Civil Engineering

 

Date of this Version

Winter 12-2011

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Interdepartmental Area of Engineering (Civil Engineering), Under the Supervision of Professors Elizabeth G. Jones and Atorod Azizinamini. Lincoln, Nebraska: December, 2011

Copyright 2011 Ardalan Sherafati

Abstract

Jointless bridges have been in service for more than 50 years. Since no expansion joint is utilized in these structures, they have longer service life, reduced maintenance and construction costs, improved riding quality, and added redundancy. Because of integrity of the superstructure with the substructure, the thermal movements as well as other longitudinal movements are transferred to substructure. These lateral movements can induce relatively large forces and moments in the substructure elements including the abutment and the piles. Typically, flexible foundations which include single row of piles are preferred in jointless bridges to reduce the stiffness of the system against longitudinal movements of the superstructure.

The main objective of this dissertation is to improve and expand the application of jointless bridges to longer bridge lengths. As the imposed movements at the pile head level due to superstructure’s displacements are linearly proportional to the length of the jointless bridge, by increasing the pile head displacement capacity the length of jointless bridges can be expanded. A parametric study has been conducted using nonlinear pushover analysis. The results of this study show that the pile head displacement capacity can be increased up to four times if rotational capacity is provided at the pile-cap connection. Further, it is shown that strong axis bending results in more displacement capacity as compared to weak axis bending, although the lateral stiffness would be smaller in the latter case. Experimental study has been carried out on the proposed connection of CFT piles to the concrete cap. It is shown that this detail can effectively reduce the moment-rotation stiffness of the connection and increase the displacement capacity up to four times.

New design procedure is proposed for HP piles supporting jointless bridges. In this approach, only compact sections are recommended in order to prevent local buckling prior to reaching full plastic moment capacity of the cross section. Further, fatigue and strength criteria are combined and displacement capacity is estimated based on the boundary conditions, axial load, soil type, and orientation of the pile.

Advisors: Elizabeth G. Jones and Atorod Azizinamini

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