Civil Engineering

 

Date of this Version

Fall 12-5-2011

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 Jones & Atorod Azizinamini. Lincoln, Nebraska: December, 2011

Copyright (c) 2011 Marcelo Ferreira da Silva

Abstract

Steel girder bridges often utilize continuity over the pier to reduce interior forces on the spans. In continuous structures with composite concrete decks, the location of maximum negative bending moment is over the interior supports. This moment produces tensile stresses in the concrete deck and compressive stress in the bottom flanges of the girders. The tensile stress in the deck leads to cracking which allow intrusion of moisture and road salt, causing corrosion of the reinforcement and supporting girders. Continued maintenance is required to forestall the deterioration; however, replacement of the deck is eventually required.

To overcome this problem, a “self-stressing” system was developed. The method induces a compressive force in the deck that is accomplished by raising the interior supports above their final elevation while the deck is cast or placement (precast panels). Once the concrete has cured the supports are lowered to their final elevation. Continuity of the steel member and the composite action with the deck produce a compressive stress in the concrete slab, which is balanced by tensile stresses in the bottom of the steel member. As a result, the cracking over interior support is diminished increasing durability and the need of girder splices may be eliminated making the overall bridge design more efficient and cheaper when compared to conventional design.

The experimental investigation was conducted to observe the behavior of the system. Time-dependent effects and behavior of the system under ultimate load were analyzed. Overall, the specimen performed as expected, shown good stability, delayed cracking, and sufficient amount of ductility. Based on the experimental program, the system appears to be a simple and viable alternative to more common method of post-tensioning the deck to obtain an initial compressive force in the concrete deck. As a result, a design guide was developed to aid bridge engineers with the implementation of the Self-stressing Method Design in practice.

Advisor: Elizabeth Jones & Atorod Azizinamini

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