Date

2017

Document Type

Thesis

Degree

Master of Science

Department

Civil Engineering

First Adviser

Pessiki, Stephen Dr.

Abstract

This research proposes a new low damage seismic resistant system that implements a manual post-tensioning procedure by inserting a spring element at the post-tensioning steel anchorage. This system is aimed at the following: (1) eliminate the need for specialized post-tensioning equipment and the associated highly trained workers required in the construction of the conventional rocking systems; and, (2) promote more sustainable seismic systems by combing with renewable materials. This report derives a set of closed form expressions that provide a useful tool for understanding the behavior of the proposed system. Also, it develops a finite element model to capture the response of the system under static pushover loads. The report also conducts an extensive parametric study using the closed form expressions and the finite element model to understand the effects of certain parameters on the lateral displacement response of the proposed system. These parameters are: (1) the axial stiffness of the spring element; (2) the length of the rocking frame; (3) the initial stress of the post-tensioning steel; and, (4) the height of the post-tensioning steel. The results of this parametric study show that the closed form expressions display an excellent agreement with the finite element results. Also, even though a rocking timber frame has constant member dimensions and post-tensioning steel area, connecting the post-tensioning steel in series with a flexible spring element could significantly increase the drift capacity of the rocking frame. This report also develops a finite element model to capture the response of the proposed system under actually recorded ground motions. Several prototype frames were subjected to 22-pair ground motions, and the results of different prototype frames were plotted and compared. The results show that even though significant ground shakes are applied to the prototype frames, the residual post-tensioning force after the earthquake of frames having flexible spring element is always more than other frames with no spring element. In fact, the frames with flexible spring elements never experienced yielding in any of the ground shakes in this study, while some frames with stiff spring element experienced significant yielding. It was also noticed from the dynamic analyses that the moment hysteresis loop for frames with flexible spring element is likely to be flat after the frame decompression (i.e. no moment increase), while the hysteresis loop of frames with stiff spring element is steeper (moment increases) under the same circumstances.

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