Long term analysis of externally prestressed composite beams

The time dependent behaviour of composite beams prestressed by external cables is analysed by assuming linear elastic behaviour for the steel and the interface shear connection, linear viscoelastic behaviour for the concrete and the hypothesis of frictionless cables. By assuming an admissible displacement field for the composite beam taking into account steel-concrete interface slipping, the balance condition is obtained by the virtual work principle. The solution is numerically achieved by introducing a suitable discretization of the time interval so that the viscoelastic problem reduces to a sequence of elastic problems, which are solved by the Ritz method. The results reported of some numerical analyses show that prestressing cables do not sensibly modify their stress in time. On the other hand, the stress state of the composite beam is strongly time-dependent due to non-homogeneity of the cross section. The stress distribution on the slab can however be optimised.