# Experimental Study on Vibration Control of
## 1 Introduction  
Suspended piping systems, which consist of water/gas pipes and cable ducts, play a crucial role in commercial buildings due to their functionality. However, the suspended piping systems can suffer not only from the dynamic loads induced by interior heat and fluid, but also from exterior seismic loads [1]. Often due to the lack of professional design for vibration mitigation, piping systems are more susceptible to damage than other structural components during earthquakes. Failed piping systems, depending on the situation, can lead to the loss of life and property. First, piping systems make up a considerable proportion of the total investment in most buildings [2], which means thatdamages to piping systems can incur high repair costs and lead to significant economic losses. Second, the damage to piping systems will induce serious secondary disasters, such as the severe and extensive flooding damage that happened in the Hawaii earthquake (2006) [3] and the Chile earthquake (2010) [4]. Furthermore, damage to the piping system may interrupt the entire building's functionality and inflict further economic loss. In past earthquake disasters, the functional interruption of hospitals [5], fire sprinkler systems [6], and water supply systems [7] affected thousands of people for several weeks. The results of the historical earthquake damage survey showed that a major contributor to the damage of piping systems was the large displacement of the pipes during earthquakes. Piping systems collide with surrounding components such as ceilings and beams when under large displacement [8], and the differential deformation caused by large displacement will lead to fractures in the piping system. There are two main types of suspended piping systems: one is to evenly arrange the vertical rods along the direction of a single pipe to hold the pipe (as shown in Figure 1a), and the other is to use the trapeze-shape basket to support pipes (as shown in Figure 1b). The common denominator between these two piping systems is that there are no lateral braces, which means that the lateral stiffness of the piping system is very small and allows for large displacement during earthquakes. Therefore, reducing the displacement of suspended piping system is an important issue to minimize damage during seismic activity. Generally, there are two methods to reduce the displacement of the piping system under seismic excitation. One method is adding braces, and the other is employing dampers for vibration control. The braces connect the pipe to a fixed structure tightly, and limit the displacement of pipes. However, the limited displacement will lead to large internal forces [9; 10]. Another disadvantage of the braces is that the implementation on suspended piping systems is typically impractical due to deficient space when various facilities are installed around the pipes. Dampers are often used for piping system vibration control in industrial structures such as nuclear plants [11]. Both elasto-plastic support devices [12; 13] and friction dampers [14] have been studied to reduce the dynamic response of nuclear power plant pipes. Numerical studies also show that viscous fluid dampers [15] have a good prospect in the vibration control of piping systems. However, they are rarely used in non-industrial settings due to their high cost and complicated structure. Recent decades have seen the rapid development in structural vibration control [16; 17], and commonly used techniques include active vibration control [18; 19; 20], semi-active vibration control [21; 22; 23; 24], passive vibration control [25; 26; 27; 28; 29; 30], and hybrid vibration control [31; 32; 33; 34; 35]. Active and semi-active controls require vibration sensors [36], and due to their advantages of fast response [37],  
Figure 1: Two kinds of suspended piping systems: (**a**) A single rod piping system; (**b**) A trapeze piping system.