Post-earthquake Fire Research Articles

Fire resistance of stiffened CFDST columns after earthquake-induced damages

Abstract Despite the awareness about the hazard gained through the past evidence, fire following an earthquake remains a predominant agent of damage to buildings and life-line structures. Often the damage caused by the subsequent fire can be more severe than the damage caused by the ground motion itself. Concrete filled double skin tube (CFDST) columns as a special composite structure are particularly prone to the inadequate steel-concrete interface bonding and subsequent local buckling during separate fire conditions and seismic action. To establish a favorable interface interaction between steel and concrete as well as to postpone overall buckling under post-earthquake fire, the effectiveness of stiffening CFDST columns with longitudinal steel stiffeners are investigated. The analyses on CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes are conducted with a sequentially coupled approach, starting with a heat transfer analysis and followed by a stress/deformation solution. In the finite element modeling, the confinement provided by both the inner and outer tubes on the compressive strength of concrete is accounted for. The effect of concrete fracture is incorporated by inserting a horizontal discrete crack model at the location of the major tensile crack. The results showed that stiffeners on the exterior surface of the inner tubes are among the most effective of various patterns studied in enhancing the fire endurance of the columns up to 64%. For stiffened CFDST columns contrary to the unstiffened ones, the fire-resistance reduction to seismic damage is usually less than 5% of the initial value. The fire-resistance rating reduction obtained for hollow ratios of 0.5 is 58%, with respect to the hollow ratio of 0.25.

An emergency response plan for cascading post-earthquake fires in fuel storage facilities

Natural disasters such as large earthquakes may rapidly result in cascading events such as post-earthquake fires (PEFs) to trigger. This is particularly the case in industrial facilities which is well known as natural-hazard triggered technological accidents (NaTechs). This study provides a response framework for NaTechs caused by earthquake in fuel storage facilities. To do this, seismic vulnerability of fuel storage tanks and possible damage fashions are studied. Considering fuel leakages can result in PEFs, possible scenarios are simulated numerically using Process Hazard Analysis Software Tool (PHAST). A case study including 20 fuel tanks adjacent one to another is investigated to simulate a domino effect when different arbitrary tanks start to ignite; hence, the worst case scenario can be determined. Based on the results of the case studied, inability to extinguish the possible PEFs over less than 9 min can lead to spreading them to the adjacent tanks. The results indicate that it takes about 40 min the adjacent tanks involve in the fires. Therefore, it is of paramount importance to provide an emergency response plan in advance to properly respond to the fires. The study here also highlights the role of preventive strategies in reducing the associated risks of PEFs in industrial facilities.

Post-Earthquake Fire Resistance of Circular Concrete-Filled Steel Tubular Columns

AbstractAn experimental study was conducted to investigate the mechanical behavior and residual capacity of concrete-filled steel tubular (CFST) columns subjected to a post-earthquake fire. Nine ci...

High-temperature performance of damaged reinforced concrete columns under post-earthquake fires

Post-earthquake fires (PEF) are a frequent phenomenon of earthquakes and usually causes severe damage to reinforced-concrete (RC) columns. To determine the high-temperature performance of RC columns damaged by PEF, the geometric-damage forms of concrete columns after an earthquake are mainly classified as cracking, concrete spalling, and residual deformation on the basis of existing hazard and experimental data. Full-scale seismic-damage column tests were performed to analyse the failure mode of components at a high temperature. Subsequently, the relative depth of cracks, thickness of concrete spalling, relative height of spalling, and residual deformation were proposed as geometric-damage parameters to calculate the thermal-field distribution. Finally, according to the relation between the geometric-damage parameters and the bearing capacity, equations for predicting the high-temperature bearing capacity of PEF concrete columns were established.

Scenario simulation of indoor post-earthquake fire rescue based on building information model and virtual reality

Post-earthquake fires occur frequently, and the seismic damage to non-structural components results in dangerous fire and evacuation environments. Both firefighters and trapped people will face serious threats to life during the rescue. Consequently, a simulation framework of an indoor post-earthquake fire rescue scenario based on building information model (BIM) and virtual reality (VR) is proposed herein. Information of structural and non-structural components is extracted from the BIM. Subsequently, the seismic damage of non-structural components is predicted according to the time-history results and fragility curves. Moreover, a smoke visualization method combining volume rendering and the particle system is also proposed. A case study of a 19-story hospital is conducted using the proposed method for establishing the fire rescue scenario. The results show that the established VR scenario has high realism and smooth interactivity, and the influence of smoke on the fire rescue is more significant than that of fallen debris.

