Pier moment-rotation behavior of high performance steel HPS70W I-girders

Abstract

This dissertation presents a study of the pier moment-rotation behavior of compact and noncompact high performance steel HPS70W I-shape girders in the context of examining two restrictions for inelastic design of steel bridge girders in the current edition of the AASHTO LRFD bridge code (AASHTO, 1998 and interim 2001). The first restriction is that inelastic design involving the moment-rotation relationship of steel girders with a yield strength exceeding 50 ksi is prohibited. Though, bridge designers are currently allowed to go to plastic moment for I-shape girders having a yield strength of 70 ksi. The second restriction is that the AASHTO LRFD inelastic design methods cannot be used on girders that do not meet the compactness requirements stated in the provisions.

To determine whether or not these restrictions should be modified, examination of the pier moment-rotation behavior of HPS70W I-shape girders was undertaken through experimental testing and numerical modeling. Large-scale laboratory experiments were performed for noncomposite girders. Finite element models of the tested specimens were then analyzed based on the material inputs obtained from experimental examination o f the stress-strain relationships for HPS70W. The inelastic moment-rotation behavior o f HPS70W girders was determined both experimentally and numerically.

The experimental and numerical responses agree well and thus validate the numerical model. These results also show that compact/noncompact and composite/noncomposite HPS70W I-girders have the strength and ductility suitable for the application of inelastic analysis and design. This research suggests that the two restrictions for inelastic design of steel bridge girders in the current AASHTO LRFD bridge code (AASHTO, 1998 and interim 2001) should be modified for such girders. This work also demonstrates that the proposed improved simplified inelastic design (ISID) procedures (Barth, Hartnagel, White, and Barker, 2001) are suitable for high performance steel, HPS70W, compact and noncompact I-girders. In addition, from the noncomposite numerical models, which were validated by experiment, finite element models were developed for composite girders and were examined. The numerical results confirm that the pier moment-rotation behavior is similar for composite and noncomposite cross sections.