ارزیابی پارامتریک دوران و جابه‌جایی دیوار حائل وزنی در زمان زلزله

پیش‌بینی میزان جابه‌جایی و دوران دیوارهای حائل در زمان زلزله همواره یکی از مراحل مهم در طراحی لرزه‌ای و یا طراحی بر اساس عملکرد در دیوارهای حائل وزنی محسوب می شود. در این مقاله تلاش شده است به روش عددی عملکرد لرزه ای دیوار حائل وزنی تحت بار هارمونیک در شرایط فرکانس تشدید و برای عوامل مختلف و تاثیرگذار مورد بررسی قرار گیرد. متغیرهای مورد بررسی در این تحقیق خاک بستر، خاک‌ریز، هندسه دیوار، شتاب ارتعاش و فرکانس ارتعاش می‌باشند. خاک بستر مطابق با آیین‌نامه 2800 شامل خاک نوع یک تا چهار، خاک‌ریز پشت دیوار شامل سه نوع خاک دانه‌ای، هندسه دیوار شامل دیوار 3 و 6 متری و همچنین باری ارتعاشی از نوع هارمونیک سینوسی و در فرکانس اساسی سیستم (مود اول ارتعاش) مورد مطالعه قرار گرفته است تا جابه‌جایی لرزه‌ای بالا و پایین دیوار و متناظر با آن دوران تعیین شود. با انجام مدل‌سازی مختلف جابه‌جایی لرزه‌ای و ماندگار دیوار حائل وزنی مورد ارزیابی پارامتریک قرار گرفته است. نتایج حاصل از این تحقیق نشان می دهد جابه‌جایی لرزه‌ای و ماندگار دیوار در فرکانس اساسی با ارتفاع دیوار و شتاب زلزله نسبت مستقیم دارد اما با مشخصات مکانیکی و سختی خاک‌ریز پشت دیوار و شتاب متناظر گسیختگی خاک‌ریز نسبت معکوس دارد.

Parametric Evaluation of the Rotation and Displacement of the Gravity Retaining Wall during the Earthquake

The retaining wall is a wall that creates a lateral support for vertically or vertically oriented walls for the soil. Simplicity of construction and ease of use are the features of the use of gravity retaining walls. The prediction of the displacement and rotation caused by the earthquake is an important point in the seismic design of the gravity retaining walls. Excessive displacement does not only damage the walls itself, but also causes irreparable damage to adjacent retaining walls. The forces imposed on the wall by the earthquake depend on factors such as the behavior of the soil under the wall, the behavior of the embankment, the flexural behavior and the wall’s inertia, and the nature of the entrance movements. One of the techniques for wall design is a powerbased method and a performancebased method. In this paper, using the ABAQUS / CAE finite element software, the seismic performance of the gravity retaining wall is evaluated under harmonic load. Four types of subsoil according with the 2800 regulations and three types of backfill (sand behind the wall) are used. Two types of wall are 3 and 6 meters under sinusoidal load at the fundamental frequency of each model and the effect of backfill, subsoil and height of the wall on the top displacement, bottom displacement and rotation were investigated. The results of this research show that as the soil around the wall is denser, the wall displacement decreases. The amount of displacement increases with increasing wall height. The higher the density of the soil in the site, the lower the maximum vertical stress on the wall. By changing the soil profile and increasing soil bed density, the mean value of the average maximum absorbed acceleration increases. Mechanical properties of the embankment such as density, internal friction and hardness, effect on the average maximum acceleration and maximum vertical stress. With increasing dynamic loading; the average maximum acceleration is increased. Under the basic vibration of the wall, the height and dimensions do not have any effect in maximum absorbed acceleration. By increasing the wall height, the vertical stress decreases. The result of this research show that dimension and physical characteristics of retaining wall and soil properties of embankment have effect on absorbed maximum acceleration and the maximum vertical wall stress in different conditions of seismic acceleration by numerical method. The numerical models were analyzed for sinusoidal harmonic loading at the fundamental frequency of the model (natural frequency of the first mode). The results of this research are summarized as follows. By increasing the wall height, the vertical stresses generated in the model are reduced. The increase in wall height does not have a significant effect on the average maximum absorbed acceleration. With increasing soil density around the wall (backfill and foundation) due to the increased hardness of the soil, the wall shows a good resistance to the forces involved and creates a lower stress in the wall. increasing the density of soil around the wall (backfill and foundation), followed by increasing density and hardness, the average maximum acceleration absorbed by the part of the backfill that is in contact with the back of the wall increases.