Research On Disaster Assessment Method Of Beam Bridge Superstructure

As an important transportation infrastructure,the bridge structure's safe operation is related to the normal operation of traffic and the safety of people's property.However,in actual projects,various disasters seriously threaten the safe use of bridge structures.Among them,as one of the main forms of disaster fire will cause irreversible damage to the bridge superstructure,which will reduce the performance and bearing capacity of the bridge structure.When the superstructure of the girder bridge is exposed to fire,the mechanical properties of its material decrease significantly with the temperature of the bridge rising and it results to losing the most of strength and bearing capacity of bridge.Therefore,how to accurately analyze the changes in the mechanical properties of the bridge superstructure under the action of fire is of great significance to ensure the normal operation of the bridge and the safety of people's lives and property.Reliability assessment is an accurate and effective method for evaluating structural performance.Through reliability research,the trend of structural performance can be analyzed,and the purpose of early warning of structural safety accidents can be achieved.However,there are few existing research results on this aspect.Reliability is used to analyze the performance of the prestressed beam bridge superstructure under fire,which can provide valuable reference for the safety and reinforcement of prestressed concrete beam members under fire.Therefore,it has important research significance and value for the reliability analysis of the beam bridge superstructure under the action of fire.The content of this article is as follows:1.The temperature curves of the material properties of the bridge structure under fire were determined,and the changes of the thermal and mechanical parameters of the concrete and steel bars before and after the fire were summarized,which provided a basic theoretical basis for the simulation in this paper.The commonly used calculation methods in reliability calculation are introduced.Through comparative analysis,it is clear that the Monte Carlo method has highaccuracy and applicability.2.Determine the nonlinear high-temperature material model of the concrete and prestressed steel strands of the beam bridge superstructure under fire conditions,and establish the finite element model of the prestressed concrete beam bridge superstructure under the fire temperature field through the finite element software ANSYS.The static stress and strain dynamics of the prestressed single beam structure and simply supported articulated plate structure under different fire conditions are studied.The results show that the change of the tensile stress and strain of the lower edge of the concrete is significantly greater than the change of the compression stress and strain of the upper edge.Compared with the local fire condition,the full beam fire has a greater influence on the deflection and the stress and strain of the steel strand.Under the fire condition of the full bridge,the modal frequency of the bridge can be reduced by a maximum of 20.76%.3.Based on Kriging interpolation method to study the calculation method of upper deflection,bending capacity and shear capacity of prestressed concrete beam bridge under fire.Combining the function functions of prestressed concrete beams under fire,the Monte Carlo sampling method is used to calculate the flexural,shear and deflection reliability indexes of prestressed single beams and simply supported hinged plates under fire,and analyze the changes with fire time.The calculation results show that the reliability of the three performances of bending resistance,shear resistance and deflection of the simply-supported hinged slab decreases linearly during the fire,and the influence of fire on the bending capacity and deformation of the simply-supported hinged slab gradually increases.The effect of resistance to shear capacity gradually weakened.