**4. Parametric Analysis**

In order to further optimize the performance of the HES, seven specimens with di fferent threshold displacements, di fferent steel plate width-thickness ratios and di fferent shapes of the steel plates in the ED zone are designed and simulated using software ABAQUS. The detailed geometric parameters are shown in Figure 7, Table 1, and Table 2. The common and specific geometric parameters are respectively listed in Tables 1 and 2. The influence of the shape of the steel plate in the ED zone is investigated by the comparison among specimens HES1, HES2, HES6, and HES7. The influence of the width-thickness ratio is studied by comparing the performance of HES2 and HES3. The threshold displacements of HES2, HES4, and HES5 are changed to investigate their influence.

#### *4.1. Parameter Analysis Under Monotonic Load*

4.1.1. The Investigation on the Influence of the Shape of the Steel Plate in the ED Zone

The monotonic behavior of four specimens with di fferent shape types for steel plated in the ED zone including the rectangular shape (HES1), the X-type (HES2), the rectangular shape with one diamond-shaped hole (HES6) and the rectangular shape with one circular hole (HES7) are simulated. Their load-displacement curves, the stress distribution of the steel plates in the ED zone and typical analyzed results are depicted in Figure 11 and Table 3.

**Figure 11.** The influence of the shape of the steel plate in the ED zone. (**a**) Load-displacement curves, (**b**) the steel plates in ED zone (HES1), (**c**) the steel plates in ED zone (HES2), (**d**) the steel plates in ED zone (HES6), (**e**) the steel plates in ED zone (HES7).


**Table 3.** Typical analyzed results.

It is observed in Figure 11a that the bearing capacity the HES with rectangular steel plates in the ED zone is the largest. Among the four shape-types of the steel plates in the ED zone, the bearing capacity of the rectangular typed specimen is larger than those others but this type of shape failed to fully develop the plastic deformation. Among the three optimized shapes, the X-shaped specimen HES2 with the smallest surface area exhibits the best performance including the initial sti ffness and bearing capacity as shown in Table 3.

4.1.2. The Influence of the Width-Thickness Ratio of the Steel Plate in the ED Zone

The monotonic behavior of specimens with optimized X-shaped low-yield-point steel plates (HES2 and HES3) are analyzed and the load-displacement curves are shown in Figure 12a. The thickness of X-shaped low-yield steel plates of specimen HES2 and HES3 are respectively set to be 10 mm and 12 mm which is the only di fference between them. With the increase of thickness, the obvious increase of shear capacity (22.5%) can be investigated and the initial shear sti ffness is slightly increased.

**Figure 12.** The monotonic load-displacement curves for HES2/HES3/HES4/HES5. (**a**) The influence of the width-thickness ratio, (**b**) the influences of the displacement of threshold.

#### 4.1.3. The Shear Sti ffness Lifting Control System

The shear displacement threshold is a significant parameter to decide on which level of shear deformation the SL zone begins to bear loads. The shear displacement threshold (D (R1-R2)) of specimen HES2, HES4 and HES5 are respectively set as 3 mm, 2 mm and 5 mm and the computed load-displacement curves are shown in Figure 12b. It is concluded that this shear sti ffness control system endows the HES with double-step character, su fficient energy dissipation ability and the ability to prevent the collapse of the structure in large earthquakes. If the shear displacement threshold is too large, the strength degradation of the steel plate in the ED zone will result in a decrease in the ultimate strength of the HES. Therefore, the shear displacement threshold could be adjusted according to the requirement of performance design.

#### *4.2. Simulated Hysteretic Curves*

As depicted in Figure 13, the shapes for the simulated hysteretic curves of the seven specimens are similar to each other and. Due to the shear sti ffness lifting control system, two stages of energy dissipation and load-bearing is investigated. When shear displacement is smaller than the threshold displacement, the shape of the hysteretic curves is similar to rectangular and the high energy dissipation performance of the ED zone is obtained. With the increase of the thickness of steel plates, the bearing capacity and the energy dissipation ability are both enhanced. The Bouc–Wen–Baber–Noori model could be adopted to describe the hysteric character and used to analyze the seismic behavior of wall systems. The gap in the SL zone could be further utilized to add some viscous damping material to increase the damping ratio according to the requirement of the wall system.

**Figure 13.** The hysteretic curves of specimens. (**a**) HES1, (**b**) HES2, (**c**) HES3, (**d**) HES4, (**e**) HES5, (**f**) HES6, (**g**) HES7.

