High performance steel bridge girder compactness

The present study employs experimentally verified nonlinear finite element modeling techniques for the study of high performance steel (HPS) I-shaped bridge girders. An evaluation as to the appropriateness of using the current American bridge specification (AASHTO 1998) provisions for cross-sectional compactness and adequate bracing is carried out within the context of applications involving A709 Gr. HPS483W high performance steel. It appears that the current AASHTO bracing provisions are inadequate when applied to A709 Gr. HPS483W bridge girders; intense interactions between local and global buckling manifestations occur in the HPS bridge girders studied herein despite satisfaction of the AASHTO requirements. As a result of the interaction between local and global instabilities, the application of the separately defined AASHTO cross-sectional compactness criteria becomes invalid. An alternate bracing requirement is proposed for use with HPS bridge girders as part of this research. This new bracing scenario does not require any additional costs in fabrication or materials since only the placement of the required bracing is changed with respect to current practice and not the total number of braces. Once the new bracing scenario is implemented, the notion of cross-section compactness once again has validity and thus correlates with HPS I-shaped girder flexural ductility. New flange and web compactness criteria are proposed for use with A709 Gr. HPS483W bridge girders braced in the manner specified herein.