Inelastic drift-based approaches for preliminary seismic assessment of buildings

There is no provision for consideration of seismic resistance in building design codes of practice in low-to-moderate seismic regions in this world. This could cause a significant loss of life and economic hardship under a moderate earthquake. This is due to the high population density and the extensive infrastructure in the urban areas. Thus there is an urgent need to implement a seismic assessment scheme for building structures composed of a preliminary assessment and a detailed assessment. In this thesis the methods are proposed for the preliminary seismic assessment which is a crucial step and a screening procedure for identifying deficient building structures from a pool of buildings for more detailed assessment.;Existing preliminary seismic evaluation procedures are mainly for low to medium rise building structures, in which shear deformation is dominant. Thus an evaluation procedure for high rise building structures is proposed with consideration of inelastic behaviour and higher vibration mode effect. A method of analysis for estimating quickly the natural fundamental period of vibration for tall building structures is first proposed from the continuous flexural-shear cantilever. Then an inelastic interstorey drift ratio model is derived from the principle of capacity spectrum analysis and modified modal pushover analysis for the assessed buildings. Numerical investigations on the representative tall wall-frame structures show that the seismic responses of the buildings predicted by the proposed inelastic interstorey drift ratio model agree well with those obtained from response history analysis.;A systematic and effective assessment procedure for the preliminary assessment is developed. The proposed procedure first divides the assessed buildings into either elastic or inelastic one using a bifurcation index. For building structures that deform inelastically may be further examined by the inelastic interstorey drift ratio model. Performance of building structures is then defined based on the interstorey drift ratio by comparing those given in the current codes of practice and the literature. The proposed model is particularly suitable for assessing the buildings that are analysed in frequency domain.;A modified continuum MDOF model, based on continuum flexural-shear cantilever, is derived for analysing seismic responses of tall building, which is more suitable for rapid preliminary seismic assessment in time. It particularly suits for slender buildings that have inelastic response range and significantly higher mode effect. Conditions of model similarity is then defined which is named as the general continuum representation. For two similar continuum models, their seismic responses can be related by their height ratios for the same strength ratio based on the general continuum representation. Thus the responses of a modified MDOF model is normalised to dimensionless responses named as the generalised inelastic responses.;A spectrum-based method using the generalised inelastic response is proposed and recommended for preliminary seismic assessment of tall buildings that are relatively slender with significant higher mode effects and are normally analysed in time domain. The responses of a building structure can be predicted using the generalised inelastic responses, which are derived from the modified continuum-MDOF model through the general continuum representation. The generalised inelastic response are presented in the form of spectra which are developed by the responses of 168 modified continuum MDOF models, having 8 different degrees of structural interaction and 21 different fundamental periods under nonlinear response history analysis. The numerical investigation shows that the seismic responses from the proposed method agree well with those from the response history analysis. The proposed method provided a simple and quick, yet accurate, mean of estimating the inelastic seismic response of building structures, thus particularly being suitable for the preliminary seismic assessment.