Eight structural fire tests on an aluminum alloy shell specimen are conducted in this paper. Firstly, the test program is described in detail. Then, test results, including the test phenomenon, the ...temperature-time curves, and the displacement-time curves, are exhibited. In the structural fire tests, the specimen under ventilation-controlled fires had greater thermal and structural responses. The maximum measured air temperature was 128 ℃, and the maximum temperature of the members and the gusset plates were 85 ℃ and 80 ℃, respectively. The specimen performed arching during the test process, and the maximum displacement was smaller than the restriction value for the serviceability limit state in existing design codes. After all the tests, no damage that would influence the structural behavior was observed. Subsequently, based on the test results, two approaches, namely the empirical formula and the field simulation, are proved to be useful to predict the non-uniform temperature distribution. Finally, the global deformation patterns, the distribution of internal forces, and the variation of the ultimate bearing capacity of the shell specimen, are analyzed through numerical analysis. The results indicated that the fire located at the corner is more disadvantageous to the specimen.
Steel structures may be exposed to localized heating by a fire source nearby. Flame impingement from localized fire may lead to high temperatures in the exposed steel members, which may lead to ...structural failure. This paper numerically investigates the thermal and mechanical behaviors of restrained steel beams exposed to flame impingement from localized fires. Four steel beams with different dimensions and restraints were considered. Both developing and steady burning fires were investigated. The standard ISO834 fire was also used for comparison. The study finds that the temperature distributions within the steel beams subjected to flame impingement are highly non-uniform both across and along the beams. Along the beam length, the temperatures near the fire source may be hundreds of degrees higher than those far from the fire source. Due to different temperature distributions, the deformation mode for restrained steel beam subjected to flame impingement may be significantly different from that of a beam subjected to the standard ISO834 fire. The failure temperatures for restrained steel beams subjected to localized fires may be higher or lower than those for restrained beams subjected to the standard ISO834 fire. Reliance on the standard fire may lead to an unconservative design if the potential real fires are localized fires.
► In localized fires the steel temperature is highly non-uniform. ► Failure model in localized and standard fire might be different. ► Failure temperature in localized fire can be much lower than that in standard fire. ► Standard fire may lead to unconservative design.
This paper introduces the heat transfer model for simple calculation of the temperature field inside thin-walled sections in fire. It is dedicated for various shapes of a cross-section of structural ...elements made of metal. It utilizes the concept of an adiabatic surface temperature (AST) for determination of thermal boundary conditions. Due to the non-uniform heat exposure and arbitrary shape of the cross-section, the resulted temperature field is non-uniform. The given solution is valid for a transient heat transfer problem. The heat transfer model takes into account the practical abilities for measuring heat exposures both in experiments and numerical fire simulations and takes into account the inherent features of beam finite elements with stiffness integration at each step of an analysis, which is important for analyses of skeletal structures in fire. Finally, the heat transfer model is verified by comparison of results to the 2D finite element method solution and validated using data obtained from experiments.
•Heat transfer model for fire-structure interaction of thin-walled cross-sections is developed.•The solution has much lower computational cost comparing to 2D FEM approach, what is greatly beneficial for application in civil engineering.•The heat transfer model is validated at large range of heat fluxes.•View-factor calculations for a member within concaving box is prerequisite.
•Fire-structure simulation model was validated against localized fire test data.•Suggestion on using FDS for structural fire analysis provided.•The numerical model proposed for performance based fire ...safety design.
The engineering design practice may include fire protection design of steel structures in large volumes. Prescriptive methods in fire codes are based on the concept of fire compartmentation and might be inapplicable to large volumes. As an alternative, fire engineering performance based methods are developed, which may need sophisticated numerical models to adequately simulate the responses of structures in the design fire scenarios. This paper discusses an integrated fire-structural simulation model for performance based design. Sub-models were clearly described. The fire-structure simulation model was successfully applied to model the fire-thermal-structural behaviors in two localized fire tests on a real-scale steel beam recently conducted at the National Fire Research Laboratory (NFRL) of the National Institute of Standards and Technology (NIST). The model might be used in performance based structural fire safety design.
