Eccentric-Axial-Load Test for Composite Columns Using Bolt-Connected Steel Angles

Abstract

For better structural performance and constructability, a concrete-encased steel column that uses a steel cage prefabricated with bolt connections was developed. The steel cage consists of longitudinal steel angles and transverse steel plates. As a fundamental verification of the proposed column, an eccentric-axial-load test was performed on eight composite column specimens. Test parameters included column type (i.e., conventional concrete-encased steel column versus proposed column), shape and spacing of transverse plate, and axial load eccentricity. The test results showed that, owing to the high flexural stiffness of the steel angles placed at the corners of the cross section, the axial strength and ductility of the proposed column were greater than those of the conventional composite column using a wide flange steel section at the center of the cross section, particularly in the large eccentricity of axial load. Z-section plates and closely spaced flat plates used for transverse reinforcement provided better lateral confinement to the concrete, thereby increasing the load-carrying capacity of the proposed columns. In general, existing design methods safely predicted the axial-flexural capacities of the specimens. Nonlinear numerical analysis was performed to verify test results. The numerical analysis results agreed with the test results in terms of yield stiffness, peak strength, and postpeak strength degradation.