Effect of slab in inelastic analysis of R/C buildings under earthquake type of loading
Durrani, Ahmad J.
Doctor of Philosophy thesis
Tests on beam-to-column connections have shown that the presence of a slab significantly increased the flexural resistance of the beams under bending which caused tension in the slab. The presence of a slab in reinforced concrete buildings was studied both at the cross sectional and element modelling levels. At the cross sectional level, the experimentally observed progressive slab participation is recognized by a proposed strain distribution in the slab. The proposed strain distribution, along the flange width of a beam-slab section, accounts for the progressive increase in the slab participation with its changing pattern as a function of the strain level at the column face. The analytical prediction of the strain distribution in the slab agrees with the observed strain distribution in the slab of beam-column subassemblies. Furthermore, the increase in the yield curvature and hence a reduced postcracking stiffness of a beam-slab section resulting from the proposed strain distribution as compared with that of the uniform strain distribution is negligible. At the element level, the multi-spring model was modified to account for the recognition of different strength and stiffness in slab-in-tension and slab-in-compression directions of bending. Results from inelastic dynamic analyses of a typical multistory building with different slab participation suggest significant increases in story accelerations and base shears with increasing slab participation. The ductility requirements of the beams and columns are also significantly affected by the recognition of direction dependent stiffness in inelastic analyses. Due to a larger participation of the slab when in tension as compared with that in compression, the ductility requirement in slab-in-compression direction of the beams can get larger. Furthermore, the increased capacity of the beam-slab section affects the flexural and rotational ductility demands placed on the columns which can lead to a strong-beam and weak-column mechanism under lateral loading.