Flexural Strength and Rotation Capacity of I-Shaped Beams Fabricated from 800-MPa Steel

Flexural tests on full-scale I-shaped beams, built up from high-strength steels (HSB800 and HSA800) with a nominal tensile strength of 800 MPa, were carried out to study the effect of flange slenderness on flexural strength and rotation capacity. The primary objective was to investigate the appropriateness of extrapolating current stability criteria (originally developed for ordinary steel) to high-strength steel. For comparison purposes, specimens with ordinary steel (SM490) were also tested and showed sufficient flexural strength and rotation capacity in accordance with the AISC specification. The performance of high-strength steel specimens was also very satisfactory from the strength, but not from the rotation capacity, perspective. The inferior rotation capacity of high-strength steel beams was shown to be directly attributable to the absence of a distinct yield plateau and the high yield ratio of the material. When a higher rotation capacity is required as in plastic design, the testing clearly showed that high-strength steel beams were vulnerable to brittle fracture when full-height transverse stiffeners were welded to the tension flange in the plastic hinge region. Residual stress measurements reconfirmed that the magnitude of the residual stress is almost independent of the yield stress of the base metal.