فهرست مطالب

مهندسی عمران مدرس - سال هجدهم شماره 3 (مرداد و شهریور 1397)
  • سال هجدهم شماره 3 (مرداد و شهریور 1397)
  • تاریخ انتشار: 1397/06/07
  • تعداد عناوین: 19
|
  • سید اسحاق افتاد*، سیروس ارشادی، مجتبی صانعی صفحات 1-11
    یدر این مطالعه، میدان جریان روی سرریز اوجی در شرایط قوس محوری به کمک نرم افزار FLOW-3D شبیه سازی شد. آشفتگی میدان جریان با استفاده از مدل های آشفتگی استاندارد و RNG شبیه سازی شد. همچنین تغییرات سطح آزاد جریان به وسیله طرح VOF بازسازی گردید. در مدل عددی، دیواره های متقارن جانبی سرریز در سه حالت مختلف 60، 90 و 120 درجه به ترتیب برای دبی های 34، 34 و6/22 لیتر بر ثانیه مورد بررسی قرار گرفته است. همچنین، تاثیرات تغیر زاویه دیواره های جانبی سرریز اوجی و عدد فرود جریان بر روی مشخصات میدان جریان مورد بررسی قرار گرفت. بر اساس نتایج مدل سازی، مدل عددی مقادیر آزمایشگاهی را با دقت قابل قبولی پیش بینی نمود. به عنوان مثال، مقادیر درصد خطای نسبی نیم رخ های طولی سطح آزاد جریان برای مدل های سرریز اوجی 120، 90 و 60 درجه در شرایط قوس محوری به ترتیب برابر 83/12، 60/13 و 48/3 محاسبه شد. همچنین دراثر اندرکنش جریان و بدنه قوسی شکل سرریز، جریان فوق بحرانی موجی شکل می گیرد که به آن جریان بالی شکل یا دم خروسی می گویند که با افزایش زاویه همگرایی قوس محوری، ارتفاع پدیده دم خروسی به شکل قابل ملاحظه ای افزایش یافت و در مقابل با کاهش زاویه مذکور ارتفاع این پدیده کاهش یافت. از طرفی با افزایش عدد فرود جریان پای سرریز، ارتفاع پدیده دم خروسی با کاهش همراه شد.
    کلیدواژگان: سریز اوجی، قوس محوری، مدل سازی
  • محمد افرازی، محمود یزدانی*، مهتاب علی طالش، احمدعلی فخیمی صفحات 13-24
    آزمون برش مستقیم یکی از قدیمی ترین آزمون ها برای اندازه گیری مقاومت برشی خاک است. عوامل بسیار زیادی می تواند بر نتایج حاصل از این آزمایش تاثیرگذار باشد. به دلیل اینکه روش های آزمایشگاهی زمان بر و سخت هستند استفاده از روش های عددی در بررسی عوامل موثر بر نتایج آزمایش برش مستقیم می تواند مناسب و کارآمد باشد. در این مقاله با استفاده از برنامه اجزاء محدود – اجزاء مجزا CA2، آزمایش برش مستقیم خاک شبیه سازی شده و تاثیر عوامل مختلف در نتایج آزمایش مورد بررسی قرار گرفته است. با استفاده از این برنامه عددی، خاک توسط روش اجزا مجزا و جعبه برش با استفاده از روش اجزا محدود مدل سازی شده است. در این مطالعه، اثرات اندازه جعبه برش مستقیم، فشار تشکیل نمونه، تنش سربار، سرعت برش و اصطکاک جداره بر نتایج حاصل از آزمایش برش مستقیم مورد بررسی قرار گرفته است. نتایج این تحقیق نشان می دهد که با افزایش ابعاد جعبه برش، مقاومت کاهش می یابد در حالیکه با افزایش سربار، فشار تشکیل و سرعت برش مقاومت نمونه افزایش نشان می دهد. همچنین در صورتیکه تغییر حجم قابل توجهی در نمونه طی برش خوردن ایجاد نگردد، اصطکاک دیواره های جعبه برش تاثیر قابل توجهی بر مقاومت نمونه ندارد.
    کلیدواژگان: آزمایش برش مستقیم خاک، مدل سازی عددی، روش اجزا محدود، روش اجزا مجزا، آزمایش های آزمایشگاهی
  • میثم امیدعلیزاده، جواد شایان فر، مهدی نعمت زاده * صفحات 25-35
    سازه های بتنی طراحی شده بر اساس آیین نامه های بتنی قدیم عموما بدون ملاحظات لرزه ای موجود در آیین نامه های جدید طراحی شده اند و با توجه به نتایج آزمایشگاهی و مستندات حاصل از زلزله های گذشته در اعضای سازه های مذکور، اینگونه حاصل می شود که چنین سازه هایی در برابر زلزله عملکرد لرزه ای ضعیفی داشته و آسیب پذیر می باشند. به منظور مقاوم سازی چنین سازه هایی باید ارزیابی لرزه ای با قابلیت اتکای مناسب صورت گیرد و سپس با شناخت نوع رفتار اعضا (خمشی، خمشی-برشی و برشی) ، محل تشکیل مفاصل پلاستیک، نوع شکست و غیره، نقاط ضعف سازه ی مورد نظر را شناسایی کرده و با اتخاذ یک روش مقاوم سازی مناسب به رفع آن پرداخت. در این مقاله، برای مقاوم سازی با سیستم ژاکت بتنی و در نظر گرفتن آثار آن روی رفتار غیرخطی اعضا و متعاقبا سازه های بتنی، مدلی غیرخطی ارائه شده است. با درستی آزمایی و هماهنگی مناسب این مدل با نتایج آزمایشگاهی، قابلیت اتکا به مدل پیشنهادی اثبات می شود. در انتها، به منظور بررسی عملکرد سازه های بتنی قبل و بعد از مقاوم سازی با سیستم ژاکت بتنی، یک قاب بتنی طراحی شده توسط آیین نامه های قدیمی که در آن جزئیات لرزه ای در نظر گرفته نشده، توسط سیستم ژاکت بتنی مقاوم سازی شده است. پارامترهایی نظیر رابطه ی بار-تغییرمکان، عملکرد لرزه ای و الگوی خرابی مطابق با نقطه ی عملکرد و بیشینه تغییرشکل جانبی قبل و بعد از مقاوم سازی مورد بررسی و ارزیابی قرار گرفته است که نتایج حاصل از تحلیل های استاتیکی غیرخطی (پوش آور) ، تاثیر سیستم مقاوم سازی مذکور در بهبود رفتار سازه در تمامی ترم های یاد شده را اثبات می کنند.
    کلیدواژگان: قاب های بتن مسلح، ژاکت بتنی، تحلیل غیرخطی، مقاوم سازی لرزه ای
  • سجاد براری*، شهاب عباسی، مهدی مهدوی عادلی مهدوی عادلی، مهدی چینی صفحات 37-47
    افزایش مقاومت فشاری به بیش از 50 مگاپاسکال، کیفیت و دوام بتن جزء اهداف مهم سند چشم انداز بتن 1404 است. همواره تولید بتن با مقاومت زیاد نیازمند توجه خاص در طرح اختلاط اجزاء، استفاده از مواد مناسب، لزوم بهینه سازی مصرف سیمان و ترکیب مصالح تشکیل دهنده ی آن بوده است. در این مقاله، نمونه های مکعبی بتنی طوری تهیه شده اند که 5 متغیر موثر شامل سه نوع متفاوت منحنی های دانه بندی درشت دانه و ریزدانه، 3 نوع ابر روان کننده، میکروسیلیس با نسبت های 5، 7 و 12 درصد وزنی سیمان در دو رده ی مقاومتی مختلف با عیار سیمان متفاوت، تاثیر عیار سیمان بصورت 375، 400 و 425 کیلو گرم بر متر مکعب با نسبت آب به سیمان ثابت و تاثیر افزودن فیلر بر مشخصات مکانیکی، دوام و اقتصاد طرح بطور کامل بررسی شده است. در این آزمایش ها نسبت آب به سیمان برای مقایسه نتایج، ثابت در نظر گرفته شده است. نتایج نشان می دهند که متغیرهای درنظر گرفته شده بر مقاومت فشاری بتن های پرمقاومت بسیار تاثیر گذار بوده و استفاده از حالات بهینه ی طرح های فوق می تواند سبب بهبود مشخصات مکانیکی بتن شوند به گونه ای که با بهینه سازی اجزاء مورد استفاده می توان با عیار سیمانی 400 کیلوگرم در متر مکعب، به ساخت بتن های بسیار توانمند با رویکردی اقتصادی دست یافت.
    کلیدواژگان: بتن پرمقاومت، دانه بندی مصالح سنگی، فوق روان کننده، میکروسیلیس، مقاومت فشاری
  • مهدی خداپرست*، امیر حسین جعفری صفحات 49-59
    ضریب عکس العمل بستر یکی از پارامترهای مهم در طراحی سازه های عمرانی است. این پارامتر جز مشخصات ذاتی خاک نبوده و به عوامل متعددی بستگی دارد. یکی از عواملی که کمتر به آن پرداخته شده است عمق قرارگیری پی است. در این پژوهش با استفاده از روش عددی تاثیر عمق قرارگیری پی بر مقدار ضریب عکس العمل بستر بررسی شده است. برای این منظور نتایج 4 آزمایش بارگذاری صفحه که روی خاک های ماسه ای شهر قم و در عمق های مختلف انجام شده، استفاده شده است. نتایج حاصل از مدل سازی عددی در این پژوهش نشان دهنده تاثیر قابل توجه عمق قرارگیری پی بر مقدار ضریب عکس العمل بستر و افزایش این ضریب نسبت به عمق است. همچنین در ادامه به مقایسه نتایج حاصل از مدل سازی عددی با دو رابطه ترزاقی و باولز پرداخته شده است. بر این اساس در پی های با عرض کوچک تر از 5 متر، رابطه ترزاقی مقادیر کمتر و در پی های با عرض بیشتر از 5 متر، مقادیر بزرگ تری از مدل عددی ارائه می کند و در رابطه باولز تا عمق 5 متری از سطح زمین هماهنگی خوبی با نتایج حاصل از مدل عددی مشاهده شده است. در نهایت با استفاده از داده های به دست آمده، رابطه ای تجربی برای خاک های ماسه ای مورد بررسی ارائه می شود
    کلیدواژگان: ضریب عکس العمل بستر، خاک ماسه ای، عمق قرارگیری پی، مدل سازی عددی
  • سید مرتضی دهقان منشادی، علی خجسته *، شهریار ناطق، محمد رحیمیان صفحات 61-71
    وجود ترک در محیط های مختلف امری دور از انتظار نیست، از سویی دیگر توسعه روز افزون مواد کامپوزیتی توجه به اندرکنش ترک با محیط های ناهمسانگرد را دوچندان کرده است. همچنین ایجاد و گسترش ترک در جامدات یکی از عوامل مهمی است که برای جلوگیری از آثار مخرب ترک روی محیط باید مورد بررسی قرار گیرد. با توجه به این موضوع که ترک ممکن است در معرض مودهای مختلف شکست قرار بگیرد، بررسی ترک تحت شرایط مرزی مختلف، کمک شایانی به پیش بینی رفتار محیط دارای ترک می کند. در این پژوهش به صورت تحلیلی مودهای مختلف شکست (بازشدگی، برشی و پارگی) ترک سکه ای واقع در لایه ایزوتروپ جانبی بررسی شده است. در هر مود با نوشتن شرایط مرزی حاکم بر مساله و جایگذاری آن ها در معادلات حاکم بر محیط و تغییر متغیرهای مناسب، شرایط مرزی به معادلات انتگرالی دوگانه تبدیل می شود. در نهایت با حل معادلات انتگرالی دوگانه، مسائل مورد بررسی هر کدام به یک معادله فردهلم نوع دوم که تابعی از شعاع ترک، ضخامت لایه و خواص محیط است، منتهی می شوند که به علت پیچیدگی، این معادلات دارای جواب تحلیلی نیست. در نتیجه با به کارگیری روش عددی مناسب معادلات حل شده و ضریب شدت تنش نوک ترک سکه ای برای مودهای مختلف حاصل می شود، نتایج شدت تنش برای مصالح مختلف ایزوتروپ جانبی بر حسب نسبت ضخامت لایه به شعاع ترک سکه ای به دست آمدند. نتایج نشان‍دهنده آن هستند که ناهمسانی محیط تاثیر قابل توجهی روی ضرایب شدت تنش می گذارد و اینکه همواره با افزایش ضخامت لایه به شعاع ترک ضریب شدت تنش در مودهای مختلف افزایش و این مقدار در ضخامت های زیاد مستقل از نوع مصالح محیط به ضریب شدت تنش محیط بی‍نهایت میل پیدا می کند.
