with classic prescriptive based fire designs. Isolated building components are designed based on implicit fire relations and as international practice has shown, prescriptive fire design may be viewed as restrictive, uneconomical, and is challenged in its representation of reality. Internationally, practice has been maturing towards Performance Based Fire Design (PBFD) for composite steel deck structures for the last several decades with significant research into the behavior of these structures occurring. Herein; the first objective is to examine the development of PBFD techniques used globally through relevant experiments, experiences, and applications. The second objective is to explore the state of fire design within Canada and what can be learned from global fire design and research experiences – the international state of the art. The goal is to promote best practice discussion on where structural fire design for composite steel deck construction in Canada, and internationally, could move towards
Behavior of Prestressed Tension Steel Members Exposed to Fire
This paper presents results from fire resistance tests on three prestressed steel tension members. The test variables included degree of prestress and load level. During the tests, axial deformation, temperature, tensile force and failure times are recorded in the prestressed tension steel members. Data from fire tests indicate that during initial stages of fire, the magnitude of tension in the cable strands increases with temperature. Further increase in strand temperature leads to decrease in tension in cable strands resulting from degradation of strength and elastic modules of steel and ultimately approaching zero just prior to failure. Results from these tests indicate that load level has a significant influence on the response of fire exposed prestressed tension steel members, with higher load level leading to lower fire resistance. In addition, the temperature of failure is governed from the level of prestress in prestressed tension steel members, with higher degree of prestress leading to higher failure temperature
Structural Exposure of Steel Frame in Large Fire Incident
This paper reviews a large fire loss that occurred at a seasonally operated Canadian food-processing facility. The structure had been constructed over a 10 year period under different permits and contracts, with an exposed steel structural frame and metal cladding. The interior wall and ceiling surfaces were finished with a metal building insulation (MBI) product that incorporated a polypropylene moisture barrier. The fire occurred when the facility was not in production, resulting in limited fuel load that was confined to localized areas of the facility. The fire developed from a rack storage area that was remote from other fuel packages within the facility, and spread to adjacent areas of the building as a consequence of the polypropylene coating on the MBI. The building partially collapsed many hours after the fire started. The fire origin and cause investigation included the use of metallurgical and hardness testing of the structural steel in conjunction with computer simulations to predict the thermal exposure and fire behavior throughout the collapsed structure
Built-up Closed Cold-Formed Steel Columns with Restrained Thermal Elongation Subjected to Fire
Built-up cold-formed steel sections are widely used in building construction as primary structural elements. However, so far, the research on built-up cold-formed steel structural elements under fire situation is still scarce. Using the commercially available profiles, namely lipped channel (C) and plain channel (U), built-up closed cold-formed steel columns (R) were built and tested under fire conditions with restraint to thermal elongation. A numerical model was developed and calibrated based on the experimental tests in order to accurately reproduce the behavior of coldformed steel columns with restrained thermal elongation. It was found that the critical temperatures may be significantly influenced by the level of thermal restraint provided by the surrounding structure to the cold-formed steel column in fire
Probabilistic Evaluation o-Story Steel MRF Subject to Post Earthquake Fires
This paper investigates the structural performance of a steel moment resisting frame (MRF) subject to fire and fire following earthquake, using a methodology that is based on system level reliability analysis. The study includes probabilistic models for the quantities with uncertainty including fire load, and mechanical and thermal properties of steel at elevated temperatures. Performance of the structure is evaluated based on several different limit states, and at different fire locations. Results show that the location of fire in the frame (e.g., lower vs. upper floors and interior vs. exterior bays) affects the beam response. Compartments in the interior bays reach limit states faster than those on the perimeter, and upper floors reach limit sates sooner than lower floors. The post-earthquake damage does not affect the structural response under a fire for the considered limit states; however, fire following earthquake increases the drift demand on columns located on the perimeter of the structure.
