For noncompact sections, local buckling should not occur before the cross-section attains its moment capacity at first yield My. For a noncomposite I-shaped section bent about its major axis, My is given by

where Fy is the spe ified minimum ompression flange yield stress, Fyt is the spe ified minimum tension flange yield stress, Sc is the se ction modulus with respe ct to the compression flange, that is equal to Ix/cc, and St is the section modulus with respect to the tension flange, that is equal to Ix/ct, in which Ix and ct are given in Equations 14.5 and 14.6, respectively, and cc is equal to tfc+tft+D — ct.

Tests on noncomposite bridge girders made of HPS70W steel (Yakel et al. 2002) have demonstrated that while noncompact and compact plate girders could provide the first yield and plastic moment capacities, respectively, the compact plate girders were not able to provide an inelastic rotational ductility of 3, as implied by the AASHTO Specification for compact sections. As a result, the 10% moment redistribution for continuous girders as per Section of the AASHTO Specification (AASHTO 1998) should not be applied to girders made of 70 ksi (485 MPa) steels (AASHTO 2000b).

0 0

Post a comment