Behavior of reinforced concrete columns under variable axial loads

To study the effects of variable axial load on the seismic behavior of bridge piers, six large-scale reinforced concrete circular columns were tested. The primary experimental parameters were axial load levels, lateral as,well as axial loading patterns. The axial loading patterns included constant and variable loading, either proportional or nonproportional to the lateral forces. Experimental evidence revealed the significant effects of the magnitude and loading pattern of axial force on the seismic behavior of columns. The main effects of the variable axial load are reflected in the distinct physical failure patterns, hysteresis loops, and load-carrying capacities, compared with the case of constant axial load. The test results also provide experimental data useful for calibrating and evaluating analytical, models: It is suggested that analytical tools, like the plastic hinge model, need to be modified to account for the effects of variable axial load.