Hierarchical Bayesian Modeling of Post-Earthquake Ignition Probabilities Considering Inter-Earthquake Heterogeneity.

Post-earthquake fires are high-consequence events with extensive damage potential. They are also low-frequency events, so their nature remains underinvestigated. One difficulty in modeling post-earthquake ignition probabilities is reducing the model uncertainty attributed to the scarce source data. The data scarcity problem has been resolved by pooling the data indiscriminately collected from multiple earthquakes. However, this approach neglects the inter-earthquake heterogeneity in the regional and seasonal characteristics, which is indispensable for risk assessment of future post-earthquake fires. Thus, the present study analyzes the post-earthquake ignition probabilities of five major earthquakes in Japan from 1995 to 2016 (1995 Kobe, 2003 Tokachi-oki, 2004 Niigata-Chuetsu, 2011 Tohoku, and 2016 Kumamoto earthquakes) by a hierarchical Bayesian approach. As the ignition causes of earthquakes share a certain commonality, common prior distributions were assigned to the parameters, and samples were drawn from the target posterior distribution of the parameters by a Markov chain Monte Carlo simulation. The results of the hierarchical model were comparatively analyzed with those of pooled and independent models. Although the pooled and hierarchical models were both robust in comparison with the independent model, the pooled model underestimated the ignition probabilities of earthquakes with few data samples. Among the tested models, the hierarchical model was least affected by the source-to-source variability in the data. The heterogeneity of post-earthquake ignitions with different regional and seasonal characteristics has long been desired in the modeling of post-earthquake ignition probabilities but has not been properly considered in the existing approaches. The presented hierarchical Bayesian approach provides a systematic and rational framework to effectively cope with this problem, which consequently enhances the statistical reliability and stability of estimating post-earthquake ignition probabilities.

Storey-Based Stability of Steel Frames Subjected to Post-earthquake Fire

Post-earthquake fires occur after earthquakes and have commonly been encountered throughout history. The fires are particularly deadly and threaten the stability of buildings as possible structural damages caused by seismic loading can be exacerbated by temperature loading. Moreover, damage to insulation during seismic events causes accelerated heating in portions of members experiencing large bending moments. A method is proposed for evaluating the stability and deflection of a semi-braced structural steel frame subjected to post-earthquake fire conditions. The proposed method adopts the interstorey drift concept and assumes that each member in the frame has three segments of differing temperatures, modelling the damage to insulation near moment connections and/or midspans of flexural members. The method is presented in the form of a deflection equation, which indicates the instability of the frame when the lateral stiffness in the denominator reaches zero. The proposed method is demonstrated via a numerical example, and the duration of fire until the given frame becomes unstable is computed, with the results validated via finite element analysis. The degrees of structural and insulation damage are also varied in parametric analyses, showing that the lateral stiffness and critical temperatures of a frame subjected to post-earthquake conditions can be severely reduced.

Postearthquake fire performance of cavity-insulated CFS shear walls with gypsum and calcium-silicate sheathing

Abstract This paper presented a detailed postearthquake fire investigation of cavity-insulated cold-formed steel (CFS) shear walls lined with face-layer gypsum (GP) boards and base-layer calcium-silicate (CS) boards on both sides. Four identical full-scale specimens with 3.0 m lengths and 3.0 m widths were constructed. The first specimens were subjected to ISO834 fire without earthquake damage. The other three specimens were first tested under cyclic loading to different drift ratios, and then the fire experiments were conducted. Three types of failure modes of CFS frame are identified and the corresponding generation mechanism is discussed. The relationship between the drift ratio and fire resistance time (FRT) is presented for the shear walls with the load ratio of 0.27. Meanwhile, by substituting GP board with CS board as the base-layer sheathing, the FRT was extended from 48 min to 66 min, and the shear strength and initial stiffness were increased by 21.5% and 39%, respectively; moreover, the postearthquake FRT was extended from only 8 min to 40 min when the drift ratio reached 3.5%. The degradation mechanism of postearthquake FRT is also discussed. In addition, it is found that the fire experiments of the same CFS walls can have good repeatability, especially regarding the FRT, failure mode and time-temperature curves. Finally, for the fire design practice, the overlapped board joints on the same side of double-layer sheathing should be avoided to the greatest extent and the CFS walls with GP and CS board sheathing on either side are recommended in mid-rise CFS buildings.

