Semester

Summer

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Karl E. Barth.

Abstract

Moment redistribution refers to the design practice where the inherent ductility of continuous-span steel bridge structures is acknowledged and consideration for the redistribution of the large negative bending moments at interior supports to the less heavily stressed positive bending regions is provided. One of the key assumptions made in moment redistribution procedures is that members have sufficient ductility to sustain a given moment capacity throughout the level of rotation required for redistribution moments to develop. However, there is presently no explicit verification that this assumption is satisfied. Instead, it is assumed that sufficient ductility can be obtained by: (1) limiting the range of girders for which moment redistribution is permissible to relatively compact members and (2) limiting the amount of moment that may be redistributed. Furthermore, the restriction of these procedures to relatively compact members has limited the potential for application of these procedures to the rating and permitting processes for existing bridge structures.;The research presented herein is aimed at overcoming this limitation through a rotation compatibility approach. This method consists of direct comparison of rotation requirements for moment redistribution to available rotation (ductility) of composite or non-composite steel I-girders. An analysis procedure for determining rotation requirements is discussed along with research results illustrating the relationship between intended level of redistribution moment and required rotation for typical bridge designs. An investigation into the available rotation of typical steel I-girders is also described. It is shown that this available rotation can also be related to the intended level of redistribution moment. Thus, relating both the available and required rotations to a common parameter facilitates a direct comparison between these two quantities.;The advantages of this approach compared to current design practices are also discussed. The rotation compatibility approach offers increased design economy by providing a rational basis for determining the class of sections for which moment redistribution is valid and thereby extending the applicability of the specifications. In addition to the benefits offered by this approach in new designs, there is significant potential for economic savings through application of these procedures to bridge rating.

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