    کلیدواژگان: ترک سکه ای، ایزوتروپ جانبی، معادله فردهلم، ضریب شدت تنش
  • مریم رویین، علی اکبر آقاکوچک* صفحات 73-85
    از جمله مهم ترین اهداف طراحی و ساخت قاب های خمشی فولادی، داشتن قابلیت اتلاف انرژی زیاد بر اثر جاری شدن و تغییر شکل های پلاستیک در تیرها می باشد؛ به طوری که ایجاد مفصل های پلاستیک در تیرها بر ستون ها پیشی گیرد و بدین ترتیب شرط تیر ضعیف-ستون قوی محقق گردد. در سازه های ساختمانی متشکل از قاب های خمشی فولادی در بسیاری از موارد از دال های بتنی برای ایجاد دیافراگم های کف استفاده می شود که اکثرا با استفاده از برشگیر ها به تیر های قاب متصل می باشند. لیکن در آیین نامه ها و از جمله مبحث دهم مقررات ملی ساختمان ایران، نحوه ی در نظر گرفتن اثرات حضور این دال ها بر رفتار اتصال و کنترل رابطه ی تیر ضعیف-ستون قوی به صراحت روشن نشده است. در تحقیق حاضر تاثیر حضور دال بتنی کف طبقات بر رفتار اتصالات قاب بررسی گردیده است. بررسی تاثیر تعداد و نیز فاصله ی آغاز چیدمان برشگیرها از بر ستون در محدوده ی ثابتی از طول تیر، از دیگر موارد مطالعه شده می باشد. از نرم افزار آباکوس برای مدل سازی اجزای محدود نمونه های عددی در فضای سه بعدی استفاده گردیده است. پس از راستی آزمایی نتایج حاصل از تحلیل عددی مدل ها با نتایج آزمایشگاهی، پارامترهای مدنظر مورد بررسی قرار گرفته است. نتایج حاصل از مطالعات عددی نشان دادند که در نظر نگرفتن اثر حضور دال برای کنترل شرط تیر ضعیف-ستون قوی مبحث دهم از مقررات ملی ساختمان ایران ممکن است طراحی را دچار خطا نماید؛ به طوری که افزایش مقاومت خمشی تیرهای مختلط نسبت به تیرهای فولادی ساده، می تواند تا جایی پیش رود که عملا مفصل پلاستیک به جای تیر (ادامه دارد)
    کلیدواژگان: تیر مختلط، قاب خمشی فولادی، مدل سازی اجزای محدود، رفتار چرخه ای و یکنوا، تیر با مقطع کاهش یافته
  • بهروز عسگریان، معصومه سلطانی* صفحات 87-99
    در تحقیق پیش رو، یک تکنیک عددی جدید جهت تحلیل پایداری ستون غیرمنشوری از جنس مواد مدرج تابعی ارائه گردیده است. خواص مواد در راستای ضخامت تیر ثابت در نظر گرفته شده است، درحالی که در راستای طولی به صورت پیوسته و تدریجی و طبق قانون توانی تغییر می کند. همچنین به علت تفاوت ناچیز ضریب پواسون مصالح سازنده تیر، مقدار آن در طول عضو ثابت در نظر گرفته شده است. در مرحله نخست به منظور بررسی رفتار پایداری و ارتعاش آزاد این اعضا، معادله حرکت حاکم بر ارتعاش آزاد تیرهای غیرمنشوری با مقطع متغیر نمایی با استفاده از ترکیب بسط مک لورن و روش سری های توانی حل می گردد. درنتیجه، فرم تقریبی تغییر شکل ارتعاشی تیر به صورت یک چند جمله ای متناهی به دست می آید و با جایگذاری شرایط مرزی حاکم بر تیر و با استفاده از روش حل مقادیر ویژه مقدار فرکانس طبیعی ارتعاشی محاسبه می گردد. در ادامه به کمک اصل حداقل انرژی پتانسیل و با توجه به تشابه فرم تغییر شکل اعضای الاستیک تحت تحلیل پایداری و ارتعاش آزاد، مقدار بار کمانش بحرانی تعیین می گردد. در پایان جهت اعتبار سنجی، نتایج عددی حاصل از تحلیل پایداری و ارتعاش آزاد برای اعضای ساخته شده از مواد همگن و یا تابعی ارائه شده و تاثیر تغییرات سطح مقطع، توان ماده تابعی و نوع تکیه گاه بر بار کمانش بحرانی و فرکانس طبیعی ارتعاش مورد بررسی قرار گرفته است. در تمامی مسائل، کارآمدی، دقت و صحت روش عددی ارائه شده به اثبات رسیده است.
    کلیدواژگان: اعضای غیرمنشوری، ماده مدرج تابعی، سری توانی، اصل حداقل انرژی پتانسیل
  • سید شاکر هاشمی*، روح الله خسروی، علیرضا فیوض صفحات 101-111
    خرابی پیش رونده معمولا به گسترش یک آسیب موضعی اولیه در درون سازه که مانند یک واکنش شیمیایی زنجیره ای منجر به فروپاشی جزئی و یا کلی سازه می شود، گفته می شود. به منظور جلوگیری یا کاهش خرابی پیش رونده، راهبردهای متنوعی برای طراحی در برابر گسیختگی پیش رونده در اسناد دولتی آمریکا مانند UFC و GSAارائه شده است. در این پژوهش با استفاده از تحلیل غیرخطی پوش عمودی روی ساختمان های بتنی با سیستم دال حبابی، به بررسی عملکرد سازه پس از حذف ستون در موقعیت های متفاوت و تاثیر آن در پتانسیل ایجاد خرابی های پیش رونده پرداخته شده است. نتایج به دست آمده نشان می دهد که با افزایش تعداد طبقه عملکرد سازه های دارای دال حبابدار در برابر خرابی پیش رونده ضعیف تر شده و بهترین عملکرد را سازه های میان مرتبه از خود نشان می دهند. همچنین با افزایش نسبت طول دهانه به ارتفاع طبقه، مقاومت ساختمان ها در برابر خرابی پیش رونده کاهش می یابد. بیشترین خرابی بوجود آمده در دال حبابی برابر 25 درصد مساحت کف و در سناریوی حذف ستون میانی است که در محدوده مجاز بوده و منجر به خرابی پیش رونده نشده است. همچنین نتایج نشان می دهد در دهانه های بزرگ دال حبابی عملکرد خوبی داشته در برابر خرابی پیش رونده داشته و مسیر جایگزین لازم را برای اضافه بار ایجاد شده فراهم می کند.
    کلیدواژگان: خرابی پیش رونده، دال حبابی، تحلیل ایستایی غیرخطی، مسیر جایگزین بار
  • محمد کاظم شربتدار*، آزاده حقیقت، نعمت الله حیدریان صفحات 113-127
    قاب های مختلط خمشی بتنی - فولادی، به دلیل بهره مندی از مزایای بتن و فولاد به طور همزمان، منجر به بهبود رفتار سازه های بلند گردیده است. در طی 30 سال اخیر، به دلیل صرفه اقتصادی، مطالعات متعددی در زمینه قاب های مختلط صورت گرفته است. تجربیات نشان داده است که مهم ترین مسئله در چنین قاب هایی، اتصالات این قاب ها است. در این مقاله، به بررسی تحلیلی رفتار قاب های خمشی مختلط یک طبقه - یک دهانه و چهار و هفت و ده طبقه چهار دهانه، تحت بارگذاری جانبی پوش اور به صورت کنترل تغییرمکان، به روش اجزای محدود توسط نرم افزار سایزمو استراکچر پرداخته شده است. قاب های مختلط مورد بررسی از نوعی اتصال مرکب پیشنهادی با ستون بتنی عبوری و تیر فلزی متصل، تشکیل شده اند که نمونه این اتصال بصورت آزمایشگاهی توسط مولفین ساخته و آزمایش شده است، نتایج حاکی از عملکرد مناسب قاب های خمشی مختلط متشکل از اتصال مورد اشاره می باشد. در این بررسی جابه جایی کل قاب و دریفت نسبی طبقات در قاب های با تعداد طبقات زیاد، نسبت به قاب های بتنی متداول کاهش یافته است. همچنین مرکب سازی اتصالات در قاب های مختلط منجر به افزایش ظرفیت باربری، شکل پذیری و سختی اولیه و جذب انرژی قاب نسبت به قاب بتنی، به ترتیب به میزان 55%، 45%، 62% و 116% شده است.
    کلیدواژگان: قاب های مختلط، اتصال پیشنهادی، ظرفیت باربری، شکل پذیری، سختی
  • علی صدرممتازی*، اویس قدوسیان صفحات 129-139
    بتن خودتراکم بتنی است که نیاز به ویبره ندارد و می تواند در قالب های پیچیده و در شرایطی که تراکم بتن به سختی قابل انجام است، به سهولت مورد استفاده قرار گیرد. لذا این بتن گزینه ای مناسب برای تعمیر و تقویت انواع سازه های بتنی است. برخی اجزاء سازه ها مانند عرشه پل ها در معرض عوامل مخرب و فرآیند یخبندان و ذوب مکرر قرار دارند. به همین دلیل بررسی تاثیر موارد مختلف بر کیفیت لایه تعمیری خودتراکم، چسبندگی آن به بتن بستر و دوام آن در برابر عوامل مخرب بسیار حائز اهمیت می باشد. در این مطالعه به بررسی تاثیر حجم خمیره و نسبت آب به مصالح سیمانی و مقدار الیاف پلی پروپیلن به ویژگی های رئولوژیکی، سخت شده و چسبندگی بتن خودتراکم الیافی تعمیری به بتن بستر و دوام چسبندگی بتن لایه تعمیری و بتن بستر در برابر چرخه ه های یخبندان و ذوب پرداخته شده است. نتایج نشان داد که الیاف پلی پروپیلن خواص رئولوژیکی بتن خودتراکم را تحت تاثیر قرار داده و تاثیر منفی بر آن می گذارند. ضمن اینکه برخی ویژگی های حالت سخت شده مانند مقاومت کششی و جمع شدگی را بهبود می بخشند. با وجود بهبود چسبندگی دو لایه با افزودن الیاف، دوام این چسبندگی در برابر چرخه های یخبندان و ذوب کاهش می یابد. افزایش نسبت آب به مصالح سیمانی و حجم خمیره نیز تاثیر منفی بر چسبندگی بین دو لایه می گذارند.