Aluminum alloy shells are increasingly used in public buildings as a supporting structure for roofing enclosure construction in large spaces. In performance-based fire protection design, an empirical ...design criterion of 150 °C and relevant empirical formulas are used; however, the safety margin and prediction effect are not verified through full-scale experiments, and therefore, the effect of the roof system on the near-roof temperature field in practical engineering is yet to be investigated. In this study, a simulated fire experiment was conducted using a cylindrical aluminum alloy reticulated roof system model. The heat release rate of this restricted fuel fire source during the stable burning stage reached 8.1 MW. Fire Dynamics Simulator (FDS) was used to reproduce experimental results, and the numerical model of the shell member was simplified; further, existing empirical formulas of scholars such as Li were compared. The results indicated that although 150 °C is a large safety margin, it may limit architectural function. The simplified shell model provides an effect-equivalent approach for building thin-walled members in FDS. The shell is the main factor that delays the time required for the near-roof space to reach thermal equilibrium. The existing empirical formulas cannot be used for the studied roof system directly, and they may be improved through coefficient adjustment and other such methods.
•First fire test of full-scale aluminum alloy arched roof system.•150 °C critical criterion in performance-based design has a large safety margin.•Thermal equilibrium moment prolonged by aluminum alloy shell members.•Existing empirical formulas cannot be used to predict studied roof system.
Nowadays constructional steel has become the desired choice of structural designers because of its structural properties over other materials. However, during localized fire, structural properties of ...the portion of the steel degrades rapidly leads to the change in overall collapse pattern of steel members. In this article, the spread and rate of temperature rise along the length and across the depth of beam has been investigated. The experimental study was conducted on hot-rolled parallel flange steel member (NPB 300 × 150 × 36.52) of length 1.5 m. It is exposed under localized fire scenario in open environment. At the mid-point of beam, the simple and economical LPG fuel burner was adopted as the fire source for the test. It is simply supported to simulate free stress condition. The horizontal and vertical spread of temperature in the steel section are noted with temperature measuring device. The temperature variation in steel beam section shows the rapid decrease in temperature in natural environment. The maximum surface temperature was reached up to 760 °C. The temperature of specimen was recorded and further validated in ABAQUS the finite element software. The rate of increase of temperature in fire from initial to final stage and rate of decrease of temperature during cooling both were recorded. The temperature variation along the length and across the depth were found similar in numerical validation when compared with the observed ones. The observed and simulated data were found in good concurrence.
•Critical heat fluxes of exposed and ambient panes are 6kW/m2 and 25kW/m2.•Critical temperature difference of fire side pane is around 60°C.•The ambient pane survives three times longer due to ...radiation filter and air gap.•Heat transfer in double glazing is revealed by a heat flux based theoretical model.
Double glazing unit normally demonstrates better fire resistance than single glazing, but the knowledge on its thermal behavior and heat transfer mechanism during fire is limited. In this work, nine double glazing units were heated by a 500×500mm2 pool fire. The incident heat flux, temperature on four surfaces, breakage time and cracking behavior were obtained. The critical breakage conditions for interior and exterior panes were determined through gradually decreasing the glass-burner distance from 750mmto 450mm. It is established that in double glazing the pane at ambient side can withstand significantly more time than the pane exposed to fire. The critical temperature difference for interior pane is 60°C; the critical temperature of exterior pane breakage is much higher due to no frame-covered area. In addition, the heat flux at the time of crack initiation is 6kW/m2 for the pane at fire side, while more than 25kW/m2 for ambient side pane. To reveal the heat transfer mechanism in glazing-air-glazing, theoretical and numerical investigations are also performed, which agrees well with the experimental results.
