## 4 Comparing Lebanese Design Response Spectra  
In the present section the DRS to which NL135 refers are compared in order to check the different safety levels allowed by the Lebanese design rules. For this purpose, the four main categories listed in Table 7 were assumed as giving a good correspondence between the site/ground classifications made by PS92, UBC, IBC and EC8. It is worth noting that a clear equivalence can be held between the EC8 and the UBC/IBC classification [30], while a straightforward correlation cannot be easily assigned between PS92 and the other codes. Both EC8 and IBC classify sites based on the average shear wave velocity, denoted as \(\mathrm{v_{s,30}}\), calculated within the uppermost 30 m of the soil strata. In contrast, the French PS92 employs diverse depth criteria for its site classification. To ensure a suitable comparative analysis, a standardized depth of 30 m was here considered, facilitating the harmonization of site/ground classifications of IBC and EC8 with that of PS92. This led to deriving the four primary categories outlined in Table 7. A representation of the DRS for each of these categories, along with two specified values of the PS92 topographical factor \(\tau\), is presented  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ground Type** & **S** & **TB (s)** & **TC (s)** & **TD (s)** \\ \hline A & 1.00 & 0.15 & 0.4 & 2.0 \\ B & 1.20 & 0.15 & 0.5 & 2.0 \\ C & 1.15 & 0.20 & 0.6 & 2.0 \\ D & 1.35 & 0.20 & 0.8 & 2.0 \\ E & 1.40 & 0.15 & 0.5 & 2.0 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Values of the parameters for the Type 1 response spectrum (according to EC8).  
Figure 4: Lebanese horizontal design response spectra as obtained according to EC8 for the five soil types (A, B, C, D, E) and 5% damping ratio.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ground Type**} & \multicolumn{3}{c}{**Average Properties at 30 m Depth**} \\ \cline{2-4}  & **Shear Wave Velocity** & **Standard Penetration Resistance** & **Undrained Shear Strength** \\ \cline{2-4}  & \(\mathrm{v_{s,30}}\) **(m/s)** & \(\mathrm{N_{SPT}}\) **(Blows/30 cm)** & \(\mathrm{c_{u}}\) **(kPa)** \\ \hline A & \textgreater{}800 & - & - \\ B & 360–800 & \textgreater{}50 & \textgreater{}250 \\ C & 180–360 & 15–50 & 70–250 \\ D & \textless{}180 & \textless{}15 & \textless{}70 \\ E & Soil profile consisting of a surface alluvium layer with \(\mathrm{v_{s}}\) values of type C or D and thickness varying between 5 m and 20 m, underlayed by stiffer material with \(\mathrm{v_{s,30}}>800\) m/s \\ \hline \hline \end{tabular}
\end{table}
Table 5: Ground types according to EC8.  
in Figure 5. The diagrams on the left (Figure 5a,c,e,g) refer to \(\tau=1\) and those on the right (Figure 5b,d,f,h) to \(\tau=1.4\).  
Figure 5: Comparison between the design spectra given by the considered codes for different soil types: (**a**) Category A with \(\tau=1\) for spectra of PS92, (**b**) Category A with \(\tau=1.4\) for spectra of PS92, (**c**) Category B with \(\tau=1\) for spectra of PS92, (**d**) Category B with \(\tau=1.4\) for spectra of PS92, (**e**) Category C with \(\tau=1\) for spectra of PS92, (**f**) Category C with \(\tau=1.4\) for spectra of PS92, (**g**) Category D with \(\tau=1\) for spectra of PS92, (**g**) Category D with \(\tau=1\) for spectra of PS92, (**h**) Category D with \(\tau=1.4\) for spectra of PS92.  
The comparisons provided in Figure 5 show that different design seismic forces can be considered for structures with similar dynamic properties (fundamental period T) and for the same site/ground type. This may lead to different safety levels in the Lebanese design.