**1. Introduction**

#### *1.1. Research Status of the Connection for the Prefabricated Shear Wall System*

In order to achieve the green and sustainable development and solve the problem of environmental protection and labor shortage, it is particularly significant to develop innovative prefabricated shear wall systems appropriately employed in tall buildings and some special structures [1–3]. The in-cast shear wall system is characterized by grea<sup>t</sup> lateral stiffness and bearing capacity. The traditional prefabricated shear wall system is designed according to the in-cast structure standards and its seismic performance fails to meet the requirements of the current seismic design code of buildings in China. With the application of prefabricated structural system especially in highly seismic regions, innovative

design theories and systems are to be used to endow this new prefabricated system with high seismic and resilient performance. Therefore, the utilization of some resilient energy dissipation devices in structures is sensible to enhance the performance of prefabricated shear wall systems both in the large and super-large earthquakes [4,5].

The performance of connections between prefabricated shear walls has a significant influence on the seismic behavior of the prefabricated shear wall system. The present connections mainly include cast-in-place bolt connection, casing grouting connection, reserved hole slurry anchoring connection, bolt connection and post-tensioned prestressed connection [6–8]. Shemie [9] proposed a bolt connection between prefabricated panels which makes the connection between the wall panels more flexible and their ductility could be e ffectively utilized. Zhu et al. [10] conducted a mechanical study on horizontal and vertical joints on fabricated large slab structures, showing that horizontal seams could decrease the lateral sti ffness and the shear angle of the vertical joint has a grea<sup>t</sup> influence on the distribution of the internal forces. Noel and Soudki [11] performed a reciprocating loading test on prefabricated shear walls and found that the bearing process of the horizontal joint could be defined as three stages which are the elastic stage before slipping, the elastoplastic stage before the damage of horizontal joint and the total slip damage. In the final stage of the slip failure, the strength will drop by 20% and the mortar will be crushed. Sun et al. [12] developed a new-type vertical joint for prefabricated wall and experimental results demonstrated that these connections were strong enough to maintain the global seismic behavior of the prefabricated wall equal to in-cast ones. Smith and Kurama [13] studied the prestressed specimens and found that their strength and initial sti ffness are similar to those of cast-in-place specimens. The test piece demonstrated slight damage with a large nonlinear displacement, good self-centering ability but a little decrease in energy dissipation ability. Vaghei et al. [14,15] tested the U-shaped steel channel wall-to-wall connection and found that this type of connection performed better than loop connections. Guo et al. [16] proposed bolt connections for prefabricated wallboard structures and conducted shaking table tests on a 1/2 scale three-story model. The results show that the prefabricated structure system has the characteristics of high sti ffness, large bearing capacity, and high collapse margin ratio. Because the current design code regards grouting pile connection as an idealized steel bar, it ignores the restriction of sleeve and composite behavior of components. Son et al. [17] proposed that the sheer force of horizontal connections of members can be resisted by overlapping anchors. The shear behavior of overlapping anchors between prefabricated concrete slabs and reinforced concrete members in simulated tests is analyzed. The results show that the average shear strength of overlapping anchorage connections is 109% of the calculated value. Jiang et al. [18] studied the e ffect of new bolted connections on the mechanical properties of prestressed concrete shear walls. The results show that the strain of the joints is less than the yield strain, and the joints do not destroy. The mechanical properties of the joints are similar to those of the cast-in-place reinforced concrete shear walls. Therefore, the performance of the connection could significantly influence the structural performance especially in the final stage in the earthquake.

