Post-earthquake Fire Resistance Research Articles

Effects of Structural Size on Postearthquake Fire Resistance of HSS-CHS-SHS T-Joints under Nonuniform Elevated Temperatures

Effects of Structural Size on Postearthquake Fire Resistance of HSS-CHS-SHS T-Joints under Nonuniform Elevated Temperatures

Assessment of post-earthquake fire capacity of RC frames without seismic design

To study the importance of post-earthquake fire events, 500 reinforced concrete (RC) frames were designed without seismic considerations. These consist in three-bays frames with a variation in the number of floors from two to six (100 frames each). Numerical analyses were performed in SAFIR to investigate the influence of different types of damage, damage location, fire location and fire curves on the post-earthquake fire resistance of the structures. It was observed that the seismic damage can significantly decrease the fire resistance of the frames. In an earthquake scenario it can be expected an increase in the response times of the firefighters as well as malfunctioning and damage of active and passive firefighting measures, which means that the use of parametric fire curves without active firefighting measures can be a better approach instead of the use of the fire curve ISO 834. It was observed, for the analysed cases, that parametric fire curves without active firefighting measures led to lower collapse times when compared to the fire curve ISO 834. On the other hand, when the active firefighting measures are considered, there is a very significant number of structures that do not collapse, which indicates the importance that these firefighting measures can have in a fire after an earthquake. The development of these analysis emphasizes the impacts of applying different fire curves on the damaged structure which consequently brings attention to an adequate definition of the fire curves.

Post-earthquake fire resistance of self-centering concrete beam-column joint: An experimental investigation

Fire is an accidental disaster resulting in disastrous consequences for building. Post-earthquake fire is a secondary disaster induced by earthquake, triggering off larger destruction in a higher probability of occurrence. The potential severity of consequences to structures makes fire and post-earthquake fire safety imperative in the design of any new structures. Self-centering concrete joints are introduced as a promoting alternative to traditional reinforced concrete (RC) joints. They always exhibit excellent seismic performance and self-centering capacity, available in high-seismic zone. However, the current lack of experimental data on fire response of self-centering concrete joints means that they remain an open issue in current design codes. In this paper, full-scale quasi-static cyclic test and fire tests were conducted on two self-centering concrete joints connected with bolted angles and posttensioned (PT) tendons. The experiments aimed to explore the performance of self-centering joint in fire situations, and the impact of post-earthquake damages on fire response of self-centering joint. The deformation patterns and thermal responses of self-centering joints including temperature distribution, prestress force of PT tendons, displacements at beam ends and duration were recorded and analyzed. The results show that both self-centering joints exhibited satisfactory fire resistance with endurance over 170 min. Generally, the bolted angles and PT tendons in self-centering concrete joints showed acceptable working performance in fire. The findings unveil the actual response of self-centering concrete joints during the fire and post-earthquake fire conditions, providing experimental data for further numerical simulation and analysis. It can be used to calibrate the design approach for self-centering joints under fire and seismic-induced fire exposure.

Parametric analysis of post-earthquake fire resistance of reinforced concrete frames without seismic design

To gain a deeper understanding of post-earthquake fire behaviour, 100 reinforced concrete (RC) frames representative of a building stock designed without considering seismic loading were modelled using the software SAFIR. A total of 4400 numerical analyses were performed to investigate the impact of different assumptions, such as the type of damage, damage location, number of sides of the RC elements exposed to fire, location of the fire and different fire curves on the post-earthquake fire resistance of the RC frames. Results showed that heavily damaged frames have significantly lower fire resistance compared to undamaged frames. Variations in the number of heated sides and fire locations were found to lead to significant differences in the time until the collapse of the RC frames. Moreover, due to increased demand for assistance following a large earthquake, rescue teams are likely to experience prolonged response times, exacerbating the potential for loss of life and infrastructure. Assuming parametric fire curves without firefighting efforts is a reasonable approach in post-earthquake events. This approach led to quicker collapse times compared to the standard fire curve ISO 834. This aspect combined with a lower fire resistance of the damaged structures can ultimately lead to the loss of lives and infrastructures. Therefore, a comprehensive understanding of post-earthquake fire behaviour becomes crucial for developing recommendations that can ensure the safety of RC structures in such events.

