Evaluating the effects of loading protocol on the strength and deformation capacity of Flexure-Shear critical concrete columns

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Columns are considered critical elements with respect to the stability of buildings during earthquakes. Concrete columns with light confinement can sustain shear and axial load failures, which can lead to partial or complete building collapse. Moreover, tests have indicated that lateral cycling of non-ductile columns can impart damage that is cumulative. However, most experiments on concrete columns have used fully reversed cyclic loading protocols, whileearthquake ground motions tend to impart different types of lateral histories. Due to a lack of experimental evidence considering the effects of lateral loading protocols on the strength and deformation capacity of reinforced concrete columns, nonlinear continuum finite element models were calibrated to experimental tests for seven columns subjected to varying lateral loading protocols. Selected columns sustained flexural-shear modes of lateral strength degradation. Columns were selected to cover a range of shear stresses, cross-section, axial loads, transverse reinforcement spacing and ratios, and longitudinal reinforcement ratios. All tested columns sustained axial collapse after cumulative damage from lateral loading. Calibrated column models were then subjected to a series of loading protocols, including monotonic pushover and fully reversed cyclic loading protocols with varying number of cycles. The effects of the lateral loading protocols on damage progression, strength, and deformation capacities are discussed for the columns in light of differences in peak lateral strength, drift at peak lateral strength, drift at the initiation of lateral strength degradation, and drift at the initiation of axial strength degradation.