Seismic Resilience Improvement And Evaluation Of Existing RC Frame–shear Wall Structures Retrofitted By Seismic Isolation

Seismic resilience has become a critical issue in engineering and academia,recently.Seismic isolation,as an essential technology to enhance the seismic performance and resilience of existing structures,has been widely used.The seismic fragility model and consequence functions of rubber flexible pipes were established based on previous experiments firstly,which improves the seismic resilience assessment system of isolated structures.Taking existing RC frame-shear wall structures as an example,the seismic resilience level of such buildings was evaluated.Based on these,the individual and large-base isolation retrofit technologies were used to improve seismic resilience for the individual buildings and multiple adjacent buildings with the consideration of flexible pipes,respectively.As a key parameter of seismic isolation,the influence of yield ratio on the resilience level was identified.Accordingly,a yield ratio was recommended for the resilience improvement of the existing RC frame-shear wall stuctures,which can efficiently guide the seismic isolation retrofitting of such buildings if a resiliencebased retrofitting is expected.The main research work and conclusions are as follows:(1)Based on the experimental data of 24 rubber flexible pipes carried out by the research group,the fragility model and consequence functions of such pipe were established.The key damage state is water leakage resulted from pipes ruptured.Taking the drift ratio as the enginnering demand parameter,the fragility model and consequence functions(i.e.,repair cost and time)for such pipes of this damage status was established by using the analysis method recommended by FEMA.The corresponding consequence function of repair cost was determined by various costs,such as selling price and transportation.The measured time of disassembly and installation of 24 specimens was used for fitting the corresponding consequence function of repair time.(2)In order to assess seismic resilience of existing RC frame-shear wall structures,the correspondingly elasto-plastic models were established and critical seismic responses(e.g.,the maximum inter-story drift ratio,the maximum absolute floor acceleration)were obtained under design earthquake and maximum considered earthquake,respectively.The results indicate that all the seismic resilience level of the studied existing RC frame-shear wall structures were assessed to be level 0 and it is necessary to improve the corresponding seismic resilience.Notably,the acceleration-sensitive non-structural components controlled the repair cost,and the overall repair time of the building is determined by the structural components and the acceleration-sensitive non-structural components.It is necessary to control the inter-story drift ratio and the maximum absolute floor acceleration at the same time to improve the seismic resilience level of the structure.(3)The individual and large-base isolation retrofit technologies were used to improve the seismic resilience of existing RC frame-shear wall structures.Seismic resilience assessment were conducted with the consideration of flexible pipes and three study cases for each structure were designed using different yield ratios.Then,the influence of the yield ratio on seismic resilience were revealed.The results indicate that the repair cost and time were significantly reduced and the seismic resilience level can be increased to level 2 at least when retrofitted by seismic isolation.Besides,the repair cost of flexible pipelines is relatively large under design earthquake,while smaller under maximum considered earthquake due to the high overall repair costs,and the influence of corresponding repair time is negligible.What’s more,the inter-story drift ratio and the maximum absolute floor acceleration are both significantly controlled with the yield ratio reduced,leading to a corresponding reduce for the damage of structural components and non-structural components.Then,the seismic resilience level of the buildings can be further improved to level 3.(4)As for large-height individual structures retrofitted by seismic isolation,the damage control of acceleration-sensitive non-structural components is a key indicator for building optimization to level 3,and a yield ratio of 2% is recommended approximately.While for largebase structures with a small number of floors retrofitted by seismic isolation,the seismic resilience level of building is also controlled by the acceleration-sensitive non-structural components,and the yield ratio can be appropriately relaxed,only 2.5% recommended,the structure can be improved to level 3.