ارزیابی لرزه‌ای پل‌های بتن مسلح مورب تحت اثر زلزله‌های نزدیک گسل، با درنظرگیری اندرکنش خاک و سازه - مطالعه موردی روگذر جَک تُن واقع در کالیفرنیا

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه مهندسی عمران، واحد علوم و تحقیقات، دانشگاه آزاد اسلامی، تهران، ایران

چکیده

رفتار لرزه‌ای پل‌های مورب به عنوان ستون اصلی شبکه‌های حمل و نقل مدرن در بسیاری از شهرها، در مقایسه با پل‌های مستقیم متداول به خوبی بررسی نشده است. با مطالعه زلزله‌های گذشته می‌توان دریافت که این پل‌ها تخریبات گسترده‌ای را به دلیل چرخش عرشه و به دنبال آن بلندشدگی شاه‌تیرها تحت اثرات پیچشی حاصل از ترکیب پاسخ‌های لرزه‌ای در راستای طولی و عرضی تجربه کرده که این اثر با خردشدگی موضعی بتن عرشه ناشی از کوبش دهانه‌های مجاور به دیوار پشتی کوله‌ قابل تشدید است. از طرفی عموماً پل‌ها بر روی فونداسیونی از نوع شمع‌های طویل درجاریز واقع در حفره از پیش حفاری شده به همراه سرشمع، مستقر می‌شوند. رفتار غیرالاستیک روسازه در طول زمین‌لرزه به دلیل اثر شرایط خاک نگهدارنده بر سختی زیرسازه قویاً به مقاومت خاک بستر متکی می‌باشد. لذا هدف اصلی این مطالعه ارزیابی حساسیت پاسخ لرزه‌ای روگذرهای بتن مسلح مورب نسبت به تغییرات برخی از پارامترهای سازه‌ای، به کمک مدل‌های تحلیلی قادر به دریافت رفتار غیرخطی خاکریز-کوله و خاک- شمع تحت اثر حرکات نزدیک گسل زمین با پالس‌های قوی سرعت، مقایسه نتایج حاصل با شرایط پایه صلب و نهایتاً دریافت مناسب‌ترین شاخص شدّت حرکت زمین می‌باشد. لذا مجموعه‌ای از آنالیزهای تاریخچه زمانی غیرخطی با استفاده از هفت رکورد پالس‌گونه شدید و سه مؤلفه‌ای (دو مؤلفه افقی و یک مؤلفه قائم) بر روی پل موربی واقع در کالیفرنیا، دارای دو دهانه، پایه‌ای تک ستونه و کوله‌هایی نشیمن‌دار انجام گرفته و به کمک نتایج حاصل، اثر زاویه تورب، نحوه مدل‌سازی شرایط انتهایی و مقاومت خاک محل ساختگاه بر تقاضاهای گوناگون ارزیابی شد. به منظور بررسی اثرات مقاومت خاک بر هر یک از تقاضاها، خصوصیات مصالح خاک رُسی از محدوده نرم تا سخت و خاک ماسه‌ای از محدوده سست تا متراکم تغییر یافت. دریافت گردید که اکثر تقاضاها حتی با وجود تغییر نوع و مقاومت خاک، به افزایش در زاویه تورب کوله به عنوان عامل سخت‌تر شدن سازه، حساس بوده و اغلب روندی افزایشی را با افزایش این زاویه طی می‌نمایند. در این میان تقاضای چرخشی عرشه به نحو چشمگیری تحت تأثیر تغییرات زاویه تورب قرار گرفته در حالی که در نظرگیری انعطاف‌پذیری فونداسیون به کمک مجموعه‌ای از فنرهای غیرخطی در مدل‌سازی‌ها خصوصاً با به کارگیری روش مستقیم مبنی بر مدل‌سازی کامل اجزاء سازه و بخش وسیعی از خاک محصور شده اطراف آن، عمدتاً منجر به بهبود پاسخ‌های لرزه‌ای نسبت به پایه صلب گردید.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Seismic Assessment of Reinforced Concrete Skewed Bridges under Near-Fault Ground Motions with Considering Soil-Structure Interaction- Case Study of Jack Tone Road On-Ramp Overcrossing Located in California

نویسندگان [English]

  • Hanieh Soltani
  • Fereshteh Emami
  • Pasha Javadi
Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
چکیده [English]

Seismic behavior of skewed bridges, the backbone of modern transportation networks, has not been well studied compared to their ordinary straight counterparts. Investigating past earthquakes, it can be evident that such bridges have experienced intensive damages specially due to girder unseating under the torsional effects of seismic responses coupling in longitudinal and transverse directions, which will be aggravated by local crushing of deck concrete due to pounding between the abutments and adjacent spans. Additionally, bridges are usually supported on Cast-In-Drilled-Hole extended pile-shafts. The inelastic behavior of the superstructure during an earthquake is profoundly dependant on soil strength due to the effect of surrounding soil properties on substructure stiffness. So, the main purpose of the present research is to evaluate the seismic responses of R.C skewed overcrossing to variations in some structural parameters by applying analytical models capturing backfill-abutment and soil-pile nonlinearities under near-fault ground motions with high-velocity pulses, especially in their strike-normal component, comparing the results with fixed-base model and finally obtain the most efficient ground motion intensity measure. A set of nonlinear time history analyses was conducted using seven pulse-like ground motions containing horizontal and vertical components on a two-span skewed bridge. Then, the effects of abutment skew angle, base condition modeling approach and soil strength on the revision of various demands were assessed and compared for both flexible- and rigid-base conditions. Furthermore, various analyses were carried out with respect to possible changes in soil properties ranging from soft to stiff for clayey and loose to dense for sandy soils besides the skew angle variations. It was observed that most of the demands, despite the changes in soil strength, were sensitive to an increase in abutment skew angle as a factor of structural stiffness and will often increase incrementally with that, but deck rotation was significantly affected by these variations. Considering foundation flexibility by a set of nonlinear springs can refine structural responses in most cases, particularly by applying Direct Method, based on precise modeling of structural components besides a vast region of encompassed soil around, which will impose an improving effect on various demands relative to the fixed-base condition.

کلیدواژه‌ها [English]

  • Skewed bridges
  • Skew angle
  • Soil-structure interaction
  • Near-fault ground motions
  • Rigid base

مراجع

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نشریه مهندسی عمران امیرکبیر
دوره 53، شماره 10
دی 1400
صفحه 4433-4458

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