Bending Behavior of Composite Hybrid Beams

Theoretical moment-curvature and moment-stress relations are developed to describe the bending behavior of composite hybrid beams, which differs from that of noncomposite hybrid beams and of composite homogeneous beams. Formulas are developed for the ultimate strength of composite hybrid beams, as limited by either crushing of the concrete or yielding of the full cross section of the steel beam. Curves of moment vs (1) curvature, (2) location of the neutral axis, (3) bottom-flange stress, and (4) top-flange stress are presented to illustrate the theoretical bending behavior of composite hybrid beams and to compare this behavior with that of composite homogeneous beams. These curves show that there is a small difference between the behavior of the two types of beams as a result of web yielding In the hybrid beam. For design purposes, the small reduction in the flange-yield moment caused by web yielding can be accounted for by an approximate design formula that gives a reduced allowable flange stress. If this reduced allowable stress is used the bending stress in the web need not be checked.