Axial Compressive Behavior of CFRP-UHPC-Steel Tube Composite Short Columns

Short columns made from carbon fiber reinforced polymer(CFRP)-ultra-high performance concrete (UHPC)-steel tubes are composite columns with great application prospects. The mechanical properties and durability of composite short columns can be improved by replacing traditional concrete with UHPC. To investigate the axial compressive behavior of CFRP-UHPC-steel tube composite short columns, this work tested 18 CFRP-UHPC-steel tube composite short columns under axial compression. The failure process, failure modes, and axial compression bearing capacity were analyzed. The effects of CFRP thickness, void ratio, and steel tube thickness on the axial compressive behavior of the confined UHPC were also studied. On the basis of the twin shear unified strength theory, the calculation formula for the axial compression bearing capacity of the CFRP-UHPC-steel tube composite short columns was established. Results showed that the combined form of the CFRP-UHPC-steel tube composite short columns maximized the compressive performance of UHPC, the tensile performance of CFRP, and the compressive performance of the steel tube. Under the cooperation of the three materials, the axial bearing capacity of the composite short columns was significantly higher than that given the simple superposition of each material, and the maximal improvement degree was 81%. With an increase in the thickness of CFRP, the compressive strength and ultimate strain of the confined UHPC increased, and the axial bearing capacity of the composite short columns increased significantly. A low void ratio (φ=0.28 and φ=0.50) exerted little effect on the compressive strength and ultimate strain of the confined UHPC. By contrast, a large void ratio (φ=0.76) obviously increased the ultimate strain. The thickness of the steel tube exerted a minimal effect on the axial stress-strain curve, compressive strength, and ultimate strain of the confined UHPC. The influence degree of each factor on the axial compression behavior of the confined UHPC was established in the following order: CFRP thickness> void ratio> steel tube thickness. The calculation formula for the axial compression bearing capacity of the CFRP-UHPC-steel tube composite short columns was simple, and the results agreed well with the experimental values. Hence, this work can be used as a reference for engineering applications. © 2021, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.