Effects of structure size on post-earthquake fire resistance of CCBCC joints at non-uniform elevated temperatures

The probability of secondary fires caused by earthquakes is very high. Due to the residual stress and deformation caused by earthquakes, the mechanical behavior of cruciform combined beam-CFST column (CCBCC) joints is extremely complex. In view of this, the goal of this study is to investigate the effects of structure size on the post-earthquake fire failure mechanism of CCBCC joints under gradient temperatures. The calculation model in this article was validated using existing experimental results, subsequently 20 computational models were established to conduct parameter analysis, including the width-to-thickness ratio (γ) of the CFST column, the slenderness ratio (λ) of the CFST column, the width-to-thickness ratio (α) of beam flange, the height-to-thickness ratio (β) of beam web and the damage variable (D̃). The results have demonstrated that the post-earthquake fire resistance of CCBCC joints is mostly affected by damage variable. Parameters β, α, λ and γ also have a significant impact on the failure of these joints. An empirical bearing capacity prediction model of CCBCC joints is obtained. The research results can provide reference and data support for the design, maintenance, and reinforcement of CCBCC joints under post-earthquake fire.

Post-earthquake fire behaviour of a self-centring connection with buckling-restrained plates and pre-stressed bars: An experimental investigation

Earthquake is recognised as one of the most destructive hazards not only because of the loss and casualties caused by itself, but also the secondary disasters triggered by it. Among hazards following the earthquake, fire is the most common and threatening one that should be paid more attention. For the self-centring system initially proposed to mainly serve the seismic demands, it is necessary to understand its behaviour in post-earthquake fire scenarios to ensure comprehensive performance. However, neither the actual experimental response nor the systematic analysis has been conducted, leading to a lack of relevant knowledge. Based on that, this study mainly aims to explore the structural response and understand the failure procedure of a self-centring steel system under the earthquake-fire sequence. The focused configuration consists of buckling-restrained plates for energy dissipation and pre-stressed bars for self-centring. The quasi-static cyclic tests and standard fire tests were conducted on the cross-shaped self-centring connection derived from a prototype frame. Besides, a thermal-only test was supplemented to clearly distinguish the thermal and mechanical effects under fire. Results show that the target connection has excellent seismic performance under a peak drift ratio as high as 6%. In the meantime, it appears satisfactory post-earthquake fire resistance with endurance over 1.5 h and failure temperature higher than 900 °C. Thermal and mechanical effects are found to separately dominate the global response under post-earthquake fire, first the uneven thermal expansion and then the mechanical degradation at elevated temperatures. Moreover, buckling-restrained plates serve as the major damage element throughout the earthquake-fire sequence and fracture is detected on the side with severer seismic damage. Pre-stressed bars provide self-centring capacity under cyclic loadings but fail to retain the pre-tension in the subsequent fire. The findings reveal the actual response of the self-centring system for fundamental understanding, and can be extended for thermo-mechanical numerical calibration and further analysis, to help improve the comprehensive performance of self-centring structures under earthquake-fire sequence.

Post-earthquake fire resistance of stainless steel K-joints considering gradient temperature effect

The objective of this paper is to investigate the fire resistance of the stainless steel K-joints considering gradient temperature effect under post-earthquake fire given that there is no relevant research on this kind of the stainless steel K-joints. The possibility of a fire resulting from an earthquake is high, the residual stress and residual deformation caused by an earthquake will remarkably reduce the fire resistance of the stainless steel K-joints. It is of practical interest to explore the post-earthquake fire resistance of the stainless steel K-joints. Accuracy and reliability of computation models to the stainless steel K-joints were validated using existing test results, temperature field distribution was obtained via transient response analysis, 24 computation models were established using finite element software ANASYS, then a parameter study was conducted by considering following parameters such as the diameter ratio of brace to chord (β), diameter to wall thickness ratio of chord (α), wall thickness ratio of brace to chord (η), thickness of the fire coating protection (tfr), angle between the brace and the chord (θ) and damage variable (D~). The results demonstrated that the parameters β, α, tfr, and θ had significant impacts on the post-earthquake fire resistance associated with the stainless steel K-joints, the damage variable D~had a dramatic effect on the post-earthquake fire resistance of the stainless steel K-Joints. The findings related to this study can provide the reference value for the design, maintenance and reinforcement against the stainless steel K-joints.

