Skewed bridges have been designed for many years using approximate methods. most of these methods do not account for the high torsional moments inherent in a skewed structure. more exact methods of analysis are time consuming and the stringent budgets do not permit the design consultant the luxury of using these more elaborate and exact methods. recently, several highly skewed post-tensioned box girder bridges have been studied and designed by parsons brinckerhoff quade & douglas, inc. (pbq&d) in tempe, arizona. the high skew angle ofthese highway and railroad bridges with very heavy live loads was caused by the restricted right-of-way limitations and necessitated the use of more exact methods and/or dependable methods of analysis for these structures. five skewed bridges were analyzed, by conventional plane frame analysis and by two different programs, using a finite element method of analysis. two of these bridges were compared to verify the designs based on three dimensional grid analysis. in the preliminary stage the structures were sized and preliminary forces obtained by using caltrans "frame system" and then the finite elementmodels were generated in order to gain a better understanding of the effect of skew bending on the deformations, stresses, support reactions, and torsional moments. traditionally skewed bridges were analyzed and designed considering the longest length between the supports as the actual span length. conventional wisdom assumed that such aconservative approach would result in a very safe design. the meansor the methods to do a more precise analysis and design did not exist. the advent of computers and the implementation of finite elementmethods of analysis have given the means to take a closer look at the behavior of the skewed bridges. this paper appears in transportation research record no. 1290, third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 1.
Abstract