    کلیدواژگان: بتن خودتراکم الیافی تعمیری، چسبندگی، چرخه یخ زدگی و ذوب، حجم خمیره، نسبت آب به مصالح سیمانی
  • مرتضی عراقی*، حسین نوفرستی صفحات 141-151
    در مقاله با رویکرد ارائه روش های تثبیت خاک در پروژه های راه سازی به کاوش و مرور در متون و تحقیقات انجام شده، مطالعات زمین شناسی، بررسی وضعیت شیمیایی و شوری خاک به همراه انجام آزمایشهای مربوطه، تجزیه وتحلیل اطلاعات و ارائه نتایج مطالعات تئوریک، میدانی و آزمایشگاهی پرداخته شده است. جهت کاربردی کردن نتایج از محور کویری خور – عرب آباد به عنوان محور منتخب استفاده شده است. در آزمایش های شیمیایی وضعیت اولیه نمونه ها مشخص شد که اکثرا در رده خاک شور قرار میگیرند. برای مطالعه خصوصیات فیزیکی خاک تعداد 7 ایستگاه نمونه برداری انتخاب گردید. آزمایشهای انجام شده شامل آزمایش دانه بندی مصاالح، تراکم، نسبت باربری کالیفرنیا (CBR) و تورم بود. گزینه های تثبیت خاک شامل آهک، سرباره کلوخه ای و سرباره دانه ای ، باطله اکسید منیزیم و باطله مس بودند. برای تعیین بهینه آهک، نمونه هایی با 2، 5 و 10 درصد آهک تهیه گردید. سه ترکیب افزودنی آهک 5 درصد، منیزیت ریزدانه 5 درصد به همراه 2 درصد آهک، و باطله مس 5 درصد بهترین عملکرد را ازلحاظ افزایش CBR، یکنواختی تاثیر بر روی نمونه ها، و تورم نمونه های عمل آوری شده 7 روزه از خود نشان دادند. دلیل دیگر این بود که سه ماده افزودنی درحالی که عملکرد بهتر یا مشابهی نسبت به سرباره های آهن نشان دادند. در رابطه با منیزیت ریزدانه نیز این نگرانی وجود دارد که در درازمدت باعث تشکیل کانی تورم زای سولفات منیزیم (MgSO4) در خاک شود. بنابراین استفاده از دو ماده افزودنی آهک 5 درصد یا باطله مس 5 درصد بیشتر توصیه می گردد.
    کلیدواژگان: تثبیت خاک، آزمایشهای شیمیایی- فیزیکی? مکانیکی، خاک شور با سولفات زیاد، محور خور- عرب آباد
  • میلاد عقیلی لطف، امیر محمد رمضانیانپور * صفحات 153-167
    در سالیان اخیر ایده بازیافت نخاله های بتنی و استفاده مجدد از آن به عنوان مصالح سنگدانه‏ای (سنگدانه بازیافتی بتنی) در تولید بتن گسترش فراونی یافته است. در این بین یکی از موارد مهم در زمینه کاربرد سازه‏ای بتن‏های بازیافتی، امکان استفاده از روابط همبستگی بین پارامترهای مختلف فیزیکی و مکانیکی مانند روابط بین مقاومت فشاری و مقاومت کششی برای بتن‏های بازیافتی است. از آنجایی که ساختار بتن‏ بازیافتی تفاوت زیادی با ساختار بتن‏ معمولی دارد، پس کاربرد روابط متداول برای بتن‏ معمولی که در استانداردهای طراحی سازه های بتن مسلح منتشر شده است، برای بتن بازیافتی باید بررسی شود، که در این پژوهش به این موضوع پرداخته شده است. برای این منظور 18 طرح اختلاط با درنظرگیری کاربرد دو نوع مختلف شن بازیافتی بتنی، کاربرد با هم شن و ماسه بازیافتی بتنی و همچنین کاربرد مواد جایگزین سیمان طراحی و ساخته شد. در ادامه، نتایج این پژوهش با روابط منتشر شده توسط سایر پژوهشگران در این زمینه و همچنین روابط معمول برای بتن‏های فاقد سنگدانه بازیافتی بتنی نیز مقایسه شد. نتایج نشان داد که روابط به‏دست آمده در این پژوهش با روابط مشابه برای بتن‏های معمولی تفاوت قابل ملاحظه‏ای دارد. به صورتی که هر دو رابطه بین مقاومت فشاری با مقاومت کششی یا مقاومت خمشی، تخمین به مراتب بیشتری نسبت به رابطه ACI 318 و سایر روابط همبستگی موجود ارائه می‏دهند. علت این تفاوت را می‏توان پراکندگی بازه تغییر کیفیت سنگدانه های بازیافتی بتنی دانست.
    کلیدواژگان: سنگدانه بازیافتی بتنی، همبستگی، پوزولان، بتن بازیافتی، مقاومت مکانیکی
  • سید محمد علی زمردیان*، حمیده غفاری صفحات 169-179
    از دلایل اصلی تخریب پل ها آبشستگی موضعی اطراف پایه می باشد که با گذشت زمان و عدم کنترل آن پایداری سازه را به مخاطره می اندازد. تاکنون محققین بسیاری آبشستگی موضعی اطراف پایه های پل را موردبررسی قرار داده اند و روش های مناسبی در جهت کنترل و کاهش آبشستگی ارائه داده اند که شامل روش های اصلاح الگوی جریان در این نواحی و همچنین روش های مقاوم سازی بستر می باشد. در این پژوهش به بررسی آبشستگی موضعی پایه پل در خاک های چسبنده پرداخته شده است و استفاده از خاک چسبنده رسی از نوع رس بنتونیت به صورت اختلاط با خاک بستر، به عنوان راهکاری در جهت مقاوم سازی بستر در برابر تنش های واردشده و کنترل آبشستگی مورد بررسی قرارگرفته است. اهداف دنبال شده در این پژوهش شامل تعیین بهترین شرایط تراکمی (میزان رطوبت و درجه تراکم) ، میزان بهینه رس مورد استفاده و همچنین تاثیر مقاومت برشی بستر در میزان آبشستگی می باشد. نتایج نشان داد که استفاده از 10 درصد رس بنتونیت به صورت اختلاط با خاک ماسه ای بستر در درجه تراکم 90 درصد و رطوبت بهینه تراکم، باعث کاهش آبشستگی به میزان 100 درصد نسبت به نمونه شاهد می شود. همچنین نتایج نشان داد که رس بنتونیت تاثیر بیشتری در کاهش آبشستگی نسبت به رس کائولین دارد.
    کلیدواژگان: آبشستگی موضعی، پایه پل، خاک چسبنده، بنتونیت، کائولین
  • فرهود کلاته* صفحات 181-194
    در مقاله حاضر مدل عددی جهت بررسی و تعیین توزیع فشار هیدرودینامیکی در مخزن سد در اثر تحریک ناشی از زمین لرزه ارائه شده است. با توجه به تعدد پارامترهای موثر در نحوه تغییرات توزیع فشار هیدرودینامیک در این تحقیق سعی شده با استفاده از روش حجم محدود به شیوه حل صریح, امکان بررسی عدم تقارن شکل مخزن در توزیع فشارهیدرودینامیک لحاظ گردد. بدین منظور از المان های چهارضلعی با الگوی سلول مرکزی استفاده شد و با توجه به تغییرات ناچیز فشار هیدرودینامیک در امتداد عرض مخزن با استفاده رابطه لایب نیتز با متوسط گیری در این امتداد, معادله دیفرانسیل دو بعدی حاکم در صفحه مرکزی مخزن با ارضاء شرایط مرزی حل گردید. امکان جذب امواج فشاری توسط رسوبات کف مخزن و دیواره های جانبی و تاثیرآن بر توزیع فشارهیدرودینامیک در شرایط مرزی مورد استفاده منظور شده و همچنین شرط مرزی نسبتا" دقیق برای مرز جذبی انتهای مخزن اعمال گردید.
    کلیدواژگان: فشار هیدرودینامیک، روش حجم محدود، اندرکنش سد مخزن، سد بتنی وزنی، شرط مرزی دور دست مخزن
  • مهدیه کلانتری، ابوالفضل اکبرپور*، محسن خطیبی نیا صفحات 195-206
    جریان آب زیرزمینی توسط مدل آب زیرزمینی به وسیله مجموعه ای از معادلات حاکم که بیانگر فرآیندهای فیزیکی رخ داده در سیستم هستند، شبیه سازی می شود. در این مدل ها برای کل سیستم، یک معادله دیفرانسیل در نظر گرفته می شود و توسط روش های عددی متعددی همچون تفاضل محدود، روش اجزای محدود و روش بدون مش حل می گردد. در این تحقیق معادله جریان آب زیرزمینی در شرایط ماندگار در آبخوان آزاد مورد مطالعه قرار گرفت. برای حل این معادله از روش ایزوژئومتریک بر اساس توابع پایه نربز (NURBS) و بی اسپلاین استفاده شد. این روش برای آبخوان دشت بیرجند حل و سطح آب زیرزمینی محاسبه و ترسیم شد. نتایج نشان داد استفاده از این روش حجم محاسبات را به طور چشمگیری کاهش و دقت آن به دلیل استفاده از توابع پایه نربز محاسبه شده بر اساس هندسه دقیق، بالا است، به طوری که میانگین خطای نسبی و خطای جذر میانگین مربعات به ترتیب 000256/0 و 459/0 متر بدست آمد.
    کلیدواژگان: شرایط ماندگار، آبخوان آزاد، روش ایزوژئومتریک، توابع پایه نربز، بیاسپلاین
  • حسین کلهر، حسین گنجی دوست*، بیتا آیتی صفحات 207-220
    در این تحقیق عملکرد گیاه وتیور Chrysopogon zizanioides و نخل مرداب Cyperus alternifolius در حذف همزمان شوری و بارآلی با پنج کیفیت فاضلاب مختلف با شوری به ترتیب (dS/m 0، 5/2، 5، 5/7 و 10) ، COD به ترتیب (mg/L 0، 75، 150، 225 و 300) و آب خالص به عنوان شاهد بررسی شد. نتایج نشان داد که هر دو گیاه در راکتورهای با شوری کمتر عملکرد بهتری به لحاظ رشد و حذف شوری و بارآلی از خود نشان دادند. نشانه های مسمومیت شوری شامل سوختگی و پلاسیدگی در برگ ها در گیاه های وتیور و نخل مرداب به ترتیب در شوری بالاتر از dS/m 5/7 و 5 مشاهده شد. میزان کاهش شوری در تیمارهای مختلف برای گیاه وتیور، متفاوت و از 53 الی 4 درصد متغیر بود. میزان کاهش بار آلی نیز در تیمارهای گوناگون از 60 الی 12 درصد مشاهده شد. برای گیاه نخل مرداب میزان کاهش شوری و بار آلی در تیمارهای مختلف به ترتیب از 29 الی 1 درصد و 49 الی 5 درصد متغیر بود. آزمون مقایسه T مستقل نشان داد که افزایش شوری بر مشخصه های مورفولوژیک هر دو گیاه در بازه اطمینان 95 درصد به صورت معنی داری تاثیر گذار است. همچنین برازش رگرسیون تعمیم یافته نشان داد که وجود بارآلی روی مشخصات مورفولوژیکی گیاهان تاثیر قابل توجهی ندارد و تنها میزان شوری فاضلاب کنترل کننده مشخصات رشدی گیاه می باشد.
