Torsional effects in structures subjected to strong ground motion
Lu, Shi
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https://hdl.handle.net/2142/19150
Description
Title
Torsional effects in structures subjected to strong ground motion
Author(s)
Lu, Shi
Issue Date
1990
Doctoral Committee Chair(s)
Hall, William J.
Department of Study
Civil and Environmental Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
The dynamic characteristics and torsional behavior of structures during strong ground motion were investigated; both linear and nonlinear material behavior were considered. Emphasis was placed on the strong torsional coupling associated with the beating phenomenon in the seismic response of structures with small static eccentricity and closely spaced frequencies. In order to study the response of structures subjected to complex loading histories, structural models were analyzed through the use of a numerical procedure (Newmark's $\beta$ method) combined with a generalized nonlinear material model in the force-displacement space. Parametric studies were made for the dynamic amplification of the torsional response of simple structural systems. An amplification factor of about 2.5 was observed for static eccentricity in structural response arising from earthquake ground excitation.
To further comprehend the torsional effects in low-rise structures, two buildings that were extensively instrumented during the 1987 Whittier Narrows Earthquake were analyzed in the light of the seismic requirements in the current building codes. The theoretical demonstration of the beating phenomenon was confirmed by the field recordings in the symmetric steel moment-resisting-frame structure with closely spaced frequencies; similar confirming results were obtained for the other structure. The behavior and response of the two structures were observed to be somewhat different from that envisioned and assumed by the direct design procedure employed by the codes. Some suggestions for improvement in building code provisions are offered.
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