Coupling effect between masonry spandrels and piers

In-plane performance of masonry load-bearing walls was tested in a quasi-static fashion by loading individual brickwork perforated walls with constant normal force and increasing lateral force. Fifteen full-scale unreinforced frames were constructed by professional bricklayers, from ordinary bricks and lime-mortar according to ancient techniques, so as to be representative of historic masonry. Each wall was subjected to two monotonic loadings (with unloading), up to the full drop-off in the stiffness and complete development of the kinematic mechanism. The specimens exhibited significant overstrength with respect to the strength provided by the masses and high deformation capacity, which are not adequately represented by code provisions for analysis of ancient masonry buildings. The overstrength is here described by several key parameters, namely: (1) Level of coupling piers by spandrels, (2) virtual work done by interlocking and friction forces, (3) and maximum tensile stress in the top spandrel and nodal panels. The paper attempts also to calibrate the behavior factors (q) for masonry frames that are not overly conservative, as code-prescribed q-factors are. Thus, another key issue in the paper is to derive q-factors directly on the basis of the measured values to reproduce the overstrength, allowing for the normal force in the piers and the masonry texture of the wall.