Pseudodynamic Testing of Masonry Infilled Reinforced Concrete Frame

Abstract

Seismic evaluation of a two-story, two-bay reinforced concrete frame infilled with masonry was performed by pseudodynamic testing of a half-scale specimen. The second-story infill included window openings. The specimen was subjected to four tests of increasing magnitude based on the Taft ground motion. Explicit numerical integration with a small time step, soft-coupled load system, and an iterative actuator control algorithm limited the displacement errors normally associated with pseudodynamic testing of stiff structures. The final sequence of tests produced diagonal cracking in the upper story, but primarily bed joint shear cracking in the lower story. Relations between the type of observed cracking and story drift-story shear response are explored. Compressive strut mechanisms are defined from the experimental values of moments and axial forces in the frame and infill panel strains. Estimates of story stiffness from several simple strut models were found to bound the experimentally measured values for both the first- and second-story walls prior to significant damage. Friction-based analytical estimates of panel shear strength were found to underestimate the measured strength and to be sensitive to the assumed coefficient of friction. Available methods for estimating shear strength that neglect infill-frame interaction were found to largely underestimate measured shear strength.