    کلیدواژگان: گیاه پالایی، تحلیل آماری، وتیور، نخل مرداب
  • غلامرضا قدرتی امیری*، بهنود گنجوی، ابوالفضل غلامرضاتبار صفحات 221-236
    در این پژوهش توزیع تغییرمکان نسبی طبقات در قابهای خمشی فولادی طراحی شده بر اساس روش طراحی پلاستیک مبتنی بر عملکرد، تحت رکوردهای قوی مورد مطالعه قرار می گیرد. روش طراحی پلاستیک مبتنی بر عملکرد بر دو اصل جابجایی نسبی هدف و مکانیزم تسلیم از پیش تعیین شده استوار است. روش طراحی مذکور بر اساس تئوری طراحی پلاستیک شکل گرفته و مقدار برش پایه طراحی با استفاده از اصل بقای انرژی استخراج می گردد. همچنین ابعاد اعضا بر اساس روش طراحی پلاستیک مبتنی بر یک الگوی تسلیم از پیش تعیین شده مشخص می شوند. در این راستا قاب های خمشی فولادی 4، 8، 12 و 16 طبقه ی طراحی شده به روش پلاستیک به کمک نرم افزار OpenSees مدلسازی شده و در حالات بدون اثر اندرکنش خاک- سازه و با احتساب اثر اندرکنش تحت رکورد قرار گرفته اند. بر اساس تحلیل های دینامیکی غیرخطی پارامتریک در حالت شکل پذیری ثابت، مقادیر تغییرمکان نسبی طبقات تعیین و مورد مطالعه قرار گرفتند. همچنین پارامترهای موثر بر توزیع خسارات و نیز کارآمدی الگوهای بارگذاری جانبی مختلف مورد ارزیابی گرفتند. در این مطالعه اثرات اندرکنش خاک- سازه بر توزیع تغییرمکان نسبی و تاثیر آن بر توزیع خسارات، بصورت پارامتریک بررسی شده است. نتایج حاکی از آن است که اثرات اندرکنش خاک- سازه بطور عمده بر پاسخ غیر ارتجاعی سازه موثر بوده و به شدت اندرکنش وابسته می باشد. نتایج همچنین بیانگر آن است که پارامترهایی مانند پریود اصلی سازه (T) ، شکل پذیری (μ) نیز سبب تغییر توزیع تغییرمکان نسبی قاب ها می گردد.
    کلیدواژگان: تغییرمکان نسبی طبقات، طراحی پلاستیک مبتنی بر عملکرد، اندرکنش خاک و سازه، مکانیزم تسلیم
  • ماندانا ناجی ابهری*، مرضیه ایرانشاهی، مسعود قدسیان صفحات 237-249
    جریان های گل آلود عامل عمده و مهم انتقال رسوبات بداخل مخازن سدها، دریاها و اقیانوس ها می باشند. شناخت دینامیک این جریان ها به منظور پروسه های رسوبگذاری و فرسایش بسیار مهم و اساسی می باشد. در این تحقیق تاثیرات حضور دو مانع بر ساختار حرکت جریان گل آلود به صورت آزمایشگاهی مورد بحث و بررسی قرار خواهد گرفت. پروفیل های سرعت و غلظت جریان در شرایط شبه پایا با استفاده از دستگاه سرعت سنج صوتی Vectrino در بالادست مانع اول، فضای بین دو مانع و پایین دست مانع دوم اندازه گیری شده و با پروفیل های سرعت و غلظت در حالت بدون مانع مقایسه شده اند. مقادیر دبی در واحد عرض جریان و نرخ انتقال بار معلق بر اساس مقادیر سرعت و غلظت اندازه گیری شده، محاسبه شده اند. تاثیر تغییرات عدد فرود چگالی ورودی بر دبی جریان عبوری در واحد عرض و نرخ انتقال بار معلق بررسی شده است. نتایج نشان می دهد احداث موانع در مسیر جریان سبب شکل گیری نواحی جدید در پروفیل های سرعت خواهد شد و باعث می شود یک حوضچه آرام کننده جریان در بالادست مانع اول و فضای بین دو مانع شکل گیرد و محیط مناسب برای ته نشینی ذرات فراهم گردد. روند تغییرات نرخ انتقال بار معلق و دبی جریان عبوری در واحد عرض تابعی از موقعیت نسبی موانع هستند. بگونه ای که روند تغییرات این پارامترها با تغییرات عدد فرود چگالی ورودی در بالادست مانع اول متناسب و در فاصله بین دو مانع و پایین دست مانع دوم معکوس خواهد بود.
    کلیدواژگان: جریان گل آلود، موانع، عدد فرود چگالی ورودی، دبی جریان عبوری در واحد عرض، نرخ انتقال بار معلق
|
  • Sehagh Oftad *, Cyrus Ershadi Pages 1-11
    Weirs are one of the common structures for regulating and measuring of flow. Also, this structures with different forms such as normal weir, side weir and ogee spillway are widely used for various purposes. In some cases, due to practical restrictions the ogee spillways with curvature in plan are designed. An ogee spillway is located at the top of the reservoir of dam. Dams may also have bottom outlets with valves or gates which may be operated to release flood, and a few dams lack overflow spillways and rely entirely on bottom outlets. In such situations study of flow distribution over the ogee spillway and other related parameters, might be important. In this study, the flow field over thw ogee spillways in axial arc condition was simulated by FLOW-3D software. In the FLOW-3D model, the Navier-Stokes and continuity equations were discretized using the finite difference method. The computational domain was divided into a mesh of rectangular cells. All variables (except for velocity values) were placed at the center of the computational cells (staggered grid arrangement). To solve the governing equations, control volumes were defined around each dependent variable. The surface fluxes, body forces and surface stresses were computed in terms of surrounding variables. Most terms in the governing equations were explicitly evaluated. To solve the flow field of a non-compressible fluid, the continuity and the Navier-Stocks equations were solved. On the other hand, to validate the numerical results, the experimental measurements that were performed in Soil Conservation and Watershed Management Research Institute at reservoir with dimensions 1.4 m length, 0.30 m width and 0.18 m height. The experimental model was made of plexiglas plates which was a model of prototype at the scale of 1:75. Moreover, to measure the flow discharge, a sharp triangular weir with apex angle of 90˚ in the output of channel was used. The flow field turbulence was modeled using the standard and the RNG turbulence model. According to numerical model results, the RNG turbulence model had more accuracy than the standard turbulence model. Also, variations of flow free surface were reconstructed by volume of fluid (VOF) scheme. In this numerical model, the effects of the side symmetrical walls of ogee spillway were examined for cases 60o, 90o and 120o in discharges 34, 34 and 22.6 lit/s, respectively. The applied boundary conditions were chosen according to the physical model. Therefore, the depth and discharge specific values were for inlet boundary condition. At the outlet boundary of the model, the outlet boundary condition was used. All the solid walls of the model were defined as the “Wall” boundary conditions. Also, a symmetry plane was determined at the top layer of the computation field. According to numerical results, the acceptable agreement was obtained between numerical results and experimental measurements. For example, the relative error percent of longitudinal profiles of flow free surface were calculated 12.83, 13.60 and 3.48 percentage for cases 120o, 90o and 60o, respectively. Also with increasing angle of axial arc, the height of rooster tail increased significantly. In addition, by increasing Froude number, the height of rooster tail reduced.
    Keywords: FLOW-3D, Ogee spillway, Axis arch, Numerical simulation, FLOW-3D
  • Mohammad Afrazi, Mahmoud Yazdani *, Mahtab Alitalesh, Ahmad Ali Fakhimi Pages 13-24
    Determination of soil engineering properties such as shear strength is essential to analysis many geotechnical problems. Therefore, determination of the reliable values for this parameter is very important. For this purpose, direct shear test as one of the oldest test to examine the shear strength of soils, is conducted on soil samples. There are too many factors which could affect results of direct shear test. Laboratory tests are expensive, difficult and time consuming, hence using numerical method to simulate experimental test and study effective factors could be useful. In this paper direct shear test was numerically modeled using CA2 hybrid finite element-discrete element method code. CA2 solves explicitly equations of motion together with macro or micro-constitutive equations. In this study, shear box is modeled using finite element grids and a discrete element model is implemented for simulation of soil specimen within the box. Appropriate boundary conditions are assigned to the box, normal stress is applied to the specimen using finite element grid and shear velocity was finally applied to the model. Shear force is applied to the model by a constant velocity 4.5×10-9 meter/cycle. It should be noted that, shear velocity is applied to the upper part of shear box, and applied velocity is considered small enough to confirm that there is a quasi-static condition in numerical solution. In this study using numerical simulation, the effects of box dimension, genesis pressure, normal stress, shear velocity and box wall friction on shear strength of the soil specimen are investigated. Study of box dimension effect, shows that peak effective internal friction angle in small direct shear box and large direct shear box differs about 6°, and cohesion decreases by increasing box dimension but for box dimensions bigger than 20cm, changes in box dimension has no significant effect on resulted soil cohesions. Investigation of influence of genesis pressure shows that, incrementing genesis pressure, cohesion increases too, that can be attributed to the SOCPI model provided in CA2. In SOCPI model by increasing genesis pressure the overlap between cylinders increases. In SOCPI model by increasing overlap the cohesion increases but peak friction angel doesn’t change too much. Normal stress analysis shows that, increasing normal stress, interlocking between soil particle increases and more interlocking causes increasing cohesion of the soil model. Shear velocity is another parameter which is studied in this research. Results show that by increasing shear velocity, soil shear strength increases. It should be mentioned that shear velocity should be considered as small enough to result in a quasi-static solution; for velocity smaller than that model run time increases ineffectively. In this research, friction of shear box wall as one of the important parameters in study of soil shear strength is also investigated. When there is friction between box wall and soil particles, shear strength can be underestimated for contractant soils or overestimated for dilatant soils. In this paper, it is shown that if soil has no significant volume changes, peak shear strength is not affected by friction between soil particle and box wall.
    Keywords: Direct Shear Test, Numerical Modeling, Finite Element Method, Discrete Element Method, Experimental tests
  • M. Omidalizadeh, J. Shayanfar, M. Nematzadeh* Pages 25-35
    The vulnerability and poor seismic performance of the columns and beams of old non-seismically designed reinforced concrete (RC) frame structures has been proven time and again, both at laboratory level as well as by natural disasters in real life situations. On the other hand, a vast majority of existing structures designed with non-seismic considerations is not practically viable so that they designed and constructed with improper reinforcement detailing, with no consideration of the principles of the capacity design, inappropriate of the seismic actions, etc. Such structures need to be correctly assessed to predict their seismic performance and retrofitted, if required.
    Therefore, the assessment of seismic behavior of RC frames retrofitted using concrete jacket system would be effective. In order to realistically predict the seismic performance of such structures, providing practical and accurate models to simulate the inelastic behavior of structural members are significantly importance. Evaluation of the response of non-seismically designed RC structures by using such tools would estimate the seismic performance of the structures with high degree of confidence. According to such assessments, an efficient and cost-effective solution can be designed and developed.
