Cyclic response of masonry infilled RC frames: Experimental results and simplified modeling

The recent large interest in nonlinear seismic analysis methods, static and dynamic, has required proper strategies of modeling based on reliable, and at the same time easy to use, constitutive laws for the structural elements. Regarding the behavior of framed structures, special attention has to be devoted to infills because of the key role they play in modifying overall stiffness, strength and ductility under seismic excitation. Pointing out the attention on this topic the paper discusses a criteria for modeling the structural behavior of infills based on a macromodeling approach, that is to say on the substitution of infills with diagonal pin jointed struts. Is here shown how multilinear plastic link elements governed by a hysteretic Pivot model, available in different FEM codes, can be appropriately used to model the equivalent struts to perform linear or nonlinear analyses. In order to enlarge experimental knowledge on cyclic behavior of infilled frames structures and as reference for developing the above mentioned modeling strategy, an experimental campaign on single-storey, single-bay, fully infilled frames with different kinds of masonry and subjected to lateral cyclical loads, was carried out, and some others available in the literature are referred to. Validation of Pivot modeling approach was carried out comparing experimental results and computer simulations of the experimental tests. In the paper hysteresis parameters values calibrating Pivot law are also given for involved masonry infills typologies and some proposals for correlation between strength and stiffness of infilled frames and of masonry infills are provided as a tool for the quick calibration of the Pivot model in practical applications.