Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Structural Engineering

First Adviser

Sause, Richard

Other advisers/committee members

Wilson, John L.; Pakzad, Shamim N.; Garlock, Maria

Abstract

This research investigates the seismic response of nonlinear (NL) structures with yielding or rocking mechanisms using a modal approach. The focus is on quantifying the 1st and higher (i.e., the nth) mode responses, after the yielding or rocking mechanism forms. The static lateral load responses and the dynamic seismic responses of NL wall and frame structures are studied.To accurately quantify the nth mode seismic response of a NL structure, two time-varying modal response variables are introduced, namely the nth mode effective pseudo-acceleration and the nth mode effective deformation. These modal response variables are obtained by decomposing the total seismic response of a NL multi-degree of freedom (MDF) structure. The nth mode effective pseudo-acceleration and effective deformation variables provide unambiguous and accurate quantification of the modal response of a NL structure, which can be used to achieve better understanding of the NL response in terms of the 1st and higher modes and as benchmarks for analytical methods intended to predict this NL response using modal responses (e.g., conventional modal response spectrum analysis for NL structures). The nth mode responses of NL wall and frame structures are examined and compared with predictions from existing analytical methods.In addition, this research investigates a consistent approach to quantify the nth mode response of NL structures with clearly defined yielding or rocking mechanisms. In this approach, a set of mode shapes, which are called mechanism mode shapes, are used to decompose the seismic response of a NL structure instead of mode shapes that are based on the initial, linear-elastic state of the NL structure. Using mechanism mode shapes, the nth mode responses of NL wall and frame structures are examined. The results show that mechanism mode shapes can be used to accurately quantify and to create better understanding of the 1st mode and higher mode responses of a NL structure with a clearly-defined yielding or rocking mechanism. In addition to accurately and more consistently quantifying the 1st and higher mode seismic responses of NL structures with clearly-defined yielding or rocking mechanisms, this research also investigates methods of controlling the 2nd mode response of such NL structures by introducing an additional (second) yielding or rocking mechanism. An approach for locating and determining the strength of the second mechanism is established based on the modal properties of the NL structure. This approach is applied to NL wall and frame structures and the effect of the second mechanism in controlling the 2nd mode response is demonstrated using nonlinear time history analysis (NLTHA) results.As an application of the work on the nth mode seismic responses of NL MDF structures, this research investigates the seismic response of buildings which use the Self-Centering Cross Laminated Timber (SC-CLT) wall system as the primary lateral-load resisting system. SC-CLT walls are constructed by post-tensioning (PT) CLT wall panels to the foundation using vertical PT bars. A design-oriented analytical model based on simple closed-form equations (CFE) is introduced to estimate the lateral load response of SC-CLT walls. Numerical models of SC-CLT walls are developed using fiber elements. The analytical results (from both the CFE and fiber-based models) are compared with experimental results. The seismic response of SC-CLT wall buildings is investigated. A performance-based seismic design approach is proposed for SC-CLT wall buildings. The design approach is evaluated using NLTHA results for 6- and 11-story prototype SC-CLT wall buildings under a suite of ground motion records.

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