Development of a Simplified Procedure to Predict Dead Load Deflections of Skewed and Non-Skewed Steel Plate Girder Bridges

Abstract

Many of today's steel bridges are being constructed with longer spans and higher skew. As a result, the North Carolina Department of Transportation (NCDOT) has experienced numerous problems in predicting the dead load deflections of steel plate girder bridges. In response to these problems, the NCDOT has funded this research project (Project Number 2004-14). Common dead load deflection prediction methods, which traditionally utilize single girder line (SGL) analysis, have been shown to over predict the dead load deflections; the inaccuracy can result in various costly construction delays and maintenance and safety issues. The primary objective of this research is to develop a simplified procedure to predict dead load deflections of skewed and non-skewed steel plate girder bridges. In developing the simplified procedure, ten steel plate girder bridges were monitored during placement of the concrete deck to observe the deflection of the girders. Detailed three-dimensional finite element models of the bridge structures were generated in the commercially available finite element analysis program ANSYS, and correlations were made between the simulated deflections and the field measured deflections. With confidence in the ability of the developed finite element models to capture bridge deflection behavior, a preprocessor program was written to automate the finite element generation. Subsequently, a parametric study was conducted to investigate the effect of skew angle, girder spacing, span length, cross frame stiffness, number of girders within the span, and exterior to interior girder load ratio on the girder deflection behavior. The results from the parametric were used to develop a simplified procedure, which modifies traditional SGL predictions with empirical equations to account for skew angle, girder spacing, span length, and exterior to interior girder load ratio. Predictions of the deflections from the simplified procedure and from SGL analyses were compared to the deflections predicted from finite element models (ANSYS) and the field measured deflections to validate the procedure. It was concluded that the simplified procedure may be utilized to predict dead load deflections for simple span, steel plate girder bridges. Additionally, an alternative prediction method has been proposed to predict deflections in continuous span, steel plate girder bridges with equal exterior girder loads, and supplementary comparisons were made to validate this method.