Date of Graduation

8-2017

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Bernhardt, Michelle L.

Committee Member

Prinz, Gary S.

Second Committee Member

Wood, Clinton M.

Keywords

Dynamic analysis; Eccentrically braced frames; Nonlinear modeling; Seismic response; Shallow foundations; Soil-structure interaction

Abstract

The importance of soil-structure interaction (SSI) effects on the seismic response of buildings has been long recognized and has been researched for over 40 years. However, SSI analysis has only been applied in a few building projects because the fixed base condition is considered to provide a conservative estimation for the response of buildings under seismic loads. This assumption of a fixed base condition adopted by practitioners is not always conservative or cost-effective, especially for rigid buildings over soft soils. Additionally, for the case of ductile steel frames with eccentric configurations, the influence of SSI on their seismic performance has not been investigated. In this study, the seismic performance of eccentrically braced frames (EBFs) considering SSI effects is investigated using analytical models. Background information and modern guidelines available to consider SSI in the seismic analysis of buildings are presented and discussed. Following, a 3-story building with EBFs on shallow foundations is analyzed with and without SSI. The beam on Winkler foundation approach is used to model the linear and nonlinear soil-foundation interface behavior, considering linear-elastic, elastic-perfectly plastic, and nonlinear springs. Inter-story drifts, residual drifts, link rotations, and axial load column demands were similar for frames with flexible base and fixed base conditions when elastic and elastic-perfectly plastic springs were used. However, when nonlinear springs were used, frames with a flexible base showed a significant reduction in their responses in comparison to those observed for the fixed base condition. As a result, a reduction in frame member sizes was possible and justified through SSI analyses.

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