Study On The Influence Of Fire On The Performance Of Steel-hybrid Beam Multi-tower Cable-stayed Bridge

At present,there is less research on bridge fires at home and abroad,and little research on the fire resistance of steel-combined composite beam cable-stayed bridges.And the steel-combined composite beam cable-stayed bridge span is large,is an important traffic node,suffered from fire may lead to significant economic losses and serious social impact,therefore,study on the steel-combined composite beam cable-stayed bridge in the fire scene damage seems essentially important.The main research contents and results of this paper are as follows.(1)Have investigated the causes of bridge fires,summarized the research status of tanker truck fires,cable-stayed bridge fires and steel-combined girder fires at home and abroad,combined with relevant literature,and proposed a research method based on heat transfer,fire dynamics software FDS and large finite element software ANSYS as tools to conduct coupled analysis of the fire source temperature field,structural space temperature field and the mechanical response of the bridge structure in the fire scene,and selected a reasonable heat release model and the material parameters required for thermal and structural analysis;(2)Using the Pingtang Super Cable-stayed Bridge in Guizhou Province as a support project,the FDS software was used to establish a fire analysis model for the bridge,and the scope of influence of the 200 MW tanker fire and the spatial transient temperature field of six representative bridge fire scenarios were obtained,and ten typical fire scenarios of cable damage were selected based on the bridge characteristics and fire temperature field distribution of the support project;(3)Based on the ANSYS software,the two-dimensional diagonal cable cross-section was established,and the internal temperature field of the cable in the fire scene was obtained by using the most unfavorable temperature curve of the cable surface to warm up,and the mechanical properties of the cable at high temperature were combined with the mechanical properties of the cable material to clarify the degree of reduction of the mechanical properties of the cable under each typical fire condition;the beam unit model of the relying project was established by using ANSYS to obtain ten typical fire conditions,considering the influence of the performance of the cable under each condition on the safety performance of the diagonal bridge by fire loss;(4)The thermal analysis part of ANSYS software was used to build a detailed model of the main beam section,and the temperature change curve of the fire source obtained by FDS software was used as the heating curve to obtain the temperature field of the main beam in the fire scenario,and the two-dimensional concrete panel thermal analysis model was further built,and the temperature field of the concrete panel under sufficient fire extension time was analyzed;the refined model of thermal analysis and the finite element whole bridge model were assembled and modeled,and the thermal structure coupling analysis was carried out to obtain the mechanical response to the whole structure of the cable-steel bridge after considering only the high temperature of the steel-composite beam;the safety performance of the cable-steel bridge in the real fire scenario was considered,and the finite element model that also considers the fire damage to the cable and the main beam was built for thermal structure coupling analysis;(5)The ANSYS software was used to build a solid model of the pylon limb in the relying project,and the FDS software was used to analyze the most unfavorable temperature changes on all sides of the pylon,and the temperature field distribution of the pylon limb in the fire scene was obtained;the thermal-structural coupling method was used to analyze the effect of fire on the safety performance of the cable-stayed bridge,and the comparative analysis showed that the effect of fire on the pylon limb in the multi-tower cable-stayed bridge was slightly greater than the effect of fire on the main beam of the side pylon limb;the fire scene in which the pylon limb and the main beam underneath the pylon limb were fireed together was further analyzed,and the comparison showed that the effect of fire on the main beam on the safety performance of the cable-stayed bridge was slightly greater than that of fire on the main pylon limb;(6)Suggested a fire-resistant design for the structural response of the cable,tower and beam structures of the cable-stayed bridge in a fire scene.