Fire Performance of Steel Tubular Columns Filled with Normal Strength Concrete
The main goal of this paper is to predict the fire resistance rating (FRR) of composite concrete filled tubular (CFT) columns without external fire protection. In order to do that, the response of axially and eccentrically loaded columns to mechanical load in fire conditions is investigated. This study is based on data from 41 available full scale tests of columns filled with siliceous aggregate normal strength plain concrete, tested in the last 25 years by various researchers [1-6]. Analyses are carried out taken into account different parameters for which results are given, including different stress-strain relationships for concrete combined with two yield criterions, namely linear and hyperbolic Drucker-Prager. Different formulations of thermal expansion are investigated. Regarding properties influencing temperatures inside the cross-section, influence of formulations of specific heat of concrete and thermal gap conductance between steel tube and concrete core are investigated. Sensitivity study concerning mesh size as well as imperfections shape and magnitude is carried out. Recommendations regarding model application range are given based on evaluation of the results, which are plotted or showed against independent variables such as relative slenderness, utilization ratio or boundary conditions. Mean ratio of calculated fire resistance time to time of fire resistance measured during experimental test is presented. For the proposed model and for set of 41 tested specimens the ratio is around 1.0, with a standard deviation around 0.3 for all specimens, while standard deviation does not exceed 0.2 for pinned-fixed and fixed-fixed columns in most cases. Selected results are presented in detail.
A Streamlined Approach to Calculating the Response of Bridge Structures to Open-Air Hydrocarbon Fires
A streamlined, simplified methodology is proposed for the efficient calculation of a bridge’s response to a vehicle-based hydrocarbon pool fire resulting from a tanker truck crash via a four-step methodology: (1) calculate the fire’s characteristics and geometry; (2) calculate the heat transfer from the fire to the structural elements; and (3) calculate the temperature increase of the structural elements; and (4) calculate the resulting material and mechanical response of the structural elements. The approach synthesizes numerous calculation techniques based on both first principles and empirical data to quantify the extent of the damage caused by a specified fire threat. The methodology is used to demonstrate the design process for fire protection on a cable-stayed bridge
A Priori Round Robin Study of the Calculated Response of Loaded Steel Beam to a Furnace Test
This paper reports on a round robin study of the calculated response of structures in fire. In this instance, the tests which the study is based on are two fire tests which were conducted on two steel beams at SP’s fire resistance laboratory in Sweden. The two specimens in the test were identical having come from the same cast flow. The tests were conducted according to EN 1365-3 and the steel beams had a total length 5.4 m, spanning 5.2 m. The calculations were conducted by different groups ‘a priori’ and ‘a posteriori’ to the test itself. In the first instance a prediction of the response was made without knowledge of the measured temperatures of the steel beam, and in the second the participants were given the measured temperatures from the steel beam and asked to refine their model. This paper reports on the first stage results only. Statistical analysis of the round robin are presented to illustrate the variation which arises in the results of calculations The results of the round robin study highlight the fire research and testing community’s capability for modelling this simple case as well as the uncertainty in the calculation results. Future publications will include the 2nd stage round robin conducted ‘a posteriori’ and it is our intention to carry out future round robins with more complex structures and assemblies which will supplement this work
Experimental Study on the Fire Endurance of Post-installed Rebar Connection System
Post-installed rebar connection system (PIRCS) is being increasing used in rehabilitating and retrofitting. Since the fire exposure is one of the most severe risks in the service life of PIRCS, it is of significance to understand the behavior of PIRCS under fire. In this paper, a theoretical method was developed to predict the fire endurance of PIRCS. As the preliminary study, pull-out tests were undertaken to figure out the bond-slip behavior of post-installed rebar at elevated temperatures. To verify the proposed method, 6 specimens reinforced with post-installed rebars were tested under the ISO 834 fire with constant loads. The parametric studies were carried out on the thickness of concrete cover and embedment length. The proposed method is proved to be acceptable in accuracy and applicable in evaluating the fire endurance of PIRCS for design purposes
Improvements in Predictions for Steel Fire Doors Subjected to the Fire Endurance Test
Fire doors are subjected to fire standards tests as a means of evaluating fire resistance. However, the complexity of the heat transfer and resulting property changes over the wide temperature range makes it a challenge for manufacturers to predict how the fire doors will perform. To help advance the use of modeling tools to provide product performance insight, UL started an intensive research program to collect data and use it to validate FEA-based predictions of the thermal and mechanical responses of steel double fire doors exposed to high temperatures. The models included the necessary complexity of the product and test setup along with temperature dependency of the constituent materials over the temperature of the test to help provide helpful predictions for manufacturers. In this paper, we provide a preview of the some of the model results
Structural Fire Exposure of Transit Stations Relative to Vehicle Fires
