Experimental study and theoretical analysis of partially encased continuous composite beams

The mechanical behavior and the law of moment redistribution of the partially encased continuous composite beam (PECCB) are investigated in this paper. One common continuous composite beam and three PECCBs were tested. The main variable parameter of the three PECCB specimens is the amount of longitudinal reinforcement in the concrete slab of hogging moment region. Owing to the contribution of the web encasement, PECCBs have much slower crack propagation speed in the hogging moment region and higher ultimate capacity. The web encasement also contributes to postponing the yielding of the bottom flange, and therefore prevents local buckling in the steel girder. As the amount of reinforcement in the concrete slab of hogging moment region increases, the degree of moment redistribution of PECCBs decreases. On the basis of analyzing the moment redistribution requirement for plastic design and the ultimate rotation capacity of hogging moment section, the required and available moment redistribution factors of PECCBs are obtained. A parameter Rp is introduced to evaluate the relative relationship between the longitudinal reinforcement in the concrete slab and the rest part of the partially encased section, and the value of Rp should be restricted within 0.35 to enable full moment redistribution for plastic design of PECCBs.