# Vibration Reduction of an Existing Glass Window through a Viscoelastic Material-Based Retrofit
## 2 Proposed Method and Experimental Set-Up  
### Vibration Damping Enhancement through Constrained Viscoelastic Materials  
Recently, viscoelastic materials, which possess viscoelasticity defined as a material response that exhibits the characteristics of both a viscous fluid and an elastic solid, received great attention in civil engineering [66; 67]. A viscoelastic material combines elastic and viscous properties, returning to its original shape following stress; however, it does so slowly enough to oppose the next cycle of vibration. A recent research revealed that a viscoelastic material also has a good fatigue life, even when subjected to impact loads [68]. Viscoelastic materials used in engineering have two main types of structure, namely the free damping structure and the constrained damping structure [69]. When the base structure is deflected upon bending, the viscoelastic material deforms primarily in the extension and compression in the planes parallel to the base structure. The hysteresis loop of the cyclic stress and strain dissipates the energy. The constrained-layer damping treatment consists of a sandwich of two outer elastic layers with a viscoelastic material as the core [70]. When the base structure undergoes a bending vibration, the viscoelastic material is forced to exhibit shearing deformation due to the stiffness of the upper layer. Constrained-layer damping is more effective than the free-layer design since more energy is consumed and dissipated into heat during the work done by the shearing mode within the viscoelastic layer. In this paper, a new method based on constrained-layer damping was developed to reduce the vibration of an existing glass window using a viscoelastic material. The key component for \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Solutions** & **Authors** & **Pros** & **Cons** \\ \hline Employing both air-film & & Extensive applications; & Damping materials integrated \\ damping technology and & [PERSON] et al. [46] & better vibro-acoustic & during fabrication; not \\ viscoelastic damping materials & & damping properties; & suitable for retrofitting \\  & & good optical quality. & existing windows. \\ \hline Utilizing laminates or & [PERSON] et al. [47]; & & \\ multilayer technology to & [PERSON] et al. [49]; [PERSON] [50]; & Increased resistance to & Damping materials integrated \\ improve the vibration & [PERSON] et al. [51]; & vibrro-acoustic damping & during fabrication; not \\ damping of window glass & [PERSON] et al. [52]; & properties. & suitable for retrofitting \\  & [PERSON] et al. [53] & & existing windows. \\ \hline Increasing the damping & & & \\ between the glass and the & [PERSON] et al. [54]; & Good design flexibility; & \\  & [PERSON] [PERSON] et al. [55] & sufficient damping; & \\  & window frame & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Pros and cons of the current solutions for increasing window damping. the retrofitting of an existing glass window was a self-adhesive glass constrained viscoelastic strip (SaGCVS). As shown in Figure 1, four such strips were mounted onto the four edges of an existing window after the surface of the glass was cleaned. A self-adhesive glass constrained viscoelastic strip, as shown in Figure 1, consists of three layers: the constraining glass layer, the constrained viscoelastic layer, and the adhesive layer. The constraining glass layer is a strip of 5-mm-thick glass, which is rigid. The constrained viscoelastic layer consists of the viscoelastic material, which is soft and flexible. The constraining glass layer is pre-bonded with the viscoelastic layer, and offers constraint to the viscoelastic layer, improving its damping capacity. The other side of the viscoelastic layer is coated with the adhesive material for easy mounting onto an existing window. In this configuration, constrained-layer damping, consisting of a sandwich of two outer elastic glass layers with a viscoelastic material as the core, was formed to improve the damping of an existing window glass.