    In order to improve the seismic behaviour of old non-seismically designed RC frame structures, numerous retrofitting techniques of structural members have been adopted and studied in practical applications. Among these retrofitting techniques, the application of concrete jacketing has extensively increased. The current study has focused on evaluating the effects of concrete jacketing on flexural behaviour of RC jacketed members and seismic performance of non-seismically designed RC structures through analytical modeling approaches.
    For this purpose, an analytical model including rotational springs in members was developed. The nonlinear characteristics of these springs can be computed using moment – curvature analysis of a RC member before and after retrofitting so that each level of curvature would be converted into rotation based on the first moment-area theorem. Experimental and analytical studies have confirmed that the confinement induced by transverse reinforcements would lead to considerable enhancement in terms of strength and ductility of RC columns and beams. Thus, this effect was taken into account in determining characteristics of stress – strain concrete. On the other hands, it is well known that the response of RC members in terms of ultimate deformation could be influenced when buckling in longitudinal steel bar occurs. Therefore, in this study, a simplified methodology has been developed to take into account this effect as ultimate condition in the calculation of the moment – curvature analysis of a RC jacketed member.
    In order to prove the reliability of the proposed model, it has been validated against experiments conducted by other researchers in the literature. The results showed that the proposed model can be successfully predicted the response of columns retrofitted by RC jacketing. Moreover, the application of the developed model to assess and retrofit RC structures has been demonstrated by a case study and using pushover analysis. The response of structures in terms of initial stiffness, strength, ductility and damage patterns corresponding to performance point and ultimate displacement indicated that the seismic behaviour and performance level of the retrofitted structure were significantly improved in comparison with the original structure.
    Keywords: RC frames, concrete jacket, nonlinear analysis, seismic retrofitting
  • S. Barari*, S. Abbasi, M. M. Adeli, M. Chini Pages 37-47
    The most important aims in Concrete-1404 are compressive strength more than 50 Mpa, quality and durability. These items seems to ignore before that in Iran. The high strength concrete production always needs to use suitable materials, attention to mix design, optimizing cement percentage and other component in concrete. For reaching to a trustable mix designs and aspects of high strength concrete, it needs to be evaluated by a complete investigation which can provide all three aspects of strength, workability and durability of a 1404-concrete. In this paper, cubic concrete samples are made in a way which is affected by 5 variables. These 5 Effective ranges are included: 1) Three different types of coarse and fine aggregate gradation curves which are made of finnest through roughest grading of aggregates according to ASTM C33. 2) Three types of high water reducers used in exact same mix design to compare the effects of these 3 different kind of superplasticizers on high strength concrete. These three type are grade F with polycarboxilate-ether based, grade F with sodium naphthalene solphonate based and grade G as a super high water reducer admixture. 3) Effects micro silica with 5, 7 and 12 percentage of total cement amount are added to compare the results on high strength concrete. 360 and 410 kg cement per m3 are used in source concrete mixtures as the regular using amount in practical projects in Iran. 4) The effect of cement content, with fixed w/c and 5% micro silica, which are between 375 through 425 kg/m3. And 5) the effects of adding filler which are thoroughly investigated on mechanical properties, durability and economy plan. There are 20 mix design in 6 groups are prepared with total cementitious materials from 360 to 425 kg/m3. To compare the results, in these experiments the water cement ratio has been fixed to 0.25. The tests used in experiments were compressive strength test by 3000 KN hydraulic compressor and 24 hours water absorption test. The mechanical and durability properties are recognized by these tests. For evaluating fresh concrete properties, slump test was done. Economical aspect is studied and compared by comparing price of materials and content that are used in each mixture. The results show that the variables were impressively affected the compressive strength in high strength concrete. Using optimum conditions of the studied mixture design can improve the mechanical properties of concrete. By optimizing components in mixture design, high strength concrete can be made even with cement content of 400 kg per cubic meter. The 360 and 410 kg cement with adding 5% micro silica showed the best improving in compressive strength. Enhancing cement more than 400 kg results to decrease compressive strength. High water reducers with polycarboxilate ether based show better results in mechanical and fresh concrete properties and also in economical aspect. Adding filler to mixture led to decrease compressive strength and increase durability, however it had no effects on economical properties of high strength concrete. It can be concluded that aggregate grading can still lead to changes in compressive strength, durability and workability of HSC.
    Keywords: HSC, grading of aggregate, superplasticizer, Microsilica, compressive strength
  • M. Khodaparast*, A.H. Jafari Pages 49-59
    Subgrade reaction coefficient is one of the important parameters in the design of structures that for the first time was presented by Winkler (1867). In the Winkler method, in order to evaluate and calculate the vertical displacement of the beam, it is assumed that the deformation at each point of the beam fits with the contact pressure of the reactive bed at that point and for mathematical defining of this ratio, the term ”Subgrade reaction coefficient” was used. After Winkler so many researchers such as Baiot, Terazeghi, Vesic and Bowles have studied on this parameter. Researches show that this parameter is not a constant characteristic of soil and depends on many factors. Factors such as size, shape of foundation, soil type, bending stiffness of soil and foundation, level of under ground water and water content are effective on Subgrade reaction coefficient. One of this factor that less attention has been in prior research is the depth of foundation. In this study by using of numerical method, the effect of the depth of foundation on the amount of Subgrade reaction coefficient was studied. For this purpose the results of 4 samples of plate load test at four depths 10, 12 ,14 and 20 meters and an numerical models that consider the depth of foundation placement have been used. Plate load tests have been conducted on sandy soils of Qom city. Numerical model was done by PLAXIS 2D V8.2 software and hardening soil behavior model was used for sandy soil. The results of numerical model in this study show significant effect of the depth of foundation on the value of Subgrade reaction coefficient and that by increasing the depth, this coficient is increased and changes in foundations with smaller dimention is more and with increasing the dimention of foundation, the percentage of increasing of Subgrade reaction coefficient decreases. The increase in the depth of the foundation from a given value to the next has a small effect on the amount of response coefficient, and almost immediately afterwards, the coefficient of reaction of the bed has reached a constant. In the following, results of numerical model is compared with two formula of Terzaghi and Bowles. For the comparing with Terzaghi formula, the results of plate load test is used and for different width of foundation this amount was calculated and compared with results of numerical model. Tezaghi formula for sandy soils first presents smaller amount and then larger amount than the numerical model. Based on the results of four studied soils, with the fewer depth of test implimentation, results of Tarzaghi formula and numerical model have adaptation in fewer width of foundation. In depth of 10 to 20 meters of current research, almost in foundation width of 5 meter, the results of numerical model is adapted to Tarzaghi formula. The results of comparing the numerical model with Bowles formula shows, to a definite depth for foundation, there is good adaptation between results of this formula and numerical model and with increasing the depth, the differences between Bowles formula and numerical model increases. Finally by using of all states data and nonlinear regression method and SPSS V20 software, for studied sand soils a proposed formula was presented.
    Keywords: Subgrade reaction coefficient, Sandy soil, Depth of foundation, Numerical model
  • S. M. Dehghan Manshadi, S. Nategh, A. Khojasteh*, M. Rahimian Pages 61-71
    Nowadays fracture behavior composites play an important role in geomechanics engineering. Also, it is common knowledge that all existing structural materials contain different inter- and intra-component defect (cracks, delaminations, etc.). On the other hand, analytical techniques can provide a better physical interpretation of problems. In this paper, by using an analytical approach, effects of the fracture modes (opening, shearing and tearing) on a penny-shaped crack in a layer of transversely isotropic solid has been studied. The layer surfaces are fixed from displacement and the system is loaded symmetrically in each mode. In each mode, by substituting the boundary conditions into the governing equations of the medium, the problem reduced to dual integral equations. With the aid some mathematical methods, the dual integral equations are converted to a Fredholm integral equation which is amenable to numerical solution. These Fredholm integral equations are the functions of the thickness of the layer, the radius of crack and the properties of the layer. To evaluate the effect of anisotropic materials on the stress intensity factors(SIFs), several synthetic types of isotropic and transversely isotropic materials are selected. By employing a numerical method the opening, shearing and tearing SIFs for different ratios of layer thickness are obtained. The results for the opening SIF show that by increasing the the SIF decreases substasinaly. On the other hand, an increase in leads to increments in opening SIF. Also, the results demonstrate that the variation in has a negligible effect on the opening SIF. Moreover, an increasing in leads reductions in SIF. For the shearing SIF, has little effect on the results although by decreasing the the shearing SIF increases. Unlike the , the modulus of the young in the plane ( ) of the isotropy has substantial effect on the shearing SIF. An increase in leads increments in the shearing SIF. Also, by increasing the the SIF increases marginally. In the mode III, the tearing SIF is only the functions of (the shear modulus for the plane normal to the plane of isotropy) and . The results show that by reduction in the tearing SIF increases and by increasing the tearing SIF increases. An important point that can be inferred from the results is that by increasing the ratio of layer thickness to the radius of the penny-shaped crack all of the three SIFs increase, this increase for the lower thicknesses is much more in comparison to the greater thicknesses. Additionally, when the layer thickness gets higher, the stress intensity factors for all the materials tend to a constant coefficient. This means that when the layer thickness gets greater and tends to infinity, the SIFs become independent of the material of the layer
    Keywords: Penny-shapped crack, Transversely isotropic, Fredholm equation, Stress intensity Factor (SIF)
  • Maryam Rooin, Ali Akbar Aghakouchak * Pages 73-85
    Application of composite sections in structures is increasing in recent years. This type of structure utilizes the strength and ductility of steel as well as strength and low cost of concrete. Composite action is developed when the two load carrying structural members such as concrete slab and supporting steel beam are integrally connected and deflect as a single unit. The extent to which composite action is developed depends on the provisions of shear connectors between steel and concrete. The horizontal shear that develops between the concrete slab and the steel beam during loading must be resisted so that the slip will be restrained. A fully composite section will have no slip at the concrete-steel interface. As we know, the shear connectors provide the interaction necessary for the concrete slab and steel beam parallel to the beam. One of the most important objectives in design and construction of steel moment resisting frames, is the ability of high energy dissipation due to yieldings and plastic deformations in beams in such a way that formation of plastic hinges in beams occurs prior to that of the columns. This procedure leads to fulfilling the strong column-weak beam relation. On the other hand in steel frame structures, it is common to use concrete slab in order to construct floor diaphragms. However in design codes, specially National Building Code of Iran, it is not clearly mentioned how to consider the effects of the concrete slab on connection behavior and the strong column-weak beam relation control. In this study, the behavior of bare and composite beams in steel moment frames under monotonic and cyclic loading has been investigated through numerical modeling in ABAQUS finite element software. The requirements of National Building Code of Iran regarding the ratio of bending moment strength of columns to beams ,α, have been studied. In this regard a direct connection with uniform beam section is simulated. Rotation of beams and steel columns in different sections for formation of plastic hinges are considered as a criterion to measure these relations. In order to determine the effect of the number of shear studs (percentages of composite actions) and their location specially in protected zone within a fixed length of the girder, reduced beam sections (RBS) are modeled. The results indicated that decreasing the initial distance of shear studs arrangement from the column face leads to increasing the composite action. Analytical results also showed that the effective width of concrete slab depends on the load transfer and the force distribution. Based on the results of this study, it is suggested that in calculation of strength ratio of girders and columns, the effect of the floor slabs should be taken into account to ensure that the requirement of strong column-weak beam is fulfilled, otherwise column failure may occure before girder failure. It must also be mentioned that the relative strength of columns to girders can affect the panel zone behavior in such a way that different values of α, require different shear strength of panel zone.
