Behavior of Concrete Columns Confined with Cross Spirals under Different Loads

Abstract

This paper investigates the behavior of concrete columns under different loadings. The columns are confined with single conventional spiral or two cross spirals. The two opposing spirals (cross spirals) were developed to confine circular columns in order to enhance their strength and ductility. This new technique facilitates the passage of concrete while effectively increasing the volume of the confining reinforcement without violating the minimum spacing as specified by ACI. Twenty one 1000 mm long circular high strength columns with a diameter of 350 mm with four different steel ratios, 0.016, 0.020, 0.024 and 0.028, and various spiral spacing’s were built. The columns were tested under monotonic axial loading in order to study the influence of the new confinement technique on the axial compressive strength and ductility of bridge columns compared to columns confined with the conventional single spiral. Also, twelve reduced scale reinforced concrete circular bridge columns with two different lengths and several spiral spacing and patterns were tested. The columns were subjected to constant axial load (bridge self weight) and reversed cyclic lateral displacement (seismic load) to study the influence of the new confinement technique on the lateral strength and ductility of reinforced concrete circular bridge columns compared to columns confined with conventional single spiral. Six of the columns (1000 mm high and 200 mm diameter) were designed to study the flexural behavior, and the other six columns (500 mm high and 200 mm diameter) were designed to study the shear behavior.