Hybrid Procedure for Cracking and Time-Dependent Effects in Composite Frames at Service Load

A hybrid analytical-numerical procedure has been presented to take into account the effect of concrete cracking and time-dependent effects of creep and shrinkage in composite beams of the composite frames subjected to service load. The procedure is analytical at the element level and numerical at the structural level. The cracked span length beam element consisting of an uncracked zone in middle and cracked zones at the ends has been proposed for the composite beams to reduce the computational effort. The progressive nature of cracking of concrete of composite beams has been taken into account by division of the time into a number of time intervals. Closed form expressions for flexibility coefficients, end displacements, crack lengths, and midspan deflection of the cracked span length beam element have been presented in order to reduce the computational effort. The procedure has been validated in a limiting case by comparison with the experimental and analytical results reported elsewhere and also by comparison with FEM. The proposed procedure would lead to a considerable saving in computational time in case of large composite structures, e.g., tall composite building frames.