    Keywords: composite baem, steel moment resisting frame, cyclic, monotonic behavior, finite element analysis, reduced beam section (RBS)
  • Masoumeh Soltani * Pages 87-99
    Owing to efficiency, rising stability of structures, reduction in structural weight and cost, and the improvements in fabrication process, non-uniform beams are extensively adopted in civil and mechanical structures. Furthermore, the use of functionally graded (FG) materials has been increasing in many mechanical components due to their conspicuous characteristics such as high strength, thermal resistance and optimal distribution of weight. In the present paper, a numerical model combining the power series expansions and the Rayleigh-Ritz method is adopted for stability and free vibration analyses of axially functionally graded (FG) columns with variable cross-section. The main purpose of this paper is calculating the critical buckling loads and natural frequencies concurrently for AFG members with exponentially-varying geometrical properties. For this, a mixed power series expansions and the principle of stationary total potential energy as a first endeavor is presented. In this study, the material properties of the non-prismatic beam including Young’s modulus of elasticity and density of material are assumed to be graded smoothly along the beam axis by a power-law distribution of volume fractions of metal and ceramic. Moreover, the cross-sectional area and moment of inertia vary exponentially over the member’s length. In this regard, the power series approximation is applied to solve the fourth order differential equation of motion, since in the presence of variable cross-section and axially non-homogeneous material, stiffness quantities are not constant. All geometrical and material properties and displacement component are developed based on power series of an identified degree. The natural frequencies of the AFG beam with variable cross-section are derived by imposing the boundary conditions and solving the eigenvalue problem. The explicit expression of vibrational shape function is then derived based on this rigorous numerical method. The vibrational mode shapes of an elastic member are similar to the buckling ones. Therefore, the obtained deflected shapes of the considered non-prismatic beams can be used as deformation shape of member for the linear buckling analysis. The critical buckling load of non-prismatic beam can be then estimated by adopting the principle of stationary total potential energy. According to the steps mentioned above, for measuring the accuracy and competency of the proposed numerical procedure, two numerical examples including axially non-homogeneous and homogeneous column with non-uniform section are represented. Numerical results of the critical buckling loads and natural frequencies for various boundary conditions, different gradient index and cross-section variation are represented. Due to lack of similar research for the stability and free vibration analyses of elastic AFG beams with exponential variation of the cross-sectional area and moment of inertia, outcomes of homogeneous members are compared with the results presented in other available numerical and analytical references and those related to non-prismatic beams with material variation are then reported. The accuracy of the method is then remarked. This method has many positive points consisting of efficiency, accuracy and simplicity contrasted with more complex numerical methods. It has to be noticed that the present numerical method can be applied to determine the critical buckling loads and natural frequencies of axially functionally graded (FG) prismatic beams as well as non-prismatic ones.
    Keywords: Buckling analysis, Axially functionally graded material, Non-uniform members, Power series expansions, Principle of stationary total potential energy
  • S.Sh. Hashemi*, R. Khosravi, A. Fiouz Pages 101-111
    Usually, progressive collapse is defined as the progress of a primary local damage within the structures that, like a chain chemical reaction, causes to partial or total collapse of the structures. Although, many researches on progressive collapse under blast load have been made, it can be seen that rupture aroused in structures during strong earthquake events will not happen suddenly, but because of failure in structural design or performance, the weak elements will destroy easier. Subsequently, energy redistribution will occur that may disconnect the adjacent members. Further, the progressive collapse phenomenon will take place and subsequently cause to collapse all the structures. In the recent years, the incidence of catastrophic events such as September 11 has attracted a lot of attention to the issue of the progressive collapse and lead to be considered in the design of new structures. In order to prevent damages by reducing the progressive collapse, different strategies for designing against the progressive collapse have been presented in the government documents of USA, such as UFC and GSA. Although, many researches have been made on the progressive collapse in recent years, but the structures deck effect on the progressive collapse has not been considered sufficiently.
    Nowadays, due to the increase of the speed of construction and lightweight construction, the usage of new systems has been increased. Among these systems, Bubble Deck system is notable. This structural system functions as a two-way slab and a lightweight structural member. In Bubble Deck system, the plastic spherical hollow core (PSHC) is used instead of the concrete situated in the central zone of the cross sections around the slab’s mid-span, where the shear stress is relatively small, compared to the supports. PSHC creates a hollow space in the slab. The Bubble Deck technology uses spheres, made of recycled industrial plastic, to create air voids, while providing the strength through the arch action.
    The objective of this study is to evaluate the progressive collapse of reinforced concrete structures with Bubble Deck floor system. The behavior of structures, the amount, and the mode of the collapse distribution can be studied by various methods. SAP2000 software is used to model, design and analyze the structures. DoD2013 statement has been selected as the reference criteria, and based on that, all the uploading and collapse measurements has been determined. The equivalent nonlinear shell layered element is used to define the slab sections in numerical modeling. 48 structures with the same plans (3 spans on each direction) were modeled. Moment resisting system is chosen as lateral resisting systems. The models were in 4, 6 and 8 stories. Story height of all structures is 3.5 m, and also three types of span length to story height ratios including 1.5, 2.5 and 3.5 are investigated.
    The results show by increasing the number of floors, the structure’s performance against progressive collapse will decrease and the middle-rise structures (6 stories) have shown the best performance rather than others. Also, by increasing the ratio of span length to floor height, progressive collapse resistance is reduced. The most observed damage in the Bubble Deck floors is less than 25 percent of floor area which affected by progressive collapse in the middle-column removal scenario. This value of damage satisfy DoD2013 targets.
    Keywords: Progressive Collapse, Bubble Deck, Nonlinear Static Analysis, Alternative Path Method
  • Mohammad Sharbatdar * Pages 113-127
    In recent years, composite frames that are consist of reinforced concrete column and steel beam, have been attended by researchers due to their economic efficiency as well as their effect on improving the behavior of tall structures. In such frames, using of concrete in columns, due to the compressive strength of concrete and using of steel in the element of beam, due to high tensile strength of steel, result in reduction of elements section and structure weight and also improving its performance. Previous studies have shown that the most important issue in these frames is their connections. Moment connections of such frames are through-beam-type and through-column-type connections. Details of these connections should be in such a way that prevent the formation of plastic hinge in panel zone, and besides, has adequate ductility. Most studies, so far, have been done on the details of through-beam-type‎ and little researches have been done on the plans of through-column-type connection. Nonetheless, determination of beam-column connection with appropriate seismic performance and also force transmission mechanism is necessary. In this study, amount of the effect of proposed composite connection consist of through-‎reinforced concrete column and attached steel beam with peripheral diaphragms and inter plates, on the improvement of the behavior of composite moment frames than conventional concrete frames has been investigated ‎ that the sample of this connection has been made and tested, laboratorial, by the authors. The survey has been conducted on the amount of displacement and drift of frame’s stories and also on the loading capacity, ductility and energy absorption of frames‎. For this purpose, firstly, a composite frame of one story-one span with the proposed connection has been modeled by two finite elements softwares called Abaqus and ‏SeismoStruct and the displacement control has been analysed under pushover lateral loading, and its results have been compared with the results of reference concrete frame. To ensure of the accuracy of the modeling that has been done, load-displacement curve that is the resultant of the connection model of Abaqus and ‏SeismoStruct, has been compared with experimental results. Then, three concrete frames and three composite moment frames with four, seven and ten stories, with four 5-meters spans, 3 meters in height of each story, that had been selected from the meddle frame of a construction with dimensions of 20 meters by 20 meters in plan, and had been designed for area with high seismic risk, were modeled ‎‏by SeismoStruct software, and were analysed under mentioned loading. The results showed appropriate performance of composite moment frames which are consist of mentioned connection, especially in frames with high number of stories. In this study, the drift of the frame and the relative drift of stories, have been reduced in composite moment frames than conventional concrete frames. Moreover, using the proposed composite connections in composite frames has resulted in the increase of the loading capacity of the frame so that the maximum of force that is tolerated by composite frames with 1,4,7 and 10 stories has been increased, respectively, by 59%, 49%, 67% and 46% than concrete frames. In addition, ductility of composite frames with 1,4,7 and 10 stories has been increased, respectively, by 65%, 50%, 37% and 30% than ‎concrete frames with similar number of stories.‎ The results have indicated the increase in initial and final stiffness of composite frames than concrete frames, in average, by 62% and 10%, respectively. Furthermore, a 116% increase in the energy absorption of composite frames than concrete frames has been observed.
    Keywords: Composite frame, Proposed composite joint, Loading capacity, Ductility, Stiffness
  • Ali Sademomtazi *, Oveys Ghodousian Pages 129-139
    Self-compacting concrete as a type of concrete that has no need to vibration can use for complicated frameworks and in conditions that compaction is hard. So this concrete is an excellent choice for repair and retrofitting of many kinds of concrete structures such as marine structures, bridges and so on. These concrete structures may be under aggressive environmental conditions and harmful agents. One of the most important damages of concrete structures is because of freezing and thawing cycles especially in exposed ones, like bridge’s decks. So, study of effect of different parameters on quality of self-compacting repair layer, its bonding to substrate and its durability under chemical and physical attacks is very important. In this study, effect of paste volume, water to cementitious materials and polypropylene fiber dosages in mix design on rheological, hardened properties and bonding of repair fiber-reinforced self-compacting concrete (FRSCC) to concrete substrate and its durability for freezing and thawing cycles has been assessed. Bonding between FRSCC as a repair layer and concrete substrate had been evaluate using pull-off test. The tests that failed exactly from the bond surface considered as a successful ones, and all tests that failure had been occurred in repair layer or concrete substrate is eliminated from the results. Freezing and thawing test was conducted according to ASTM C666. Both freezing and thawing processes were made in water. To assessment of bonding of FRSCC as a repair layer to concrete substrate, we made 15 cm cubes of substrate layer with compressive strength more than 50 MPa to ensure that the failure doesn’t occur in this layer while pull-off test. After six months (to have concrete substrate without shrinkage),we saw the cubes divided them to 3 pieces. With analyzing of effects of fiber dosages on rheological properties of the mix designs, we found that an increase in fiber percentage that leads to smaller diameter in slump flow test, higher flow time in T50 test, higher time in V-Funnel test, and lower ratio in L-Box test. Also, while compressive strength had no significant changes, tensile strength and modulus of elasticity experienced a big increase through adding polypropylene fibers. Shrinkage of repair layer had a great decrease after adding polypropylene fibers. The optimum dosage of polypropylene fibers for hardened properties of the mix designs was found 0.1% by volume. We can see that because of the positive effect of fibers on decreasing of shrinkage and increasing of tensile strength of repair layers, bonding between the repair layer and concrete substrate increased greatly especially by adding 0.1% polypropylene fibers (by volume). Also, increase of paste volume and water to cementitious materials (summation of cement and micro silica) had negative effect on bonding of repair layer to substrate. That is because of increase of shrinkage of repair layer. Although, adding polypropylene fibers improved bonding of repair layer and substrate in freezing and thawing cycles, we see smaller results for bonding. We defined debonding index (DI) that presents the rate of debonding during freezing and thawing cycles. Higher DI, higher rate of debonding. As we can see, for mixes that containing polypropylene fibers, DI is bigger in comparison with the ones without them.