Surveys on Post-earthquake Fires after the 2016 Kumamoto Earthquake

Surveys on Post-earthquake Fires after the 2016 Kumamoto Earthquake

A Basic Study on Reducing Human Damages at the time of Residents Evacuation Based on Fire Extinguishing Activities of the Fire-brigades in case of Post-Earthquake Fire

A Basic Study on Reducing Human Damages at the time of Residents Evacuation Based on Fire Extinguishing Activities of the Fire-brigades in case of Post-Earthquake Fire

Evaluation of post-earthquake fire capacity of a reinforced concrete one bay plane frame under ISO fire exposure

Post-earthquake fires may appear after a large earthquake and its effects on urban areas can be even worse that the effects of the earthquake itself. The aim of the present work is to define a methodology to evaluate the consequences of the damage introduced by the seismic events on the fire resistance of reinforced concrete frames. It was performed several numerical analyses in reinforce concrete frames using the program SAFIR, considering the thermal and mechanical analysis of the structure. The variables in the analysis were the type of damage in the frames and the number of fire frontiers in the columns. The thermal analysis was performed using the standard fire curve ISO 834. The results show that the damage imposed by earthquake on reinforced concrete frames reduces the fire resistance of the frames. The time until collapse of the frames exposed to fire where was considered the most severe damage was about 2 h lower when compared to the frames without damage exposed to fire.

Postearthquake fire experiments of cavity-insulated cold-formed steel load-bearing walls lined with plasterboards

Postearthquake fire is one of the most frequent secondary disasters facing mankind. This paper presented a detailed postearthquake fire investigation of cavity-insulated load-bearing cold-formed steel (CFS) walls lined with double-layer gypsum plasterboards on both sides. Five identical full-scale specimens with 3.0 m lengths and 3.0 m widths were constructed. The first two specimens were subjected to axial compression under the condition of ambient temperature or fire, respectively. The other three specimens were first tested under cyclic loading to different drift ratios, and then the fire experiment was carried out. The relationship between the drift ratio and fire resistance time (FRT) is presented, and the following conclusions are drawn. (1) When the drift ratios are less than 2.0%, the reduction of postearthquake FRT is insignificant and should be within 10 min. However, when the drift ratio reaches 3.5%, the residual postearthquake FRT is only 8 min, and the failure mode of wall framing changes to local crushing near the bottom of studs; It is because that local buckling near the bottom of stud occurs from cyclic loading before fire tests, leading to the separation of fire-side sheathing from wall studs. (2) The effect of axial thermal expansion constraints provided by rigid floor slabs to the CFS wall studs is significant under fire conditions. It will accelerate the structural failure of load-bearing CFS walls. (3) For the gypsum-sheathed load-bearing CFS walls, the existence of cavity insulation not only reduces the FRT, but also may change the failure mode of wall studs.

Effects of thermal spalling on the fire resistance of earthquake-damaged reinforced concrete structures

An investigation is performed here on three reinforced concrete (RC) structures designed for peak ground acceleration of 0.30 g and life safety level of performance. The rebars of beams are placed in two configurations – a one-layer distribution and a two-layer distribution where each layer includes 50% of the required rebars. Based on the Tabas earthquake acceleration (occurred in 1978 in Tabas city, Iran), nonlinear dynamic analyses are performed to determine the seismic damage. The structural fire analyses are then performed based on the Eurocode 1 parametric fire curve to determine the fire-resistance ratings (FRRs) of the damaged structures. The structural fire analyses are performed for two separate scenarios – when thermal spalling is considered, and when it is ignored. Under the ‘no thermal spalling’ scenario, the results indicate that, although post-earthquake fire (PEF) loading causes some deterioration to the FRRs of the structures, it does not make the structures collapse. However, when thermal spalling is considered under the one-layer distribution; the results show that all the three structures collapse rapidly. Interestingly, when the rebars are placed according to the two-layer arrangement, the PEF analyses show that no collapse occurs. As PEFs often create chaotic situations with resulting difficulties of timely access for rescue teams, adopting a two-layer arrangement in the design process can make a significant improvement to FRRs; thus, reducing the associated risk. The suggestion here is also applicable as a functional strategy to improve FRRs of RC structures under fire-alone scenarios when thermal spalling is a concern.

Sensitivity analysis of the failure time of reinforcement concrete frame under postearthquake fire loading

AbstractToday, many scholars have drawn attention to consecutive events such as postearthquake fire (PEF). PEF is one of the rare occurrences that leads to many consequences. The resistance of structure against external loads is important for structure and earthquake engineers. The duration of structures' resistance against fire in damaged structures due to earthquake can be different from intact ones. Many parameters have an effect on the resistance of structures. This paper deals with the importance of design parameters and loading for the resistance of reinforced concrete frames during PEF loading. Three methods of Monte Carlo, Tornado diagram, and first‐order second moment have been used to analysis based on random variables. The first failure time in the reinforcement concrete frame (RC) is considered as the strength of the reinforced concrete frame to PEF load. The results depicted that among design parameters, yield stress of rebar is the most significant parameter for the resistance of reinforced concrete frames. Among the loading parameters, the intensity of the seismic load is the most important parameter. The sensitivity of the failure time of members in RC frame shows that during the low intensity of earthquakes, the cover of concrete is the main design parameter after yield strength of rebar. As the intensity of seismic loads increases, the effect of concretes' cover on the resistance of structures against fire decreases. The sensitivity of the failure time to intensity of seismic load is higher between Sa = 0.3 g to Sa = 0.8 g. Also, results show the sensitivity of the design variable decreases by increasing the intensity of the seismic load.

