Seismic Collapse Risk Evaluation And Control Methodology For Split-foundation RC Frames

With the urban development in the mountain region,it is inevitable to construct extensive mountain buildings,which foundations with different elevations support the structures.As the common structure type in the mountain buildings,the split-foundation frame is widely used.Analysis and investigations on the seismic damage in the recent major earthquakes,show that the seismic collapse mode of the split-foundation structures is different from the regular structures supported by foundations with same elevations.The effectiveness of the current standard control measures on the seismic collapse resistance of the split-foundation frame remains should be checked,and the seismic damage evolution and internal force redistribution for different layouts of the splitfoundation frame structures are still not well understood.It is important to clarify the collapse mechanism and develop a reasonable seismic collapse performance evaluation index and an effective seismic damage control method for the split-foundation frame.This study take the split-foundation frame designed by the current code as the object,and take the seismic collapse risk as the seismic perforcemance index and seismic design objective.Evaluating the seismic performance,structural layout characteristic parameter and controlling the seismic damage by seismic risk based on failure modes are three major research aspects.The main contents and achievements are summarized as follows:(1)The collapse criterion and the collapse mechanism for the RC split-foundation frame structures.Three typical component-performance-based criteria and the dynamic instability criterion based on structure are summarized.Collapse failure modes,the characteristics of floor damage and the causes of shear failure are used to implement applicability and effect of the criteria.The failure modes method based on cut-set in reliability theory is expanded to evaluate the seimic collapse performance for the splitfoundation frames.The criterion could evaluate the failure modes of the RC splitfoundation frame comprehensively and determine the collapse resistance conservatively.(2)Component-based probabilistic damage models for the RC split-foundation frame structures.In order to reflect the different damage degree and different damage forms of the RC split-foundation frame components,component-based probabilistic damage models which are the damage form-dependent of components are defined.Then the bending damge model and the shear damge model are calibrated by the hysteretic test results of corresponding failure form and the hysteretic test are selected from structural performance database of PEER.The achievements could provide the parameter recommendations for probabilistic seismic capacity models in component-based fragility function.(3)Seismic collapse risk assessment method for the RC split-foundation frame.Combined the theory of probabilistic seismic risk and the concept of the weakest failure mode,seismic collapse risk assessment method based on the typical failure mode for the split-foundation frame structures is proposed on probabilistic damage model proposed in this dissertation,and taking the annual average failure probability as the index of evaluating seismic risk.The annual average failure probability of each failure mode in the split-foundation frame structures is calculated and the weakest failure mode is evaluated.(4)Layout characteristic parameter index for the RC split-foundation frame.In view of the failure characteristic that the lower column yields first,which leads to the shear failure of the upper embedding column,the period ratio of the splitted-foundation structure to the upper structure,which reflects the relative magnitude of the seismic inertia forces of the lower floor and the upper floors,is proposed.Through parameter analysis of different layouts and failure mode risk assessment of the split-foundation RC frames with different period ratios,the correlation between the index and the shear failure risk of the upper embedding column is verified.(5)Seismic collapse risk control method for the RC split-foundation frame.Based on the seismic damage characteristics of the RC split-foundation frame,taking the seismic failure risk based on structural failure modes as the design objective,the seismic failure mechanism control design methodology for the split-foundation frame structures is suggested on the classic seismic collapse risk closed-form solution.According to the effectiveness of the current code on the shear failure risk of the upper embedding column of the split-foundation frame structures,shear-enlarged measure of the upper embedding columns is proposed by the seismic failure mechanism control design methodology.Moreover,the corresponding shear-enlarged coefficients are suggested by designing the different period ratios of the splitted-foundation structure to the upper structure.