    Keywords: repair fiber-reinforced self-compacting concrete, bonding, freezing, thawing cycles, paste volume, water to cementitious materials
  • Hossain Noferesti, Morteza Araghi * Pages 141-151
    In this paper, the approach proposed methods for soil stabilization in road construction projects has been explored in the literature. Geological studies, chemical status and soil salinity, along with relevant tests, analyze data and present the results of theoretical studies, field and laboratory tests have been done. As a case study, Khur- Arababad Desert Road (KADR) is used. KADR is located in South Khorasan province, which has a desert climate and the plain- hills are evaluated in terms of topography. The annual average daily traffic volume of the road between 8500 to 9000 has fluctuated. A total of 11 soil samples were taken for studies of soil chemistry. In this context soil samples to determine the texture, pH, Electrical Conductivity (EC), the percentage of lime and plaster were tested. Results showed that most samples are placed in the category of saline soils. Defining what type of soil salinity that the region is facing, to determine the exact concentration of sodium, calcium and magnesium ions in the samples, advanced atomic absorption method was used. The soil is very high sulfate content at all stations. To study the physical and mechanical properties of soil 7 samples were chosen. The experiments included sieve test, the sand equivalent, the determination of specific gravity, determine the plastic limit and liquid limit, proctor compaction, California Bearing Ratio (CBR) and swelling test. The results showed that the use of lime for soil stabilization with respect to the necessary CBR number is quite responsive. It also seems that even in relation to the amount of lime, Lime 2% would suffice, although higher percentages such as 5 percent of lime will obtain more reliable results. The volume changes average with increasing the percentage of lime almost showed an increasing trend. Soil stabilization options including limestone, blast furnace lump slag and Ground-Granulated Blast-Furnace Slag (GGBFS), copper and magnesium oxide tailings. To determine the optimal amount of lime, examples of the 2, 5 and 10 percent of lime was prepared. The addition of four other factors, according to previous studies was 5% and 2% lime was added to half of the samples as a catalyst. Three modes including lime 5%, fine-grained magnetite 5% with lime 2% and copper tailings 5% showed the best performance in terms of increasing the CBR, uniform effect on all the samples, and a little swelling in treated samples in 7 days. Iron slags, especially when they are combined with lime, have demonstrated effective performance to CBR increasing, But this performance fluctuated sharply and not uniform in different sampling stations. Another reason was that the exclusion of iron slags was the economic disadvantage due to the long transport distance. There is also concern regarding the use of fine-grained magnetite that Inflationary in the long run to the formation of the mineral magnesium sulfate (MgSO4) in soil. Copper tailings and lime performance in preventing soil volume changes in processed samples approximately the same and a small amount of swelling has been observed in some samples. Therefore, the use of two additives including lime 5% or copper tailings 5% more is recommended.
    Keywords: Soil stabilization, chemical-physical-mechanical tests, saline soils with high sulfate, Khor-Arababad axis
  • Milad Aghili Lotf, Amir Mohammad Ramezanianpour * Pages 153-167
    In the last few years, increase in construction rate has caused several new challenges, including waste storage problems, environmental pollution problems, excessive mining of natural resources, and shortage in sand and gravels sources. One way to address these problems and reduce the negative environmental impacts is reusing concrete waste as a new material in construction. Concrete waste could be crushed, graded, and used as aggregate, referred to as recycled concrete aggregate (RCA), in producing new concrete. There is a common agreement that recycled aggregate concrete (RAC) has inferior properties compared to natural aggregate. Nevertheless, structural usage of RAC has been growing in the last decade. However, due to different engineering properties of RCAs compared to natural aggregates (NA), it seems that the existing correlations between different mechanical properties for normal concrete cannot be used for RACs. This research focused on this topic with the aim of finding suitable correlations between different parameters such as water absorption coefficient, compressive strength, tensile strength, and flexural strength for RACs. In this research, two different types of coarse recycled concrete aggregates [CRCA-1 and CRCA-2] and one type of fine recycled concrete aggregate [FRCA] were considered. Also, for improving the mechanical properties of RACs, two types of supplementary cementitious materials (SCMs), namely 8% silica fume and 15% zeolite were used. A total of 18 concrete mixes were considered and various physical and mechanical tests were conducted on concrete samples made according to the designated mix designs. Concrete mixes were categorized in two different groups. In the first group, both FRCA and CRCA-1 were used. As for the second group, 11 mixes were considered in order to investigate the effect of SCMs on the mechanical properties of RACs. Correlations between results of water absorption coefficient, compressive strength, tensile strength, and flexural strength were investigated and compared to those for normal concretes. The results showed that substitution of NA with CRCA resulted in inferior mechanical properties of concrete. It is worth to note that FRCA had a more significant impact on the mechanical properties of concrete compared with CRCA-1. Also, utilization of 8% silica fume or 15% zeolite as a SCM had a positive effect on the mechanical properties of RACs, such that mixes containing 30% CRCA-2 and 8% silica fume or 15% zeolite had similar 28-day compressive strength to the reference mix. On the other hand, the results showed that existing correlations for normal concrete cannot be used for RACs due to different behavior of RACs compared to normal concrete. The correlation between 28-day tensile strength and 28-day compressive strength for RACs had a bigger coefficient (0.52) compared to normal concrete (0.49). As well correlation between 28-day flexural strength and 28-day compressive strength for RACs in the chosen range of compressive strength (22-43 MPa) overestimated the flexural strength compared to ACI 318's. On the basis of this research, using the equations proposed by ACI 318 for estimating the mechanical properties of RACs is not recommended, and leads to misleading results.
    Keywords: Recycled concrete aggregate, SCMs, Correlation, Mechanical properties
  • H. Ghaffari, S. M. A. Zomorodian* Pages 169-179
    The main reasons of bridge failure are local scour around the piers. In fact, they will be appeared as a scour hole in the river bed. Moreover, lack of control during the time, local scouring will threaten stability of structure. Therefore, determining of depth and dimension of the scour hole, also finding effective factors on scouring are important. Lots of researchers have studied the local scour around the bridge piers. Actually, they have proposed lots of appropriate techniques to control and to reduce scour around piers and bridge abutments. These proposed approaches are divided into two methods which are altering the flow and bed-armoring. In this research, the local scour around the bridge piers in a cohesive soils have studied. Particularly, the cohesive soils in form of mixture of Bentonite (montmorillonitic clay from 0 to 15%) and bed sediment (fine sand) used. In fact, this approach is a solution to challenge bed-armoring against existence shear stress. As a result, the proposed method will be used for controlling the scour. The experiments were carried out at the hydraulic laboratory of the Water Engineering Department, at Shiraz University, Iran. The laboratory flume was a rectangular cross section with 18 m length, 1.2 m wide and 0.4 m deep. According to channel geometry, the discharge and the depth of flow were determined to be 0.034 m^3⁄( s ) and 13 cm, respectively. In all experiments, the discharge and flow depth were constant. This study focused on the best compaction conditions, optimum clay content and the bed shear strength. The undrained shear strength of the soil was measured using an in situ miniature van shear apparatus. The best compaction conditions including optimum moisture and compaction energy. From standard Proctor test, the optimum initial water content Wopt and the optimum dry density ρdopt was determined. The compaction was expressed as the ratio of dry density ρd to maximum dry density ρdopt of the mixture. Therefore three relative compaction equal to70%, 80% and 90% used. Also, three water content optimum initial water content, optimum initial water content – 3% and optimum initial water content + 3% are used. The results indicate that for smaller clay content (5%) the shape of the scour hole was similar to that in sand sediment and is regular and symmetrical. For clay content equal to10%, scour hole is geometrically much irregular compared to that observed in sand bed and it is observed that a steeper slope of the scour hole in sediment mixture. The slope became steeper whit an increase in relative compaction. In fact, the higher relative compaction and the higher clay content increases shear strength and decreases the maximum scour depth. The samples compacted at optimum water content creates a structure with the most resistant to scour. The erodibility of samples compacted dry of optimum water content is less than samples compacted on the wet side of optimum. The results showed that under conditions which the amount of Bentonite equals at least 10% of dry weight in the mixture (Bentonite and sand sediment), relative compaction equal s to 90% and and water content equals to optimum moisture, simultaneously the local scour reduces by 100% in single pier. In addition, the influence of the compaction and type of clay mineral was investigated. The results show that Bentonite was more effective than Kaolin. If the 15% of dry weight Kaolin clay mixed with bed sand sediment to be used and relative compaction equal to 90% and water ontent equals to optimum moisture, simultaneously, the maximum scour hole was reduced only by 34%.
    Keywords: Local scour, Bridge pier, Incohesive soils, Bentonite, Kaolin
  • Farhoud Kalateh * Pages 181-194
    In the present paper a new numerical simulation method based on finite volume is developed for calculating hydrodynamic pressure distribution in the reservoir of dams during earthquake excitation. An explicit finite volume scheme is applied for discretization of dynamic governs equation. In the proposed method the asymmetry effect of reservoir shape on hydrodynamic pressure distribution can be considered. In the simulation quadrilateral elements with center cell algorithm is used. Because of the negligible changing of hydrodynamic pressure in the cross direction with averaging, the average differential partial equation in central vertical plan of reservoir is solved. The absorption effects of bottom sediment and lateral wall are included in the analysis and an exact far end boundary condition is applied in the truncation boundary. Different approaches to the solution of the coupled field problems exist solution of the entire set of equations as one discretized system, referred to as the monolithic approach. This approach is often inefficient due to its attempt to capture with one discretization methodology the completely different spatial and temporal characteristics of fluid and the structure. The second approach often mentioned is the notion of strong coupling, referring to solvers which might use different discretizations for the fluid and the structure but which employ sub-iteration in each time step to enforce coupling between the fluid and the structure. In these methods, the governing equations for fluid and structure are discretized separately in each of the sub-domains and coupled using a synchronization procedure both in time and in space without sub-iteration. Weakly –coupled schemes have been extensively applied to a variety of different fluid-structure interaction problems of engineering interest in past ten years. wo vital issues when coupling two domains are: the method of data transformation between domains and what information must be transferred. The property of fluid adjacent of a structure such as density and viscosity are also key parameters in the efficiency of a numerical scheme.A dense fluid coupled with a structure cause a strong coupling and required some special technique to overcome corresponding difficulties. Key questions with this approach include properly enforcing boundary conditions at the solid-fluid interface, and accurately transmitting tractions between the solid and fluid. The biggest complaint about the explicit staggered partitioned solution procedure is the typical instability associated with the method,that is generally caused by the time lag between the integration of the fluid and structure equations. In the typical partitioned method, the fluid and the structure equations are integrated in time, and the interface conditions are enforced asynchronously. In the solution of coupled problems using partitioned methods, it is necessary to find a cost-minimization (optimization) compromise between a few passes solution with small time steps and a more iterated solution with larger time steps. This compromise may depend, among other things, in the degree of nonlinearity of the structural problem, which may require equilibrium iterations independently of the interaction effects. From the computational point of view, a one–pass solution with no iteration would be optimal, but stability consideration may prove this impractical.
