## 4 Performance Analysis  
### Force-Bearing Performance of the MG Isolator  
Major seismic force initiates the work of the MG isolator, which slips to minimize the transfer of seismic energy to the superstructure. The following aspects are highlighted in the design of the MG slide isolator. Under minor seismic force or wind loading, the induced friction and the mitigation of the mortar bars, if any, prevent the initiation of slippage. However, as moderate seismic vibration breaks the embedded mortar bars, slippage begins at the isolator interface. As the imposed load continues to mount and reaches the load of a major earthquake, slippage proceeds. When the restrictive screws press against the stop holes in the upper and lower foundation beams, the specimens reach the displacement limit. At this point, the stop blocks come into play to guard against over-displacement of the foundation, or worse, a collapse. In accordance with the Code for Seismic Design of Buildings (GB50011-2010) [25], equation \(F_{Ek}=\alpha_{I}G_{eq}\) can be used for calculating the horizontal seismic force imposed on the foundation of a masonry structure (\(F_{Ek}\): benchmark value for seismic influence upon the structure in the horizontal direction; \(\alpha_{1}\): coefficient for horizontal seismic influence as the structure reaches the natural vibration cycle T1; \(G_{eq}\): the aggregate of the vertical loading imposed and the gravity of the specimen itself). Considering the relatively short cycle of low-rise buildings, the authors believe that the maximum horizontal seismic acceleration, \(\alpha_{\max}\), can substitute for \(\alpha_{1}\) in the equation. In areas where buildings are designed to withstand earthquake intensities of level eight (0.20 g), \(\alpha_{max}\) is to be 0.16 and 0.90 for minor and major earthquakes respectively. In accordance with the Code for Seismic Design of Buildings (GB50011-2010) [25], the ground acceleration in an eight-degree seismic area under middle seismic influence is 0.20 g, while for minor and major earthquakes, the coefficients for seismic influence top at 0.16 and 0.90, respectively (or \(\alpha_{max}\) equals 0.16 and 0.90, respectively), which is calculated on the premise that the probability of exceedance in terms of earthquake intensity is 10% within the life cycle of the structure. In such cases, the MG isolator should be designed as follows. The slide isolator should not initiate under a lateral force (or \(F\)) of 0.16 \(G_{eq}\) or less. As this force reaches 0.90 \(G_{eq}\) or less, the isolator slippage plays a major part in the mitigation of the seismic influence (protecting the superstructure), while the stop block suffers very little from elastic-plastic deformation. When the lateral force exceeds 0.90 \(G_{eq}\), the stop block, though showing visible signs of elastic-plastic deformation, has not yet been damaged; therefore, severe damage or collapse of the superstructure will not occur. Table 5 lists the seismic influences and the initiating load of slippage for each specimen. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**IDI** & **Specimen No.** & **GGBW-1** & **GGBW-2** & **GGBW-3** & **GGBW-4** \\ \hline \(IDI_{max}\) & 1.86\% & - & 2.14\% & 1.21\% \\ \(IDI_{final}\) & 2.29\% & - & 4.06\% & 1.67\% \\ \(IDI_{final}/ID_{max}\) & 1.23 & - & 1.90 & 1.38 \\ \hline \end{tabular}
\end{table} 
Table 4: The inter-story drift, _IDI_: the index of inter-storey drift with respect to the storey height. See Table 6 for a comparison of the specified loads of the specimens (initiating loads for slippage, split limit and loading limit) obtained and that of the loading limit and major seismic forces. Table 7 presents the average slippage loading that was measured. The slippage loading is the load imposed in either the positive or negative direction during each loading cycle after the specimen reaches the initiating load. At this point, the displacement increment increases rapidly even though the loading increment remains insignificant.