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Title: Confinement Reinforcement of High-Strength Reinforced Concrete Tied Columns under High Axial Load

Author(s): Wen-Cheng Shen and Shyh-Jiann Hwang

Publication: Structural Journal

Volume: 120

Issue: 3

Appears on pages(s): 145-155

Keywords: confinement crosstie; high axial load; high-strength concrete; high-strength reinforcement; lateral drift capacity; reinforced concrete column; seismic hook

DOI: 10.14359/51738505

Date: 5/1/2023

The use of high-strength concrete (HSC) in high-rise buildingscan reduce the size of structural members and increase the residential space. However, the behavior of HSC at ultimate loads is more brittle than that of normal-strength concrete. Hence, the ACI 318-19 building code requires that all the column longitudinal bars be confined by seismic hooks when using HSC (fc′ > 70 MPa [10.15 ksi]) or under high axial loads (Pu > 0.3Agfc′). The requirement for crossties with seismic hooks at both ends might cause a huge impact on the assemblage of the column reinforcement cage during field installation. This research proposes an experimental study of full-scale column specimens with a 600 x 600 mm (23.62 x23.62 in.) cross-sectional dimension subjected to quasi-staticcyclic loading under constant high axial load. These column specimens are composed of both HSC and high-strength reinforcement. Test results show that if crossties with a 90-degree hook at one end are alternated, the column specimen maintains satisfactory seismic performance. This change in detailing can facilitate the field installation of the reinforcement cage for columns using HSC or underhigh axial loads.