Paper Title
Computation of Natural Frequencies of 2D Unreinforced Masonry Infilled RC Frames with Openings and Partial Filling

Abstract
Unreinforced masonry infills are a necessary part of reinforced concrete framed structures. This is one of the most common types of construction across the world. In gravity loads design, these infills are considered as non-structural elements which is justifiable. But from an earthquake point of view, that the interaction of infill with RC frame has a role to play is evident from many earlier studies. From a functional point of view, the openings in the infills are a significant parameter to consider because of their influence on the lateral stiffness and strength. Hence, computation of natural frequencies of a structure with infills with openings, assumes importance under dynamic loading. This paper presents computation of natural frequencies of 2D RC unreinforced masonry (URM) using simplified multiple node to one node constraint (MTOCO) with independent node at the center of gravity of the infill, with mass and inertial properties of the infill. This method of modelling is then compared with other micro modelling methods. The state-of-the-art Virtual Performance Solution (VPS) Implicit FE solver is used for modelling infills as micro and MTOCO models. To assess the degree of consistency between these three numerical methods, Modal Assurance Criterion (MAC) [9] is used. This gives a good statistical indicator and a degree of consistency between mode shapes of numerical approaches adopted. Keywords - Infill with Openings, Modal Assurance Criterion, Multi to One Nodal Constraint, Unreinforced masonry, Virtual Performance Solution