Assessment of the behaviour factor for the seismic design of reinforced concrete structural walls according to SANS 10160 : part 4

[摘要] The South African code for the design loading of building structures, namely SABS0160 (1989), was revised with the requirements for seismic design prescribed in SANS10160: Part 4: Seismic actions and general requirements for buildings. SANS 10160:Part 4 incorporates the seismic design provisions of several seismic codes of practice,however, the influence of the value prescribed for the behaviour factor has not beenestablished with regard to South African conditions.The behaviour factor is used by most seismic design codes to account for the energydissipating effects of plastification in structural systems when subjected to earthquakeground motion, to reduce the elastically determined forces to be designed for. However,a considerable difference is observed in the values of the behaviour factor prescribed forthe design of reinforced concrete walls between the leading international seismic codes.The aim of this study is to assess the value of the behaviour factor prescribed in SANS10160: Part 4 for reinforced concrete structural walls under the influence of SouthAfrican seismic conditions and code requirements.A method of quantifying the value of the behaviour factor was developed andimplemented in the study by Ceccotti (2008). This method entails estimation of themaximum analytical behaviour factor as the ratio of seismic intensity at failure of thestructure to the seismic intensity prescribed by the design code. Such a method isadopted for this study where the lateral force resisting systems of six-, eight- and tenstoreybuildings are investigated with nonlinear static analysis to quantify the maximumcomputationally-determined value of the behaviour factor.Firstly, it is observed that it is possible to quantify the value of the behaviour factorthrough the use of a computational study. The nonlinear static method of analysis isshown to provide reliable results in the estimation of the behaviour factor for a sixstoreybuilding, however, does not perform well for taller buildings. Further investigation with the use of dynamic time-history analysis is proposed to evaluate theinfluence of the factors identified in this study.The behaviour of structural walls, designed for reduced forces with the prescribedbehaviour factor of 5.0, exhibits high yield strengths and resists the design seismicaction entirely elastically. This high strength is found to be due to thereliability/redundancy factor prescribed by SANS 10160: Part 4 and because of the highvalues of structural overstrength. Similar studies observed high values of structuraloverstrength for buildings designed for low seismic intensity, which were shown toresult from the fact that the resistance required to gravity loading became more criticalthan the seismic loads in the design of the structural system.This study identifies several factors that influence the value of the behaviour factor,such as the number of walls in the lateral force resisting system; the number of storeysof the buildings; available displacement ductility of the structural system; and theground type designed for.

[发布机构] Stellenbosch University