Forming new steel-framed openings in load-bearing masonry walls: design methods and nonlinear finite element simulations

Forming new openings in load-bearing masonry panels is a frequent activity in engineering practice, often accomplished through very simplified design methods despite the complexity of the mechanical behaviour of the masonry and its interaction with the frame. Scientific literature and building codes provide little information. The Italian building code and the local regulation of Tuscany give some dimensional prescriptions and basic guidelines. Different simplified design methods in the literature lead to wide-ranging results. Here, the problem is approached through nonlinear finite-element analyses. The masonry is modelled through a rotating crack constitutive model, and the interaction between steel-frame and masonry, through cohesive-frictional interface elements. Sensitivity analyses are carried out by varying geometrical and mechanical parameters and the responses are compared in terms of capacity curves. The influence of the steel-profile cross-section, the position of the opening within the wall, and the degree of connection between the steel uprights and the masonry are evaluated. The study is extended to three-dimensional structures to determine the impact of the local operation of the opening formation on global behaviour. Based on the results obtained, some indications and guidelines are proposed.