This paper presents a discussion of factors affecting fire development in rapid transit vehicles1 and the subsequent thermal exposure considerations relative to open transit stations. The primary fire hazard in rapid transit stations would typically be the train itself, which would correlate with highly localized exposure which is inconsistent with the type of standard time-temperature curve fire exposure that is assumed within a building code context. The application of an engineering analysis to evaluate the potential fire exposure analysis to the structure requires consideration of applicable methodology, risk context, and appropriate structural performance criteria. In this study an example analysis of two generalized open transit station configurations is outlined using Computational Fluid Dynamics to evaluate the thermal exposure of structural steel elements using a range of fire sizes
Strategies for Enhancing Fire Performance of Steel Bridges
Bridge fires can lead to significant economic and public losses; however, no provisions are specified for fire resistance of bridge structural members in current codes and standards. This paper presents an approach for mitigating fire hazard in bridges. The approach comprises of two steps, estimating fire risk in a bridge, and then developing strategies for enhancing fire resistance of a critical bridge. An analytical procedure is employed to derive a fire-based importance factor to estimate the vulnerability of a bridge to fire, and then a sequential finite element analysis is carried out to develop strategies for mitigating fire hazard in that bridge. The validity and applicability of this approach is demonstrated through a case study on a steel bridge that experienced fire recently. Through this case study, it is shown that the proposed approach can be used as a practical tool for identifying critical bridges from the point of fire hazard and then developing solutions to overcome fire hazard in such critical bridges
Performance of Prestressed Concrete Bridge Girders Exposed to Fire
This paper presents an investigation into performance of prestressed concrete bridge girders exposed to fire. A numerical model, in the form of a computer program, for tracing the behavior of prestressed concrete (PC) bridges with T girders subjected to fire is presented. The three stages associated with the numerical procedure for evaluating fire resistance of PC bridge girders; namely, fire temperature calculation, cross sectional temperature evaluation and strength and deformation analysis in girders are explained. A simplified approach to account for deformations under fire conditions is incorporated into the model. The applicability of the computer program for tracing the response of PC bridges, due to combined effect of fire and structure loading, is demonstrated through a case study. Through the results of case study, it is shown that the type of limit state adopted in defining failure has significant influence on the fire resistance of PC bridge girders
Ballistic and Fire Resistance of Hybrid GRP Reinforced Timber Doors
This paper presents the results of Ballistic resistance tests on timber doors. Timber is known to be very weak in resisting bullet shots particularly the frame which may represents the weakest path in the door against ballistics. The newly developed doors consist of sandwich layers of GRP and timber which can significantly increase the bullet resistance of the doors. GRP is one of the new emerging bullet proof materials that have strength around 6-8 times more than steel. High tensile steel hinges and locks were used to resist the bullets’ impact and were attached securely to the door and the frame to avoid punching failure. The bullet proof test of the doors was performed according to the EN1522:1999 standards aiming towards FB4 resistance which consist or .44 Magnum handgun at 440 m/s speed of the 15.62 gm bullet mass. Details of the tests and prototypes are presented in the paper. The doors were able to pass a test of 60 minutes exposure to ISO 834 fire curve. The paper ends with concluding remarks on improving the bullet proof resistance of timber doors
Applying Fire-LCA Methodology to Fire Protection Systems in Buildings
The use of Fire-LCA output data as input to fire engineering design models are demonstrated for a simple case of a load bearing column protected by mineral wool. The Fire-LCA model takes accidental fires into account as a possible end of life scenario for the building elements, affecting environmental impact and service life. The method only considers preprocessed LCA data and uses simple engineering tools
Development of Fire Field Model Incorporating Pyrolysis for Burning of Flame-Retardant Polystyrene in Enclosures
In this paper, the research and developments this novel flame-retardant polystyrene is presented and their fire field modelling are reviewed. The state-ofthe- art, comprehensive and robust fire model based on computational fluid dynamics techniques is developed for flame-retarded polystyrene to further understand and predict their fire characteristics and performances for full-scale applications in buildings and assist performance-based fire engineering designs. The established fire model and the associated methodology can be a generalized framework for fire behaviors and performances of other flame-retardant polymeric materials
Assessment and Rehabilitation of Fire Damaged Reinforced Concrete Building – A Case Study
This paper presents a case study of fire damaged reinforced concrete frame structure built with a central core and supported on raft foundation. A fire broke on top floor (16th floor) and spread down to fourth floor for about 10 hours duration. Damage assessment was carried out based on facts, observations and data collection through visual and structural surveys, material testing through destructive and nondestructive (NDT) testing, and load test to estimate residual strength. Crack patterns were recorded, depth of spalling of concrete and deflections measured, and interpreted to identify critically damaged structural members, assess residual capacity and requirement of strengthening to resist design loads. In addition, finite element structural analysis was conducted using ETABS by integrating changed material properties due to elevated temperatures and results compared with original structural design.
