Title:
Confinement Reinforcement of Cyclically Loaded Normal-Strength Concrete Tied Columns under High Axial Loads (Prepublished)
Author(s):
Wen-Cheng Shen and Shyh-Jiann Hwang
Publication:
Structural Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
column; confining reinforcement; crosstie configuration; high axial load; ultimate drift ratio
DOI:
10.14359/51749406
Date:
12/18/2025
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. The ACI 318-25 building code specifies that confining reinforcement should be proportional to the applied axial load when the axial load exceeds 0.3Agf'c 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 RC column specimens subjected to quasi-static cyclic loading while under a constant high axial load. The objectives are to validate the ACI 318-25 confinement requirements and to evaluate the feasibility of relaxing seismic hook requirements. The results confirm that columns designed in accordance with the ACI 318-25 building code 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.