Post-earthquake fire resistance of bolted end-plate connection joint with end-plate and web stiffeners

This paper aims to study the fire resistance of the extended end-plate connection (EEPC) joints under post-earthquake fire (PEF) by considering different earthquake damages, which can reduce the fire resistance of the EEPC-joints. The effectiveness and accuracy of the computation models were verified by using the existing test results. Then, the fire resistance of 8 kinds of the EEPC-joints with different stiffening strategies were compared and analyzed. The results showed that the extended end-plate connection with pentagon end-plate stiffeners and web stiffeners had the best fire resistance and was selected to conduct a parametric analysis under PEF. In order to investigate the effects of different parameters on the fire resistance of the EEPC-joints under PEF, 25 computational models of the extended end-plate connections with pentagon end-plate stiffeners and web stiffeners were established. Then, a parametric study was performed by considering the column flange width-thickness ratio (α), beam web height-thickness ratio (β), ratio of beam end-plate stiffener thickness to beam end-plate thickness (γ), ratio of the thickness of column web stiffeners to the thickness of the column end-plate (λ), ratio of the thickness of beam end-plate to column end-plate (ξ), the thickness of non-intumescent fire retardant coating and damage variable (D~). The results showed that damage variables had significant influence on the fire resistance of the EEPC-joints under PEF. The findings of this study can provide the needed reference for fire resistance design of the EEPC-joints under PEF.

Post-earthquake fire resistance of tall steel concentrically braced frames

The fire which occurs after an earthquake causes great problems for buildings situated in moderate to high seismic regions. In this article in order to have an understanding regarding the impacts of post-earthquake fire on the structures, implementing the finite element method, the behaviour of tall steel concentrically braced frames when subjected to this type of loading was investigated. The simulation under seismic loading was done using the nonlinear time history analysis. Assuming the post-earthquake situation of the structure as the initial condition, the mechanical-thermal analysis was applied using the temperature-time diagram on the exposed elements. The analysis results showed that regardless of the earthquake record and fire scenarios for the tall steel concentrically braced frames, the fire resistance duration was short and the impacts of the previous earthquake on the structure fire resistance were not considerable.

Post-Earthquake Fire Resistance and Residual Seismic Capacity of Reinforced Concrete Columns

Post-Earthquake Fire Resistance and Residual Seismic Capacity of Reinforced Concrete Columns

Fire resistance of thin-walled tubular T-joints with internal ring stiffeners under post-earthquake fire

Abstract The objective of this paper is to computationally investigate the fire resistance of earthquake-damaged thin-walled tubular T-joints stiffened with internal rings at elevated temperatures. An earthquake can cause severe damage to the T-joints, thus may lead to the reduction of fire resistance after that. Additionally, given the needs in improving the performance of T-joints using stiffeners, the behaviors and fire performance of these stiffened T-joints under post-earthquake fire (PEF) is of great interests. A computational model, validated with the existing experimental results, is established to conduct the analysis of the fire resistance behavior of the stiffened tubular T-joints under PEF. Then, by using this model, the stiffening strategies for tubular T-joints using 1 internal ring, 2, and 3 internal rings, are evaluated along with the unstiffened case to investigate their effectiveness in improving the fire resistance capability under PEF. Later, a parametric study is performed for the stiffened T-joints with 3 internal rings under PEF using the validated computational model. 24 finite element models are analyzed under different damage levels, by considering the following key geometric parameters: the diameter ratio (β), the wall thickness ratio (γ) of the T-joint's chord and brace members, the diameter-thickness ratio (α) of the chord member, and the thickness ratio η of ring-stiffener and chord along with the damage variable ( D ˜ ) to account for the level of the T-joint being damaged. The results on different stiffening strategies and the parametric study reveal that the significant influence of the damage variable and the sensitivities of other influencing parameters. The findings from this study provide needed evidence for potential design recommendations for post-earthquake fire resistance of stiffened tubular T-joints.

Fire resistance behavior of earthquake-damaged tubular T-joints at elevated temperatures

The objective of this paper is to establish a computational model and use the model to investigate the fire resistance capability of tubular T-joints after earthquake through a parametric study. Past events statistics suggest that an earthquake may cause severe damage to the structural members, thus leads to the reduction of fire resistance after that. However, the available studies are limited to the investigations of the mechanical behavior of reinforced or unreinforced T-joints at either ambient temperature or fire alone. A computational model of the tubular T-joints is developed to simulate the behavior of the earthquake-damaged T-joints under evaluated temperature. The developed computational model is validated with the existing experimental results. Then, by using this model, a parametric study is conducted to investigate the impact of the several geometrical parameters in terms of the diameter ratio and the wall thickness ratio of the T-joint's chord and brace members along the diameter-thickness ratio of the chord member along with the damage variable to account for the level of the T-joint being damaged (or how large is the residual stress and deformation of the T-joint after the earthquake). The parametric analyses demonstrate that the significant influence of the damage variable and provide needed evidence for potential design recommendations for post-earthquake fire resistance of tubular T-joints.

