## 1 Introduction
The displacement reduction factor offered by the TMD ranged from 1.5 to 7 depending on the wind conditions [13]. Due to their cost effectiveness and minimal need for maintenance, metal dampers of various shapes (X-shape, V-shape) are used as supports for nuclear plant piping systems to reduce their seismic-induced displacements [14; 15]. Friction dampers are another substitute for piping system supports [16; 17; 18]. In the study by [PERSON] et al. [17], with steel-steel friction supports, the displacement of the pipe was reduced by 90% under both broad-band and narrow-band excitations, and the acceleration was reduced by 50% and 80% respectively. However, these damper systems are mostly used in industrial infrastructure, and are rarely used for building piping systems (e.g., commercial and residential). In the field of civil engineering vibration control, passive control [19; 20; 21; 22], semi-active control [23; 24; 25], active control [26; 27; 28], and hybrid control [29; 30; 31; 32] have been extensively studied and demonstrated. In particular, passive control is the most widely used type of control system due to its simple structure, easy maintenance and high reliability [33; 34; 35]. The bounding tuned mass damper (PTMD) is a new type of passive damper. In order to dissipate energy, the PTMD utilizes the bounding of a mass against an energy dissipating material. The natural frequency of the PTMD can be tuned to that of the host structure in order to more efficiently dissipate energy [36]. Some of the notable advantages of the PTMD are the simplicity of the design and the robustness of the device. The simplicity of the design allows the PTMD to be easily adapted to different conditions and usages; and since the PTMD is robust and can maintain its performance for long periods of time, the need for maintenance is reduced. In recent years, PTMD has been extensively studied for implementation in different types of facilities [37; 38; 39; 40], including frame structures [41], subsea jumpers [42; 43], power transmission towers [44], etc. In a previous study by the authors [45], two types of PTMDs (spring steel type and pendulum type) associated with viscoelastic (VE) material were designed. The results indicated that VE-PTMDs performed well in suppressing the vibration of a suspended piping system. With their hysteretic behavior [46], shape memory alloys (SMAs) are another popular energy dissipating material used in control systems [47; 48; 49; 50; 51]. As will be further discussed in the following sections, SMAs have unique material properties originating from their transition from martensite to austenite states. The phase change is highly hysteretic and is a source of energy damping, leading to the unique superelasticity and shape memory effect of SMAs. This phase change can be manipulated by controlling the temperature of the SMA [52; 53; 54; 55], such as through an electrical current [57]. Many researchers have taken advantage of this unique property to develop adaptive TMDs in active and semi-active control schemes to enhance the damping capabilities of the TMDs [58; 59; 60; 61]. However, SMAs have been never used in a PTMD before. Based on the demonstrated damping characteristics of SMAs, the PTMD may benefit in terms of increased performance from the integration of SMAs into its design. In this paper, two types of PTMDs are employed to suppress the vibration of suspended piping systems. Unlike the previous experiments [45], the energy dissipating material is changed from VE material to shape memory alloy (SMA). The SMA-PTMDs are tested in free vibration and forced vibration, and the control performances are compared with a TMD control and a VE-PTMD control. The results show that SMA achieves a desirable equivalent damping coefficient to effectively suppress the vibration of the suspended piping system.