Confinement Reinforcement of Cyclically Loaded Normal-Strength Concrete Tied Columns under High Axial Loads.

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Bibliographic Details
Title:	Confinement Reinforcement of Cyclically Loaded Normal-Strength Concrete Tied Columns under High Axial Loads.
Authors:	Shen, Wen-Cheng¹, Hwang, Shyh-Jiann²
Source:	ACI Structural Journal. May2026, Vol. 123 Issue 3, p165-177. 13p.
Subjects:	Concrete columns, Axial loads, American Concrete Institute, Concrete, Structural mechanics, Cyclic loads, Shear reinforcements
Abstract:	In high-rise buildings, lower-story columns must withstand significant seismic shear forces while maintaining sufficient deformation capacity. This capacity is provided through effective confinement using transverse reinforcement. ACI CODE-318-25 specifies that confining reinforcement should be proportional to the applied axial load when the axial load exceeds 0.3Agfc' and requires all longitudinal bars to be laterally supported with seismic hooks. However, the implementation of seismic hooks at both ends of crossties brings challenges for on-site reinforcement assembly. This study experimentally investigates full-scale reinforced concrete (RC) column specimens subjected to quasi-static cyclic loading while under a constant high axial load. The objectives are to validate the ACI CODE-318-25 confinement requirements and to evaluate the feasibility of relaxing seismic hook requirements. The results confirm that columns designed in accordance with ACI CODE-318-25 satisfy the required 3% deformation capacity. Furthermore, satisfactory seismic performance can be achieved with crossties incorporating alternating 135-degree and 90-degree hooks, although at the expense of increased confining reinforcement. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	In high-rise buildings, lower-story columns must withstand significant seismic shear forces while maintaining sufficient deformation capacity. This capacity is provided through effective confinement using transverse reinforcement. ACI CODE-318-25 specifies that confining reinforcement should be proportional to the applied axial load when the axial load exceeds 0.3Agfc' and requires all longitudinal bars to be laterally supported with seismic hooks. However, the implementation of seismic hooks at both ends of crossties brings challenges for on-site reinforcement assembly. This study experimentally investigates full-scale reinforced concrete (RC) column specimens subjected to quasi-static cyclic loading while under a constant high axial load. The objectives are to validate the ACI CODE-318-25 confinement requirements and to evaluate the feasibility of relaxing seismic hook requirements. The results confirm that columns designed in accordance with ACI CODE-318-25 satisfy the required 3% deformation capacity. Furthermore, satisfactory seismic performance can be achieved with crossties incorporating alternating 135-degree and 90-degree hooks, although at the expense of increased confining reinforcement. [ABSTRACT FROM AUTHOR]
ISSN:	08893241
DOI:	10.14359/51749406