Effect of earthquake damage on the behaviour of composite steel frames in fire

Fire loading following earthquake loading is possible in any building in a seismic-prone area. However, most design approaches do not consider fire following earthquake as a specific loading case. Moreover, seismic design philosophies allow a certain degree of damage in structural elements which make structures more vulnerable when subjected to post-earthquake fire. This study uses three-dimensional numerical models to investigate the effect of earthquake damage on the fire resistance of composite steel-frame office buildings. A total of two types of earthquake damage, fire insulation delamination and residual lateral frame deformation, are investigated. It is concluded that earthquake damage can significantly reduce the fire resistance of composite buildings, with delamination of fire protection having the greatest effect. The results of this study can be used by designers to improve the post-earthquake fire resistance of composite buildings.

Post-earthquake fire resistance of steel buildings

Current design procedures do not account for the concomitant or subsequent occurrence of earthquakes and fires, which has so far been justified by the low probability of occurrence of accidental actions. Nevertheless, fires are often triggered as a consequence of damage caused by the earthquake and are responsible for casualties and major additional damage to buildings and other constructions. Despite a number of research studies on the topic, it is at present unclear as to what extent the occurrence of a previous earthquake could affect the response of a structure to fire.The response of a moment-resistant steel frame to post-earthquake fires (PEFs) is investigated and compared with the response of the undamaged frame exposed to fire only, by means of numerical analyses performed using a commercial finite element software. The frame considered as a case study is not insulated against fire, but it is designed to comply with the service damage limitation prescribed in EN1998-1 (2004). The nonlinear seismic response to 7 different earthquakes, scaled at the same peak ground acceleration (PGA), is analyzed; then two of these earthquakes are selected for the post-earthquake fire (PEF) computations and a number of critical fire scenarios are identified, based on the vicinity of the fire to the highest permanent deformation induced by the earthquakes. The structural elements involved in each fire scenario are considered to be exposed to a standard fire and the collapse mode and time are determined by means of large deformation analysis.The comparison of the mode and time of the frame collapse for all the investigated scenarios shows a minor influence of the effect of the two considered earthquakes on the fire resistance of the frame. The current study shows that nonlinear geometric effects do not have a significant effect in the behavior of the building during fire, when the structure is designed to comply with the service damage limit states prescribed in EN1998-1 (2004).

Firewalls and post-earthquake fire resistance of reinforced-concrete frames

Post-earthquake fire (PEF) contributes significantly to loss of life and property following large earthquakes in urban regions. In the absence of adequate PEF provisions in the codes and criteria, an investigation is performed on a reinforced concrete portal frame, divided into two unequal parts by a firewall. Acknowledging that firewalls could break down after earthquake, three fire exposure scenarios are assumed: only the left part exposed, only the right part exposed and the entire frame exposed. In the first two scenarios, the firewall remains intact, whereas in the third it is assumed to be broken down. The building is first pushed to displacement corresponding to the life safety level of performance based on FEMA 356 code. Then, using a natural fire curve, fire analysis is performed. Fire-alone analysis is performed to provide a point of reference. No failure occurs in any of the fire-alone scenarios, or when exposing the smaller part of the building to the PEF. In contrast, exposing the larger part and the entire frame to PEF makes the frame fail at around 50 min and 25 min, respectively. This shows the importance of firewalls to reduce vulnerability of reinforced concrete buildings in case of PEF. The approach used allows designers to choose the position and configuration of firewalls to best protect a building against PEF.

Numerical evaluation of the post-earthquake fire resistance of CFRP-strengthened reinforced concrete joints based on experimental observations

This article describes experimental and numerical studies on the structural resistance of two reinforced concrete beam-column joints. While both specimens are of similar configurations as for geometry, amount and type of steel reinforcement and concrete strength, the second is strengthened by means of carbon fibre-reinforced polymer (CFRP) at the vicinity of the joint in order to relocate the plastic hinge away from the column extremity towards the beam. Both specimens are subjected to a cyclic load followed by a generalised exponential fire curve, which implicitly represents a post-earthquake fire (PEF). The PEF resistance of the specimens subjected to various damage levels such as immediate occupancy (IO), life safety (LS) and collapse prevention (CP) is then evaluated based on finite element analysis. The results show that while the fire resistances of the original specimen subjected to LS and CP damage levels are about 32 and 15 min, respectively, they increase in the CFRP-strengthened specimen to about 43 and 23 min, respectively. This represents a 25% increase at LS level and a 35% increase at CP level.

