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مهندسی عمران مدرس - سال هجدهم شماره 6 (بهمن و اسفند 1397)

نشریه مهندسی عمران مدرس
سال هجدهم شماره 6 (بهمن و اسفند 1397)

  • تاریخ انتشار: 1397/12/10
  • تعداد عناوین: 17
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  • سمیرا ابراهیمی حسین آبادی، حمزه شکیب* صفحات 1-12
    قاب های مهاربندی شده برون محور، به دلیل دارا بودن توام مزایای قاب های خمشی و مهاربندی شده هم محور، در ساختمان ها بسیار مورد استفاده قرار می گیرند. تیرهای پیوند این قاب ها، مانند یک فیوز شکل پذیر، علاوه بر جلوگیری از کمانش مهاربندها، مقدار زیادی انرژی زلزله را نیز جذب می کنند و به همین دلیل نقش حائز اهمیتی دارند. تیرهای پیوند قوطی شکل به دلیل پایداری پیچشی ذاتی، نیاز به مهارجانبی ندارند و کمانش پیچشی جانبی در آن ها، نسبت به تیرهای پیوند I شکل کمتر رخ می دهد و به همین دلیل استفاده از آن ها در پایه های پل و ساختمان های بلند توصیه می شود. تیرهای پیوند بلند به دلیل فراهم آوردن شرایط مناسب جهت اجرای بازشوها دارای مزیت معماری هستند با وجود این رفتار تیرهای پیوند بلند تحت بارهای شدید لرزه ای در مقایسه با تیرهای پیوند کوتاه از نظر سختی، مقاومت، ظرفیت دوران، ظرفیت استهلاک انرژی قابل مقایسه نبوده و در سطح پایین تری قرار دارد. در این تحقیق، ابتدا مدلی برای بهبود رفتار تیرهای پیوند قوطی شکل بلند در قاب های مهاربندی شده برون محور ارائه شده است و سپس رفتار دینامیکی غیرخطی قاب های فولادی برون محور 6 طبقه با 2 طول تیرپیوند (خمشی - برشی و خمشی) مختلف، مقاطع عرضی قوطی شکل با آرایش های مختلف سخت کننده، تحت تاثیر 3 رکورد دور و 3 رکورد نزدیک گسل مورد بررسی قرار گرفته است. نتایج بررسی ها نشان می دهد که آرایش مناسب سخت کننده های تیرپیوند قوطی شکل بلند، تاثیر مهمی در کاهش نیاز تغییرمکانی این قاب ها دارد که این کاهش در حدود 19% برای رکوردهای دور از گسل و 32% برای رکوردهای نزدیک گسل می باشد.
    کلیدواژگان: قاب های مهاربندی شده برون محور، تیرپیوند قوطی شکل، رکوردهای دور و نزدیک گسل، سخت کننده
  • محمد ابوییان جهرمی، احمد جمشیدی زنجانی*، احمد خدادادی دربان، حسین شفیع زاده مقدم صفحات 15-26
    اندازه گیری غلظت کل فلزات سنگین به تنهایی نمی تواند معیار مناسبی برای سنجش میزان خطر آن ها باشد و میزان ریسک فلزات سمی به قابلیت انحلال و دسترسی زیستی آن ها بستگی دارد. در این پژوهش جهت تعیین میزان دسترس زیستی و انسانی فلزات سنگین، پس از نمونه برداری از خاک های سطحی در 65 ایستگاه از محدوده های معدن سرب و روی باما و روستای مجاور به آن و تعیین غلظت کل فلزات سنگین، آزمایش های استخراج تک مرحله ای به کمک استخراج کننده های EDTA و گلایسین بر روی نمونه ها اعمال گردید. برای ارزیابی میزان خطر فلزات و بر اساس غلظت استخراج کننده ها از شاخص BRAI استفاده شد. بیشترین درصد دسترسی زیستی و انسانی از غلظت کل در محدوده مورد بررسی، مربوط به فلز کادمیوم بود و کمترین مقدار آن به سرب اختصاص داشت. همچنین درصد دسترسی زیستی در محدوده روستا بیشتر از محدوده معدنی بدست آمد. به علاوه مشخص شد که گلایسین مقادیر بیشتری از فلزات را در مقایسه با EDTA استخراج می کند. میانگین اعداد بدست آمده برای شاخص BRAI با استخراج کننده های EDTA و گلایسین در محدوده معدنی به ترتیب 47/3و 32/4 و در محدوده روستای مجاور به ترتیب 79/4 و 46/5 بدست آمد. این اعداد ریسک و خطر بالا را برای انسان و گیاه در هر دو محدوه معدنی و روستا را نشان می دهد.
    کلیدواژگان: فلزات سنگین، دسترسی زیستی، دسترسی انسانی، استخراج تک مرحله ای، معدن سرب و روی باما
  • الهام اسراری*، محسن بذر افکن صفحات 27-37
    فلزات سنگین یکی از بزرگترین مشکلات زیست محیطی در دنیای امروز می باشند.گسترش صنایع بزرگ ،افزایش جمعیت و کاهش منابع آبی، اهمیت تصفیه فاضلاب و استفاده مجدد از منابع آبی را آشکار میسازد . از طرف دیگر بخش بزرگی از تاسیسات و حوضچه های تصفیه فاضلاب از بتن ساخته میشود. pH متغیر و وجود عوامل خورنده در محلول فاضلاب باعث آسیب دیدن و کاهش عمر بتن میشود. استفاده از موادی نظیر کائولین باعث افزایش جذب آلاینده های موجود در محلول فاضلاب و بالا رفتن دوام بتن مورد استفاده می شود. از بین روش های فراوان حذف آلاینده های محلول در آب ، روش جذب سطحی با بازدهی بالا همواره مورد توجه پژوهشگران بوده است. در تحقیق پیش رو به بررسی فرایند حذف فلز سنگین کروم با استفاده از بتن اصلاح شده حاوی خاک رس کائولین و همچنین پارامترهای موثر بر جذب پرداخته شده است. شرایط بهینه در این پژوهش برای جذب این فلز pH=5 ، غلظت اولیه آلاینده (mg/l)1000 ، کائولین به میزان %30 وزنی ریزدانه مصرفی در ساخت بتن ، زمان تعادل 360 دقیقه و ظرفیت جذب 3.06 میلی گرم بر گرم جاذب بدست آمده است. پوشش دادن سطح بتن با جاذب کائولین میتواند یک راه حل ابتکاری و مفید برای بالا بردن میزان حذف آلاینده ، کاهش هزینه و تسریع فرایند جذب باشد. در این حالت ظرفیت جذب به 29.5 میلی گرم بر گرم جاذب افزایش می یابد..با توجه به اینکه شرایط بهینه با استفاده از فاضلاب سنتتیک به دست آمده است . میزان جذب  کروم در نمونه واقعی پساب ، پساب حاوی کروم از یک کارخانه آبکاری ، 90.3 درصد به دست آمد. با توجه به نتایج به دست آمده استفاده از کائولین میتواند موجب بالا رفتن کارایی جذب کروم توسط بتن گردیده و نیز طول عمر و دوام بتن را افزایش دهد.
