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MPC |
| Title: | Moment-Rotation Tests of High Performance Steel I-Girders |
| Principal Investigators: | Bryan A. Hartnagel |
| University: | Colorado State University |
| Status: | Completed |
| Year: | 2000 |
| Project #: | MPC-196 |
Bridge designers now have a new choice of steel available for consideration when planning a bridge. High-performance steel (HPS) grade 70W is currently available for bridge construction. The HPS70W was developed under a cooperative research program between the Federal Highway Administration (FHWA), the U.S. Navy, and the American Iron and Steel Institute (AISI). However, current bridge design provisions limit the flexural strength of girders with yield strength greater than 50 ksi (350 Mpa) to the yield moment capacity. The flexural capacity of similar bridge girders designed with yield strength less than or equal to 50 ks i (350 Mpa) is equal to the plastic moment capacity if certain restrictions are met. Further, if the designer chooses, an inelastic analysis of the girder is allowed with steel yield strengths less than or equal to 50 ksi (350MPa). Inelastic analysis and design methods offer larger cost savings compared to the elastic analysis provisions. Even with the disadvantage on the flexural capacity, HPS is still competitive with Grade 50 steels because of material savings obtainable with HPS. If these restrictions could be lifted or even relieved, the use of HPS would provide significant cost savings.
The AASHTO Load and Resistance Factor Design (LRFD) Specification considers Any girder cross section with a specified minimum yield strength exceeding 50 ksi to be non-compact. This limits the load carrying capacity of the cross section to a maximum of the yield moment. The capacity of girders with a specified minimum yield strength less than or equal to 50 ksi can be as large as the plastic moment, provided certain cross section properties are met. Research has shown that the capacity of girders fabricated from steel with a specified minimum yield strength greater than 50 ksi can sustain loads larger than the yield moment. However, more research is necessary before changes in the design specification can be implemented.