Plastic Hinge Relocation in Reinforced Concrete Frames as a Method of Improving Post-earthquake Fire Resistance

Post-earthquake fire (PEF) presents a risky situation to buildings that have been partially damaged in a prior earthquake, particularly in urban areas. As most standards ignore the possibility of fire after earthquake, buildings are not adequately designed for that possibility and thus PEF is a high-risk load needed to be scrutinized further, codified and become part of a routine design. An investigation based on sequential analysis inspired by FEMA356 is performed here on a two story RC frame, at the Life Safety performance level and designed to the ACI 318-08 code, after it has been subjected to a spectral PGA of 0.35g. The results show that structures previously damaged by the earthquake and exposed to PEF are considerably more vulnerable than the structures, which have not been damaged previously. A method of strengthening using Carbon Fiber Reinforced Polymer (CFRP) wraps is introduced in order to relocate plastic hinges away from the column faces towards the beams. This method increases the structural load carrying capacity, and thus reduces the potential damage from a potential earthquake, improving the fire resistance. The results show a considerable improvement in the PEF resistance of the frame.

Post-Earthquake Fire performance-based behavior of unprotected moment resisting 2D steel frames

Post-Earthquake Fire (PEF) can lead to the collapse of buildings that are partially damaged in a prior earthquake that occurred immediately before the fire. The majority of standards and codes for the design of structures against earthquake ignore the possibility of PEF and thus buildings designed with those codes fail prematurely when subjected to PEF. A sequential analysis based on FEMA356 is performed here on the Immediate Occupancy (IO), corresponding to a structure designed as school occupancy, and Life Safety (LS) performance levels, corresponding to a structure designed as reside ntial occupancy, of two steel moment resisting frames. These frames are first subjected to an earthquake load with the PGA of 0.35g. This is followed by a fire analysis, using both the ISO834 model and the Natural fire model. The time it takes for the structure weakened by the earthquake to collapse under fire is then calculated. As a point of reference, fire only analyses are also performed for the undamaged structures. The results show that earthquake weakened structures are more vulnerable to fire than undamaged structures. The results also show that both fire resistance and PEF resistance of the frame designed as school are more than the frame designed as residential. Whilst the investigation is for a certain class of structures (steel moment resisting frames, 5 stories), the results confirm the need for the incorporation of PEF in the process of analysis and design and provides some quantitative measures on the level of associated effects.

An Engineering Solution to Improve Post-Earthquake Fire Resistance in Important Reinforced Concrete Structures

An investigation based on sequential analysis is performed here on the Immediate Occupancy performance level of important structures designed to the ACI 318–08 code after they are subjected to earthquake level with PGA of 0.30 g. This is followed by a fire analysis of the damaged structure, from which the time it takes for the damaged structure to collapse is calculated. As a benchmark, the fire analysis is also performed for the undamaged structure and before the occurrence of earthquake. The results indicate that the vulnerability of structures increases when a previously damaged structure is exposed to fire. A post-earthquake fire (PEF) factor as a function of the required fire resistance time is then proposed to improve the fire resistance of important buildings subjected to PEF. Whilst the investigation is for a certain class of structures (important building, intermediate reinforced structure, 5 stories) and the results can only be expected to be applicable to the cases investigated, it is hoped that it paves the way for further research into this important phenomenon.

A Post-Earthquake Fire Factor to Improve the Fire Resistance of Damaged Ordinary Reinforced Concrete Structures

Post-earthquake fire (PEF) is considered as one of the most problematic potentially possible disasters in urban areas, as it may result in a conflagration. Most standards and criteria, however, ignore the possibility of fire after earthquake and therefore, majority of conventional buildings are not designed to resist thermal loading after an earthquake. Thus, there is high likelihood of rapid collapse for those buildings damaged partially after an earthquake, which are subjected immediately to a following fire. An investigation based on sequential analysis inspired by FEMA356 is performed in this paper on two RC frames; three and five stories at the Life-Safety performance level and designed to the ACI 318-08 code after they are subjected to a spectral PGA of 0.35g. This is followed by a five-hour fire analysis of the weakened structures, from which the time it takes for the damaged structures to collapse is calculated. As a point of reference, the fire resistance is also determined for undamaged structures and before the occurrence of earthquake. The results show that the structures previously damaged by the earthquake and exposed to PEF are more vulnerable than those that are not damaged. A CPEF greater than 1 is then introduced as a function of fire extinguishing or evacuating time that can be multiplied by the base shear at the time of design in order to increase members sizes and thus improve the PEF resistance. Whilst the investigation is for a certain class of structures (ordinary buildings, intermediate reinforced concrete structure, three and five stories), the results confirm the need for the incorporation of post earthquake fire in the process of analysis and design, and provides some quantitative measures on the level of associated effects.