Study On The Mechanism Of Progressive Collapse Resistance Of Base-isolated Structure

The progressive collapse of building structures often causes serious loss of life and property and bad social impact.In recent years,various types of seismic isolation structures built in large numbers in schools,hospitals,emergency shelters,etc.around the world are also exposed to the potential risk of progressive collapse.Due to their special structural forms,the existing research results of anti-progressive collapse around traditional seismic structures were difficult to be fully applied.In this regard,this thesis conducts experimental and numerical simulation research on the performance of base-isolated structures against progressive collapse,and mainly accomplished the following aspects:(1)Three base-isolated of beam-column specimens were designed through experiments based on the static nonlinear analysis method of Pushdown analysis to study the effects of the type of isolated bearing,bearing stiffness,and tensile effect of the plate on the progressive collapse mechanism and bearing capacity of the foundation isolated structure.The results of the test demonstrate that the collapse resistance of the members can be significantly increased by increasing the horizontal stiffness of the seismic isolation layer;in addition,the plate tie effect,which takes into account the synergistic action of the beam and plate,will also increase the collapse resistance;furthermore,because of the seismic isolation layer’s weak lateral restraint effect,the plastic hinge at the beam end can sustain damage;based on the energy balance principle,the dynamic analysis of the collapse resistance of the base-isolated structure concluded that the common bearing base-isolated structure still had 7.6%residual progressive collapse resistance in the case of the center column bearing.(2)The Digital Image Correlation method was used to test the development of damage and crack cracking in the process of large deformation of base-isolated structure nodes,and the change of displacement and strain of specimens is obtained by the algorithm analysis.The analysis results were compared with the displacement values measured by traditional displacement meters,and the error was analyzed to verify the superior of DIC technology in the measurement of large structural deformation.(3)The test served as the foundation for the numerical model’s validation,and the finite element analysis showed a strong correlation with the outcomes of the experiment.The effects of the seismic isolation layer stiffness,concrete strength,the size of the seismic isolation layer beam and the bearing’s failure position of the seismic isolation layer,as well as the different number of layers on the progressive collapse resistance of the base-isolated structure were discussed and analyzed on the basis of the results of the reasonableness of the numerical model.The study demonstrates that:increasing the horizontal stiffness of the seismic isolation layer and increasing the size of the seismic isolation layer beams can improve the collapse resistance of the base-isolated structure;increasing the concrete strength has little impact on the remaining structural bearing capacity when the corner bearing failed.The failure modes of the inner and side column bearings were symmetrically distributed,while the remaining structural resistance of the side column bearings after failure was significantly lower than that of the inner column bearing failure condition due to the lack of restraint,and the bearing capacity of the corner column bearings was the lowest when they fail,so it was necessary to take measures to improve their resistance to progressive collapse.As the number of floors increases,the ability of the base-isolated structure to resist progressive collapse was significantly improved.