*4.1. Hysteresis Behaviour*

The recorded hysteresis curves of all the specimens under cyclic loading are presented in Figure 9. Based on Figure 9a–c, the hysteresis curves of the specimens W1, W2, and W3 are considerably linear in the initial elastic stage. After the walls cracked, the area of the three hysteresis curves slightly increased, and the shapes of the hysteresis curves transformed from the original shuttle to the reversed "S" shape, showing a partial pinching effect. The area of the hysteretic curves of W1 and W3 nearly stayed the same due to the flexural effect, and the profile of the two hysteresis curves remained stable until the specimens failed. In addition, the area of the three hysteresis curves showed a marked difference. The area of the hysteresis loop of W2 was the best, followed by that of W1, while W3 was the worst. For W1 and W2, the specimen W2 with higher compression stress had a better energy dissipation compared to W1, indicating that the increase in compressive stress can improve the energy dissipation capacity of specimens. However, for W2 and W3, specimen W3, with a higher aspect ratio, had a worse energy dissipation compared with W2, indicating that the increase in aspect ratio can reduce the energy dissipation capacity of specimens.

**Figure 9.** Hysteretic curves of five specimens: (**a**) W1; (**b**) W2; (**c**) W3; (**d**) W4; (**e**) W5.

As shown in Figure 9d,e, the hysteresis loops of W4 and W5 have a similar linear relationship in the initial elastic stage. During this time, the horizontal drift of the top walls and residual deformation were small after unloading. The area of the hysteresis loops of the specimens was small and nearly overlapped. After the walls cracked and entered into a plastic stage, especially after the maximum load, the hysteresis loops showed partial pinch effect, and the area of hysteresis loops was significantly increased, which indicated that the structural columns had an apparent energy dissipation capacity. Compared with W4, the maximum bearing capacity of W5 was slightly lower than that of W4, which indicated that the increasing bearing capacity of RAC structural columns was lower than that of ordinary concrete structural columns.

#### *4.2. Skeleton Curve*

The skeleton curve is the envelope curve obtained by connecting the peak points of the P–D hysteretic loop of the first cycle in each loading stage, mainly reflecting the cracking load and ductility of the wall.

As can be noticed in Figure 10a, before the specimen crack, the three skeleton curves of the specimens are a straight line in the elastic stage. After the specimens cracked, the three skeleton curves started becoming nonlinear in the plastic stage. When the lateral load closed to the maximum load, the skeleton curves gradually tilted toward the axis with increasing lateral drift. Besides that, the three skeleton curves show an apparent di fference. Comparing the specimens W1 and W2, the maximum load of W2 was higher than that of W1, and the specimen W2 had a steeper degraded section after cracking, indicating that increasing the compression stress can increase the bearing capacity and decrease the ductility of specimens. The cracked load and maximum load of W3 were lower compared to W2, and the horizontal section of W3 was longer after cracking, which indicated that the increasing aspect ratio could reduce the bearing capacity and increase the ductility.

**Figure 10.** Skeleton curves of specimens: (**a**) W1, W2, and W3; (**b**) W4 and W5.

It can be seen from Figure 10b, the bearing capacity and the deformation property of the specimens W4 and W5 are obviously higher than that of W1, W2, and W3. The sti ffness degrades of the two specimens W4 and W5 was similar before cracking. After cracking, the two skeleton curves showed obvious di fferences in the elastic-plastic and failure phases. The maximum load of the specimen W4 was higher in comparison to the specimen W5, and the specimen W4 had a relatively smooth descending section, which reflected that the specimen W4 with ordinary concrete structural columns had the better bearing capacity and ductility than that of the specimen W5 with RAC structural columns.