    کلیدواژگان: کروم، کائولین، بتن اصلاح شده، فاضلاب صنعتی
  • فاطمه جعفری، علی اکبر صالحی نیشابوری * صفحات 39-50
    یکی از راهکارهای موثر برای استهلاک انرژی پاییندست سازه های هیدرولیکی مانند سرریزها، تنداب ها و دریچه ها، پرش هیدرولیکی است. از جمله سازه های استهلاک انرژی، بلوک های آرام کننده) Baffle blocks (است که در قسمت میانی حوضچه به منظور اتلاف انرژی به صورت متمرکز کار گذاشته می شود و عملکرد آن بلوکها در حالت پرش هیدرولیکی مستغرق متفاوت از پرش هیدرولیکی آزاد است؛ به طوری که در پرش هیدرولیکی مستغرق همراه با بلوک، جریان میتواند تنها به صورت دو نوع رژیم اتفاق بیافتد؛ جریان منحرف شده به سطح (Deflected Surface Jet) یا بطور مختصر رژیم) DSJ (و یا به صورت جت دیواره ای دوباره متصل شونده (Reattaching Wall Jet) یا بطور مختصر رژیم) RWJ (. در این مقاله به بررسی تاثیر پارامترهای فاصله بلوکها از دریچه، ارتفاع بلوکها، شکل بلوکها و عدد فرود جت ورودی بر روی استهلاک انرژی ناشی از بلوکها پرداخته شده است. بدین منظور از نرم افزار فلوئنت برای شبیه سازی جریان استفاده شده است. میدان محاسباتی با استفاده از شبکه منشوری گسسته شده است. برای دقت بیشتر از مدل آشفتگی هفت معادلهای RSM استفاده شد که در درستی آزمایی نتایج بهتری تولید کرد. در مجوع 05 مدل برای مقادیر مختلف پارامترهای فوق طراحی و اجرا شد و درصد استهلاک انرژی تحت شرایط مختلف به دست آمد. نتایج بیانگر این است که عدد فرود مقطع بازشدگی دریچه مهم ترین عامل در استهلاک انرژی به شمار میآید. همچنین دیده شد با کم شدن فاصله بلوکها از دریچه ورودی، درصد استهلاک انرژی زیاد میشود؛ مشروط به اینکه شرایط هیدرولیکی و هندسی منجر به ایجاد رژیم DSJ شوند.
    کلیدواژگان: استهلاک انرژی، پرش هیدرولیکی مستغرق، بلوک های میانی، شبیه سازی عددی، حوضچه آرامش _
  • جاوید چاخرلو، بهمن شروانی* صفحات 51-61
    در تولید بتن پودری واکنش پذیر از مواد و مصالح پودری بسیار ریزدانه شامل ماسه کوارتزی، میکروسیلیس و پودر کوارتز به عنوان مصالح استفاده می شود. این بتن دارای مقاومت فشاری بالا نسبت به بتن معمولی می باشد، که در سال های اخیر توجه زیادی را به خود جلب کرده است. با استفاده از این نوع بتن می توان وزن سازه را به مقدار قابل توجهی کاهش داد و از ویژگی های مهم آن می توان به مقاومت فشاری زیاد، نفوذ پذیری کم، دوام و مقاومت سایشی بالا و شکل پذیری زیاد که می تواند جذب انرژی بیشتری در هنگام زلزله داشته باشد. در این پژوهش می خواهیم از پودر سنگ آهک به جای قسمتی از ماسه سیلیسی استفاده نماییم. برای این منظور پس از بدست آوردن طرح اختلاط بهینه بر اساس مقاومت فشاری و روانی و قطر پخش شدگی میز جریان، ابتدا پودر سنگ آهک را بصورت جایگزین با درصدهای 0، 10، 20، 30 به جای ماسه سیلیسی جایگزین کرده و در ادامه از پودر سنگ آهک به عنوان جایگزینی-افزودنی با درصدها و طرح های مختلف استفاده شده است. آزمایش های انجام شده روی این نمونه ها شامل آزمایش روانی میز جریان و جذب آب حین عمل آوری و مقاومت فشاری در سنین 7 ، 28 و 90 روزه می باشد. نتایج آزمایش ها نشان می دهد که با افزایش پودر سنگ آهک تا 20 درصد جایگزینی با ماسه سیلیسی باعث افزایش مقاومت فشاری شده، کاهش بسیار جزئی در روانی و همچنین باعث کاهش جذب آب حین عمل آوری می شود.
    کلیدواژگان: بتن پودری واکنش پذیر، مقاومت فشاری، روانی، عمل آوری، پودر سنگ آهک
  • علیرضا حبیبی*، یاسر رحمانی، سرکوت سعید پور صفحات 63-72
    بتن علاوه بر دارا بودن خواص سازه ای مناسب، یکی از مناسب ترین و پر کاربردترین مصالح برای ساخت حفاظ تابشهای هسته ای نوترون و گاما می-باشد. در این میان استفاده از بتن سنگین به جای بتن معمولی باعث کاهش ضخامت عضو محافظتی به میزان قابل توجه خواهد شد. با توجه به حجم زیاد بتن ریزی در نیروگاه های اتمی، بهینه سازی طرح اختلاط این نوع بتن می تواند تا حد زیادی منجر به کاهش هزینه ساخت شود، هدف اصلی از تحقیق حاضر توسعه یک روش طرح اختلاط بتن سنگین براساس اصول بهینه سازی می باشد. بدین منظور ابتدا مدل بهینه سازی طرح اختلاط بتن سنگین تعریف می شود، سپس با استفاده از یک الگوریتم بهینه سازی طرح اختلاط بهینه برای بتن با مقاومت مورد نظر بدست می آید. نتایج عددی نشان می دهد که با کاهش مقادیر سنگدانه و سیمان و افزایش مقدار ریزدانه در طرح اختلاط به صورت همزمان، مقدار هزینه طرح اختلاط کاهش پیدا می کند.