Mechanical analysis of a portal steel frame when subjected to a post-earthquake fire

Although current design code can manage the separate action of a fire or an earthquake, which causes a significant threat to the human life and to the integrity of the structures, the dual effect of a Post- Earthquake Fire (PEF) stands as a major hassle to designers and rescuers alike. Algerian seismic design code, RPA99v2003, with no exception does not consider the possibility of a subsequent fire after an earthquake, whose effect can significantly weaken the steel frame and destroy its fire protection. This paper presents the evaluation of the fire resistance for a two-storey steel portal frame, damaged by an earthquake simulated through spectrum response of Chlef, scaled three in the Algerian Seismic Code. First, the design of the steel structure considers seismic actions by a static nonlinear analysis. Second, it is followed by a fire analysis using an ISO834 standard fire model, considering that the structure is partially damaged. The finite element simulation and numerical analysis of the structure in post-earthquake fire condition yield the bilinear capacity curve at ambient temperature and the variation of local and global displacement at high temperature. A final comparison of the damaged (PEF) and undamaged (FIRE) frames subjected to the different fire scenarios is done.

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.

Influence of fireproof damage on structural performance of post-installed anchor joint subjected to post-earthquake fire

To study explore the influence of post-earthquake fireproof coating damage on structural behaviour of steel-concrete post-installed joint, a three-dimensional FE model has been established by ABAQUS software. Parametric analysis has been carried out and the earthquake level on fireproof coating of post-installed joint by changing thickness of fireproof coating is analyzed under the condition of thermal-force coupling. By damage degree variation of fireproof coating, the influence of fireproof coating damage of anchor plate on fire endurance and bearing capacity of post-installed joint is further analyzed.

Effect of pre-cyclic damage and high temperature on residual tensile behavior of concrete

In view of devastating outcomes of post-earthquake fires, it is imperative to propose a model for the fire-resistance capacity of a seismically-damaged concrete structure. For this purpose, the effects of cyclic damage and high temperature on residual tensile behavior of normal strength concrete are investigated in this paper. Monotonic tensile tests are performed on cylindrical concrete specimens which have been initially subjected to strain-controlled cyclic tensile load or have been exposed to high temperature. Residual mechanical behaviors are expressed in terms of cyclic damage or high temperature, respectively. Test results indicate that the residual tensile strength and stiffness decrease while residual peak strain and post-peak strain increase with the increase of damage and temperature. Finally, a modified stress-strain model is proposed to describe the residual tensile stress-strain relationship of concrete considering the effect of cyclic damage and high temperature. The modeling results fits well with the experimental curves.

Post-earthquake Fire Performance of a Generic Fireproofed Steel Moment Resisting Structure

ABSTRACT Post-earthquake fires can result in rapid collapse of structures damaged partially due to prior earthquakes. An investigation is performed here on a seven-story fireproofed steel moment resisting structure designed for the life safety (LS) level of performance and a fire resistance rating (FRR) of 120 min based on the ISO834 fire. Introducing the specifications of fireproofing materials, the structure is first pushed to arrive at its target displacement at the LS level in order to detect the locations where the fireproofing materials have delaminated. The damaged structure is then subjected to three independent fire scenarios in stories 1, 4, and 7. The results indicate that when the fire is in story 1, 4, and 7, the FRR of the structure declines to 48, 39, and 37 min, respectively. A series of sensitivity analyses is also performed to understand how the length of delamination can effect on the FRR. To do this, the delamination lengths are changed to 150%, 75%, and 50% that of the pushover results, and then the PEF analyses are re-performed. The new analyses show that the changes made have no considerable effect on the overall FRR implying that the location of delamination has a dominant role in declining the FRR rather the extent of damage.

High Risk of Post-Earthquake Fire Hazard in Dhaka, Bangladesh

According to a recent survey conducted by the Fire Service and Civil Defense in Dhaka, Bangladesh, more than 400 hospitals and clinics are facing a dreadful risk of fire hazard [...]