Influence of Skew Angle on Continuous Composite Girder Bridge

The design of skewed bridges is becoming more customary in the engineering community. In this paper, the effect of the skew angle on continuous composite girder bridges is presented using three-dimensional finite-element analysis. Seventy-two models of two-span bridges with various span ratios ($N=1$, 1.55, and 1.82), skew angles (0–60°), and various arrangements of intermediate transverse diaphragms are analyzed. All models were subjected to AASHTO HS20-44 loading. Results for skewed bridges are compared with the reference nonskewed bridge, as well as to the AASHTO standard specifications and AASHTO LRFD specifications. The results show that as the skew angle increases, the support moment in interior and exterior girders rapidly decreases. It decreases about 10% when the skew angle is less than 20° and reaches 33% for a 45° skew angle. The shear force increases in the pier support at the exterior girders and decreases at the interior ones with increasing skew angle. For exterior girders, the ratio of shear force increases up to 1.3 for a skew angle of 45°. The AASHTO standard specifications overestimate the maximum bending moment by 20% for a skew angle of 30° and $N=1$ and by 50% for a skew angle of 45°. The overestimation of shear force is about 10% for a skew angle of 45°. The AASHTO LRFD specifications overestimate the longitudinal bending moment and shear force. This overestimation increases with an increase of the skew angle and reaches 12% for a skew angle of 20° and 45% for a skew angle of 45°. The results show that transverse diaphragms perpendicular to the longitudinal girders of the bridges are the best arrangement for load distribution. Comparing the results of the simplified relationships of the skewed decks with the finite-element analysis shows that the results of the proposed equations are conservative for continuous-skewed bridges. It is noted that the results pertain to those bridges with specific configurations and the results may change if the presumed conditions vary, although the tendency should be similar.