## 2 Experimental Assessment of Curtain Wall Seismic Performance
### Expected Displacement Control Effects of Seismic Fasteners  
In general, the curtain wall structure constitutes a groove so that the glass can be inserted into the frame. Here, there is a movable clearance between the grooves in which the glass is fitted. The spacing of the clearance is between approximately 5 and 20 mm, depending on the type of curtain wall. With this clearance, it is possible to buffer in the left and right directions when an earthquake occurs. However, in the event of earthquakes, seismic performance up to 150 mm must be achieved, depending on the seismic grade. Through the static seismic performance assessment, it was confirmed that the conventional curtain wall was too weak to ensure structural stability in the event of earthquakes. However, because earthquakes result in dynamic behavior rather than static behavior, verification was required. In the AAMA 501.6 standard, the performance assessment is only considered in the \(X\)-axis in-plane direction in the representative dynamic seismic performance test method. However, because displacement can occur in three directions (\(X\)-, \(Y\)-, and \(Z\)-axis) when earthquakes occur, verification of all cases is required, and a curtain wall system capable of responding to movement in three axes is required. Accordingly, in this study, as shown in Figure 5, a curtain wall system was designed to control the displacement during earthquakes via the use of seismic fasteners that can withstand a maximum displacement of 150 mm and can cope with three-axis displacement. A cross-sectional drawing of the prototype design is shown in Figure 6.  
Figure 4: Main vulnerabilities of non-seismic curtain wall: (**a**) external weather sealant breakage; (**b**) glass fallout; (**c**) curtain wall frame breakage; (**d**) expansion joint breakage.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Lateral Displacement** & **Cycle** & **Vulnerabilities** & **Remarks** \\ \hline Seismic classification & & & \\ (Special) & 3 & None & \\ (0.010 \(\times h_{sx}\)) = \(\pm\)36.00 mm & & & \\ \hline Seismic classification (I) & 3 & Partial breakage of weather sealant installed outside & Distance between anchor \\ (0.015 \(\times h_{sx}\)) = \(\pm\)54.00 mm & & frame & points of curtain wall mullions \\ \hline Seismic classification (II) & 3 & Expansion of breakage area of weather sealant & \(h_{sx}\) = 3600 mm \\ (0.020 \(\times h_{sx}\)) = \(\pm\)72.00 mm & & installed outside the curtain wall & (\(h_{sx}\) = xth story height) \\ \hline Purpose of displacement & 3 & Glass breakage and fallout & \\ in this study \(\pm\)150 mm & & Residual deformation after weather sealant breakage & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Summary of seismic performance evaluation results.  
The design's structure connects the lower part of the upper frame to the floor slab so that the vibration of the building generated by the external force caused by earthquakes is not transmitted to the curtain wall. Thus, the curtain wall can slide in the longitudinal and transversal directions of the building, as shown in Figure 7. In addition, it is composed of a movable clip and a rail that can move left and right (\(X\)-axis) or up and down (\(Z\)-axis). The structure can be fixed to the structure by bolting or welding, and was designed so that a displacement of up to 150 mm can be absorbed by the fastener.  
In addition, to cope with the displacement in the \(Y\)-axis direction, a separate inter-story module was applied, as shown in Figure 8, so that it can be operated separately without restraint between the upper and lower frames. As a result, it is free from stress concentration and buckling when displacement in the \(Y\)-axis direction occurs.  
Figure 5: Seismic fastener prototype (\(X\)-axis).  
Figure 6: Developed fastener prototype design.  
Figure 7: Displacement absorbing principle of seismic fastener: (**a**) \(X\)-axis movement; (**b**) \(Z\)-axis movement.