Multi-span precast concrete segmental bridges are commonly constructed using the balanced cantilever method, which essentially involves sequentially extending precast segments outwards from each pier in a balanced manner. A gap of 100 to 200 mm wide is usually provided around the mid-span location between the last two approaching segments to facilitate erection. In-situ concrete is then cast to ‘stitch’ the segments together, thus making the bridge deck continuous. In the current practice, the in-situ concrete stitches are usually designed to be capable of sustaining considerable sagging moment but only minimal hogging moment. Failure of stitches may occur under exceptional circumstances that may potentially trigger a progressive collapse. However, relatively little research in this area has been carried out. In view of this, the author is motivated to undertake an extensive study of the behaviour of in-situ concrete stitches and the effects of their performance on the robustness of typical segmental bridges. Experimental study is carried out to examine the behaviour of in-situ stitches under different combinations of internal forces. Series of stitch specimens of different configurations are tested. Subsequent parametric studies are conducted numerically to examine the effects of various parameters on the load-displacement characteristics of the stitches. Formulae for strength estimation are proposed based on the results. A study of robustness involves analyzing the collapse behaviour of a structure in an extreme event and the analysis should be carried out up to and then well beyond the state of peak strength of structural members. A finite element programme for post-peak analysis is therefore developed for the present study. As the ability of a member section to sustain large inelastic deformation can ultimately affect the robustness of a structure, an investigation is conducted to examine the effects of steel content, yield strength and prestressing level on the ductility and deformability of prestressed concrete sections. Using the programme developed, the formation of collapsing mechanisms of a multi-span segmental bridge deck in an extreme event is examined. A typical bridge deck is subject to prescribed accidental load on its span in order to analyze the sequence of failure. Substantial redistribution of internal forces along the deck is observed as failures initiate, thus causing subsequent failures of other deck sections even though they have been designed to resist the internal forces at the ultimate limit state. The results indicate that any span of a multispan bridge may become a temporary end-span in the event of collapse of an adjacent span and the strength of the sections must be designed accordingly to prevent progressive failure. As a span becomes a temporary end-span, the in-situ concrete stitches may experience substantial moment and shear, and their failure could potentially trigger progressive collapse of the entire bridge deck. Towards the end of the thesis, important design considerations that can enhance the performance of in-situ concrete stitches and robustness of precast concrete segmental bridges are presented. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

This research project is the second part of a research program carried out by Itagawa (2005) who studied the seismic response of a half-scale model of an existing Montreal bridge built in the 1960's. This project studies the seismic behaviour of the retrofit carried out on the frame structure studied in the first part of the research program. The retrofit was made following the requirements of the current Canadian Highway Bridge Design Code (CHBDC). The philosophy of the CHBDC is to provide flexural yielding in the ductile elements so that brittle failure modes such as shear are prevented. This capacity-design approach resulted in a ductile response and significant energy dissipation of the retrofitted structure. / The retrofit was designed in accordance with the CHBDC provisions. The cap beam and the beam-column joint regions were strengthened with a reinforced concrete sleeve containing additional transverse and longitudinal bars so that plastic hinging would form in the columns. This retrofit represents minimum intervention to improve the response of the frame. The retrofit frame was then subjected to both gravity loads and reversed cyclic loading to simulate seismic loading on the structure. The predictions of the response of the retrofitted frame provided reasonable estimates of first yielding in the column and the general yielding of the frame. Although the columns would not meet the requirements for ductile columns, they had sufficient shear strength and did exhibit a displacement ductility of about 2.3.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references (leaves [187]-191).

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references (leaves 270-276). Online version available on the World Wide Web.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1916. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed April 23, 2009)

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 188-194). Also available via the Internet.

Thesis (M.S.)--University of Nevada, Reno, 2008. / "May, 2008." Includes bibliographical references (leaves 58-59). Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Apr. 9, 2009). PDF text: xi, 152 p. : ill. (chiefly col.) ; 6 Mb. UMI publication number: AAT 3341867. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 86-88).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed July 21, 2009). PDF text: xxiv, 162 p. : ill. (some col.) ; 8 Mb. UMI publication number: AAT 3350499. Includes bibliographical references. Also available in microfilm and microfiche formats.