Modelling shear-flexure interaction in equivalent frame models of slender RC walls

Experimental results for quasi-static cyclic tests on reinforced concrete (RC) walls have shown that shear deformations can constitute a significant ratio of the total deformations when the wall is loaded beyond the elastic regime. For walls, which form a stable flexural hinge at their base, the ratio of shear to flexural deformations remains approximately constant over the entire range of imposed displacement ductilities. This is contrary to the common modelling approach of treating the shear deformation as decoupled from the flexural deformations, which leads to constant shear deformations rather than a constant ratio of shear to flexural deformations once a flexural mechanism is formed and the shear force carried by the wall no longer increases. This paper proposes a simplified method of incorporating shear-flexure interaction effect in equivalent frame models of flexure dominated RC walls. In particular, appropriate modifications to the constitutive V-γ law for the wall base section are proposed as a function of the corresponding flexural response. The suggested methodology is implemented in a finite element model consisting of two interacting spread inelasticity subelements representing inelastic flexural and shear response. The complete numerical model is incorporated in the general finite element code for damage analysis of RC structures IDARC and it is first validated against experimental results of single RC walls subjected to cyclic loading. In a second step, it is applied in inelastic static and dynamic analyses of a tall wall-frame system. It is shown that ignoring shear-flexure interaction may lead to unsafe predictions in particular regarding seismic demands at the critical ground storey level.