Deteriorated hysteresis behavior of reinforced concrete multi-column bridge bents with varying axial loads

Multi-column reinforced concrete bridge bents are composed of more than two columns connected by a relatively rigid cap beam. Due to the framing action, the exterior columns would be subjected to increased or decreased varying axial load, and the total hysteresis behavior of the bridge bent is mixed. Two single-column specimens were tested under constant and varying axial loads to realize the effects of the varying axial load on the deteriorated hysteresis behavior of columns. An axial load variation equation was derived based on a two-column bent specimen tested in the literature to approximate the varying axial load. Test results indicate that the column subjected to the varying axial load would exhibit an asymmetrical hysteresis behavior in terms of the maximum strength, stiffness, and failure condition. The envelope curve of the column exhibits a negative and positive post-yielding stiffness under increased and decreased varying axial loadings, respectively. Compared to the constant axial load condition, the increased varying axial load would aggravate the stiffness degradation of columns by around 10% and slightly decrease the ultimate drift capacity by about 5%. Moreover, the increased and decreased varying axial loads would result in very different pinching behaviors upon reloading.