A multiscale approach for modeling of infilled frames

The behavior of existing reinforced concrete buildings towards to the seismic actions is strongly affected by the infill walls. Although they assume an important role in the global response of the buildings, modeling of infilled frames is quite complex as a result of the many variables involved. These factors (such as the various constructive solutions; the non-homogeneous and anisotropic mechanical behavior of the masonry texture; the interaction between masonry panel and surrounding frame; the in-plane and out-of-plane behavior) make uncertain the structural response. The technical literature on the issue suggests approaches that ranging from the macro-scale analysis to micro-scale analysis. The different proposals confirm the complexity to simulate the kinematic mechanism between elements of the panel (mortar and bricks) and between infill panel and surrounding frame. Furthermore, these different models cannot be applied in general. They are most of the times calibrated on experimental tests carried out on samples packaged with materials and executive methods that are specific of the test place. Therefore, there is the need to define simplified models that take into account the geometry, mechanical properties of the masonry walls and elements of the surrounding frame. The present study proposes a meso-scale approach (a "Rigid Blocks Method") for simulating of the infilled frames in order to define the main parameters that characterize the simplified "Equivalent Strut model" (i.e. the macro-modelling of the infill walls). With the meso-scale model the infill wall is supposed as a mechanism consisting of rigid blocks connected by axial and shear elastic-plastic springs. The model is usually used for in-plane dynamical analysis of masonry structures. The use of an equivalent rod for modeling the infill panels is a simplified approach purely numeric. It is simple and reduces the computational costs when it is need to evaluate the global behaviour on building scale. The results achieved with the proposed approach are as result of extensive numerical tests on samples of infilled frames, with or without openings, which have geometries and material properties within significant ranges.