Study On The Fire-resistant Capacity Design Method Of CFST Compression Column Based On Reliability Theory

Concrete-filled steel tubular columns are widely used in high-rise and super high-rise buildings because of their good mechanical properties.At the same time,the fire protection design of the building structure must be considered.The structural design method at room temperature in our country is based on reliability,the structural design method at high temperature essentially follows the partial coefficient at room temperature.Considering the change of material performance at high temperature,it is necessary to develop the reliability design method of CFST structure at high temperature.To fully account for this change,this paper starts with the reliability theory,first obtains the partial coefficient of material strength at high temperature,and puts forward a set of fire resistance design method of CFST column by using the calculation theory of ax ial bearing capacity of CFST column members at high temperature.The specific research contents are as follows:In view of the demand of prediction of the fire resistance limit of members at high temperature,the calculation formula of the axial bearing ca pacity of CFST column at high temperature is presented.Based on the current unified theory for calculating the bearing capacity of CFST column at room temperature,combined with the superposition principle,CFST column is regarded as a kind of composite material.The confinement of hoops,the confinement of s teel tubes and the superposition of steel bars are consid ered respectively,the calculation method of the bearing capacity of CFST columns under high tem perature is deduced.Then,the stability coefficient is obtained by using The Berley formula,so as to obtain the calculation formula of the bearing capacity of the component under axial pressure,and the correctness of the theoretical calculation formula is proved by comparing with the experimental data.Aiming at the problem of high cost and low efficiency of component fire-resistance test,the finite element model of CFST column at high temperature is established.Based on ABAQUS finite element software,the bearing capacity of CFST column at high temperature is numerically studied.And the method of thermal sequence coupling,the temperature field model of the component is established first according to the provisions of ISO-834.The temperature field distribution of CFST column is given.Then the mechanical field model of the component is established.Through thermal coupling analysis,the fire resistance bearing capacity of components is determined.The numerical simulation results of the finite element model are compared with the experimental data to verify the correctness of the finite element model.In order to meet the requirement of component fire resistance design,the partial coefficient of material at high temperature is proposed.Based on the reliability theory of structural design at room tem perature,the strength test data of steel and concrete under high temperature are collected.Then,the partial coefficient of material strength corresponding to the ductility failur e index of concrete filled steel tubular column is obtained by the first an d second order moment method.Based on the theoretical calculation formula of the axial bearing capacity of CFST column under high temperature,by introducing the partial coefficient of the materials mentioned above,the fire protection design formula of CFST columns under high temperature is obtained.