Dynamic Behavior of Underground Viscoelastic Pipelines Under Seismic Impact in the Form of Real Earthquake Records

3. THE RESEARCH FINDINGS AND DISCUSSION


_{Consider the problem on the Oxy plane when the pipeline is loaded in the Oxy plane, i.e. the seismic movement of the soil occurs in the horizontal plane at an angle to the longitudinal axis of the pipeline, while the ends of the pipeline are pinched. Based on the algorithm of computer implementation, the task is solved. Mechanical and geometric parameters are selected in the following form: E=5·102 MPa; δ=0.08 m; R=0.2 m; T=0.3 s; ρ=940 kg/m3; DH=0.4 m; Cp=600 m/s; µgr=0.2; μtr=0.24; Ab=0.1; α=0.25; β=0.05. The length of the pipe in question is 20 m.
Numerical results are obtained for displacements and force factors taking into account boundary conditions. The results of the numerical implementation are shown in Figures 1-5 in the form of changes in the longitudinal displacement and stress along the pipeline axis at a given time and in time in the pipeline sections under the action of a real earthquake record.}

Figure.1. A real record of the longitudinal movement of the soil in time during an earthquake, recorded in the city of Gazli in 1976.	Figure. 2. Change in the longitudinal movement of the pipeline over time at a distance of x=1 m

_{When calculating the pipeline for seismic resistance, variants of setting the soil movement during earthquakes in the form of real earthquake records were used. The movement of the soil is given in the form of real records of earthquakes in the town Gazli May 17, 1976. The intensity of seismic impacts in the epicentral zones reached 9 points.
Fig. 1 shows a real record of the longitudinal movement of the soil in time during an earthquake, recorded in the town Gazli May 17, 1976 [25]. Figure 2 shows the change in the longitudinal displacement of the polymer pipeline in time at x=1 m and at a given time along the axis of the pipeline. Comparison with Figures 1 and 2 shows that here, near the fixed end of the pipeline, the maximum displacement is several times less than the maximum displacement in a given seismic wave.
Along the pipeline at this time, the disturbance covers the entire length of the pipeline, having a maximum value near the middle of the pipeline (see Figure. 3).}

a	b
Figure. 3. The change in the longitudinal movement of the pipeline over time at a distance of x=10 m and along the axis of the pipeline at a fixed time t=18.44 s
а		b
c		d
Figure. 4. Change in the values of the normal and tangential stresses of the underground pipeline over time at specified points and along the pipeline at a fixed time t=18.44 s

_{Figure 4 shows the obtained normal and tangential stresses of the underground polymer pipeline. 4, and the normal voltage is considered at the ends of the pipeline x=0 and x=20 m. In this case, the voltage fluctuations coincide with the phase of the seismic load. Fig. 4, c, d shows the change in the tangential voltage over time at the pinched ends and along the axis of the pipeline at a given time t=18.44 s. Along the pipeline at a fixed time, the normal stresses, as shown in Fig. 5, at the pinched ends have maximum values.}

a	b
c	d
Figure. 5. Change in the values of Q12, N of the underground pipeline in time at specified points and along the pipeline at a fixed time t at α=30^0

_{The variation of the shearing force and the longitudinal force over time at a fixed time along the pipeline axis is shown in Figure. 5. The shearing force (Figure. 5, b) and the longitudinal force (Figure. 5, d) at the pinched ends have their maximum values}