Behavior at the Corners of Skewed, Single-Span, Cast-in-place, Post-tensioned Box Girder Bridges

Author

Phillip Mathew Holthaus, Southern Illinois University CarbondaleFollow

Date of Award

1-1-2009

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Hsiao, Kent

Abstract

In today's textbooks, analyzing prestressed members and bridges takes a two-dimensional approach. Two-dimensional analysis is the only way to analyze prestressed bridges and members because otherwise the hand calculations are extremely difficult. Skewed bridges, however, need to be analyzed and designed three-dimensionally. Based on engineering inspection, it is possible to tell how a non-skewed symmetric bridge will behave. However, the knowledge of how a skewed bridge will behave cannot be obtained by inspection only. Finite element analysis can be used to model a bridge and discover how the bridge will react to dead loads and post-tensioning forces. When a bridge is built on a skew, the acute corners of the bridge support much less concrete weight than the obtuse corners of the bridge. If the post-tensioning force causes a decrease in load at the acute corners of the skewed bridge and if the skew of the bridge is great enough, there is a concern that there could be uplift at these acute corners of the bridge. Uplift at any corner of the bridge should not be allowed. The objective of this study is to investigate a simple span skewed box girder bridge to see if any uplift occurs at the acute corners of the bridge due to post-tensioning forces. After careful study of a skewed simple span cast-in-place post-tensioned box girder bridge, it was found that the post-tensioning force actually transfers more downward force into the acute corners of the bridge. Based on this study, the post-tensioning force will not cause uplift in the acute corners of the skewed bridge.