Seismic Failure Mechanism Of Split-Foundation Reinforced Concrete Frame Structures

In recent years,with the steady progress of urban development,the flat construction land is increasingly scarce.Hence,it is inevitable to develop the sloping land,which results in a visible increase in the proportion of mountain buildings being constructed in hillside areas.Studies of the several major earthquakes in the past years have shown that the mountain buildings are more vulnerable to severe earthquake damage than buildings on flat ground,and their seismic failure mechanisms are significantly different.The seismic failure mechanism and its influencing factors of mountain building structures are not only the basic problem but also essential concern in the performance-based seismic design process.In this study,taking the most commonly used mountain building structure,split-foundation RC frames(SFRCF)as the object.The systematic methods for analysis,evaluation,grading,and control of the seismic failure mechanism of SFRCF have been carried out.The results can be a guide for seismic failure mechanism control or retrofit of mountain building structures.The main research contents are as follows:(1)Improved pushover analysis procedure for SFRCF.According to the characteristics of stiffness and mass distribution of SFRCF,the piecewise lateral load mode is proposed.It can identify the weak story of SFRCF under rare earthquakes and provides an effective and computational efficiency tool for the failure mechanism analysis of such building structures.In addition,this method can take the upper ground motion amplification effect into consideration during the seismic analysis procedure.(2)Seismic failure mechanism characteristics of SFRCF.The main factors affecting the seismic failure mechanism of SFRCF were analyzed by combining the stress and deformation characteristics of SFRCF under lateral loads.Nonlinear finite element models that consider the flexural-shear coupling failure mechanism effect of the special members in the SFRCF were developed.The influence of structural configuration on the failure mechanism and overall seismic performance of the SFRCF are studied.(3)A proper index of regularity for SFRCF.A regularity index,the average upper base lateral stiffness ratio,which can consider the uniformity of the stiffness distribution of the vertical lateral resisting components in the upper ground story is proposed.This index is closely related to the internal force and earthquake damage level of the special members in SFRCF and can be used to evaluate the irregularity of SFRCF.(4)A method for the irregularity classification of SFRCF and the strategy corresponding to control the seismic failure mechanism of SFRCF.In combination with the regularity index of SFRCF,the irregularity levels are classified,and the seismic failure mechanism control methods for SFRCF at each irregularity level is proposed.The effectiveness of the proposed methods is verified by several typical examples.It provides a new perspective on the seismic performance improvement of SFRCF.