    کلیدواژگان: طرح اختلاط، بهینه سازی، بتن سنگین
  • وحید حسن زاده وایقان، میرعلی محمدی* صفحات 73-82
    کانال ها و رودخانه های عریض به جهت داشتن نسبت عرض به عمق جریان،b/h، زیاد، خصوصیات هیدرولیکی متفاوت تری نسبت به کانال های روباز معمولی دارند. در این تحقیق با استفاده از یک مدل فیزیکی صحرایی، کانالی عریض به طول 60 متر و عرض 5/1 متر که دارای نسبت عرض به عمق جریان بین 12 تا 56 است، مشخصات هیدرولیکی کانال های عریض با جداره ثابت بتنی، شامل الگوی جریان، منحنی دبی- اشل و مقاومت جریان مورد بررسی قرار گرفته است. بر اساس مقادیر اعداد بی بعد فرود، رینولدز و رینولدز برشی جریان بدست آمده، مشخص گردید که رژیم جریان از نوع زیربحرانی- آشفته است. طبق نمودار دبی-اشل-tailgate مشخص می شود که با افزایش دبی جریان، ارتفاع tailgate مورد نیاز در پایین دست کانال عریض برای ایجاد عمق نرمال، کاهش می یابد. نتایج تحقیق گویای آن است که برای دبی های بزرگتر از 35 لیتر بر ثانیه ضریب زبری مانینگ، n، اندازه گیری شده، به مقادیر n ارائه شده در منابع هیدرولیک برای کانال بتنی بسیار نزدیک است. ولی برای دبی های کوچکتر از 35 لیتر بر ثانیه ضریب زبری مانینگ اندازه گیری شده n، 15% بیش از مقدار ارائه شده در منابع هیدرولیک می باشد. همچنین بر اساس نتایج، با افزایش عمق جریان، ضریب زبری مانینگ، n، کاهش و با افزایش عدد رینولدز، ضریب زبری n به صورت خطی ملایم کاهش پیدا می کند. نتایج تحقیق نشان می دهد که در کانال عریض، با افزایش عدد فرود جریان از 26/0 تا 40/0، ضریب زبری مانینگ، n، در محدوده022/0 تا 016/0 کاهش می یابد
    کلیدواژگان: کانال عریض جداره ثابت، مدل فیزیکی، نمودار دبی-اشل، مقاومت جریان
  • حمیدرضا نجاتی*، امین خدایار صفحات 95-105
    درزه ها و ترک ها جزء لاینفک سازه های سنگی بوده که بر اساس نوع کاربری سازه تحت تاثیر مجموعه ای از بارهای استاتیک و دینامیک قرار می گیرند. یکی از مهمترین عامل گسیختگی سازه های سنگی گسترش همین درزه ها و ترک های موجود در سنگ می باشد. ریز ترک ها در سنگ معمولا به دو شکل طبیعی و القایی مشاهده می شود. در این تحقیق، تاثیر ریز ترک های القایی بر رفتار مکانیکی نمونه های سنگی بررسی شده است. برای این کار از حرارت برای القای ریزترک در داخل نمونه استفاده شده است سپس آزمون های آزمایشگاهی شامل اولتراسونیک، مقاومت فشارشی تک محوره و برزیلی در آزمایشگاه انجام گرفته و الگوی شکست نمونه ها در آزمون مقاومت فشاری تک محوره مورد بررسی قرار گرفته است. نتایج آزمون های آزمایشگاهی نشان می-دهد که الگوی شکست نمونه های گرانیتی با افزایش ریز ترک ها از حالت "جدایش محوری" به حالت "شکست برشی" تبدیل می-شود . به عبارت دیگر افزایش تعداد ریز ترک ها در نمونه های گرانیتی باعث تغییر الگوی شکست نهایی نمونه ها از حالت شکست شکننده به شکست شکل پذیر می شود. همچنین با استفاده از نرم افزار RFPA، ناهمگنی ناشی از ریزترک ها به صورت عددی مدلسازی شده و تاثیر آن بر الگوی شکست نمونه ها مورد بررسی قرار گرفته است. بر اساس نتایج بدست آمده از مدلسازی عددی مشخص گردید که علت تغییر در الگوی شکست نمونه های سنگی با افزایش ریز ترک های القایی، کاهش ترک های کششی و افزایش ترک های برشی در نمونه ها می باشد.
    کلیدواژگان: الگوی شکست، ریزترک ها، رفتار مکانیکی، گرانیت
  • محمد قنبردزفولی، مسعود دهقانی، عادل عساکره*، بهزاد کلانتری صفحات 107-120
    به دلیل ایجاد نیروهای متمرکز و لنگرهای خمشی بالا در محل اتصال شمع به رادیه در سازه های با بارهای زیاد، استفاده از رادیه شمع منفصل می تواند گزینه مناسبی جهت فونداسیون این نوع سازه ها باشد. در این سیستم شمع ها و رادیه به هم متصل نمی باشند و از یک بالشتک شنی در فاصله بین شمع و رادیه به منظور بازپخش نیروها استفاده می شود. در این حالت بار از طریق رادیه و بالشتک شنی به شمع ها منتقل می شود. در این تحقیق مطالعه آزمایشگاهی بر روی رادیه شمع منفصل واقع بر خاک ماسه ای به منظور بررسی پارامترهایی نظیر ضخامت بالشتک شنی و فاصله شمع ها بر رفتار بار-نشست، سهم شمع ها و رادیه از کل بار و همچنین پخش نیروی محوری و تنش اصطکاکی در طول شمع های مرکزی و گوشه انجام گرفته است. نتایج نشان داده ضخامت بالشتک شنی و فاصله شمع ها نقش مهمی در رفتار بار نشست، و سهم شمع ها از کل بار و همچنین نحوه توزیع تنش در طول شمع دارد. در یک ضخامت بهینه بالشتک شنی و یک فاصله بهینه شمع ها کمترین نشست مشاهده شده است. با افزایش ضخامت بالشتک شنی سهم شمع ها از کل بار کاهش می یابد. همچنین سهم شمع ها از کل بار نیز تابعی از فاصله شمع ها می باشد. در قسمت های بالایی شمع ها تنش های اصطکاک منفی ایجاد می شود. با افزایش ضخامت بالشتک شنی مقدار اصطکاک منفی بیشتر می شود. در شمع های گوشه اصطکاک منفی بیشتری نسبت به شمع های مرکزی ایجاد می شود که باعث پایین آمدن محور خنثی می گردد.
    کلیدواژگان: رادیه شمع منفصل، مدل آزمایشگاهی، ماسه، بالشتک شنی
  • حامد رحمن شکرگزار*، مریم زارع آقبلاغ، احمد علی خدایی اردبیلی صفحات 121-130
    در این تحقیق، تاثیر تغییر نوع خاک، فونداسیون و ضریب اطمینان طراحی بر پاسخ لرزه ای ساختمان فولادی ارزیابی شده است. بدین منظور ساختمان پنج طبقه از نوع قاب خمشی ویژه واقع بر دو نوع خاک متفاوت (II و IV) درنظر گرفته شده است. دو نوع فونداسیون سطحی برای این ساختمان با ضرایب اطمینان 2، 3 و 4 در ظرفیت باربری طراحی گردیده اند. به منظور ارزیابی عملکرد مدلهای اجزا محدود، با لحاظ اندرکنش خاک فونداسیون سازه توسط نرم افزار اپنسیس ساخته شده است. این مدل ها تحت تحلیلهای استاتیکی و دینامیکی غیرخطی توسط هفت رکورد زلزله قرار گرفته و پاسخهای آنها با یکدیگر مقایسه گردیده است. نتایج بدست آمده حاکی از آن است که در قابهای خمشی واقع بر خاک نوع IV، سازه با فونداسیون منفرد، ظرفیت و برش پایه کمتری نسبت به سازه با فونداسیون نواری و مدل دارای تکیه گاه صلب دارد و ماکزیمم تغییرمکان نسبی بین طبقات در مدلهای با فونداسیون نواری بیشتر از مدلهای با فونداسیون منفرد و مدل دارای تکیه گاه صلب میباشد. بررسی اثر تغییر ضریب اطمینان طراحی فونداسیونها نشان میدهد که ظرفیت سازه ای، ماکزیمم برش پایه و ماکزیمم تغییرمکان نسبی طبقات در سازه با فونداسیون منفرد، با افزایش ضریب اطمینان، افزایش می یابد، اما این کمیت در سازه با فونداسیون نواری تاثیر چندانی ندارد. در قابهای خمشی واقع بر خاک نوع II، ضریب اطمینان طراحی و نوع فونداسیون تاثیر چندانی بر ظرفیت سازه و پاسخ دینامیکی ندارد.