With the increasing use of combustible materials in façades to reach energy performance of buildings, fire safety is a growing issue. Many believe that façades have no or little impact on the spread of fire in buildings. Two large scale tests have been carried out in Croatia in March and May 2014 by a team of experts from Sweden, Slovenia and Croatia and representatives from Fire Safe Europe and Croatian Association for Fire Protection. In each test three specimens were constructed where three different types of ETICS systems were erected on brick walls. ETICS with combustible insulation (EPS) + organic render, ETICS with combustible insulation (EPS) + organic render and with fire barriers around the openings and ETICS with non-combustible insulation (MW) + organic render were performed and tested. Measurements of the temperature change was performed according to BS 8414 on all three specimens, by using Type K thermocouples mineral insulated and additional temperature measurements were performed by using plate thermometers, together with thermo couples, respectively. Load cells were installed in order to monitor the change of the mass of the wood cribs, i.e. the rate of fuel consumption. Additionally, the specimens were visually monitored and the temperature was measured by using the infrared thermography. This paper presents the testing results from the test performed in March 2014 of these three different types of ETICS system regarding their fire performance according to the BS 8414 standard. Through the testing of three different types of ETICS system regarding their fire performance it has been revealed that façade fires can in fact spread very rapidly depending on the type of materials used. Also existing standardized full scale fire tests do not cover all essential parameters for the development of a fire. Through the additional measurements carried out during the testing valuable information to supplement and upgrade existing fire tests standards were gathered.
Development of a Matrix Method Based Framework for the Thermo-Mechanical Analysis of RCC Frames
Reinforced concrete frames are one of the predominant structural systems which are commonly used in India. Fire resistance is an important design aspect as fire is one of the most severe environmental conditions to which structures may be exposed to during their life time. Typical fire resistance analysis involves evaluation of temperature across the structural member and incorporation of the thermal effects in structural analysis by temperature dependent material models of concrete and steel employing various numerical schemes. The main limitation of these methods is that they evaluate the fire resistance of individual structural components and they lack the competency to quantify the response of whole structure. Thermo-mechanical analysis can be carried out in commercial finite element software like ANSYS but modeling an entire structure is computationally very intensive. To alleviate these difficulties, a matrix analysis methodology has been developed incorporating the effects of thermal strains as well as temperature dependent material models of concrete and steel. The key strength of matrix analysis lies in its computational efficiency compared to ANSYS while producing results of reasonable accuracy. Numerical examples are presented to demonstrate the efficacy of the developed methodology
Fires in the open or in large enclosures are characterized as localized fires, e.g., vehicle fires in transportation infrastructures, small shop fires in transport terminal halls, and workstation fires in open plan office buildings. Compartment fires start from localized burning. The current structural fire design approaches are developed for fully-developed compartment fires, the gas temperatures of which can be approximated as uniformly distributed in the compartment. In localized fires, the gas temperature distributions are spatially non-uniform. There is lack of knowledge about the behavior of structures subjected to localized fires. Design guides and engineering approaches are needed for structural safety design in localized fires. This paper discusses the application of localized fires for structural safety design. Some recent studies on the thermal calculation and structural analysis of steel members subjected to localized fires were presented. Simple fire models were provided to calculate the temperature of exposed steel members in a localized fire. Thermo-mechanical simulations were performed to investigate the failure mode of bare steel members in a localized fire. The studies found that due to thermal gradient, a bare steel member may fail in a totally different way in a localized fire than in a standard fire; and the failure temperature for a bare steel member in a localized fire might be hundreds of degree lower than that in a standard fire. Using the proposed simple models, an engineering approach was also provided to determine the safety distance from a bare steel column to a fire source, which could be used in a performance-based fire safety design