Studies On Analysis Method Of Performance-Based Seismic Design Of Site-Structure System

As construction scope developing and land resources diminishing continuously in city, mass of high-rise buildings are constructed in disadvantage area where exist liquefaction, subsidence and destabilization slop.The field nonlinearity and stabilization has significant influences on structural seismic performance.Based on the design concept of 'three-level and two-stage',the research scope of this paper is focus on upgrading the practicability and realization of performance-based seismic design theory.The other influences factors,such as field nonlinearity and slope stabilization,are also considered.The primary contents include:1.A new wave selection method in time history analysis is proposed based on the small database of strong ground motions,in which the influence of higher vibration modes can be considered in structure design.The principle of the method is both the error at platform segment and weighted error near each period between standard spectra and response spectra of the waves are controlled in a specified scope.On the other hand,Simulation method of artificial wave with complete non-stationarity is proposed.Not only the overall spatial variability and non-stationary amplitude are considered,but also the non-stationary of frequency is also taken into consideration.Non-stationarity of wave amplitude is expressed by the traditional envelope function,and frequency non-stationary is incarnated by phase difference spectrum.Aiming at the power spectral density function of Clough-Penzien model, value of peak ratio of ground motion in simulation is advised.2.Multiple performance objectives are discussed and several advices are proposed. Taking one multi-story frame structure and a high-rise frame-shear wall structure as example, four performance objectives of frequent seismic design as buildings of category C,frequent seismic design as buildings of category B,non-yielding design under moderate earthquake as buildings of category C and elastic design under moderate earthquake as buildings of category C are studied.Engineering quantity analysis and incremental dynamic analysis indicate that the collapse resistant capacity can't be improved evidently for frame structure designed according to moderate seismic at 6 intensity fortification zone while the capacity enhanced greatly in 7 or 8 intensity zone.However,the quantity are also increased significantly for moderate seismic design in 7 or 8 intensity zone,so it must be cautious in design,or it is impossible to realize.Finally,collapse resistant capacity of frame structure in Wenchuan is also analyzed with the strong ground motions recorded in Wenchuan,in which the building are designed according to seismic fortification 7(pre-earthquake) and 8(post-earthquake) respectively.3.A three level performance objective of seismic capacity evaluation for field-shoring-structure system is proposed and realized in design.It is concluded by the analysis of a real project in Fujian province that only slight subsidence without sliding occurred under frequent earthquake;moderate subsidence and certainly sliding at adjacent river bank generated under moderate earthquake;significant subsidence and sliding will be caused by rare earthquake.The seismic inner force of shoring structure indicate that the scheme of double-row supporting pile can meet the objective of 'no cracks under frequent earthquake,no yielding under moderate earthquake and no collapse under rare earthquake'.4.The seismic performance of field and shoring structure under multi-point excitations at bedrock are analyzed using the generated multi-point artificial waves.It is shown that the ground motion parameters,horizontal relative displacement and vertical subsidence of field, as well as the seismic inner force of supporting piles can usually be diminished.However, some seismic responses are still amplified,such as moment of retaining wall at river bank and horizontal relative displacement at the top of supporting piles.5.The influences of field nonlinearity on seismic performance of super high-rise building under bidirectional horizontal seismic excitation are analyzed.It is indicate that,for high-rise frame-shear wall structure,the absolute acceleration,story drift and seismic inner force of structural member at different stories may be amplified on the consideration of the field nonlinearity,so it may approach to danger when reduced according to Chinese seismic code.Under bidirectional horizontal seismic excitations,the larger reduction factor shall be taken as the influences of field nonlinearity on seismic response at the two directions are different.As a result,single reduction factor specified in Chinese seismic code is irrational.