    کلیدواژگان: اندرکنش خاک - فونداسیون - سازه، نوع خاک و فونداسیون، قاب خمشی فولادی ویژه کوتاه مرتبه، ضریب اطمینان
  • داود زارعی، عباسعلی تسنیمی* صفحات 131-141
    استفاده از تیرهای همبند فولادی در دیوارهای برشی بتن مسلح به علت عملکرد لرزه ای و انعطاف پذیری بهتر و همچنین اجرای راحت تر و ابعاد کوچکتر آن نسبت به تیرهای بتنی رو به گسترش می باشد. جهت اجتناب از خرابی ماندگار اتصال تیر فولادی به دیوار بتنی، می توان از تیر فولادی دارای المان تعویض پذیر استفاده نمود. در این مقاله یک تیر همبند فولادی طراحی شده بر اساس استاندارد 2800 و مبحث دهم مقررات ملی ساختمان طراحی و ساخته شده است. همچنین المان تعویض پذیر و بخش های کناری آن بر اساس ضوابط تیر پیوند مبحث دهم مقررات ملی ساختمان طراحی و ساخته شده است. مجموعه دو دیوار طرفین تیر و تیرهمبند تعویض پذیر با مقیاس 1 به 3 ساخته شده و با تاریخچه جابجایی چرخه ای بر اساس تغییر شکل نسبی طبقات مورد آزمایش قرار گرفته است. با توجه به نتایج بدست آمده، رفتار غیر خطی تیر همبند به المان تعویض پذیر محدود شده است اما با توجه به مقاطع استفاده شده و نیروهای موجود در تیرها، رابطه استفاده شده از مبحث دهم جهت طراحی تیرهای کناری نیاز به اصلاح دارد. همچنین بر اساس سختی محاسباتی و سختی اندازه گیری شده سیستم و بر مینای طول مهاری تیر فولادی در دیوار بتن مسلح، روشی برای محاسبه سختی واقعی این مجموعه برای طراحی سازه ها و محاسبه جابجایی طبقات پیشنهاد شده است.
    کلیدواژگان: دیوار برشی بتن مسلح، تیر همبند فولادی، المان تعویض پذیر، محل تکیه گاه موثر
  • علی زارعی، ابوالفضل حسنی* صفحات 143-153
    در این تحقیق از 0 ، 5 ، 10 ، 15 و 20 درصد خرده لاستیک، به عنوان جایگزین ریزدانه در روسازی بتنی استفاده گردیده است، همچنین در یک حالت دیگر نیم درصد الیاف فلزی حاصل از بازیافت تایرهای فرسوده به این نمونه ها افزوده شد و نتایج حاصل از این تحقیق بیانگر این است که مقاومت فشاری نمونه های با جایگزینی خرده لاستیک به میزان 5 ، 10 ، 15 و 20 درصد خرده لاستیک، نسبت به نمونه شاهد، به ترتیب دارای کاهش 6/1 ، 9/36 ، 9/49 و 1/63 درصدی و نمونه های با 0 ، 5 ، 10 ، 15 و 20 درصد جایگزینی خرده لاستیک و 5/0 % الیاف فلزی، به ترتیب دارای کاهش 3/0 ، 2/11 ، 7/33 ، 5/41 و 3/44 درصدی بوده است، بنابراین مشاهده می شود که عملکرد بتن حاوی خرده لاستیک و الیاف فلزی، ازلحاظ مقاومت فشاری نسبت به نمونه حاوی خرده لاستیک به تنهایی بهتر بوده و کاهش مقاومت کمتری خواهد داشت و همچنین با جایگزینی 5 ، 10 ، 15 و 20 درصد خرده لاستیک در بتن، مقاومت کششی غیرمستقیم آن دارای 5/7 ، 3/15 ، 4/21 و 2/31 درصدی خواهد بود و  با افزودن 5/0 % الیاف فلزی به بتن با جایگزینی 0 ، 5 ، 10 ، 15 و 20 درصد خرده لاستیک، مقاومت کششی غیرمستقیم به ترتیب به میزان 8/67 ، 7/46 ، 4/32 ، 8/17 و 5/3 درصد افزایش می یابد و این نتیجه حاصل می شود که مقاومت کششی بتن، در اثر افزودن الیاف فلزی افزایش و در اثر افزایش میزان جایگزینی خرده لاستیک، کاهش خواهد یافت.
    کلیدواژگان: تایرهای فرسوده، مقاومت فشاری، مقاومت کششی غیرمستقیم، روسازی بتنی، بازیافت
  • محمد عالم باقری*، رضا شیخ زاده شایان صفحات 155-167
    درگذشته تحلیل لرزه‏ای سدهای بتنی اغلب به‏صورت ایده آل با استفاده از مونولیت‏های دوبعدی در سازوکار تحلیل و طراحی در نظر گرفته‏شده و اثرات زلزله معمولا با تعریف یک ضریب زلزله اعمال می‏شده است. اما در سال‏های اخیر تاکید بیشتر بر تحلیل‏های تاریخچه زمانی غیرخطی و نیز آنالیز شکست سدهای بتنی در فضای سه‏بعدی شده است. همچنین با پیشرفت دانش درزمینه ی مهندسی زلزله و توسعه روش‏های دقیق‏تر برای برآورد شدت زلزله‏های محتمل ازجمله روش تحلیل دینامیکی افزایشی، فرآیند تحلیل و ارزیابی لرزه‏ای سازه‏ها کامل‏تر گردیده و تاثیر پارامترهای بیشتری را می‏توان در ارزیابی ریسک هر سازه لحاظ کرد. در تحقیق پیش رو، پاسخ لرزه‏ای سدهای بتنی وزنی-قوسی تحت اثر تحریکات زلزله در یک تحلیل المان محدود سه‏بعدی بررسی می‏شود. اثرات ناشی از در نظرگیری اندرکنش سد-مخزن-پی، رفتار غیرخطی بتن و همچنین الگوهای متفاوت شعاع قوس سد مطالعه شده و درنهایت سهم پاسخ هریک از عوامل پایداری در برابر تحریکات لرزه‏ای مورد ارزیابی قرار می‏گیرد.
    کلیدواژگان: سد بتنی وزنی-قوسی، پاسخ لرزه ای، تحلیل سه بعدی، اندرکنش سد - مخزن - پی، رفتار غیرخطی
  • محمد طاهری پور، مهدی قاسمیه* صفحات 169-180
    در این تحقیق رفتار اتصالات با صفحه انتهایی گسترش یافته تحت اثر بارگذاری های ترکیبی شامل اعمال هم زمان لنگر خمشی، لنگر پیچشی و یا نیروی محوری بر اتصال بررسی شده است. تاکنون مطالعات چندانی در این زمینه بر روی اتصالات خمشی با ورق انتهایی صورت نگرفته است و اندرکنش نیروهای مذکور می تواند رفتار اتصال را به نحو چشم گیری تغییر دهد. ابتدا مدل اجزای محدود اتصال تحت بار خمشی تهیه و سپس با مقایسه با نتایج آزمایشگاهی از صحت مدل های اجزای محدود اطمینان حاصل شد. سپس به بررسی رفتار اتصال، تحت اثر هم زمان خمش و نیروی محوری پرداخته شد. در این حالت، نیروی محوری نه چندان زیاد، می تواند مود گسیختگی و ظرفیت خمشی اتصال را تغییر دهد. در ادامه با توجه به اینکه در حالاتی نظیر اعمال بارگذاری خارج از محور، لنگرهای پیچشی و خمشی به صورت هم زمان بر تیر اعمال می شوند، اثر این نوع بارگذاری نیز مورد بررسی قرار گرفت. نتایج نشان می دهند که حضور پیچش علاوه بر کاهش سختی اولیه اتصال، سبب افزایش تنش در یک سمت اتصال و کاهش آن در سمت دیگر شده و نیز می تواند مود گسیختگی اتصال را به کمانش پیچشی جانبی تیر تغییر دهد. در انتها اثر ترکیب بارهای خمشی، پیچشی و محوری بر اتصال بررسی گردید. در این حالت، اعمال نیروی فشاری در همه ی نمونه ها، سبب رخداد کمانش پیچشی جانبی در تیر شده و رفتار ترد اتصال را در پی دارد. در مقابل اعمال نیروی کششی، ضمن کاهش ظرفیت خمشی اتصال، اثر پیچش وارده و پتانسیل رخداد کمانش پیچشی جانبی در تیر را کاهش می دهد.
