Study On Damage And Progressive Collapse Resistance Of Base-isolated Structure Under Fire

Fire is a devastating disaster,which has caused serious losses to human life,property,safety and so on.In all fire accidents,the proportion of building fires is particularly prominent.In recent years,because of the excellent performance of isolation structure in the earthquake,more and more people pay attention to it,which makes the base isolation structure used in lifeline buildings such as the hospital,the communication and so on.But it also increases the probability of accidental fire occurring in the base-isolated structure.The performance of reinforced concrete structure and the rubber isolation bearing will be greatly affected when the baseisolated building is subjected to fire,and the damage to the rubber isolation bearing is worse.When the rubber isolation bearing is damaged,if the residual structure can not effectively bear the internal force changes caused by the bearing damage,further damage will occur,and then form the progressive collapse of the structure.To this end,this paper has carried on the following content research:1)Thermal performance of materials in fireIn case of the fire,the surface of the structure will be affected by heat radiation and convection,and then the temperature load will be transferred to the interior of the structure by heat conduction.The temperature field distribution and mechanical properties of structural members at high temperature are closely related to the thermal performance of materials.Therefore,based on a large number of previous studies,the thermal properties of steel,concrete and other materials are selected.And ABAQUS is used to fit the constitutive model of temperature dependence of the rubber material to carry out subsequent numerical simulation work.2)Damage of isolated structure in fireThe damage model of structure can be divided into three levels: material,components and the whole structure.Scholars have done some research on the damage model of the structure under fire,and put forward the damage index at different levels.Based on the study of the damage index of structural members in fire,the single parameter damage index of rubber isolated bearing in fire(that is,the damage of members in fire is only related to one parameter of stiffness)is studied in this paper.The results show that the damage index of the rubber isolated bearing increases with the increase of fire time,and the rubber isolated bearing damages at 75 min in the fire.The protective layer plays an important role in reducing the attenuation of the fire resistance of the rubber isolation bearing.3)Analysis of temperature field and progressive collapse resistance of the baseisolated structure frame based on solid element modeling under fireIn this paper,a solid frame model of the base-isolated structure is established,and the temperature field distribution and displacement response of the structure under different fire positions are studied.And the frame is subjected to three fire conditions,namely,the bearing on the side,middle and double middle suffering fire,and then the performance and progressive collapse resistance of the structure under fire are studied.The results show that: the temperature field of half and full of the rubber isolation bearing under fire,three-side and four-side of the reinforced concrete column under fire present single axis symmetry and double axis symmetry respectively;The displacement response of the structure under fire is larger when the structure isolation layer is under fire;The stress variation of the isolation layer beam is more obvious than that of other layer beams under the three working conditions,so the isolation layer beam should be well designed;The sides of the beams of the upper structure under the fire failure of the side bearing and the double middle bearings both produce plastic hinges,and the progressive collapse of the structure is judged according to GSA standard,while the residual structure locally enters the plastic stage after the fire failure of the middle bearing,and the progressive collapse of the structure does not occur.4)Analysis on the performance and progressive collapse resistance of baseisolated structures based on the multi-scale modeling under fireLimited to the high requirement of calculation cost in the ABAQUS solid modeling,the multi-scale modeling and analysis of base-isolated structure are realized by building the fire-affected part as solid element and replacing the non-fireaffected part with fiber beam element and non-fire rubber isolation bearing with linear element.The results show that: the multi-scale modeling and analysis method of base-isolated structure can simulate the whole structure performance of baseisolated structure under local fire;the distribution law of internal force,displacement,curvature,section stress and plastic hinge of rubber isolation bearing after fire failure is related to the number and position of failure bearing;single internal force index is not comprehensive in structure progressive collapse judgment,so,multiple internal force indexes should be used to increase the accuracy of judgment results.