Earthquakes and Structures, Vol. 6, No. 4 (2014) 409-436 DOI: http://dx.doi.Org/10.12989/eas.2014.6.4.409 409 Seismic response of masonry infilled RC frames: practice-oriented models and open issues Carmine Lima^, Gaetano De Stefano*^ and Enzo Martinelli* Department of Civil Engineering, University of Salemo, 84084 Fisciano (SA), Italy (Received January 31, 2013, Revised December 16, 2013, Accepted January 13, 2014) Abstract. Although it is widely accepted that the interaction -between masonry infill and structural members significantly affects the seismic response of reinforced concrete (RC) frames, this interaction is generally neglected in current design-oriented seismic analyses of stmctures. Moreover, the role of masonry infill is expected to be even more relevant in the case of existing frames designed only for gravitational loads, as infill walls can significantly modify both lateral strength and stifihess. However, the additional contribution to both strength and stiffiiess is often coupled to a modification of the global collapse mechanisms possibly resulting in brittle failure modes, generally related to irregular distributions of masonry walls throughout the frame. As a matter of principle, accurate modelling of masonry infill should be at least carried out by adopting nonlinear 2D elements. However, several practice-oriented proposals are currently available for modelling masonry infill through equivalent (nonlinear) strut elements. The present paper firstly outlines some of the well-established models currently available in the scientific literature for modelling infill panels in seismic analyses of RC frames. Then, a parametric analysis is carried out in order to demonstrate the consequences of considering such models in nonlinear static and dynamic analyses of existing RC structures. Two bay-frames with two-, three- and four-storeys are considered for performing nonlinear analyses aimed at investigating some critical aspects of modelling masonry infill and their effects on the stmctural response. Particularly, sensitivity analyses about specific parameters involved in the definition of the equivalent strut models, such as the constitutive force-displacement law of the panel, are proposed. Keywords: masonry infill; nonlinear analysis; existing structures; reinforced concrete; stmt models 1. Introduction A significant part of the overall existing building stock in earthquake-prone areas, such as Italy and the Mediterranean basin, was constmcted in the first two or three decades after World War II (Ricci et al. 2011). Although reinforced concrete (RC) frames are recognised as one ofthe most common stmctural fonn for low- to medium-rise buildings in the world, such buildings were generally designed and constmcted according to the code provisions of that time and without considering any possible seismic-induced effects (Asteris 2003). Moreover, such stmctures are »Corresponding author. Assistant Professor, E-mail: e.martinelli@unisa.it ^Research Assistant, E-mail: clima@unisa.it ''Ph. D., E-mail: gaetano.destefano@gmail.com Copyright©2014Techno-Press, Ltd. http://www.techno-press.org/?journal=eas&subpage=7 ISSN: 2092-7614 (Print), 2092-7622 (Online)