بررسی عوامل موثر در تحلیل دینامیکی پی واقع بر محیط متخلخل اشباع تحت اثر ارتعاشات افقی و پیچشی با استفاده از روش مدل مخروطی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده مهندسی عمران و محیط زیست، دانشگاه صنعتی شیراز، شیراز، ایران

2 دانشکده مهندسی عمران، واحد شهرکرد، دانشگاه آزاد اسلامی، شهرکرد، ایران

3 دانشکده مهندسی عمران، واحد شهرکرد، دانشگاه آزاد اسلامی، شهرکرد، ایران دانشکده مهندسی و معماری، دانشگاه تریسته، تریسته، ایتالیا

چکیده

تحلیل لرزه ای پی های ماشین آلات واقع بر روی محیط ها ی متخلخل اشباع می ­تواند با روش های متعددی انجام شود. برخی از این روش ها مانند روش اجزای مرزی، روش اجزای محدود پیچیده و روش اجزای محدود مرزی مقیاس شده بسیار دقیق هستند.  برخی روش ها، مانند روش مدل مخروطی، روش ساده و کاربردی اما با دقت مناسب و قابل قبول می باشند. در این مدل توده خاک با مخروط هایی ناقص مدل می­ گردد و انتشار امواج در این مخروط ها تا زمانی که موج به اندازه کافی میرا شود و و اثر آن در پاسخ پی تاثیر قابل اغماضی داشته باشد، دنبال می شود. در این پژوهش کاربرد روش مدل مخروطی در تعیین سختی دینامیکی با لحاظ نمودن اثر آب حفره ای (رویکرد دو فازی)، برای شرایط مختلف خاک زیر پی بررسی شده است. برای به دست آوردن سیستم معادلات دیفرانسیل حاکم بر ارتعاشات افقی و پیچشی در یک محیط متخلخل با در نظر گرفتن اثر اتساع خاک، بررسی دقیقی انجام شده است. همچنین اثر پارامترهای مختلف از جمله ضخامت لایه، پوکی، ضریب نفوذپذیری بر پاسخ پی تحت ارتعاشات برشی و پیچشی بررسی شده است. نتایج بدست آمده از این تحقیق نشان می‌دهد که فرمول‌های مدل مخروطی می‌توانند سطح خوبی از دقت و راندمان محاسباتی بالا را برای پیش‌بینی ارتعاشات افقی و پیچشی فونداسیون های واقع بر محیط متخلخل اشباع ارائه دهند. همچنین محیط­ دو فازی نسبت به محیط یک فازی میرایی قابل ملاحظه­ ای در فرکانس­ های پایین از خود نشان می ­دهد و این در حالی است که برای بستر سنگی عمیق­، تفاوت زیادی برای میرایی به چشم نمی­ خورد. علاوه بر این، هر چه ضخامت لایه بیشتر باشد عملکرد آن نزدیکتر به حالتی است که پی واقع بر روی یک نیم فضا است و چنانچه ضخامت لایه‌ی اول تقریبا بیشتر از 20 برابر شعاع دیسک باشد می‌توان محیط را با دقت خوبی مانند یک نیم­ فضا، صرف نظر از سایر لایه­ ها، تحلیل نمود. همچنین، با افزایش ضریب نفوذپذیری لایه، تأثیر این پارامتر در تحلیل علی الخصوص در فرکانس های کوچکتر، افزایش می­ یابد و کاهش ضریب نفوذپذیری منجر به افزایش میرایی می‌گردد. بخش دیگری از نتایج بدست آمده از این تحقیق نشان می دهد که پارامتر پوکی در ضرایب سختی افقی و پیچشی تاثیر بسیار ناچیزی دارد هر چند که حساسیت تحلیل دینامیکی به پوکی برای فرکانس­ های بالای بار متناوب قائم قابل ملاحظه است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Investigating the effective factors on the dynamic analysis of foundations located on saturated porous medium under the effect of horizontal and torsional vibrations using the cone model method

نویسندگان [English]

  • Fatemeh Hajari 1
  • Hossein Rahnema 1
  • saohrab mirassi 2
  • Mohammad Momeni 3
1 Department of Civil and Environmental Engineering, Shiraz University of Technology, Shiraz, Iran
2 Dept. of Civil Engineering, Islamic Azad University, Shahrekord Branch- Lordegan Center, Shahrekord, Iran
3 1- Department of Civil and Environmental Engineering, Shiraz University of Technology, Shiraz, Iran Department of Engineering and Architecture, University of Trieste, Trieste, Italy
چکیده [English]

Seismic analysis of machine foundations located on saturated porous media can be carried out with several methods. Some of these methods are very accurate such as the boundary element method, complex finite element method, and scaled boundary finite element method. Other methods, such as the cone model method, is not only simple and practical but also have appropriate and acceptable accuracy. In the cone model, the soil mass is modeled with incomplete cones and the propagation of waves in these cones is followed until the wave is sufficiently damped and its effect on the foundation response is negligible. In this research study, the application of the cone model method in determining the dynamic stiffness, taking into account the effect of pore water (two-phase approach), has been investigated for different soil conditions. The system of differential equations governing horizontal and torsional vibrations in a porous medium is obtained by considering the effect of soil dilatancy. Also, the effect of different parameters such as layer thickness, porosity, and permeability coefficient has been investigated on the foundation’s response under shear and torsional vibrations. The obtained results show that the cone model can provide a good level of accuracy and high computational efficiency for predicting the horizontal and torsional vibrations of foundations resting on saturated porous media. Also, the two-phase environment shows considerable attenuation in low frequencies compared to the one-phase one, and in the case of deep rock bed, there is no significant difference in attenuation. In addition, the greater the thickness of the layer, the closer its performance is to the case where the foundation is based on a half-space, and if the thickness of the first layer is more than 20 times the radius of the disk, the environment can be accurately described as a half-space regardless of other layers. Also, with the increase of the permeability coefficient of the layer, the influence of this parameter in the analysis increases, especially in smaller frequencies, and the decrease of the permeability coefficient leads to an increase in damping. Another part of the results obtained from this research shows that the porosity parameter has a very small effect on the horizontal and torsional stiffness coefficients, although the sensitivity of the dynamic analysis to porosity is significant for high frequencies of vertical alternating load.

کلیدواژه‌ها [English]

  • Cone model
  • wave propagation
  • dynamic analysis of foundations
  • horizontal and torsional vibrations
  • saturated porous medium

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نشریه مهندسی عمران امیرکبیر
دوره 55، شماره 5
مرداد 1402
صفحه 1057-1080

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