Stresses in the Negative Moment Region of Composite Steel Bridges

Principal Investigator:

Jerome Hajjar, Former University Researcher, Civil, Environmental and Geo-Engineering

Project Summary:

The new AASHTO LRFD Specification (1994) requires the use of shear connectors in the negative moment region of steel bridge girders, or otherwise requires the use of more conservative nominal design strengths. It has been typical for bridge engineers to avoid designing steel members which include welded details of this type in the negative moment region. In addition, the fatigue endurance of the stud itself is calculated using an equation which is based on experiments which neglect the effect of concurrent tension in the tension flange base metal due to flexure. Coupled with this, recent research at the University of Minnesota on a comparison of field measurements with elastic analysis results of strains in a steel curved girder bridge (MT/DOT bridge no. 27998) indicates that proper accounting for composite action in the negative moment region of continuous steel bridge girders is required to predict the stresses accurately. This proposed project is a pilot study to determine what future research, if any, is required to determine whether use of shear connectors in the negative moment region of steel girders poses a serious fatigue problem. The primary task includes conducting a thorough literature review to determine what experimental and computational research has been conducted on the fatigue strength of shear connectors, particularly those attached to base metal which is in tension. A secondary objective of this project is to expand the ongoing MT/DOT research project 74708 to permit more detailed investigation of the effect of modeling of composite action on the prediction of stress ranges in the negative moment region. Where appropriate, a detailed plan for future research will be developed for these two integrated topics.

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