Empirical Models for Lateral Stiffness and Strength of Masonry-Infilled RC Frames Considering the Influence of Openings

Abstract

Lateral load behavior of reinforced concrete (RC) frames infilled with fly-ash brick masonry having various sizes of central openings was investigated experimentally. Results showed that the infilled frames with openings exhibited significantly different lateral load behavior than the corresponding infilled frames without openings. The drift limit states corresponding to commencement of major events during the lateral loading (initiation of major cracks in frame members, peak load, and 80% of postpeak load) were found to improve significantly due to the presence of openings when designed in accordance with current earthquake standards. The presence of openings in masonry infills modifies two of the most important design parameters, lateral stiffness and strength, for which nonlinear prediction models were developed by carrying out statistical analyses of the experimental results. Empirical models were used to estimate the stiffness and strength of frames tested in past studies and were found to be more accurate and consistent compared with several existing predictive relations. A normalized lateral load–drift relationship for different performance levels of such frames was also propounded based on the observed damage events. The empirical equations can be used very conveniently to simulate the variations of stiffness and strength (global response) of the infilled frames with openings under lateral loads.