1. Introduction
The latest earthquakes such as the Tohoku/Kumamoto earthquake in 20114)/20165) revealed that RC columns with wing walls having high stiffness suffered from serious damage, which resulted in restoration and demolition. To discuss this issue, the authors have proposed and verified a new rein. arrangement for columns with wing walls which removes the vertical wall rein. anchorage to let the wing walls resist the only compression, and then clarified the effectiveness for damage control6). This new structural detail is expected that the short-term allowable bending moment may be improved because the tensile exterior rein. in the wing walls is not anchored, resulting in no yielding. Therefore, static loading tests using two columns having wing walls with/without vertical wall rein. anchorage were conducted. Furthermore, the current paper discusses specific conditions the short-term allowable bending moment increases/decreases through parametric analyses.
2. Test plans
Two 1:2 scale specimens were designed as classified into type FB based on AIJ Standrad7) by modifying confining rein. ratio and vertical wall rein. ratio based on the specimen in the authors’ past study6). Specimen CWJ2 did not have vertical wall rein. anchorage, while Specimen CWJ2A anchored vertical wall rein. to the lower stub. (Figs. 2-3 and Table 1). Static cyclic loads were applied to the specimens (Figs. 4-5 and Table 4).
3. Test results
In specimen CWJ2/CWJ2A without/with vertical wall rein. anchorage, the concrete/vertical wall rein. reached the short-term allowable stress first. The curvature of specimen CWJ2 was larger than that of specimen CWJ2A because the vertical wall rein. of specimen CWJ2 was not under tension by removing the vertical wall rein. anchorage (Fig. 7). The shear force of specimen CWJ2 at the short-term allowable bending moment was equivalent to that of specimen CWJ2A because the longitudinal rein. strain of specimen CWJ2 was larger than that of specimen CWJ2A (Fig. 8-9).
4. Parametric analyses
A method for bending analyses was presented to simulate the experimental behavior of the specimens (Figs. 10-11). Based on the analytical method, a series of parametric analysis was performed with five parameters of wall thickness, concrete strength, column longitudinal rein. ratio, wall length, and vertical wall rein. ratio.
In the case of the column with wing walls on both sides, the short-term allowable bending moment ratio 𝑀r (Fig. 15) was effectively improved by the wall thickness and concrete strength because the increase of wall thickness/concrete strength increased the curvature of the specimen without anchorage, which resulted in the increase of column rein. stress (Figs. 17-18). On the other hand, the reduction of the short-term allowable bending moment was limited under the compressive axial force ratio beyond 0.1, except for specific conditions. In the case of the column with a wing wall under tension, 𝑀r was effectively improved by concrete strength and vertical wall rein. ratio (Fig. 22). In the case of the column with a wing wall under compression, there was little difference in 𝑀r due to the parameters because the tensile exterior rein. in both specimens was the column longitudinal rein., which resulted in almost no difference in the curvature at the short-term allowable stress.
5. Conclusions
The present paper investigated the structural characteristics of the column having wing walls without vertical wall rein. anchorage proposed in the authors’ previous study6) mainly focusing on the short-term allowable bending moment. The findings from the experimental and analytical studies are summarized.
