•Fire simulations show a five-stage fire development in two different spread scenarios.•A longer fire path increases the variability of the temperature field in space and time.•Computationally ...efficient coupling enables analyses of large frames in complex fire scenarios.•The response of the frame is sensitive to its orientation with respect to fire path.•Coverage of elevated temperatures along girders leads to their load-bearing failures.
This paper presents a unidirectional coupling methodology for combining fire simulation based on computational fluid dynamics (CFD) with finite element (FE) analysis to study the response of long-span steel truss beams exposed to non-uniform temperature distributions. Fire Dynamics Simulator (FDS) was used to simulate the fire scenarios, and Abaqus was used for the FE analyses. Adiabatic surface temperatures from the fire simulations were transferred to the Abaqus model using a coupling tool called FDS2FEM. The coupling methodology was validated using two experimental studies, and it was then used to analyse the response of a long-span steel truss beam inside a warehouse building exposed to two travelling fire scenarios (fire spread perpendicular to or along the truss beams) in the building. The fire simulations showed that the fire load arrangement, ignition location and ignition distance from the ventilation opening determined the severity of the thermal field, temperature heterogeneity and the fire spread behaviour. The computational efficiency of the coupling scheme enabled the structural analysis for a large-scale structure under highly time- and space-dependent thermal exposure. The FE analyses indicated that the direction of fire spread with respect to the truss beam determined if either vertical or lateral displacement at the mid-span of the girder was dominant. The analyses also showed that a long truss beam exposed to highly non-uniform temperature fields exhibits a variety of responses like thermal bowing, lateral oscillations, efficient load redistribution, local deformations, and global failure.
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.
•A new API approach for simulation of muli-physical problem.•Linking computational fluid dynamics, thermal and mechanical analysis.•Elaborated concept of Adiabatic Surface Temperature.•Validations on ...timber and concrete members exposed to fire.
Structural fire assessment belongs essentially to the design of steel, concrete or timber structures. The article presents a weakly-linked computational approach, employing the concept of adiabatic surface temperature (AST). The simulation comprises computational fluid dynamics (CFD), heat transport and solid mechanics. Application programming interfaces in linked codes (FDS, OOFEM) define methods for steering, data storage, visualization or fields mapping. The linked simulation is successfully validated on timber and concrete structural elements exposed to fire.
•A new calculation method for adiabatic surface temperature is proposed.•The new method is validated through actual fire experiments.•The new method shows improved accuracy when compared to an ...existing method.
Adiabatic surface temperature (AST) is a useful and convenient concept to characterize the thermal boundary condition that a solid surface is exposed to. Plate thermometer (PT) is often used to calculate AST. However, in an ambient temperature condition, the calculated AST is known to be significantly lower than actual AST. Faced with this challenge, a new method to calculate AST using PT is proposed in the current study. A correlation to determine AST from measured PT temperature in steady state is first developed in a radiation-only environment. Based on this correlation, a correlation for AST is derived for a mixed radiation/convection environment, i.e., for any given convective heat transfer coefficient. AST calculated based on the proposed method is validated against two pool fires.
Coupled CFD fire simulations and thermomechanical FE analyses typically consist of fire simulations, heat transfer analyses and structural response analyses, mutually coupled by three coupling steps. ...There are two coupling approaches, one-way and two-way coupling, where two-way coupling includes the effects of the structural response on fire propagation. In the first part of this paper, one- and two-way coupling approaches including the coupling steps are proposed to include coupling at the structural level. Then a case study comprising an office space with a 12-plate thin-walled steel façade under fire conditions is introduced, as well as the related CFD and FE models. A newly developed automated coupling interface and subprograms are used to perform several one-way and two-way coupled analyses using a coarse and fine CFD mesh for the case study. Slight differences are found in the results of identical simulations due to random effects in the fire simulations. Nevertheless, it can be concluded that two-way coupling is feasible, and that significant differences in the façade failure progression illustrate its effectiveness. Future research includes additional developments of both the fire and structural models, as well as verification and parametric studies to further confirm the findings.
•One- and two-way coupling approaches including their coupling steps are proposed to include coupling at the structural level.•A case study is carried out that comprises an office space with a 12-plate thin-walled steel façade under fire conditions.•Two-way coupling is feasible, and significant differences in the façade failure progression illustrate its effectiveness.•Verification is needed by tests for the mutual influence of fire and structural behaviour at the overall structural level.
Fire exposure of timber leads to charring, surface cracking and timber burnout, shifting the external thermal load deeper into the timber domain. This phenomenon plays its role mainly in situations ...of longer fire exposure. The majority of current approaches and models assume initial geometry during the whole analysis, leading generally to the overestimation of the insulation effect of the charred layer and to a limited burnout. This paper presents a heat transport model which is supplemented with a moving boundary condition, a criterion for the finite element deactivation and the internal heat source. Comparison with experiments using a constant radiative load testifies that the moving boundary condition becomes important after approximately 10 min of fire exposure and rather leads to a constant charring rate observed in several experiments.
In this paper, a coupled fire-structure model combining the finite volume and finite element methods, which captures the essential physics of the problem has been developed. The model is based on a ...multi-physics framework where the essential physics pertaining to the combustion process of the fire and resultant thermo-mechanical response of the structure, in particular, of natural fibre reinforced composites, has been incorporated. In addition, a relatively new concept of adiabatic surface temperature has been introduced as a practical means to transfer data between fire and thermal/structural models at the gas-solid interface. The model predicts the temperature, stress distribution and deformation behaviour of composite beams under combined thermal and mechanical loads.
The thermal response of bodies engulfed in di-tert-butyl peroxide (DTBP) pool fires is studied numerically. High heat release rates, high velocities and high emissive powers portray the combustion of ...DTBP. This makes exceptionally hazard for bodies engulfed in DTBP fire accidents. The concept of adiabatic surface temperature (AST) is applied for DTBP pool fires to circumvent the difficulty of defining the fire exposure boundary condition at the solid surface. Adiabatic surface temperatures (AST) are computed for pool diameters 1.13 m and 3.4 m using the fire dynamics simulator. The thermal response of cask in a 1.13 m DTBP pool fire is studied to verify the concept of AST. It is found that a cask encounters twofold the heat fluxes in DTBP fires than in diesel pool fires. More than 30% of the net heat flux to the cask is a direct result of the convective heat exchange between the fire and the cask. This implies that the regular safety guidelines formulated for hydrocarbon pool fires are not adequate for the safety of the bodies engulfed in DTBP pool fires.
•Thermal exposure of bodies in DTBP fires is estimated.•Bodies in DTBP fires experience two times higher heat fluxes than in diesel fires.•Nearly 30% of the net heat flux is due to convection.•Safety standards to bodies in hydrocarbon fires are not adequate for DTBP fires.
Summary
A new more insulated and faster responding plate thermometer (PT) is introduced, which has been developed for measurements particularly in air at ambient temperature. It is a cheaper and more ...practical alternative to water‐cooled heat flux meters (HFMs). The theory and use of PTs measuring incident radiation heat flux and adiabatic surface temperature are presented. Comparisons of measurements with PTs and HFMs are made. Finally, it is concluded that incident radiation in ambient air can be measured with HFMs as well as with the new insulated type of PT. In hot gases and flames, however, only PTs can be recommended. At elevated gas temperatures, convection makes measurements with HFMs difficult to interpret and use for calculations. However, they can be used in standard or well‐defined configurations for comparisons.
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