## 4 Finite Element Modelling  
In this study, an existing school building was used in the analyses and a seismic base isolation design was made for this building. The existing structure was modeled as base-isolated using lead rubber bearings and the finite element method. In the building structural system, the columns were 350 \(\times\) 600 mm in size and the beams were 300 \(\times\) 600 mm in size, and the building storey plan is given in Figure 4. TBEC 2018 [31] was taken as a reference in the design of the dampers used in the base isolation. Detailed structure features are given in Table 4.  
Figure 3: Comparison of blast and seismic loads: (**a**) Seismic versus blast overlap; (**b**) Seismic versus blast loading time histories; (**c**) Seismic versus blast response for fixed-base buildings; (**d**) Seismic versus blast response for base-isolated buildings [35]. In order to determine the rotation rates at the column and beam ends, plastic hinges were defined at the ends of the columns and beams while modeling the structures in nonlinear calculation methods. Additionally, moment-curvature diagrams were used in defining plastic hinges. In the definition of column joints, plastic hinges were defined for each column by entering the vertical reaction force values (normal force) of each storey (Figure 5). The existing structure was concrete class C25 and the Mander confined concrete model [36] was used (Figure 6). Longitudinal reinforcements were S420 steel grade and transverse reinforcement was S220 steel grade. \begin{table}
\begin{tabular}{c c} \hline \hline  & **Feature of Building** \\ \hline Grade of Concrete & C25/30 \\ Grade of Steel & S420 \\ Storey Height (Units: m) & 3.80 \\ Size of beams (Units: mm) & 300 \(\times\) 600 \\ Reinforcement Arrangements for beam sections & 3\(\updownarrow\)14 + 2\(\updownarrow\)12 \\ Size of columns (Units: mm) & 350 \(\times\) 600–600 \(\times\) 350 \\ Reinforcement Arrangements for column sections & 16\(\updownarrow\)16 \\ Slab Thickness (Units: mm) & 140 \\ \hline \hline  & **Feature of Isolators** \\ \hline Number of isolators & 28 \\ Design period of DBE, T\({}_{\text{D}}\) (Units: s) & 2.5 \\ Effective Stiffness, k\({}_{\text{e}}\) (Units: kN/m) & 405.69 \\ Post-Elastic Stiffness/Lead Core Stiffness, k\({}_{\text{2}}\)/k\({}_{\text{1}}\) & 0.077 \\ Yielding Force F\({}_{\text{y}}\) = F\({}_{\text{Q}}\) (Units: kN) & 115.60 \\ Total Design Displacement; D\({}_{\text{D}}\) (Units: mm) & 93 \\ Maximum Displacement D\({}_{\text{M}}\) (Units: mm) & 778 \\ Damping & 0.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Features of structures and isolators. Figure 4: Structural plan layout of three-storey RC frame structure. Scaling laws were used to estimate the blast loads to be impacted on the structure. Peak incident overpressure was obtained by obtaining blast load functions by keeping the blast load constant at different distances. Thus, an estimation was made about possible building damage using FEMA 426 [2] data (Table 1). In addition, an assumption that a hatchback was detonated was made to be used in calculations according to the explosive carrying capacity of the vehicles. Blast loads were obtained using Hopkinson scaling laws. Explosion effects were applied to each storey of the building at different distances, and load functions expressing the effects of the vehicles exploding at different distances on the storey levels were calculated and are given in Figure 7.  
When the maximum explosion pressures are evaluated according to the distances, it is estimated that structures exposed to blast pressure in the range of 68.95-82.74 kPa will collapse according to Table 1. In the range of 12.41-20 kPa, it is expected that there may be collapses in the walls. In this case, a structure exposed to 227 kg TNT explosion from 5 m and 10 m distance is expected to be at the collapse level.