Influence of bond-slip effect and shear deficient column in the seismic assessment of older infilled frame R/C structures

Presence of masonry infills and detailing of reinforcement can have a significant influence on the response of the older R/C frames under seismic excitation. After several major earthquakes failure of infilled frames were observed due to the presence of shear deficient columns and inadequate detailing of smooth reinforcing bars near the joints. These aspects are quite often neglected in linear or nonlinear models because of the modelling complexity and increase in computational effort. The objective of this work is to identify the consequences of bond-slip in critical zones such as plastic hinge locations and the presence of shear deficient columns.To investigate these effects on the response of a sample 2D frame, three different infilledframe configurations are analyzed using an accurate yet viable approach based on the diagonal strut scheme (ASCE41/FEMA356): a) bare frame, b) partially infilled frame (pilotis frame) and c) uniformly infilled frame. Bond-slip effects are directly incorporated into the nonlinear fiber section models (Spacone et al. 1996) through the simplified approach proposed by Braga et al. (2012), and nonlinear shear behavior of columns is aggregated at the element level. Static pushover analyses and Incremental Dynamic Nonlinear Response History Analyses (IDA) are performed spanning a wide range of hazard levels. Results show that incorporation of infill-induced shear damage and bond slip into the frame models the results in 1) significant loss of strength for the uniformly infilled configuration; and 2) increase of flexibility for the bare-frame and partially infilled configurations.