Measurement and Finite Element Modeling of the Non-composite Deflections of Steel Plate Girder Bridges

Whisenhunt, Todd Walter. Measurement and Finite Element Modeling of the NonComposite Deflections of Steel Plate Girder Bridges. (Under the direction of Emmett Sumner PhD., P.E.) The inability to accurately predict the non-composite steel girder deflections that occur during the deck construction of skewed and stage-constructed bridges is a problem that has resulted in many costly construction delays and maintenance and safety issues for the North Carolina Department of Transportation (NCDOT). In an effort to correct these problems, NCDOT has funded this research (Project Number 2004-14) that involves developing a simplified method of more accurately predicting the non-composite deflections of steel plate girder bridges. This study involved quantifying the inability to accurately predict the non-composite deflections of steel plate girders by measuring the deflections for several bridges in the field as the concrete deck was placed. By measuring the deflections as they occurred, the true non-composite deflection behavior of the bridge was captured and compared to the behavior predicted by the current analysis method used in the design. The current analysis method incorporates single girder line models to predict the noncomposite girder deflections without accounting for any transverse distribution of the construction dead loads through the cross-frames that connect the girders. It was concluded from this study that the current analysis method over predicts the non-composite deflections by an average of 38 percent for the interior bridge girders and an average of 6 percent for the exterior girders. In order to more accurately represent the non-composite deflection behavior, detailed three dimensional finite element models were created for each of the actual bridges measured in the field. Parameters such as bridge skew, cross-frame stiffness, stay-in-place metal deck forms, and partial composite action were considered in the development of the finite element models. These models more accurately represented the torsional behavior of the bridge girders and allowed dead loads to be distributed transversely via the cross-frames used to connect the girders. The finite element bridge models predicted non-composite girder deflections that were within 6-14 percent of the field measured deflections. It was also concluded from both the field measurements and the finite element deflections that stay-inplace metal deck forms can have a significant affect on the non-composite behavior of skewed plate girder bridges. The affects of stay-in-place metal deck forms in bridge deflection behavior is not currently considered in the analysis or design process. This study the first part of a larger research project that ultimately will develop a simplified method to more accurately predict the non-composite deflection of steel plate girders. MEASUREMENT AND FINITE ELEMENT MODELING OF THE NONCOMPOSITE DEFLECTIONS OF STEEL PLATE GIRDER BRIDGES by TODD WALTER WHISENHUNT A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science CIVIL, CONSTRUCTION, AND ENVIRONMENTAL ENGINEERING