Simulation of Seismic Collapse in Nonductile Reinforced Concrete Frame Buildings with Masonry Infills

Improved analysis methods and guidelines are presented to simulate the seismic collapse of nonductile concrete frame buildings with masonry infills. The analysis tools include an inelastic dual-strut model that captures the post-peak behavior of the masonry infill and its interaction with the surrounding frame. The dual compression struts capture the column-infill interaction that can cause shear failure of the columns and loss of their vertical load carrying capacity. A rigid softening shear degradation model is implemented in the beam-column elements to capture the shear failure of nonductile RC columns. Guidelines are presented to determine the strut model parameters based on data from 14 experimental tests on infill frames. The models are applied in three-dimensional nonlinear dynamic analyses of a three-story nonductile concrete frame prototype building with infills. The incremental dynamic analyses technique is utilized to understand the effect of the infill-column interaction and the rocking of shallow foundations on collapse performance, including a parameter study to examine the sensitivity of the results to the assumed strength and deformation parameters of the infill walls. Collapse assessment of the prototype building indicates that incorporating infill strut-column interaction and the shear degradation of columns is critical to the prediction of the collapse capacity of nonductile infill frames. Otherwise, the omission of this deterioration mechanism leads to unconservative collapse capacity predictions. The analyses further demonstrate that rocking of shallow foundations has a favorable effect on the collapse performance of infill frames and that the infill strut strength has considerably greater influence on collapse performance than the infill strut deformation parameters. (C) 2014 American Society of Civil Engineers.