Abstract
Increasing fire-induced bridge failures are demanding more precise behavior prediction for the bridges subjected to fires. However, current numerical methods are limited to temperature curves prescribed for building structures, which can misestimate the fire impact significantly. This paper developed a framework coupling the computational dynamics (CFD) method and finite element method (FEM) to predict the performance of fire-exposed bridges. The fire combustion was simulated in CFD software, Fire Dynamic Simulator, to calculate the thermal boundary required by the thermomechanical simulation. Then, the adiabatic surface temperatures and heat transfer coefficient were applied to the FEM model of the entire bridge girder. A sequential coupled thermomechanical FEM simulation was then carried out to evaluate the performance of the fire-exposed bridge, thermally and structurally. The methodology was then validated through a real fire experiment on a steel beam. The fire performance of a simply supported steel box bridge was simulated using the proposed coupled CFD-FEM methodology. Numerical results show that the presented method was able to replicate the inhomogeneous thermomechanical response of box bridges exposed to real fires. The girder failed due to the buckling of a central diaphragm after the ignition of the investigated tanker fire in no more than 10 min. The framework presented in this study is programmatic and friendly to researchers and can be applied for the estimation of bridges in different fire conditions.
Highlights
Fire-induced damages to bridges appear as an increasing concern as more bridges failed due to vehicle fires [1,2,3]. e fire threat to bridges can be worse along with the prominent development of transport of inflammable products
Used profiles included ISO834 [6] and ASTM119 [7] curves. is simplification can lead to obvious deviation to the bridge performance because the temperature curves designed for buildings underestimate the inhomogeneous thermal environment caused by bridge fires such as tanker fires usually have more intensive combustion processes than common indoor fires
Concrete piers were modeled as solid obstructions and steel girders were considered as thinwalled panels assigned with thermal material property varying with temperatures as specified in Europe standard [25]. e bottom edge of the computational domain was modeled as a concrete floor whose temperature remained constant at 20°C, and other space edges were passively opened to the surrounding environment. e open boundary is where fluid is allowed to flow into or out of the computational domain depending on the local pressure gradient. e boundary condition for the pressure depends on whether the local flow is incoming or outgoing
Summary
Fire-induced damages to bridges appear as an increasing concern as more bridges failed due to vehicle fires [1,2,3]. e fire threat to bridges can be worse along with the prominent development of transport of inflammable products. General studies simplified the fire condition as the temperatures increased over time developed for building structures, such as the ISO834 [6] curve and ASTM119 fire [7], which belong to the layered temperature model developed for indoor fires [8] Such investigations [9,10,11] to predict the fire performance of bridges are basically a thermomechanical finite element method (FEM) simulation by applying the simplified fire-induced surrounding temperature field to a hypothetical exposed structural portion. According to the CFD-FEM-based study [13] and experimental validation [14] on a supported bridge, this coupled approach can predict the structural behavior in a more complex but more precise way. This approach can be applied in future endeavors aiming at capturing a more precise fire response of bridges
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