MODELING IN-PLANE BEHAVIOR OF BRICK MASONRY INFILLS IN RC FRAME BUILDING

Abstract

Brick masonry construction is common in almost all parts of the India. The easy availability, cheap in cost and requirement of less skilled labors are the factors responsible for their wide spread common use. The presence of masonry infill walls can modify lateral strength, stiffness, and ductility of structure. In seismic areas, ignoring the frame-wall interaction is not always on the safe side, since, under lateral loads, the infills significantly increase the stiffness resulting in possible change in the seismic demand due to the significant reduction in the natural period of the composite structural system. The analytical modeling of infilled frame is a complex issue because, these structures exhibit highly nonlinear inelastic behavior resulting from the interaction of the masonry infill and surrounding frame. Detailed seismic performance assessment procedures have been given in FEMA 356 and 440 for reinforced concrete frames with solid masonry infill walls. These documents contain provisions for the calculation of stiffness of solid infills mainly by modeling infill as an equivalent diagonal strut. However, such provisions are not specified for infilled frame with openings. Door and window openings are usual parts of infill walls for functional and architectural reasons. The present study proposes a reduction factor for effective width of diagonal strut over that of the solid infill with a central opening. Finite element solutions are verified using experimental result reported in literature. Parametric studies are carried out for one bay-one storey, one bay-two storey, one bay-three storey, two bay-one storey, two bay-two storey, and two bay-three storey frames to examine the effect of central opening of different sizes. Based on these, a reduction factor is proposed to determine the strut width for openings of specific aspect ratio present in the infilled frame