    کلیدواژگان: اتصالات خمشی، ورق انتهایی، بارگذاری ترکیبی، پیچش، کمانش پیچشی جانبی
  • ساجده فرمانی، مهناز قایینی حصاروییه*، صالح حمزه جواران صفحات 181-192
    در این مقاله به حل معادلات ناویر-استوکس و لاپلاس با روش اجزاء محدود مبتنی بر المان های مختلط فوریه پرداخته شده است. توابع انترپولاسیون پیشنهادی با استفاده از غنی سازی توابع پایه ی شعاعی مختلط فوریه به شکل  حاصل شده اند. توابع حاضر شامل خصوصیات توابع پایه ی شعاعی حقیقی فوریه و گوسی می باشند. این خصوصیات مفید باعث توانایی بسیار بالای روش پیشنهاد شده می شود. از جمله مزیت توابع شکل پیشنهادی می توان به دارا بودن همزمان میدان توابع مثلثاتی، نمایی و چند جمله ای اشاره کرد؛ در حالیکه توابع کلاسیک لاگرانژ تنها میدان توابع چند جمله ای را اغنا می کنند. چند مثال معیار عددی در رابطه با کاربرد توابع پیشنهادی در روش اجزاء محدود برای حل معادلات ناویر-استوکس و لاپلاس مورد استفاده قرار گرفته است. برای نشان دادن کارایی و دقت روش حاضر، نتایج روش پیشنهادی با نتایج حاصل از توابع کلاسیک و همچنین حل تحلیلی مقایسه شده است. نتایج این مقایسه ها حاکی از دقت بسیار بالاتر روش پیشنهادی می باشد.
    کلیدواژگان: معادلات ناویر - استوکس و لاپلاس، روش اجزاء محدود، المان های مختلط فوریه، توابع شکل کلاسیک لاگرانژ
  • پرویز قدوسی، علی اکبر شیرزادی جاوید*، بهنام بزرگمهر صفحات 193-206
    تا کنون مطالعات متعددی بر روی خواص رئولوژی و زمان گیرش در مخلوط های با پایه سیمانی انجام پذیرفته است، لیکن ارتباط بین این دو مشخصه مهم تا کنون بررسی نگردیده است. لذا هدف از انجام این پژوهش بررسی ارتباط بین خواص رئولوژی و زمان گیرش در مخلوط های بتن خودتراکم می باشد. در این پژوهش شش طرح مخلوط بتن خودتراکم در نظر گرفته شد که در آنها اثر تغییر نسبت آب به سیمان، افزودنی دوده سیلیس و سرباره کوره آهن گدازی در نظر گرفته شد. در تعیین زمان گیرش از روش مقاومت الکتریکی استفاده گردیده و همچنین عملکرد این روش در تعیین خصوصیات رئولوژی مورد ارزیابی قرار گرفته است. از آنجایی که روش مقاومت الکتریکی در تعیین زمان گیرش فاقد استانداردی مدون می باشد، لذا به منظور راستی آزمایی نتایج از روش استاندارد مقاومت در برابر نفوذ بر اساس استاندارد  ASTM-C403 نیز استفاده شده است. در بخش بررسی خواص رئولوژی نیز بررسی ها در دو بخش کارایی و بررسی رئومتریک انجام گرفته است. از نتایج بدست آمده مشخص گردید که مخلوط هایی که دارای جریان پذیری بالاتری هستند، زمان گیرش کمتری را ثبت کرده اند. همچنین مشخص شد که مخلوط های بتنی که تنش جاری (استاتیکی و دینامیکی) بالاتری دارند، زمان گیرش کوتاه تری را ثبت نموده اند.  بدین ترتیب با روابط بدست آمده ارتباط این دو متغیر مهم( خواص رئولوژی و زمان گیرش )ارزیابی گردید.
    کلیدواژگان: زمان گیرش، رئولوژی، کارایی، مقاومت الکتریکی، بتن خود تراکم
  • محمد یعقوبی سربیشه، محمد تقی احمدی* صفحات 221-231
    یکی از عوامل مهم و تاثیرگذار در پایداری سدهای وزنی و طراحی آن، میزان بار برکنش میباشد. آیین نامه های مختلف با توجه به پارامترهایی نظیر میزان ارتفاع آب در مخزن و نیز پایین دست سد، یک توزیع چند خطی را برای بار برکنش در زیر سد در نظر می گیرند. در این تحقیق، مدلسازی از چند سد وزنی از نوع پاین فلت به منظور حساسیت سنجی اینگونه توزیعها نسبت به ارتفاع سد صورت گرفت. در کلیه تحلیل ها، بدنه ی سد کاملا نفوذ ناپذیر در نظر گرفته شده و توده سنگ پی به صورت یک محیط همگن و همسان فرض شده است. از مقایسه بین تنش های ایجاد شده در محل اتصال سد و پی در این مدلها، با تنش های حاصل از اعمال توزیع بار برکنش در زیر سد مطابق آیین نامه اداره مهندسی ارتش آمریکا مشخص شد که میزان خطای این گونه الگوهای رایج با ارتفاع سد رابطه ی مستقیم دارد. به طوریکه با افزایش ارتفاع سد میزان خطای مربوط به تنش در بخش حساس شالوده سد حتی تاحدود 40 درصد رشد می کند. در این گروه از سد ها این خطا به 12 برابر خطای قابل انتظار در سدهای کوتاه تر نیز افزایش پیدا می کند. این مساله در برخی موارد می تواند ایمنی سد را کاملا تهدید کند. این تحقیق الگوی پیشنهادی دیگری جهت اعمال بار برکنش در زیر سدهای وزنی معرفی کرده و ضرورت استفاده از روش های دقیق تر در برآورد میزان بار برکنش در زیر سدهای وزنی بلند را نشان می دهد.
