The Structural Strength And Fire Resistance Analysis Of Reinforced Recycled Concrete Structures At High Temperature

Recycled concrete structure is widely used in various structures as a sustainable environmental protection material.Under normal circumstance,recycled concrete structure not only needs to meet the requirements of usability,applicability and aesthetics of the structure,but also needs to have the structural safety and the ability to resist disasters,including common disasters and fires.At present,there are a lot of researches on the mechanical properties of reinforced recycled concrete scale members at room temperature and fire resistance at high temperature at home and abroad,but there are still few researches on the performance of reinforced recycled concrete full-scale members and recycled concrete frames at high temperature.Therefore,it is an urgent problem to analyze the behavior changes and mechanical characteristics of recycled reinforced concrete frame under fire,so as to establish the theoretical analysis method of fire resistance design of recycled reinforced concrete frame.This thesis establishes a full-scale reinforced recycled concrete beam and a three-dimensional solid element model of reinforced recycled concrete frame,and analyzes its fire resistance performance by simulating the mechanical characteristics of the structure under fire by using indirect sequential coupling.This paper also systematically analyzes each the influence of parameters on the structural strength and fire resistance limit.The main research contents and conclusions of this thesis are as follows:(1)the principle and method of sequential coupling thermal analysis and calculation of finite element software are proposed,and the relevant fire resistance test data of reinforced recycled concrete members are collected,and the appropriate thermal parameter model and thermal constitutive model of materials are selected.The temperature field calculation model and thermal field calculation model of reinforced recycled concrete members are established by using finite element software.The validity of the model is verified by comparing the calculated results with the experimental results.(2)Respectively Established a full-scale finite element calculation model for reinforced recycled concrete beams at room temperature and high temperature,regeneration of full scale reinforced concrete beam under the action of room temperature mechanical properties,high temperature under the action of the temperature field distribution and thermal coupling damage characteristics of recycled concrete simply supported beam and refractory properties are studied.By changing the replacement rate of recycled aggregates,reinforced yield strength,longitudinal reinforcement ratio,temperature load,protective layer thickness and intial load level ratio,the stress performance of recycled concrete beams at the fire resistance of the full-scale reinforced recycled concrete beams under high temperature are analyzed when different parameters are changed.The analysis results show that under the action of fire,the longer the structure is exposed to fire,the higher the internal temperature of the structure.Moreover,recycled concrete has good thermal inertia,which leads to a large temperature difference between the inside and outside,as the replacement rate of recycled aggregate increases,the temperature of the cross-section measurement point of the component decreases,and the fire resistance of the structure increases;The fire resistance limit time of the recycled concrete beam with total substitution ratio is greater than that of the recycled concrete beam with half substitution ratio,as increase the thickness of the protective layer,decreasing the yield strength of reinforcement and the ratio of longitudinal reinforcement It can effectively improve the fire resistance of reinforced recycled concrete components.as increase the heating time and the initial load level ratio It can reduce the fire resistance of reinforced recycled concrete components.(3)Through the establishment of full-scale reinforced recycled concrete frame,the fire resistance performance of recycled concrete frame under the combined action of horizontal load,vertical load and high temperature is studied,and the influence mechanism of vertical load ratio(axial compression ratio,the load on the beam)and horizontal load ratio(horizontal load size)on the stress and fire resistance performance of recycled concrete frame structure is systematically analyzed.The results show that with the increase of axial compression ratio and the load on the beam,the fire resistance time of recycled concrete frame columns decreases gradually,and the fire resistance performance also weakens;and the horizontal load in the elastic region has little effect on the fire resistance of reinforced recycled concrete frame.