In this paper, experimental investigation and numerical simulation of steel beam to square concrete-filled steel tube (CFST) column composite joints that use reinforced concrete (RC) slabs subjected ...to localized and global fire conditions are presented. Eight joints were tested under the ISO 834 fire standard, and the effect of different parameters including the load ratio of beams, the beam-to-column ratio of linear stiffness, and different fire scenarios was studied during testing. The failure patterns and the thermal responses of the structural members including the temperature distribution, axial displacement of columns, vertical deflection of the beam ends, and fire resistance of the joints were recorded and discussed. The results show that tube buckling of the square CFST columns, flange buckling of the steel beams, and separation between the top flange of the steel beams and the RC slabs were the primary failure patterns of this type of joint. Moreover, the temperatures of structural members within the connection zone were lower than those in the other regions. Compared with other factors, the load ratio of the beams demonstrated a significant influence on the displacement of the structural members and the fire resistance of the joints. A three-dimensional finite element analysis (FEA) model was built to simulate the fire performance of this type of composite joint. The simulation results were compared to the test results in terms of failure patterns, temperature distributions, displacements, and fire resistances, and good agreement in general was achieved. Finally, the FEA model was adopted to examine the effect of parameters on the fire resistance of the composite joints with axial and flexural constraints applied at the ends of the beam.
•Performance of steel beam to square CFST column composite joints using RC slabs subjected to fire.•Furnace tests to assess fire resistance of steel beam to square CFST column composite joints using RC slabs.•FEA model for fire resistance analysis of steel beam to square CFST column composite joints using RC slabs.
Current design approaches to assess the lateral torsional buckling capacity of steel beams in fire are based on the assumption of uniform steel temperature. This paper investigates the effect of ...temperature gradients on the lateral torsional buckling behavior of steel wide flange (W) beams in fire conditions. The effects of localized fires and the temperature gradients they produce in steel beams were studied. Laterally unrestrained beams of various dimensions were subjected to a range of load ratios. The location of the localized fire was varied to provide different heating conditions. The standard ISO834 fire, and a uniform temperature condition in which the steel temperature was ramped linearly were used for comparison. The study shows that temperature gradients within a steel W-beam may have a detrimental effect on the lateral torsional buckling capacity of the beams in fire. The critical temperature, defined as the maximum temperature in a steel beam at which the beam undergoes lateral torsional buckling, in real fires may be hundreds of degrees lower than that in the standard ISO834 fire. The critical temperature in real fires may also be lower than that in the uniform heating condition. Design approaches based on the standard ISO834 fire or uniform steel temperature assumption may give unconservative results if the potential real fires are localized fires.
•Temperature gradient may have significant negative effect on LTB.•TLTB in a real fire may be much lower than in the standard fire.•TLTB in a real fire may be lower than in uniform heating condition.•Location of fire source has significant effect on LTB.•Standard fire may lead to unconservative design.
Steel structural members in different application areas may be subjected to localized flame impingement instead of flashover scenario due to several reasons. Though extensive research has been ...performed to study component level systems in conventional fires (ISO 834, ASTM E119, other parametric fire curve), the behavior of beam column rigid connection in localized fire is still not investigated in details. To understand the behavior of beam-column connection under localized fires, the present paper deals with a detailed numerical investigation of the behavior of a moment resisting frame (MRF) assembly with fully welded beam column connection in terms of connection rotation and forces under different positions of localized fire source underneath the exposed beam. For fire scenarios where the frame survived during the entire duration of fire, the post fire rotation of the connection located at far end from the fire source was found to be higher than the near end. Secondly, for cases where the frame failed, it was observed that for identical strength of weld and base material, failure is likely to initiate at the weld line connecting the bottom flange of the beam located at far end from the fire source. Finally parametric studies were performed with different weld sizes and it was concluded that size of weld has significant effect on increasing the joint survival time for MRF exposed to localized fire.
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