Effect of creep and shrinkage on composite steel - concrete beams

A mathematical model for the analysis of the instantaneous and time-dependent response of simply supported composite steel-concrete beamswith stiff or flexible shear connectors (full or partial interaction) undersustained service loads is proposed. The age-adjusted effective modulus(AAEM) method is used to model the creep and shrinkage characteristicsof the concrete slab. The method proposed permits evaluating the stressredistribution between the concrete slab and the steel beam and theincrement of the deflections, which occur gradually with time as a result ofcreep and shrinkage of the concrete slab. The method was programmed ona microcomputer and it is also simple for manual calculations and permitsobtaining solutions in closed form, which can be useful for practicalapplications. By using the proposed model, an extensive parametricanalysis is performed to investigate the influence of the main parametersthat affect the magnitudes of creep and shrinkage of the concrete slab andconsequently, the time-dependent behavior of composite beams. Theinfluence of reinforcing the concrete slab and the influence of theconnection system on the migration of the stresses from the concrete slab tothe steel beam and deflections are also fully investigated. The adequacy ofthe proposed method is checked by comparing the analytically calculatedresults with experimental results reported in previous literature, and goodagreement is obtained. Finally, for practical applications, design charts areconstructed to facilitate the calculation of the elastic (short-term) and final(long-term) deflections at the midspan section of a simply supportedcomposite beam with full interaction under a uniformly distributed load.(H)