Abstract
This paper proposes a novel reinforced ultra-high-performance concrete (UHPC)-normal strength concrete (NSC) composite column. The main feature of the reinforced UHPC-NSC composite column is the use of an exterior UHPC cover, which is helpful for improving the load-carrying capacity, deformability, and crack resistance. This study focused on the axial behavior of the reinforced UHPC-NSC composite column. A total of 12 specimens were designed to investigate the axial behavior of the composite column under compression. The thickness of the exterior UHPC cover, volumetric stirrup ratio, and construction method were considered as the main experimental parameters. The failure modes and strain–stress relationships are discussed in this paper. By introducing the exterior UHPC cover, the peak confined strength obviously improved. The compressive strain at the peak confined strength was mainly determined by the deformability of the plain UHPC material. The composite column resulted in a unique sudden drop immediately after the peak confined strength, owing to the rapid loss of the confining stress from the exterior UHPC cover. A trilinear model is proposed to describe the strain–stress relationship of the composite column. The results obtained by the modified model are in good agreement with the test results.
Highlights
Ultra-high-performance concrete (UHPC) has been extensively investigated and is widely used in practical engineering, owing to its excellent mechanical properties, such as its high elastic modulus, high compressive and tensile strength, and strain hardening in tension
Remark: tu is the thickness of exterior UHPC cover; s is the spacing between adjacent stirrups in middle area; ρv is the representative volumetric stirrup ratio
normal strength concrete (NSC) column exhibited similar failure modes as those observed in many previous studies
Summary
Ultra-high-performance concrete (UHPC) has been extensively investigated and is widely used in practical engineering, owing to its excellent mechanical properties, such as its high elastic modulus, high compressive and tensile strength, and strain hardening in tension. The use of ECC in the tensile area delayed the debonding failure between the ECC materials and the attached fiber-reinforced polymer sheet The deformability of this composite beam was obviously larger than that of a common reinforced NSC beam. The abovementioned studies have demonstrated that the partial employment of high-performance cement-based materials with NSC is an effective approach toward simultaneously improving the structural performance and reducing the cost. This paper proposes a reinforced UHPC-NSC composite column to enhance the load-carrying capacity and resistance of earthquake-induced crack, while maintaining low cost. The exterior UHPC cover is expected to simultaneously provide the axial load-carrying capacity, crack resistance, and circumferential confinement for the inner NSC core. According to the test results, a modified confined model is proposed for the reinforced UHPC-NSC composite column
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