    Keywords: Hydrodynamic pressure, Finite volume method, Dam-reservoir interaction, Concrete dams, Far End Boundary condition
  • Mahdiye Kalantari, Abolfazl Akbarpour*, Mohsen Khatibinia Pages 195-206
    Solving the governing equations of a system is the most important issues that is always discussed in science and engineering fields. Since there are few equations that have analytical solution, many numerical methods have been proposed for solving the equations that have no analytical solutions. Numerical methods are developed by the advent of computers. Today, with using computers and these methods together, complicated equations in diverse areas can be resolved. Several numerical methods such as finite element method (FEM), finite difference method (FDM) and meshless (MFree) method have been suggested for solving partial differential equations. In this study, Isogeometric analysis method is engaged as a numerical method. Isogeometric analysis was developed by Hughes in 2005 in order to eliminate the gap between the world of finite element analysis and computer modeling. This method uses the same basis functions, in the process of modelling. Isogeometric method provides the possibility of simulation in irregular and complex geometry domains and also removes errors due to the multiple elements. Two variable NURBS basis functions are defined by B-spline basis functions. B-spline basis functions are calculated by the Cox–de Boor recursion. In this study, Birjand aquifer is modeled in two dimensions by the Isogeometric analysis using four-point Gauss integration method. The mentioned aquifer is defined by 1274 points and 836 control elements. After creating the geometry of the aquifer by control points and knot vector, NURBS basis functions and their derivatives were calculated. Then, with using input information, such as hydraulic conductivity coefficients, boundary conditions, precipitation rates and the sources and sinks, water table is computed. In order to allocate hydraulic conductivity coefficients of the aquifer, the domain is divided by the GIS software to multiple homogeneous Thiessen. According to the location of NURBS elements in the aquifer, a value has been assigned to NURBS elements. In Birjand aquifer there are boundary conditions with constant head. For enforcing the boundary conditions, 83 points of control points were defined as fixed head. There are 190 wells in the Birjand aquifer, the Extracted water from the wells were used as the discharge rate in the model. Also, 15 percent of the amount of rainfall was considered as the recharge rate in 2011-2012 period, the value of recharge rate is 0.0000727 m/day based on rain gauges. In order to ensure the accuracy of modeling the results of Isogeometric method is compared with finite difference method solutions and observation data, the relative mean error of Isogeometric method is 0.000256. With using Isogeometric method the consumed time for running the MatLab code is around 400 seconds. In order to evaluate the model, three criteria is calculated. Mean error (ME), mean absolute error (MAE) and root mean square error (RMSE) whose values are 0.09, 0.34, and 0.459 respectively. The values of the error and computation time has shown the power of this method in modeling of groundwater flow. Finally, Birjand aquifer groundwater balance was calculated using the input values, extracted water and water storage in plain. By studying the model balance and actual balance of aquifer and comparing them with each other, it is determined that the change in the volume of the aquifer in the time period considered is close to that of the aquifer, which indicates the accuracy of the model.
    Keywords: Steady Condition, Unconfined aquifer, NURBS Basis Function, B-Spline
  • Hossei Ganjidoust * Pages 207-220
    High salinity wastewater is one of the main environmental issues. Using biological treatment systems to treatment this kind of wastewater is hard due to loss of microorganisms. Phytoremediation is one of the main methods to treat this type of wastewater, which is an environmental friendly and a low cost process. In this research we aim to study operation of two plants, including chrysopogon zizanioides known as Vetiver grass and Cyperus alternifolius know as umbrella, to simultaneous removal of salinity and organic loading. We assume five different combination of wastewater which are called statistical treatments and characterized by different amount of salinity and COD. Statistical treatments contain wastewater with Electrical conductivity 0,2.5,5,7.5,10 (ds/m) and 0,75, 150, 250, 300 (mg/L) COD respectively. Pure water is used as control treatment. Results show that in reactors with low level of salinity, both plants have better operation in removing of salinity and organic loading. For electrical conductivity above 5 and 7.5 ds/m, signs of salinity stress including Chlorosis and withering seen in leaves of both plants. For chrysopogon zizanioides, different statistical treatments results in different removal of organic loading range from of 60 to 12 percent. Salinity removal is ranged from 53 to 4 percent. For Cyperus alternifolius reduction in organic loading and salinity are respectively varied from 49 to 5 and 20 to 1 percent. Results of this study in laboratory scale shows that using phytoremediation method in constructed wetland for different combination of salinity and organic loading results in 17 and 15 percent reduction in salinity and wastewater for each unit of chrysopogon zizanioides and Cyperus alternifolius respectively. By increasing the level of salinity the trend of electrical conductivity is decreased. For the wastewater with 2.5 ds/m electrical conductivity, the most absorbing salinity absorbing is seen for both plants, which is 53 percent for chrysopogon zizanioides and 30 percent for Cyperus alternifolius. Reduction in capability of absorbing salt occurred for both plants due to completeness of salt aggregation capacity of the plant. By increasing the electrical conductivity of wastewater solution, wither and reduction in operation of the plant is seen as well. Increasing the salinity level results in decreasing the trend of organic loading reduction. COD removal for chrysopogon zizanioides is greater than Cyperus alternifolius in all reactors, which is related to natural characteristics of this plant, higher tolerance of salinity fluctuations and different phytoremediation mechanism. In statistical analysis of morphological characteristics of plants, the statistical population is all plants for different combination of wastewater and statistical controls. For each plant, results of different statistical treatments are compared to each other. The null hypothesis for independent tests assumes that the waste water treatment doesn’t have effect on morphological characteristics of the plant. So, rejecting this hypothesis means that all combination of wastewater doesn’t have the same effect on morphological characteristics. This hypothesis is considered separately for each of morphological characteristics by use of two sided independent sample T-test. These characteristics included dry weight, mean leaf area, mean stem diagonal and root volume. Results indicate that increasing salinity will affect the morphological characteristics with 95% confidence. Fitting the generalized linear regression shows that existing of organic loading doesn’t have meaningful effect on morphological characteristics, and level of salinity of wastewater affect the growing characteristics of the plant.
    Keywords: phytoremediation, statistical analysis, chrysopogon zizanioides, Cyperus alternifolius
  • Gholamrezar Ghodrati Amiri *, Behnoud Ganjavi, Abolfazl Gholamrezatabar Pages 221-236
    It is well known that structures designed by current codes experience large inelastic deformations during major earthquakes. However, current seismic design practice in almost all seismic design provisions such Iranian Seismic Code is based on elastic structural behavior and accounts for inelastic behavior only in an indirect manner through certain modification factors such as strength reduction factor. Under moderate to severe earthquakes, inelastic activity, including severe yielding and buckling of structural members can be unevenly distributed in the structure, which may result in global collapse or costly repair work. Recently, a new design method has been developed and referred to as Performance-Based Plastic Design (PBPD). This method directly accounts for inelastic behavior by using pre-selected target drift and yield mechanism as key performance limit states. In this paper, for the first time, the effect of soil-structure interaction (SSI) on drift demands distribution along the height of the steel moment frame (SMF) structures designed with performance-based-plastic design (PBPB) approach under strong ground motions are parametrically investigated. The soil beneath the structure is considered as a homogeneous elastic half space and is modelled using the concept of Cone Models. For the the steel moment frame structures, the design base shears are calculated by using the modified energy balance equation and new lateral force distribution based on inelastic analyses. The new distribution of the lateral forces for performance-based plastic design was used from shear proportioning factors that were derived from the relative distribution of maximum story shears obtained from nonlinear dynamic analyses. Then, plastic design method is employed to design the beams and columns with the calculated design base shear and to satisfy the requirements for strong column-weak beam mechanism, which results in the pre-selected yield mechanism. The plastic design procedure proposed herein can be one of the simplified approaches without requiring sophisticated computer nonlinear analyses, by using the preselected yield mechanisms and target drifts. The energy dissipation capacity of the structure designed by these procedures can be less than that required to prevent collapse under severe ground motions. The purpose of this design procedure is to avoid collapse mechanisms characterized by poor energy dissipation capacity, such as soft-story mechanisms. To this end, the plastic hinges should be developed only in beams and at the column bases of the structure during severe earthquakes. The system is then subjected to 20 different earthquake ground motions and the analyses are performed directly in time domain using direct step-by-step integration method. Effect of various parameters including fundamental period, inelastic behavior, SSI key parameters on strength reduction factor and structural damage distribution are examined. The adequacy of different lateral loading patterns is also parametrically investigated. Results indicate that only mid-rise SMFs designed based on current PBPB approach could have the best performance in SSI systems. It is also demonstrated that under slight and moderate SSI effects, SMFs designed according to various load patterns tend to more uniform distribution as compared to the fixed-base counterparts. However, all of them lose their efficiency when the SSI effects and inelastic response are pronounced. Moreover, the influence of SSI key parameters, fundamental period and ductility ratio on dispersion of the drift results are evaluated and discussed.
    Keywords: Drift Distribution, Performance-Based-Plastic Design, Soil-Structure Interaction, Yield Mechanism
  • Mandana Naji Abhari * Pages 237-249
    Turbidity currents account for transporting sediments into reservoirs, seas, and oceans. Therefore, understanding dynamics of these currents for sedimentation and erosion is very important. In this paper, the effects of two obstacles on the behaviour of turbidity currents investigated experimentally. An 11 m long rectangular channel (11 m×0.6 m×1.0 m) with the bottom slope of 0.25% was used to run the experiments and a 3 m3 tank along with a constant head tank were served as the turbid water supplier. Two triangular obstacles were installed at predefined locations from the sluicegate. Then the experiments were carried out and the results compared with those from without obstacle condition. Velocity and concentration profiles at the upstream of first obstacle and between the first and second obstacles are measured by Vectrino at quasi-steady conditions and compared to those of without obstacle conditions showing a significant decrease of velosity in the presence of the two obstacles specially between the two obstacles and also at the downstream of the second obstacle. Fluid volume discharge per unit width and suspended sediment transport rate are calculated based on measured velocity and concentration. Also, the effects of inlet Froud number on the fluid volume discharge per unit width and suspended sediment transport rate was investigated. The results show that presence of obstacles introduces new regions to velocity profiles and two ponds of turbidity currents are formed at the upstream of the first obstacle and between the two obstacles. The hydraulic conditions at these ponds make a suitable condition for the suspended particles to be trapped and hence the sedimentation. Variation of the suspended sediment transport rate and the fluid volume discharge per unit width depend on obstacle location. These parameters at the upstream of the first obstacle are directly in proportion to the inlet Froud number while at the downstream the second obstacle and between the obstacles are inversely proportional. By decreasing the inlet Froud number, the volume discharge per unit width increases at the upstream of the first obstacle wheras, the amount decreases between the obstacles. Also, as the inlet Froud number decreases, the suspended sediment transport rate increases at the the upstream of the first obstacle but the value decreases between the obstacles and downstream of the second obstacle resulting the increase of the trap efficiency. The obstacles become more effective in controlling the turbidity currents when the inlet Froud number decreases. The first obstacle is 1.8 times more effective on reduction of local sedimentation rate than the second obstacle. These parameters at the upstream of the first obstacle are directly in proportion to the inlet Froud number while at the downstream the second obstacle and between the obstacles are inversely proportional. By decreasing the inlet Froud number, the volume discharge per unit width increases at the upstream of the first obstacle wheras, the amount decreases between the obstacles. Also, as the inlet Froud number decreases, the suspended sediment transport rate increases at the the upstream of the first obstacle but the value decreases between the obstacles and downstream of the second obstacle resulting the increase of the trap efficiency. The obstacles become more effective in controlling the turbidity currents when the inlet Froud number decreases. The first obstacle is 1.8 times more effective on reduction of local sedimentation rate than the second obstacle.
    Keywords: Turbidity current, Obstacles, Inlet Froud number, Fluid volume discharge per unit width, Suspended sediment transport rate