Flexural Strength of Composite HSB690 I-Girders in Negative Moment

Abstract

The flexural behaviors of composite I-girders made of a high performance steel, HSB690, having a yield strength of 690 MPa in negative moment, were numerically investigated by applying an incremental ultimate strength analysis with material and geometrical nonlinearities. A total of twenty-nine example sections with various slenderness ratios of compression flanges and webs were carefully selected such that they meet the requirements in Appendix A6 of AASHTO LRFD, except the first requirement that the yield strength not exceed 485 MPa (70 ksi). Results of the numerical scheme adopted in this study were verified by comparing the flexural strengths computed by FEA to those of experimental results produced by other researchers. Numerical results for moment versus rotation curves, stress distributions, and failure modes were investigated and presented. The effects of initial imperfections, residual stresses, and mechanical properties of reinforcing steels on the ultimate flexural behavior of the girders were also closely investigated. The applicability of the negative flexural resistance equations in AASHTO LRFD for HSB690 composite I-girders was examined by comparison of the ultimate flexural strengths obtained from the numerical analyses. It was found that the upper limit on the yield strength of 485 MPa as one of the three major prerequisites to using the Appendix A6 in AASHTO LRFD can be removed from the provisions. Therefore, the flexural resistances of HSB690 girders in negative moment can be more efficiently evaluated by utilizing the procedures in Appendix A6 of AASHTO LRFD than those of Article 6.10.8 in AASHTO.