#### *1.2. Research Status of the Shear-Type Metal Damper*

Many scholars have conducted extensive research on the behavior of metal dampers used in structural systems. Metal dampers as passive energy dissipation devices commonly serve as non-structural members reciprocating to absorb the input seismic energy and protecting the structural members. This energy dissipation is obtained by plastic deformation in which the structural member is in elastic [19]. Low-yield-point steel has the advantages of low yield strength, large elongation, and good ductility. Its high plastic deformation ability could enhance the structural energy dissipation ability [20]. The shear metal damper proposed by J.M. Kelly was widely used in the damping design of building structures due to simple structure and excellent performance. Whittaker et al. [21] proposed geometrically optimized X-shaped mild steel dampers and triangular soft steel dampers. Zhang and Zhang [22] experimentally researched di fferent ways of weakening the sti ffness of the damper in which the shape in the middle has a grea<sup>t</sup> influence on the ductility and the flange plates of di fferent shapes have no obvious influence. Abebe et al. [23–25] conducted experimental research and simulation on the hysteretic behavior of low-yield steel shear dampers. Mortezagholi et al. and Zahrai et al. [26,27] proposed a damper with a circular cross-section by geometrically optimized parameter analysis. In order to solve the connection problem between lead blocks and components, Cheng et al. [28] proposed a ba ffle-type lead damper and its test results demonstrated excellent energy consumption ability. According to the above study, metal dampers could achieve good energy dissipation ability but their failure would result in degradation of the structural sti ffness. To some degree, the high rigidity of in-cast structural systems would limit the performance of dampers and the sti ffness degradation of the prefabricated structures would result in the collapse especially in large and super-large earthquakes. U-shaped metal yield damper introduced by Jamkhaneh et al. [29] has been tested about its mechanical displacement, lateral strength, elastic sti ffness, and energy dissipation ability. Lin et al. [30] developed a detachable buckling restrained shear plate shock absorber. The influence of key design factors, such as the length-width ratio of the slab and the number of internal composite plates, on the seismic performance of the damper, is studied, and the design formulas for calculating the elastic sti ffness and ultimate strength of the damper are proposed. Zhu et al. [31] proposed a metal shear plate damper with an optimized shape. The test results show that the metal shear damper has stable energy dissipation capacity and good low cycle fatigue performance. Belleri et al. [32] proposed that the use of passive energy dissipation and re-centering devices could limit the structural damage. Mazza et al. [33,34] successfully proposed a design procedure for the damper braces to attain a designated performance level according to a certain proportion of reinforcement and further developed a new displacement-based design procedure to proportion hysteretic damped braces considering the e ffect of a structure's seismic degradation. These procedures are verified to be highly e ffective when being utilized in designing frame structures.

Some gap dampers are proposed by Rawlinson et al. [35] and De Domencio et al. [36] which could be designed to be engaged after an expected displacement and they depict good performance when being utilized in base-isolated structural system. Therefore, an innovative type of wall-to-wall horizontally connecting structure with high energy dissipation and sti ffness lifting ability is proposed, which is expected to enhance the seismic and resilient performance of prefabricated shear wall systems.

This study proposes an innovative "double-step" horizontal-connection and energy-dissipation structure (HES) with the character of high energy dissipation and capacity lifting after the decrease. In its first step, it weakly connects two adjacent shear walls and mainly dissipates the input energy. In its second step, it could strongly integrate two respectively working adjacent shear walls into one unit to obtain one stronger structure member to resist the collapse of the structure system. The design procedure of the HES is briefly depicted in Figure 1. First, a shear walls structural system analytical model is built and analyzed in a predicted earthquake is. After that, the shear bearing capacity Vf and the allowable horizontal displacement ΔWH of the shear wall are calculated. The shear threshold displacement D of the HES is determined according to the allowable horizontal displacement ΔWH, by which the input energy during the earthquake is dissipated by the ED zone before yield the shear wall. The shear bearing capacity Vf of shear wall is employed to predict the shear capacity of the SL zone of the HES VHSE to ensure that the HES could strongly integrate two respectively working adjacent shear walls into one unit to obtain one stronger structure member to resist the collapse of the structure system. Numerical analysis is performed to comprehensively study the hysteretic behavior of the HES utilizing the validated finite element models. Their hysteretic load-displacement curves, skeleton curves, shear deformation, and failure mode are discussed in detail and the optimized design methods are suggested.

**Figure 1.** Design flow chart of the horizontal-connection and energy-dissipation structure (HES).

#### **2. The Mechanism of the HES**
