UTrAp 2.0: Linearized Buckling Analysis of Steel Trapezoidal Girders

Steel trapezoidal box-girder bridges have been gaining popularity due to their aesthetic appeal and structural efficiency. The completed closed section resists torsion very efficiently, making it an attractive choice for curved bridges. Under construction loading, however, the section is open or pseudo-closed, offering very little torsional capacity. Thus, the construction stage is critical in the response of these systems.

The stability of a girder in the construction process is of particular concern. Numerous failures of individual brace members have been observed, and global buckling failures have occurred in two bridges under construction in the past several years, one of which resulted in loss of life. In order to provide a tool for understanding and predicting the buckling behavior of steel trapezoidal girders, the elastic analysis program UTrAp has been modified to include a buckling analysis capability. UTrAp 2.0 performs a linearized buckling analysis, using the finite element model developed previously. Geometric nonlinearity is included, but material nonlinearity is not taken into account. The program finds the buckling load as a scalar multiple of the applied load, assuming linear-elastic behavior. Included in the output are deflections and rotations of the girder to assist a designer in visualizing the buckled shape. A comparison with the results of general finite element software shows that UTrAp 2.0 accurately predicts the linearized buckling load.