Creep and shrinkage effect on the dynamic analysis of reinforced concrete slab-and-beam structures

In this paper, a solution to the dynamic problem of reinforced concrete slab-and-beam structures including creep and shrinkage effects is presented. The adopted model takes into account the resulting in-plane forces and deformations of the plate as well as the axial forces and deformations of the beam, due to the combined response of the system. The analysis consists of isolating the beams from the plate by sections parallel to the lower outer surface of the plate. The influence on creep and shrinkage effects of the time between the casting and the loading of the plate and the beams is taken into account. A lumped mass matrix is constructed from the tributary mass areas to the nodal mass points and a stiffness matrix is computed using the solution of the corresponding static problem. Both free and forced vibrations are considered and numerical examples of practical interest are presented. The discrepancy between the eigenvalues obtained using the present analysis, which better approximates to the actual response of the plate–beam system and the corresponding ones which ignore the in-plane forces and deformations requires the adopted model.