Basha Dorose

Date of Award

January 2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Iraj Mamaghani

Abstract

Steel bridge piers have found wide application in highway bridge systems around the globe. Steel tubular bridge piers, compared with concrete ones, are light and ductile. They can be built under severe constructional restrictions, such as in limited spaces throughout urban areas like New York and Tokyo, where the effective use of the limited spaces are desired strictly. They are also applied to locations where heavy superstructures are unfavorable, such as on soft ground, reclaimed land and bay areas.

In general, steel bridge piers are designed as single columns of the cantilever type, or one to three-story frames. Steel columns in highway bridge systems are commonly composed of relatively thin-walled members of closed cross-sections, either box or circular in shape, because of their high strength and torsional rigidity. Such structures are considerably different from columns in buildings. The former are characterized by: failure attributed to local buckling in the thin-walled members; irregular distribution of the story mass and stiffness; strong beams and weak columns; low rise (1-3 stories); and a need for the evaluation of the residual displacement. These make them vulnerable to damage caused by local and overall interaction buckling in the event of a severe earthquake. A sound understanding of the inelastic behavior of thin-walled steel tubular columns is important in developing a rational seismic design methodology and ductility evaluation of such structures.

For this purpose, this thesis deals with the stability and ductility evaluation of thin-walled

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circular steel bridge piers under cyclic loading. The basic characteristics of the thin-walled circular steel bridge piers and several methods in improving strength and ductility capacity of such structures was investigated. A procedure for ultimate strength and ductility evaluation of thin-walled circular steel bridge piers was developed. The application of the procedure was demonstrated by comparing the computed strength and ductility of some bridge piers with test results. The developed procedure is applicable for both the design of new, and retrofitting of existing, thin-walled circular steel bridge piers. The effects of some important parameters, such as width-to-thickness ratio, column slenderness ratio and residual stress, on the stability and ductility of thin-walled circular steel bridge piers, will be presented and discussed. A reasonably good agreement between the experiment and the analysis confirms the validity of the finite element modeling adopted in this study. From this study it is found that with the increase in eccentric distance, the load-carrying capacity of the eccentrically loaded columns in the eccentric side is greatly decreased, while in the opposite side it is increased. The results of this study also indicate that the buckling modes of the eccentrically in-plane loaded columns are almost the same as those of the centrally loaded columns when the eccentric distance lies within 30 percent of the column height. It was found that the strength and ductility of the eccentrically loaded columns can be conveniently obtained from those of the centrally loaded columns.

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