# Static and Seismic Responses of Eco-Friendly Buried Concrete Pipes with Various Dosages of Fly Ash
## 3 Static and Seismic Loading
### Seismic Loading  
Once an earthquake occurs in a region, the diverse directions of ground motion are incensed due to stress waves in the ground. Generally, the changes of ground motion parameters, such as motion amplitude, frequency, and movement duration will happen as seismic waves pervade the overlying soil and become deflected when reaching the surface [39; 40]. According to the study by [PERSON] [41], the range of predominant frequencies for most earthquakes resulting in crucial damage is between 1 to 2 Hz along with an acceleration which has an amplitude around 0.5 g. On the other hand, [PERSON] [42] discussed the mechanism of earthquakes, and the nature of the movements is not radically attributed to the previous earthquakes as changes in the earth crust would not have rapidly appeared. In the FE software (ANSYS), seismic records of each earthquake are commonly described through acceleration, velocity, and displacement for each structure. Since the interaction between soil and structure is to be evaluated through obtaining the optimal displacement of GPC pipes, two specific records of time-history ground motion belonging to the Tabas (Iran, 1978) and Friuli (Italy, 1981) Earthquakes have been considered to assess the effects of each earthquake on the response of the GPC pipe in this study. The peak value corresponding to the ground displacement which was applied by a series of harmonic components for the Tabas and Friuli earthquakes are 0.093 m and 0.025 m, respectively (Figures 10 and 11). In addition, the acceleration generated by each earthquake is given as shown in Figures 12 and 13. The former with the peak value of 0.6 g belongs to the Tabas earthquake and the latter with the approximate value of 0.046 is recorded for the Friuli earthquake. The typical static and seismic loadings are shown in Table 9.  
Figure 9: The static loading applied in the middle part of the GPC pipe in ANSYS. Figure 11: The X-displacement series of the Friuli earthquake, Italy 1981 (Peer Ground Motion Database [43]). \begin{table}
\begin{tabular}{c c c} \hline Static Loads & Gravity (Soil weight) N & 9.81 \\ \hline \multirow{3}{*}{} & Traffic loads (Pa) & 74,137 \\ \cline{2-3}  & Internal sewage water pressure in the pipe & 276,000–414,000 Pa \\ \cline{2-3}  & Fault displacement in the middle part of GPC pipe & 0.1 m \\ \hline \multirow{3}{*}{} & Peak displacement of TABAS earthquake (m) & 0.093 m \\ \cline{2-3}  & (Tabas (Iran), 1978) & History time (s) & 19.78 (s) \\ \hline \multirow{3}{*}{} & Seismic Loads (2) & Peak displacement of Friuli earthquake (m) & 0.025 m \\ \cline{2-3}  & (Friuli (Italy), 1981) & History time (s) & 15.175 (s) \\ \hline \end{tabular}
\end{table} 
Table 9: The values of the seismic and static loadings applied in FE. Figure 10: The X-displacement series of the Tabas earthquake, Iran 1978 (Peer Ground Motion Database [43]). Determination of the Critical Node for Evaluating the Displacement of GPC Buried Pipe under Applied Loads  
The modeling strategy used in this study emphasizes more on the numerical results in previous investigations because of the lack of experimental observations regarding the downward displacement of the underground pipe. [PERSON] et al. [44] argued that the uplift force which is twice the thrust force applied on the upper half of the pipe can be considered as the critical state under the equilibrium condition of applied loads for a numerical model of a buried pipe. In addition, [PERSON] et al. [45] expressed a similar attitude that the maximum value of P/2 on the upper half of the pipe, which illustrates the acceptable satisfaction between numerical and experimental tests, can be considered as the critical state in the case of underground pipe displacement; hence, the node 20, located on the upper half and the middle length of GPC pipe, has been chosen for this purpose.