Evaluation of AASHTO-LRFD Design Methods for Thermal Loads in Fixed-Flexible Twin-Walled R/C Bridge Piers
Publication: Journal of Bridge Engineering
Volume 16, Issue 6
Abstract
The design of reinforced concrete fixed-flexible twin-walled bridge piers for lateral loads is an ambiguously defined task for bridge engineers. As the bridge experiences lateral loads, primarily from temperature fluctuations and time-dependent effects, the walls undergo cracking, requiring designers to consider sectional stiffness reductions. Two types of finite-element models were generated of the recently constructed Wakota Bridge in South St. Paul, Minnesota, one using a design-level program (SAP2000) and the other using a research-level program (ABAQUS). For an arbitrary temperature load, a commonly used refined design method, implemented in the design-level program, was evaluated for accuracy of reduced section properties relative to a more descriptive progressive cracking solution provided by the research model. The refined design method with four stiffness update segments was found to provide a balance between accuracy and analysis effort. A staged construction model of the Wakota Bridge, defined in SAP2000 to incorporate time-dependent effects of the construction sequence, indicated that pier forces for the design options in the AASHTO-LRFD Specifications for simulating reduced section properties (i.e., refined analysis with stiffness updates versus gross sections with reduced load factors) correlated to within approximately 10%. Additionally, of the two temperature change procedures in the AASHTO-LRFD Specifications, Procedure B produced moments for the Wakota Bridge that were as much as 25% larger than those from Procedure A.
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Acknowledgments
This research was funded by a grant from the Minnesota Department of TransportationMNDOT (Mn/DOT). The views expressed herein are those of the writers and do not necessarily reflect those of the sponsors. The authors are grateful to the members of the Mn/DOT Technical Advisory Panel (Dave Dahlberg, Arielle Ehrlich, Keith Molnau, Dustin Thomas, Paul Stenberg and Shirlee Sherkow) for their advice and guidance during the research. Lastly, the authors also thank Chris Burgess (Figg Engineering Group) and Jeffrey Cavallin (Parsons Corp.) for their input regarding various design aspects of concrete bridges.
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© 2011 American Society of Civil Engineers.
History
Received: Aug 16, 2010
Accepted: Mar 3, 2011
Published online: Mar 5, 2011
Published in print: Nov 1, 2011
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