    کلیدواژگان: بار برکنش، سد وزنی بلند، آیین نامه، اجزای محدود
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  • Samira Ebrahimi Hosein Abadi, Hamzeh Shakib* Pages 1-12
    Eccentrically braced frames (EBF) by covering the advantages of moment-resisting frames (MRF) and concentrically braced frames (CBF) have been used as seismic load resisting systems in buildings for more than two decades. In eccentrically braced frames (EBFs), the link beams transmit bracing forces through themselves into the columns and other bracings and, in the end, create dominant forces in the bracings. Link beams, similar to ductile fuses, in addition to avoiding bracing buckling, attract earthquake energies. In eccentrically braced system, failure and yielding should happen in the link beams, and other members of the structure must remain in elastic behaviour. On the other hand, link beams prevent transmitting of more forces to the other members by yielding, therefore, link beams are so important. Typically, the link beams, which are relied upon for energy dissipation through inelastic deformation, have had a wide-flange or I-shaped cross-section that requires lateral bracing to prevent lateral torsional buckling. This has limited the use of wide-flanges or I-shaped cross-sections in bridge piers and towers, as lateral bracing is difficult to provide in those situations. Tubular cross-sections of link beams have substantial torsional stability, making them less susceptible to lateral torsional buckling than I-shaped cross-sections in eccentrically braced frames, and may thus not require lateral bracing. Long link beams due to providing proper conditions for the openings performances have architectural advantages. Nevertheless, the behaviour of long link beams within sever seismic loads is not comparable to short link beams in stiffness, strength, rotation capacity and energy dissipation capacity, i.e. it is at lower level. Therefore, using long link beams is not recommended in buildings and particularly besides the columns. In this study, a method is presented for arraying the stiffeners of long tubular link beams to improve the behavior of long tubular link beams in eccentrically braced frames. Long link beams at the distance of 1.5b from both ends of the link beams make flange buckling. Now if this distance strength by any way, the flange buckling delay and the rotation capacity of link beams are increased. For this purpose in this investigation, the stiffeners have been used in the middle of the flange vertically in this diatance and the link beam web has been considered as a stiffener that its distance from the middle stiffeners of link beam flange is 0.5b. In long tubular link beams when the middle stiffeners of the link beam flange do not present, Tension-Field will not create and link beam flange will buckle because of moment. When the middle stiffeners of the link beam flange present at its both ends, then Tension-Field will be created. In this investigation, the formulas presented for determining the stiffener sizing of long tubular link beam flange. In this investigation, non-linear dynamic behavior for 6-stotories eccentrically braced frames with different two length of link beams (shear-flexural and flexural), tubular cross sections with two arraying of stiffeners under the influence of three records of far-fault and three records of near-fault are studied. The result of investigations indicates that flange stiffeners of long tubular link beams have important influence in decrease of displacement demand of eccentrically braced frames that approximately 19% for far fault earthquake records and 32% for near fault earthquake records.
    Keywords: Eccentrically braced frame, Tubular link beam, Far, near records of fault, Stiffener
  • Mohammad Abouian Jahromi, Ahmad Jamshid Zanjani*, Ahmad Khodadadi Darban, Hossein Shafeezadeh Moghadam Pages 15-26
    Measuring total metal concentration of heavy metals cannot be a suitable indicator to evaluate their danger and human health risk. Their toxicity depends on their mobility and bioavailability. In the present study, sixty-five surface soil samples in the Bama zinc-lead mining and residential area were collected to assess metal bioavailability. Since the mine is near to the metropolitan area (Isfahan) and a village is located in vicinity of the mine, assessing potential adverse effects of the surface soil on human health is a crucial issue. Firstly, total concentration of metals, using acid digestion method (Pb, Zn, Cu, Mn, Fe and Cd) as well as L.O.I and carbonate contents were determined for precisely understanding on pollution condition. Enrichment factor was used to determine the accumulation or non-accumulation of metals at Bama mining area and its residential area, using Fe and Mn as references elements. Single extraction tests were conducted to reveal bioavailability and human bioaccessibility of metals, using EDTA and glycine as extractants. Moreover, Bioavailability risk assessment index (BRAI) was used to assess the risk of metal bioavailability/bioaccessibility. Based on BRAI, qualitative mapping of health risk distribution was presented, using ordinary kriging method. High concentrations and enrichment factor of Pb, Zn and Cd were determined at mining area. Their high concentrations in mining area may be due to Bama host rocks where significant contents of mentioned metals were accumulated. The amount of L.O.I was higher in mining area, indicating the ability of its soils to carry more polluted metals. Cu created no pollution and health risk due to its low total and bioavailable contents at study area. Based on single extraction methods, the absorption percent for the toxic metals were different. The highest percent of bioavailability and human bioaccessibility was allocated to Cd and the lowest was for Pb. Further, it was found that glycine extracted more amounts of metals in comparison with EDTA,Since pH is in lower values using glycine solution, greater amount of metals can be changed into solution forms due to acidic pH of glycine. So the single extraction test exhibited higher bioaccessible fraction of metals. Bioavailable and bioaccessible percent of toxic metals was higher in residential area as mineral soils are in poor condition. Pearson correlation coefficient showed that Pb, Zn, Cd and carbonate contents were highly correlated at residential area. This is expressing that the metals probably are bonded with carbonate at residential area, which may increase the possibility of their mobility and release under changing conditions. Based on EDTA extractant, BRAI index was calculated 3.46 and 4.2 for mining and residential area, respectively. Further, on the base of glycine extractant, result of BRAI was calculated 4.2 and 4.6 for mining and residential area, respectively. The calculated BRAI represent a high risk for human beings and plants in both the mining and residential areas. Moreover, results revealed that higher degree of bioavailability/bioaccessibility for the residential area in comparison with the mining area. It could be concluded the higher potential health hazard for the residence beside the mining area.
    Keywords: Heavy metals, Bioavailability, human bioaccessibility, Single extraction, Bama zinc-lead mine
  • Elham Asrari*, Mohsen Bazrafcan Pages 27-37
    Nowadays, heavy metals are one of the greatest environmental problems. This problem intensifies by development of great industries and increasing of pollutant and contaminant resources daily. Increasing of population and reduction of water resources detect importance of waste treatment and reuse of water resources. Studies on treatment of effluents containing heavy metals have showed that adsorption to be a highly effective technique for removing heavy metals from aqueous solutions. The aim of this research was to use of absorbent materials (kaolin clay) to remove chromium (VI) from the wastewater in discontinuous system According to the results, optimum conditions of chromium removal were, pH=5, primary concentration of pollutant: 1000(mg/l), fine grained weight of consumed kaolin in constructing concrete: 30%, equilibrium time: 360 minutes, absorbing capacity: 3.06 mg/g absorbent. Covering the concrete surface with kaolin absorbent can be an innovative and useful solution for increasing the rate of elimination of pollutant and contaminants, cost reduction and accelerating the absorption process. Absorbing capacity of chromium is 29.5 mg/g absorbent in this condition respectively. Real waste sample are used for confirming the application of concrete in ordinary conditions of wastewater basin in accordance of optimum conditions of kinetics wastewater. Elimination rates of heavy metal of chromium were 90.3% in optimum condition with real samples that has been got from industrial factory. Therefore, it could be concluded that modified concert presents a good potential for treatment of Cr in wastewater. However, further research should be applied for continuous removal of heavy metal in large-scale. According to the result , mixing Kaolin in the concrete could be used to increase the Durability and adsorption efficiency of Chromium .
