## 1 Introduction  
RC members designed to undergo flexural failure will develop a plastic hinge at the critical section, located away from the end of a member by a length corresponding to the effective depth (d), when the longitudinal reinforcement experiences flexural yield under repeated loads like seismic loads. According to past research, flexural RC members, exhibit ductile behavior through moment redistribution after plastic hinge formation [1, 2, 3]. However, they may not engage in ductile behavior if concrete undergoes compressive failure due to insufficient lateral confinement at the critical section, located away from the end by a length corresponding to the effective depth (d).  
The ductile behavior of RC columns, which are subject to axial force, is dominantly influenced by the lateral confinement effect of concrete near the plastic hinge zone. Proper lateral confinement of RC members by transverse reinforcement will prevent buckling of longitudinal reinforcement and, at the same time, ensure effective moment redistribution [4, 5, 6, 7].  
Past studies have showed that the lateral confinement capacity of columns is influenced by the amount and configuration of transverse reinforcement surrounding the core concrete, and by the yield strength, with circular cross-sections having better lateral confinement than square cross-sections [8, 9, 10, 11, 12]. However, columns are usually designed to have square cross-sections to enable joining with beams, and for more convenient longitudinal reinforcement configuration at the column-beam joints. While RC members with circular cross-sections can provide lateral confinement to the core concrete using hoop reinforcement, square cross-sections provide lateral confinement to the core using square ties for an arrangement of longitudinal reinforcement. However, the square tie will only have the central part of the square column to be laterally confined, thus reducing the lateral confinement effect. Buckling of longitudinal reinforcement occurs under axial force and lateral force, and this in turn results in brittle failure [13]. As such, there have been many cases of columns with square ties being destroyed in earthquakes.  
Extensive research has been conducted on transverse reinforcement configuration of square RC columns from the 1980s to the early 2000s. Studies have confirmed that transverse reinforcement with more circular shapes has increased lateral confinement capacity. [14; 15; 16; 17; 18]. According to a study of [PERSON] et al. in 1996 [19], it has been reported that spiral transverse reinforcements can improve the strength and ductility of RC columns, and the need for research on spiral transverse reinforcement applicable to square cross-sections has been highlighted.  
In past research, the authors of this study developed spiral transverse reinforcement with alternating squares and octagons for use in square RC columns [20]. Compared to existing ties, spiral transverse reinforcement not only improves constructability and lowers costs, but also offers excellent structural performance. However, more systematic research is needed on the yield strength and axial force ratio, which are key factors affecting lateral confinement capacity.  
This study presents the results of performed experiments with the configuration of transverse reinforcement, yield strength of transverse reinforcement, and axial force ratio as main variables to assess the lateral confinement performance of spiral transverse reinforcement, comprised of alternating squares and octagons, designed to be close to a circular shape. Based on the experimental results, the effects of yield strength and reinforcement configuration on lateral confinement were evaluated, and the relationship between main variables and ductile behavior was examined.