# Investigation of the Structural Dynamic Behavior of the Frontiuns Gate
## 5 Discussion  
The Frontinus Gate in Hierapolis in Denizli, Turkey has a very long history. This monumental masonry gate is composed of three openings in squared travertime blocks, with masonry arches, flanked by two round towers. It is difficult to investigate the structural health of existing masonry monuments using seismic code requirements that are prepared for new masonry constructions. The work carried out was aimed at getting a better insight on the seismic response of the Frontinus Gate. To accomplish this objective, a discrete element model was created using the present geometry of the structure. Dynamic nonlinear analyses were performed under real earthquakes and synthetic ground motions. Interpretation of the numerical model results lead to the following conclusions:  
1. Modal analysis, assuming elastic behavior, is a very useful first step to obtain insight into the dynamic characteristics of the structure.
2. The nonlinear dynamic analyses indicate that the Frontinus Gate, in the current state, under an earthquake with a magnitude of 6, would be expected to suffer moderate damage. Under the synthetic earthquake with a return period of 475 years, the observed structural response and damage patterns are serious although it does not mean the collapse of the monument.
3. In the case of occurrence of an earthquake with a return period of 2475 years, the models show that the monument would not be able to withstand it, resulting in a large number of blocks collapsing completely.
4. Considering the seismic sensitivity of the Frontinus Gate, the results obtained are consistent with the present state of the structure, with the round towers having more seismic damage potential than the masonry arches.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{3}{c}{**Maximum Relative Displacement (m)**} \\ \hline  & Point 1 & 0.0416 \\
**Dinar,** & Point 2 & 0.0826 \\
**Turkey 1995 Earthquake** & Point 3 & 0.1024 \\  & Point 4 & 0.0226 \\  & Point 5 & 0.0440 \\ \hline
**Ground motion level 1** & Point 1 & 0.3472 \\
**Case 1:** & Point 2 & 0.7614 \\
100\% of the first synthetic earthquake combined with & Point 3 & 0.9380 \\
30\% of the second synthetic earthquake & Point 4 & 0.2090 \\
**Ground motion level 1** & Point 2 & collapsed \\
30\% of the first synthetic earthquake combined with & Point 3 & collapsed \\
100\% of the second synthetic earthquake & Point 4 & 0.1890 \\
**Ground motion level 2** & Point 5 & 0.6338 \\
**Case 1:** & Point 1 & 0.0621 \\
100\% of the first synthetic earthquake combined with & Point 2 & 0.1444 \\
30\% of the second synthetic earthquake & Point 3 & 0.1298 \\
**Ground motion level 3** & Point 4 & 0.0440 \\
**Ground motion level 2** & Point 1 & 0.0906 \\
**Case 2:** & Point 2 & 0.1841 \\
30\% of the first synthetic earthquake combined with & Point 3 & 0.1981 \\
100\% of the second synthetic earthquake & Point 4 & 0.0488 \\  & Point 5 & 0.0438 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Maximum displacement relative to base.  
Although the Frontius Gate is still standing at the site, showing an outstanding endurance, under seismic excitation with a magnitude of 6 or greater, a high vulnerability of large portions of the structure can be expected.  
Conceptualization, O.S.; methodology, O.S., J.V.L.; investigation, O.S.; writing--original draft preparation, O.S.; writing--review and editing, J.V.L.; visualization, O.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
We would like to gratefully acknowledge the Denizli Provincial Directorate of Culture and Tourism for providing valuable information for the Frontiinus Gate.  
The authors declare no conflict of interest.