اثر ضخامت جداره بر اندرکنش جانبی لوله فولادی مدفون و خاک ماسه‌ای متراکم در گسلش امتداد‌لغز

تحلیل تنش‌های ناشی از زلزله و بررسی اثرات ناشی از فشار خاک بر لوله‌های مدفون از چالش‌برانگیزترین مباحث مطرح در طرح لرزه‌ای شریان‌های حیاتی می‌باشد. خطوط لوله مدفون سازه‌های طویل مستقر در محیط نیمه‌بی‌نهایت خاک محسوب شده و به‌صورت تیرهایی بر بستر فنرهای معادل خاک شبیه‌سازی می‌شوند. مشخصات فنرهای بستر نیز از روابط آئین‌نامه‌ای (مانند asce1984 و ala2001) تعیین می‌شوند. مشخصات فنرهای معادل خاک لوله در آئین‌نامه‌ها فقط تابع قطر لوله و مشخصات خاک است. تحقیقات متعدد نشان داده است که اندرکنش خاک لوله تابع عوامل دیگری مانند ضخامت جداره لوله، جنس مصالح لوله و شرایط بارگذاری نیز می‌باشد. در این تحقیق ابتدا دو آزمایش بزرگ‌مقیاس روی لوله‌های فولادی پیوسته مدفون در خاک ماسه‌ای متراکم به انجام رسید. شبیه‌سازی‌های اجزای محدود با استفاده از داده‌های آزمایشگاهی به‌دست‌آمده، راستی‌آزمایی گردید. در ادامه یک بانک اطلاعاتی مشتمل بر 24 شبیه‌سازی اجزای محدود از لوله‌های مدفون ایجاد شد. نتایج مدل‌های عددی به نرم‌افزار bpsios وارد شد تا مشخصات فنرهای اندرکنشی خاک لوله محاسبه گردد. با در نظر گرفتن اثر ضخامت جداره لوله، رابطه جدیدی برای اندرکنش خاک ماسه‌ای متراکم و لوله فولادی در شرایط گسلش امتدادلغز ارائه شد. نتایج نشان داد که نیروی اندرکنش خاک و لوله و سختی‌های اولیه و ثانویه فنرهای اندرکنشی به‌شدت متاثر از ضخامت جداره لوله می‌باشند.

assessment of the effects of pipe’s wall thickness on lateral steel pipe-dense sandy soil interaction subjected to strike-slip faulting

seismic stress analysis and investigation of soil’s lateral pressure on buried pipelines are among the challenging subjects in the seismic design of lifelines. buried pipelines are considered as long structures buried in a semiinfinite medium of soil and be modeled as beams on spring support of the soil, in a conventional technique. the specifications of the support springs were determined using the codes’ relations (such as asce 1984 and ala2001 guidelines). the specifications of pipesoil equivalent springs are presented as a function of the diameter of the pipe and soil’s mechanical properties. numerous researches were shown that the pipesoil interaction is highly dependent on other factors; such as the wall thickness of the pipe, material type of the pipe, and the loading condition as well. in this research, in the first step, two fullscale tests on steel continuous pipes buried in dense sandy soil were done. a computer program (bpsios) was developed in matlab and abaqus to generate the specifications of pipesoil interaction springs through an optimization algorithm. bpsios determined the forcedisplacement relation for the pipesoil equivalent springs so that the deformed shapes of the pipe were matched with its real values for any given base displacement. the experimental data were analyzed by bpsios to present a comparison with the code’s results. the numerical models were validated and verified using the experimental data in the second part of the study. the finite element simulations were employed to develop a numerical database. the database included twentyfour nonlinear 3d shellsolid finite element models. they were constructed and analyzed in abaqus. the database consisted of steel buried pipes with four diameters (in the range of 100 to 400 mm) and sixlevel of wall thickness (from d/t = 11 to 48). the pipes were widely used in supply lines in natural gas distribution networks. the results of the models were fed into bpsios software to determine the specifications of pipesoil interaction springs. considering the wall thickness of the pipe, a new relation was established for lateral pipesoil interaction of dense sandy soil and steel pipes in place of a strikeslip fault. the sensitivity and 3d regression analyses were done, using matlab curvefitting toolbox, to develop a new form of relations for pipe soil interaction. the sensitivity analyses showed that the wall thickness of the pipe had a great level of effect on the exerted lateral force on the pipe. the results of the numerical models, made by bpsios, show that the asce1984 presented results are only valid in the case of small pipes with d/t = 48. however, the ala2001 guideline presents greater values of the interaction forces, which are closer to the results for moderate pipes. the proposed pipesoil relation is dependent on the diameter and wall thickness of the pipe and exclusively specified for the material properties of the steel pipe, dense sandy soil, and strikeslip loading condition. it was found that the wall thickness of the pipe had a great effect on the initial and secondary stiffnesses of the pipesoil equivalent springs. however, the yield displacements were found in the previously presented values for most of the cases.