    Keywords: Chromium, kaolin, Modified concrete, Industrial wastewater
  • Fatemeh Jafari , S. Ali Akbar Salehi Neyshabouri * Pages 39-50
    The hydraulic jump takes place in both natural and manufactured systems. As it can be seen in streams, rivers and water distribution and irrigation networks formed downstream of hydraulic structures such as spillways, sluice gates, and drops. Generally, it is necessary to construct special structures downstream of flow in order to prevent damage caused by the high energy of water in supercritical velocities and also to dissipate the extra kinetic energy of hydraulic jumps. Stilling basin is one of these structures which is constructed downstream of spillways or waterfalls. Baffle blocks are often used to stabilize the jump, decrease its length and increase the energy dissipation. In order to make stilling basin with its dissipating equipment effective, the design should be in a way that the tailwater depth becomes greater than or equal to the sequent depth, otherwise, the jump doesn’t occur completely and will be swept out of the basin, resulting in scour of the downstream channel. If the flow rates become more than the design discharge, the tailwater depth will be greater than the one required for a free hydraulic jump. These situations are common in low head hydraulic structures including low diversion dam spillways and gates. Under such conditions, the hydraulic jump will be submerged. For submerged hydraulic jumps with blocks, two different types of flow have been observed, the deflected surface jet regime (DSJ) and reattaching wall jet regime (RWJ). There was also a transition state in which the flow could be changed from one state to the other by some external disturbance. In this article, a numerical study was conducted to investigate the influence of some parameters, consist of block height and shape, Froude number and distance of blocks from the gate, on the performance of submerged hydraulic jumps with blocks as energy dissipators. 3D RANS simulations have been applied by Fluent software. RSM turbulence model was used which illustrated much precise results in verification. In total fifty-four models with different geometrical and hydraulic situation according to the four mentioned parameters have been created and the percentage of dissipating energy is presented in each case to find the most effective condition. It was observed that the Froude number is the most important factor in the study of dissipating energy; such that the percentage of dissipating energy increases almost ten percent per one unit raise in Froude number. Furthermore, the existence of a slope at the back of blocks does not have an effect on energy dissipating, but it can be implemented to avoid cavitation. In addition, the percentage of dissipating energy goes up as the blocks are mounted closer to the gate and also provided the condition which leads to the deflected surface jet regime. The more turbulence in the deflected surface jet regime makes the desirable condition in which baffle blocks perform more efficiently as energy dissipators in comparison to reattaching wall jet regime. Finally, it can be concluded that for effective energy dissipation, block dimensions and all conditions should be provided in a way to form submerged hydraulic jump as the deflected surface jet regime.
    Keywords: Energy dissipation, submerged hydraulic jumps, baffle blocks, numerical simulations, stilling basin
  • Javid Chakherlou, Bahman Shervani Tabar* Pages 51-61
    In the production of reactive powdered concrete, fine-grained powder materials such as quartz sand, microsilica, and quartz powder are used as materials. This concrete has a high compressive strength compared to conventional concrete, which has attracted much attention in recent years. With this type of concrete, the weight of the structure can be significantly reduced, and its important features include high compressive strength, low permeability, durability and high abrasion resistance and high ductility that can absorb more energy during an earthquake. . In this research, we want to use limestone powder instead of a part of silica sand. For this purpose, after obtaining optimal mixing scheme based on the compressive strength and flow strength and diffusion diameter of the flow table, first replace the limestone powder with 0, 10, 20, 30 instead of silica sand, and then the powder Limestone has been used as a substitute-additive with different percentages and designs. The experiments performed on these samples included the psychological testing of the flow table and water absorption during treatment and compressive strength at the age of 7, 28 and 90 days. The results of the experiments show that by increasing the limestone powder up to 20% replacement with silica sand increases compressive strength, reduces very little in the psychological and also reduces water absorption during processing. In the production of reactive powdered concrete, fine-grained powder materials such as quartz sand, microsilica, and quartz powder are used as materials. This concrete has a high compressive strength compared to conventional concrete, which has attracted much attention in recent years. With this type of concrete, the weight of the structure can be significantly reduced, and its important features include high compressive strength, low permeability, durability and high abrasion resistance and high ductility that can absorb more energy during an earthquake. . In this research, we want to use limestone powder instead of a part of silica sand. For this purpose, after obtaining optimal mixing scheme based on the compressive strength and flow strength and diffusion diameter of the flow table, first replace the limestone powder with 0, 10, 20, 30 instead of silica sand, and then the powder Limestone has been used as a substitute-additive with different percentages and designs. The experiments performed on these samples included the psychological testing of the flow table and water absorption during treatment and compressive strength at the age of 7, 28 and 90 days. The results of the experiments show that by increasing the limestone powder up to 20% replacement with silica sand increases compressive strength, reduces very little in the psychological and also reduces water absorption during processing. In the production of reactive powdered concrete, fine-grained powder materials such as quartz sand, microsilica, and quartz powder are used as materials. This concrete has a high compressive strength compared to conventional concrete, which has attracted much attention in recent years. With this type of concrete, the weight of the structure can be significantly reduced, and its important features include high compressive strength, low permeability, durability and high abrasion resistance and high ductility that can absorb more energy during an earthquake. . In this research, we want to use limestone powder instead of a part of silica sand. For this purpose, after obtaining optimal mixing scheme based on the compressive strength and flow strength and diffusion diameter of the flow table, first replace the limestone powder with 0, 10, 20, 30 instead of silica sand, and then the powder Limestone has been used as a substitute-additive with different percentages and designs. The experiments performed on these samples included the psychological testing of the flow table and water absorption during treatment and compressive strength at the age of 7, 28 and 90 days. The results of the experiments show that by increasing the limestone powder up to 20% replacement with silica sand increases compressive strength, reduces very little in the psychological and also reduces water absorption during processing.
