High-Rise Buildings with Transfer Floors: Drift Calculations

8/11/2019 High-Rise Buildings with Transfer Floors: Drift Calculations

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Transfer

Slab

High-Rise Buildings with Transfer Floors: Drift Calculations

Yasser M. ABDELBASSETPhD candidate, CairoUniversity, & Structural Eng.Dar Alhandasah, Shair andParteners, [email protected]

Yasser Abdelbasset, born 1980,received his BSc and MSc degreesfrom Cairo University, Egypt

Ezzeldin Y. SAYED-AHMEDProfessor, the AmericanUniversity in Cairo(on-leave from Ain ShamsUniversity), Cairo, [email protected]

Ezzeldin Sayed-Ahmed, born 1963,received his BSc and MSc from AinShams University, Egypt and his PhDfrom the University of Calgary,Canada.

Sherif A. MOURADProfessor and Dean ofEngineering, CairoUniversityCairo, [email protected]

Sherif Mourad, born 1962,received his BSc and MSc fromCairo University, Egypt and hisPhD from the University ofCalifornia, Irvine, USA

Summary

In many high-rise buildings, architectural requirements may result in a variable configuration forthe vertical structural elements between the stories of the building. To accommodate such verticalelements discontinuity, a "transfer" floor conveying vertical and lateral loads between upper andlower stories must be introduced. A drawback of the transfer floor is the sudden change in the

building's lateral stiffness at its level: the structure becomes susceptible to the formation of a soft-story mechanism under moderate to severe earthquakes. These buildings generally showedconventional elastic behaviour for frequent earthquake but suffer extensive crack in the vicinity oftransfer floors for rare earthquake. However, for design purposes current numerical modeling ofhigh-rise building adopts reduced stiffness for the vertical elements for strength analysis and fullstiffness for serviceability and drift analysis: a tradition that needs to be verified. A 3-D numericalmodel is built-up for a high-rise building with such vertical irregularities and analyzed using elasticresponse spectrum and nonlinear time-history analysis techniques. The effect of transfer floors onthe buildings drift is investigated where judgment for adopting a full or reduced stiffness for the

vertical elements is scrutinized.

Keywords:drift, response spectrum, stiffness, seismic loads, time history, transfer floor.

1. Introduction

Architectural demands for high-rise buildings in whichcolumns may have different arrangement in a certainlevel(s) become familiar. Many high-rise buildings arecurrently constructed with this kind of vertical irregularitywhere transfer floors are provided to account for thediscontinuous vertical element (columns and/or shear walls)in order to accommodate the functions (Figures 1). High-

rise buildings with transfer floors generally suffer no cracks(conventional elastic behaviour) when subject to frequent(minor) earthquake. However, severe cracking in thevicinity of the transfer floor is encountered when these

buildings are subjected too rare (medium to major)earthquakes. Despite this fact, reduced stiffness forcracked vertical structural elements (columns and walls)is normally adopted for strength design of these buildingswhile full stiffness are adopted for serviceability and driftdesign: a strategy which needs to be scrutinized.

This work is presents the first milestone of a wider researchthat serves to either verify the previously mentioned

analysis strategy for drift calculations or suggest a suitablealternative and, if so, recommends quantification for the

Fig. 1: High-rise building with atransfer slab.
mailto:[email protected]:[email protected]

8/11/2019 High-Rise Buildings with Transfer Floors: Drift Calculations

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High-Rise Buildings with Transfer Floors: Drift Calculations

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