Mechanical Performance Analysis Of Perstressed Continuous Beam Bridge Under Fire

The development of China's bridge and other infrastructure is speeding up dramatically with the development of economy.However,a variety of security risks such as conflagration are coming along.When a bridge catches the fire,not only can the fire cause the traffic jam and death,but also it can bring many disasters to the bridge.For example,the collapse or even the permanent loss of it will follow.Therefore,it is urgent for us to solve these problems.However,the research of bridge under the fire in our country is only in its infancy.Further more,the level of it falls far behind the actual needs of engineering.In a word,to accelerate the study of bridge under the fire is of a great necessity.This paper takes Dadeng Bridge in Xiamen as a research object,and the main contents are as follows:?Based on the experimental study of domestic and foreign scholars,the paper sums up the relationship between the mechanical properties and thermal parameters of concrete and prestressed steel after high temperature fire.Such as the concrete heat conduction coefficient,elastic modulus,thermal expansion coefficient and the relation equation of temperature;the relationship between prestressed reinforcement yield strength,ultimate strength,thermal conductivity,specific heat and density with temperature change.?Based on the thermodynamics,the method and process of finite element method for solving temperature field and stress field are established;The transient heat conduction differential equation is derived by the Galerkin method;The time domain of the structure is divided into different time units,and the finite difference method(Crank-Nicolson)is used to make the difference.?The combination of continuous box girder bridge Dadeng bridge engineering background,reference bridge fire field data and results,to determine the boundary conditions of the model,analysis and selection of concrete,prestressed reinforcement constitutive model,build finite element model of Dadeng bridge.?On the basis of the model,respectively studied three different types of fire,including deck fire,fire under the bridge and fire in the bridge.Then dividing them into ten different fire conditions,analysis the temperature range of key points,the floor the deflection time history,different sections of the stress changes and stress time history curves of prestressed reinforced floor.?Considering the actual fire with Dadeng bridge,the analysis of the temperature changes by the fire floor at different depth,and compared the changes in mechanical properties under the action of gravity and lane loading.Also,the effect of fire on the material was studied,including concrete,prestressed reinforcement and so on.In addition,the influence of serviceability limit state of bridge on fire is analyzed.