Strut-and-Tie Model for seismic design of confined masonry buildings

Abstract

The Strut-and-Tie-Model (STM) of a confined masonry wall, with or without opening, consists of an equivalent system, in which the masonry wall is modelled as compression struts and the reinforced concrete (RC) confining elements are modelled as is (i.e., as present in the wall). Tension ties are ignored owing to the negligible tensile strength of masonry. Although the joints of tie-column and tie-beams are not intended for moment resisting, these are yet treated as the moment resisting in numerical model to avoid instability. Consequently, a typical compression strut is connected to the joints at either end with moment released. Purpose of this paper is to outline the guidelines for developing STMs for seismic design of confined masonry wall panels, including single- and multi-storey wall panels with and without openings. Behaviour of two single-storey adjacent panels with or without openings, are also considered. Although the main objective is to develop STMs for walls subjected to lateral seismic loading, the effect of gravity load has been also considered in the analysis. Well distinct STM configurations are noted for the single storey panels. STM for adjacent wall panels and multistorey wall are shown to be arrived at from that of the individual single storey panels. Throughout this paper, the masonry is modelled using equivalent properties and hence, the effect of relative variation of mortar and brick properties are not adequately captured. This may have considerable influence on the resulting STM configurations. Although STM should be evolutive in nature enabling prediction of different failure modes of CM walls, the scope of the analytical model in this paper is limited to the linear-elastic analysis and hence, the strut orientation is likely to be altered as the building ventures into the inelastic regime. Nevertheless, the STM proposed in this paper may be used as the basis of developing such an evolutive model enabling a displacement based design framework of confined masonry buildings.