# Non linear seismic response of asymmetric buildings.

Thesis

Javed, Khalid 1999. Non linear seismic response of asymmetric buildings. Thesis University of East London
Authors Javed, Khalid The study presented in this thesis is an attempt towards a better understanding of thecoupled lateral-torsional response of buildings subject to seismic ground motion. Someof the problems identified in the past studies are thoroughly investigated and some newareas of study are explored.Some of these problems encountered in the literature include (a) the existence of severaldefinitions of uncoupled torsional to lateral frequency ratio (b) an arbitrary selection ofstructural parameters in a parametric analysis resulting in a physically inadmissiblestructure and (c) the effect of nonlinearity. Because of the simplified models with eithereccentricity in one direction or the ground motion applied in only one direction, theeffects of a bi-directional loading have not been investigated in detail. These effectsmay include the relative differences in the amplitude or phase components of theindividual accelerograms and their orientation with respect to the building. The phaseproperties of accelerograms are of particular interest and these have not received muchattention in the past.Using analytical methods such as Chasle's[16] and Gerschgorin's[39] theorems, theequation of motion of a bi-eccentric system is derived and all of the existing problemsregarding the definition of structural parameters and their bounds are studied in depth.To facilitate nonlinear parametric study, a paraboloid non-linear elastic stiffness modelis proposed. Fourier spectral methods are used to study the frequency domaincharacteristics of the accelerogram pair. The difference in phase and amplitude of thecomponent frequencies in each direction are studied for their effects on the response.For phase difference, cross-correlation function is used as a comparative statisticalindicator. USA earthquake records obtained from US National Geophysical Data Centreare grouped into four soil types and the analysis is performed for each group in order toexplore the soil-dependency of the aforementioned effects on the response. Computerprograms are written in FORTRAN for both parametric and numerical model analyses.The latter can handle any number and orientation of columns with the assumed nonlinearstiffness properties. Newmark's and Runge-Kutta methods of numericalintegration with adaptive step size control have been used to calculate parametric andthe hysteretic responses of the system. The response to harmonic ground acceleration isused as a preliminary investigation into the response to actual accelerogram frequencycomponents.The study has developed relationships for different definitions of the uncoupledtorsional to lateral frequency ratio. Detailed derivation of the Equation of Motion has clarified the confusion that produced different definitions in the past studies. Graphicaldescriptions of the admissibility bounds on system parameters are produced. Thevariation in the response quantities is studied for a range of amplitude and phasecontents of the applied ground acceleration. The difference in phase and amplitude in xand y ground accelerations have been found to affect the response quite significantly.More generally, the relationship of these differences to the torsional mode amplificationhas been observed. The effects of structural frequency and eccentricity parameters arealso studied. Graphs showing the relationship between, the angle of incidence of theaccelerogram with respect to the principal axis of the building, and the phase differencein the accelerogram pair, have been produced.The proposed analysis involving the bi-directional ground acceleration on a bi-eccentricsystem is an improvement on the current methods employed in design practice. Furtherwork is, however, required before simplified design recommendations can be made andsome proposals for future research are given at the end of this thesis. seismic ground motion; architecture; building design; engineering; coupled lateral-torsional response; earthquakes 1999 http://hdl.handle.net/10552/1260 1999 11 May 2011 This thesis supplied via ROAR to UEL-registered users is protected by copyright and other intellectual property rights, and duplication of any part of the material is not permitted, except for your personal use for the purposes of non-commercial research and private study in electronic or print form. You must obtain permission from the copyright-holder for any other use. Electronic or print copies may not be offered, for sale or otherwise, to anyone. No quotation from the thesis may be published without proper acknowledgement. File Access LevelRegistered users only