Abstract: The deflection assessment 0±steel—concrete composite beams at the serviceability Iimit state is normally based on the linear elastic analysis，and the yielding occurring in the steel that will influence the accuracy of the linear deflection output of the beams，however would be neglected in design practice．Several key factors that affect the deflection calculation of composite beams are discussed，supplemented by analysis of the effects of the deflection to span ratio，span to depth ratio，longitudinal slips between the steel and concrete，residual stress in the steel and self-weight stress during construction．It is suggested that the strain leading to a potential yield in composite beams should be considered in the deflection check of composite beam design．

Keywords：steel-concrete; composite beam; deflection design; yielding; slip