UTrAp: Finite-Element-Based Software for the Analysis of Curved Trapezoidal Girders under Construction Loads

Due to advances in fabrication technology, the use of steel trapezoidal box girders for curved interchange structures has become popular. The rapid erection, long span capability, economics, and aesthetics of these girders make them more favorable than other structural systems. The response of composite box girders with live loading, as well as the behavior of quasi-closed box girders during construction, must be considered during the design process. Considering both cases, the design for construction loading is the least understood and is the most important. Stresses due to construction loading can reach up to 60-70 percent of the total design stress for a given cross section.

In this report, we document the development and usage of the software package UTrAp. This program allows for the analysis of curved girder bridge systems in a more rigorous manner than traditional grid analysis approaches. UTrAp utilizes a finite element methodology to determine stresses and strains throughout the cross-section of a bridge girder. In addition, internal and external brace members are modeled explicitly so that no assumptions are required (e.g., equivalent plate method) for determining member forces. Unlike currently available software, UTrAp has the capability of modeling the effects of semi-cured concrete. The developed software has been designed to be computationally efficient and easy to use for bridge designers. A graphical user interface (GUI) has been developed along with the finite element analysis routines to aid in entering data and visualizing analysis results. A comparison to measured field data shows that UTrAp provides an accurate characterization of girder response under construction loads.