# Base Isolation Compared to Capacity Design for Long Corner Periods and Pulse-Type Seismic Records
## 3 Results
### Time Histories for Both Structural Approaches  
Figure 9 shows absolute acceleration time histories in the mass centre for the INCERC 1977 spectrum-compatible accelerogram at the base of the structure (or quite over the isolation level for the base-isolated structure) and at the top of the building. The isolated structure manages most of the earthquake-induced movement at the isolation level and just 37% acceleration amplification is registered at the building top for the first strong pulse. As comparison for the building designed according to the capacity method, base horizontal accelerations are amplified by up to 84% at the building top.  
Figure 10 shows the relative displacement time histories in the mass centre for the INCERC 1977 spectrum compatible accelerogram at the building's base (or quite over the isolation level for the base-isolated structure) and at the building top.  
Relative displacements are amplified by up to 85% along the building height for the stiffened building, whereas for the base-isolated building negligible relative displacement differences are registered at the building top compared to the isolation level  
The maximum relative displacement for the isolated building is delayed by 0.2 s at the building top with respect to the base of the building. The results for the stiffened building show the peak almost at the same time.  
The base-isolated building experiences half of the top displacements registered for the stiffened building (see Figure 11a). Drift values are negligible for the base-isolated structure (Figure 11b).  
Figure 12 shows the deformed shapes of the analysed structure, at maximum ground acceleration. The base-isolated structure experiences a rigid body movement while the fixed base structure presents a bending-shear deformation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Result** & **INCERC 1977** & **INCERC 1986** & **INCERC 1991** & **Spectrum Compatible** \\  & **Original** & **Original** & **Original** & **Tc = 1.6 s** \\ \hline Maximum base shear force [kN] & 1308 & 573 & 550 & 2068 \\ Maximum interstorey drift [\%] & * & * & * & * \\ Maximum acceleration at the & & & & \\ underground level [g] & 0.19 & 0.10 & 0.091 & 0.26 \\ Maximum acceleration at the & & & & \\ building top [g] & 0.21 & 0.06 & 0.079 & 0.27 \\ Maximum isolator displacement [m] & 0.21 & 0.007 & 0.005 & 0.32 \\ \hline \hline \end{tabular}  
* interstorey drift ratios smaller than 0.1%.  
\end{table}
Table 5: Results from dynamic non-linear analysis, base-isolated building.  
Figure 9: Absolute acceleration time histories, INCERC 1977 spectrum compatible ground acceleration record: (**a**) classic building; (**b**) base-isolated structure.  
Figure 10: Relative displacement [m] time histories, INCERC 1977 spectrum compatible ground acceleration record: (**a**) classic building; (**b**) base-isolated structure.  
Figure 11: (**a**) Relative displacement [m] time histories at building top, INCERC 1977 spectrum, compatible ground acceleration record; (**b**) drift time histories at level 1, INCERC 1977 spectrum, compatible ground acceleration record.  
Figure 12: Deformed shapes at maximum ground acceleration: (**a**) classic building; (**b**) base-isolated structure.