Simplified Evaluation of the Additional Shear Demand Due to Masonry Infills

Masonry infills enclosed in reinforced concrete (RC) frames exert a significant stiffening and strengthening action that can result favorable or adverse in the case earthquake-induced loads. The force increment is transferred to the RC frame column ends as an additional shear force, potentially causing local shear failures at the end of the columns. The additional shear demand due to masonry infills cannot be evaluated by the common equivalent strut models. On the other hand, refined finite element models are not computationally effective to be used in practice. With the aim to maintain the simplicity of the equivalent strut approach with-out losing the information about the actual shear force on the columns, this paper presents a detailed study about the infill-frame shear transfer mechanism. Refined 2D nonlinear models of real experimental tests on infilled frames have been de-fined using the OpenSees / STKO software platform. Shear demands on the columns are extracted by integrating the nodal forces at specific section cuts of the RC members. The same simulations are made using the equivalent strut approach. An analytical relationship if finally proposed to estimate the additional shear demand at the ends of the columns. The latter relates the additional shear demand to the current axial force on the equivalent struts and the geometrical and mechanical properties of the infilled frames. The formula can be easily implemented to perform shear safety checks at the columns ends when performing seismic assessments.KeywordsInfilled framesShearMasonryReinforced concreteOpenSeesSTKO.