Effects of bond-slip and masonry infills interaction on seismic performance of older R/C frame structures

The seismic response of older R/C frames can be particularly sensitive to interaction with masonry infills, poor section detailing and smooth reinforcing bars. These aspects are quite often neglected in design and assessment both with linear and nonlinear models due to the modelling complexity and inherent increase in computational effort. This work presents a review of practical nonlinear models available in literature and quantifies, at the system performance level, the influence of bond-slip in critical plastic hinge locations and interaction effects with infill panels and shear deficient columns. Bond-slip effects are directly incorporated into the nonlinear fiber section models through a simplified approach and nonlinear shear behavior of columns is aggregated at the element level in conjunction to the common diagonal infill strut scheme. Three different infilled frame configurations are analyzed: a) bare frame, b) partially infilled frame (pilotis frame) and c) uniformly infilled frame. Static pushover analyses and Incremental Dynamic Nonlinear Response History Analyses (IDA) are performed spanning a wide range of hazard levels. Comparative analysis with concurrent incorporation of infill-induced shear damage and bond-slip quantify the loss of strength for the uniformly infilled configuration and the increased deformations for the bare frame and partially infilled configurations in terms of seismic performance parameters.