## *4.3. Skeleton Curves*

The skeleton curves (Figure 14a) are obtained by the peak point of the envelope in the first cycle of each loading step which could be used to evaluate the performance of the strength, shear stiffness and ductility. The double-step mode of the seven specimens is basically coincident which is mainly controlled by the shear displacement threshold. The comparison HES structural specimens with different threshold displacements, different thicknesses, and shapes of steel plates in the ED zone are respectively shown in Figure 14b–d. It can be seen that the energy-dissipation process of the ED zone is slightly extended as the threshold displacement increases. However, the bearing capacity of the SL zone is not obviously influenced by the threshold displacement. With the increase of thickness, both the bearing capacity of the ED zone and the HES increases. The yield displacement depends on neither the thickness nor the bearing capacity. The X-shaped steel plates with the smallest surface area exhibit the highest bearing capacity in shapes optimized from the rectangular shape which is suggested to be utilized in the ED zone.

**Figure 14.** Skeleton curves. (**a**)HES1-HES7, (**b**)HES2/HES4/HES5, (**c**)HES2/HES3, (**d**)HES1/HES2/HES6/HES7.

#### *4.4. The Energy Dissipation Ability of the ED Zone*

It can be seen from Figure 15a that, basically, the HES specimens with the rectangular shape of steel plates in the ED zone exhibit larger bearing capacity in the same deformation. But the rectangular steel plate would result in stress concentration and the failure in the bolt connection boundary. The specimen HES2 with optimized X-shape steel plates in the ED zone exhibits the highest energy dissipation capacity compared with that of specimen HES6 and HES7. Because of the thickness increase of steel plates in the ED zone, the energy dissipation capacity of specimen HES3 is larger than that of specimen HES2 as shown in Figure 15b. Figure 15c depicts that the specimens with the larger threshold displacement would dissipate less energy before the SL zone coming to work. When the SL zone begins to bear the load and the plastic deformation of the bolts would increase its energy dissipation ability.

**Figure 15.** Accumulative energy dissipation curves. (**a**) HES1/HES2/HES6/HES7, (**b**) HES2/HES4/HES5, (**c**) HES2/HES3/HES4, (**d**) HES1-HES7.

#### **5. Summary and Conclusions**

The inherent out-of-plane stiffness and strength of the HES are mainly provided by the steel plates in the ED zone. The strong connections to the two adjacent walls of the HES can also ensure its in plane performance. In the further study a kind of supporting structure will be developed in the SL zone to enhance its out of place performance. This study mainly analyzed the in-plane monotonic and hysteretic behavior of the HESs using software ABAQUS. Seven specimens of the HES are designed with different parameters and the influence of the parameters on their performance is investigated giving some optimized suggestions. The failure mode of the HESs is observed and their typical performance load-displacement is proposed with the character of double-step. Because of the design of the shear stiffness lifting control system, the ED zone would firstly come into plastic dissipating the input seismic energy and the SL zone would come into play when the large deformation occurs in a large and super large earthquake. Therefore, the HES can be used as the horizontal connecting member for the shear wall system and simultaneously enhance its seismic and resilient performance. On the basis of the above simulation and analysis, the following conclusions are obtained.

(1) The proposed shear displacement threshold control system endows the HES with the ability of energy dissipation, stiffness lifting and shear strength lifting by the separate function of the ED zone and the SL zone. The bolt connection in the ED zone and the functional bolts could be easily and rapidly replaced when being damaged in the earthquake, which largely enhances the resilient performance and the recovery capability of the structural system. The threshold can be adjusted according to the requirement of the structural performance, this proposed The HES could be used in prefabricated shear wall system and the performance-based design could be applied.

(2) The rectangular shape for the steel plate in the ED zone exhibits good energy dissipation performance and is easy for construction. According to the parameter analysis of the shape, the

X-shaped steel plate in the ED zone exhibits the best performance and this type is suggested to be utilized in the HESs.

(3) The shear deformation of the HES is caused by the horizontal displacement of the shear walls. When being employed in shear wall structures, the ultimate drift ratio of the HES in this study is about 4%, which could be adjusted to meet the requirement of corresponding horizontal displacement of the shear wall. The ductility coefficient of the steel plate in the energy dissipation zone is about 15 and the use of the low-yield-point steel could effectively enhance the energy dissipation ability in small shear deformation during small earthquakes.

**Author Contributions:** C.Z. and L.Z. provided the conceptual design of the novel composite wall; L.Z. and L.K. conceived and designed the FE models; L.Z. and L.K. analyzed the data; L.Z. and L.K. wrote the paper; L.Z. and C.Z. revised the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Natural Science Foundation of China (Grant No. 51708318, 51678322), the International Postdoctoral Exchange Fellowship Program (Grant No. 20190015), and the Ministry of Science and Technology of China (Grant No. 2017YFC0703603).

**Acknowledgments:** The research is financially and technically supported by the Taishan Scholar Priority Discipline Talent Group program funded by the Shandong Province, the Cooperative Innovation Center of Engineering Construction and Safety in Shandong Blue Economic Zone scheme funded by the Shandong Province and the first-class discipline project funded by the Education Department of Shandong Province.

**Conflicts of Interest:** The authors declare no conflict of interest.
