Time-dependent Analysis of Prestressed Composite Beams

The viscoelastic analysis of composite steel-concrete continuous beams, with prestressed slab and flexible shear connectors, is presented. Two prestressing systems, involving the application of prestressing forces before or after the connection of the concrete slab to the steel beam, are considered. The mathematical formulation of the problem involves internal compatibility equations between beam and slab and between slab and prestressing cables. Such conditions are formulated taking into account the integral-type creep law for the concrete slab. With the model proposed, some relevant examples were investigated and discussed. Partial longitudinal prestressing of the slab, performed using cable with length less than the whole structure, is also analyzed. Particular attention is paid to examining the ''primary'' and the ''secondary'' effects of the prestressing, and the shear force distribution at beam-slab interface. A parametric study is then performed by varying the stiffness of shear connectors and the combining time between slab and beam.