# PTMD Control on a Benchmark TV Tower under Earthquake and Wind Load Excitations
## 1 Introduction  
Along with the construction of higher and more complex civil structures, there have been concerns about their safety under natural disasters, such as typhoons and earthquakes. It is nearly impossible for the designers to fully predict the excitations during the service stage; if the designers try to enhance the capacity of the structure against all possibilities, the loadings will largely increase the cost of the construction. Structural control is considered to be an effective approach to adapt the host structures to different kinds of harmful excitations and enhance their safety and serviceability [1; 2; 3]. Passive control approaches, such as tuned-mass-dampers (TMD), viscous dampers, viscoelastic dampers, and base isolation techniques have advantages of low cost and easy implementation [4]. Particularly, TMD is considered to be one of the most effective passive devices and has many applications, such as the CN tower in Toronto and the Taipei 101 building [5]. It possesses the merit of easy maintenance and can be implemented even on existing structures. The TMD absorbs inertial force from the host structure to reduce its motion, with its effectiveness determined by its dynamic characteristics, stroke, and theamount of added mass it employs. The potential of the TMD has been verified in reducing vibrations under a variety of excitations [6]. A TMD consist of a mass, a damping mechanism, and a restoring mechanism with certain stiffness connected to the host structure. During operation, the TMD is tuned to a certain frequency and a certain amount of the vibration energy will be transferred to the movement of the mass of the device. However, studies have pointed out that passive devices are hard to adjust once they are installed and their robustness is questionable when the host structure is subjected to different excitations. Since TMD can only reduce vibration components whose frequencies are close to the tuned frequencies, it is believed that the most significant limitation of the TMD is its narrow effective bandwidth and the high sensitivity to even a small change in the tuning [7; 8; 9; 10]. Thus, it is considered to be unsuitable for vibration control under broadband earthquake inputs [11]. As a result, various schemes have been proposed to improve the TMD for better robustness and reliability [12]. For example, a nonlinear hysteretic damper has been supplemented for enhanced energy dissipation [13; 14; 15; 16; 17]. [PERSON] et al. [18] demonstrated the effectiveness of such a TMD by implementation in the Taipei 101 building. These enhanced TMDs were found to be more effective than the conventional ones in a certain range of excitation frequencies. Another common alternative is to incorporate TMDs with active and semi-active devices [19; 20]. Active mass dampers (AMD) have been developed and widely used in the civil engineering field [21; 22; 23]. Active tuning of TMDs can be achieved by using active springs [24; 25], and some scholars tried to use shape-memory alloy (SMA) to achieve on-line adaptation [26; 27]. [PERSON] and his coworkers developed semi-active tuned mass dampers (STMD) using semi-active variable stiffness systems [28; 29], the STMD is able to be tuned to the desired frequencies instantaneously. Some researchers incorporated magnetorheological (MR) dampers into TMD to enhance adaptability [30]. The MR damper generates extra dissipation energy in the TMD and emulates positive and negative stiffness in order to adjust the stiffness of the TMD [31]. [PERSON] et al. [32] conducted an experiment on a cable installed with TMD-MR and great control results were obtained. [PERSON] et al. [33] found that multiple semi-active tuned mass dampers can give significant reduction on both the steady-state and transient responses. Although the active and semi-active TMDs possess better performance, they are also liable to control algorithms and must be equipped with sensors and external power sources, which are not guaranteed to function normally under severe events.