Response of transfer plate when subjected to earthquake

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Response of transfer plate when subjected to earthquake

 

Author: Li, Chi-shing
Title: Response of transfer plate when subjected to earthquake
Degree: Ph.D.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations.
Earthquake resistant design -- China -- Hong Kong.
Tall buildings -- China -- Hong Kong -- Earthquake effects.
Department: Dept. of Civil and Structural Engineering
Pages: xxxviii, 324 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1835535
URI: http://theses.lib.polyu.edu.hk/handle/200/1350
Abstract: Hong Kong is a region of moderate seismic risk. However, buildings in Hong Kong are traditionally designed without seismic resistance provisions. It is well known that the use of the transfer plate system in a high-rise building structure causes an abrupt change in the lateral stiffness. If that building is under seismic attack, a "soft-storey" mechanism may be formed. Since transfer plate systems are often used in reinforced concrete high-rise buildings in Hong Kong, there are potential risks in the above circumstances. In this study, simple analytical models and analysis procedures for engineering application purposes are developed to assess the seismic performance of a high-rise building with a transfer plate, designed to non-seismic resistance requirements. It was considered in this study, based on (1) the seismic responses of transfer plates, (2) the level of seismic resistance of high-rise buildings with transfer plates, (3) the formation of possible "soft storey" mechanism in a storey below the transfer plate, and (4) the mode of failure through cycles of linear time-history analyses. Experimental results of a shaking table test, conducted by the Institute of Engineering Mechanics in Harbin, on a 1:20 scale high-rise building with a transfer plate model, were used to verify the numerical simulations conducted in this study. Pseudo-dynamic tests on a 1:4 scale transfer plate model were also carried out in this study to assess the seismic resistance of a transfer plate. From these numerical and experimental results, some findings were obtained and used in the development of two new analytical approaches. They are as follows: When compared the numerical results using the conventional elastic ETABS program with the rigorous finite element analyses and experimental data obtained through this study, it indicated that numerical analyses were carried out on high-rise building structures using the conventional elastic ETABS program with a rigid floor diaphragm assumption were underestimated. In order to correctly evaluate the responses of high-rise buildings using the ETABS program, a new approach, namely advanced simplified un-coupled approach, based on alternative modelling method was developed and used in this study. It was found that storey stiffness is significantly enhanced by the coupling of all the vertical structural elements (shear walls, core walls and columns) with the slabs/transfer plate. In addition, stiffness factors should be applied to account for the coupling effect of structural elements with the slabs/transfer plate. The stiffness factors are 1.2 for low-rise beam and column frame buildings, 2.0 for low-rise core wall and column frame buildings and 1.7 for high-rise wall-frame buildings. Using the above new approach, this study also contends that it is possible to predict the inelastic behaviour of buildings structures through cycles of linear elastic time-history analyses by reducing the stiffness of the damaged structural members, determined from the previous time-history analyses. Based on the comparison of the experimental data and numerical results, displacement factors should be applied to the numerical results for estimating the actual storey drifts under a severe earthquake attack. The experimental and numerical results have indicated that typical local high-rise buildings with transfer plates may have sufficient strength to resist an earthquake action up to the seismic intensity of VIIth degree. There is indication that main structural failures may occur immediately above the transfer plate. Notwithstanding the presence of a transfer plate, stiffness below the transfer plate is significantly improved by the coupling of the columns, core walls, with the transfer plate. This important finding indicates that current methods, such as SEAOC, UBC and the Chinese seismic design code, used in the classification of a "soft-storey" are not appropate for this type of high-rise building. Therefore, a second new analytical approach, namely ratios of deflection (Ru) and inter-storey drift (RAu), were introduced and used in this study, to predict the presence of a soft storey in a high-rise building with due allowance for the change in flexural and shear stiffness. The ratios have proved to be more satisfactory in the classification of a soft storey". Based on the numerical results obtained from the rigorous finite element analysis, it has been demonstrated that rigid diaphragm behavior can be assumed for the transfer plate system in a high-rise building structure. This study has provided new means to accurately predict the seismic responses of reinforced concrete high-rise building structures by using the advanced simplified un-coupled approach. The presence of a soft-storey can be more accurately assessed, using the two new ratios (Ru and RAu) developed in this study.

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