    Keywords: Reactive Powder Concrete, Compressive Strength, Flow, Curing, Limestone powder
  • Alireza Habibi* Pages 63-72
    The procedures for measuring, mixing, transporting, and placing heavyweight concrete are similar to those used in conventional concrete construction; however, special expertise and thorough planning are necessary for the successful completion of this type of concrete .The use of heavyweight concrete in construction is a specialized field, Heavyweight concrete is used in counterweights of bascule and lift bridges, but it is generally used in radiation shielding structures to absorb gamma rays and differs from normal weight concrete by having a higher density and special compositions to improve its attenuation properties. When heavyweight shielding concrete is used to attenuate neutrons, sufficient material of light atomic weight, which produces hydrogen, should be included in the concrete mixture. Some aggregates are used because of their ability to retain water of crystallization at elevated temperatures, which ensures a source of hydrogen not necessarily available in heavyweight aggregate Cements would be suitable for conventional concrete and produce the required physical properties, are suitable for use in heavyweight concrete. Low-alkali cement should be used when alkali-reactive constituents are present in the aggregates and a moderate or low-heat cement should be used for massive members, To avoid high and rapid heat of hydration and resultant cracking, it is advisable not to use Type III cement or accelerators unless the concrete temperature is controlled by specially designed refrigeration systems. Thorough examination and evaluation of heavyweight aggregate sources are necessary to obtain material suitable for the type of shielding required. These sources are limited, and a material survey should be conducted to determine availability, chemical and physical qualities. The supplier’s sources should be inspected to evaluate rock composition, abrasion resistance, and density since these properties may vary from one location to another within a deposit. The purchaser must realize that mineral ores are not as uniform as normal weight concrete aggregates and make appropriate allowances Limited resources and increasing use of concrete, particularly in the industrial production cause that the heavyconcrete be useful. In order to optimize production of heavyconcrete, the most basic parameters that must be changed is the mix design. Optimization of the concrete mixture design is a process of search for a mixture for which the sum of the costs of the ingredients is lowest, yet satisfying the required performance of concrete, such as workability strength and durability. For this purpose, heavy concrete mix design optimization model is firstly defined and then optimal mix design will be achieved, by using an optimization algorithm. The experimental data were utilized to carry out analysis of variance. To develop a polynomial regression model for compressive strength in terms of the five design factors ( cement, coarse aggregate, fine aggregate, water and density ) considered in this study The numerical results shows that the amounts of coarse aggregate and cement are simultaneously reduced and amount of the fine aggregate is increased in the optimum mix design. Considering mass production concrete in nuclear power plants, this optimal mix design methods and reduce the cost of concrete can greatly reduce the cost of construction
    Keywords: mix design, heavy concrete, optimization
  • Vahid Hasanzadeh Vayghan, Mirali Mohammadi* Pages 73-82
    The stage-discharge relationship is a type of resistance to flow evaluation that is used to determine the depth or the hydraulic radius if the flow discharge, channel cross-sectional shape and the properties of bed materials are specific. Wide channels as well as plane bed rivers, due to having higher ratios of width to depth, b/h, they have specific hydraulic characteristics than that of the normal open channels. In this research work, the hydraulic characteristics of widening channels including flow pattern, stage-discharge relationship and flow resistance, by using a physical model of a rigid boundary with 60 m length, 1.5 m wide and a bed slope of 0.001 that has b/h ratios of 12 to 56 are experimentally investigated. The construction material of channel model is concrete bed and concrete block walls were used. To insulate the channel bed and walls, a thick layer under the concrete was also used. Due to its wide width and length, the physical model of this study has low scale effects and the obtained results are closer to the normal open channels as well as the plain bed rivers. Based on the values of obtained for the Froude, Reynolds and Shear Reynolds numbers in model, it was found that the flow regime is subcritical and turbulent. According to the results of model, stage-discharge-tailgate relationship is shown plotted and it is found that as the flow rate increases, the tailgate height that required at the downstream end of the channel to produce a normal depth, increases. On the basis of normal depths obtained in the widen channel model, a reliable stage-discharge relationship is presented. The results show that this relationship has a higher coefficient than that of a natural channel stage-discharge relationship. Results, also reveals that between the calculated and measured the Manning coefficient, n, in the wide channel model, a difference (about 10%) is observed. The results of the research show that, for discharges greater than 35 lit/s, the measured Manning roughness coefficient, n is very close to the n values presented in literature. However, for the discharges less than 35 lit/s, the measured values of Manning’s n is 15% higher than the amounts provided in literature. The results of the present research show that by increasing the ratio of hydraulic radius to the roughness height of the bed (Rh/ks), the Manning roughness, n, decreases linearly. Also, based on the results, it was found that by increasing flow depth, The Manning roughness, n, decreases and by increasing Reynolds number, Re, the Manning n decreases linearly. The results also show that in the wide channel model, the Manning roughness coefficient, n, decreases from 0.022 to 0.016 by increasing Froude number, Fr, from 0.26 to 0.4, but n values increases by increasing depth ratio, b/h. According to the results of the experiments, in a range of Reynolds number, 700
    Keywords: Wide Rigid Boundary Channel, Physical Model, Stage-Discharge Relationship, Flow Resistance
  • Hamid Reza Nejati *, Amin Khodayar Pages 95-105
    It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced micro-cracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce micro-crack in the specimens. In the next, Uniaxial compression test for determination of stress-strain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure. It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced micro-cracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce micro-crack in the specimens. In the next, Uniaxial compression test for determination of stress-strain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure. It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced micro-cracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce micro-crack in the specimens. In the next, Uniaxial compression test for determination of stress-strain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure.
    Keywords: failure mode, micro-crack, mechanical behavior, Granite
  • Mohammad Ganbardezfouli, Masoud Dehghani, Adel Asakereh*, Behzad Kalantari Pages 107-120
    Because of the existence of concentrated forces and high bending moments at the junction of pile and raft in structure with high load using the non-connected pile raft foundation can be an appropriate option for the foundation of the mentioned structures. In this system, the piles and the raft are not connected and a cushion is used between the piles and the raft to redistribute the forces.in this state load transmit from raft to pile by arching mechanism that forming in cushion layer. The behavior of pile raft because of the interactions such as: pile-pile, pile-soil, pile-raft, raft-soil is very complicated. The pile use in pile raft for two purpose 1- reduce the settlement and 2- increase the bearing capacity. In this study, a series of experimental tests were conducted on a non-connected pile raft located on a sandy soil in order to investigate the effect parameter such as cushion height (H) and pile spacing (S) in forms of non-dimensional (H/B & S/D) on load-settlement behavior, share of piles and raft from total load and axial stress and frictional stress in center and corner piles. For this purpose, states H/B= 0.17, 0.34, 0.5 and S/D=2, 4, 6 were investigated. The axial stress in piles measured according to strain gauges that installed in perimeter of piles. The results shows that in three state S/D=2, 4, 6 optimum state occur in H/B=0.34. With increase the H/B the forces applied in pile is decrease and then the share of piles from total load decrease. The maximum share of piles from total load occur in H/B=0.17 and the minimum occur in H/B=0.5. In low level of load major of load protected by raft that with increase the load level, share of piles from total load increase and stable in a specified value. Due to the fact that part of the load is transmitted to piles by the soil around the pile, the maximum force applied to the piles does not occur at the tip of the pile and a negative friction is formed in the upper part of the pile. In the upper part of the pile, the displacement of the soil is more than the displacement of the pile, resulting in the formation of a negative friction and the formation of a positive friction in the bottom of the pile. With increase the H/B the value of negative friction is increase and neutral axes (a location of piles that displacement of soil and pile are equal) move down. In various pile spacing (S/D=2, 4, 6) and in three state (H/B= 0.17, 0.34, 0.5) maximum bearing pressure observed in S/D= 4. In S/D=2 maximum interaction effect (pile-pile) and minimum Enclosed of sand and in S/D=6 minimum interaction effect (pile-pile) existed and enclosed of sand has few effect because of high distance of piles. In three state H/B= 0.17, 0.34, 0.5 minimum share of piles from total load in S/D=6 and maximum share of piles in S/D=4 observed. Maximum negative friction in S/D=6 and minimum negative friction in S/D=4 observed. In all state in corner piles negative friction is more than center piles.
    Keywords: non-connected pile raft foundation, Laboratory model, sand, cushion
  • Hamed Rahman Shokrgozar*, Maryam Zare Aghblagh, Ahmad Ali Khodaiee Ardabili Pages 121-130
    Shallow foundation is one of the most common types of foundations used in mid–rise buildings in high seismic zones. The effects of soil-foundation-structure interactions are generally not significant in the structure with rigid bases, while the nonlinear behavior of soil and soil-structure interaction phenomenon cause various changes in the seismic response of structures with flexible bases. When a structure supported on shallow foundations is subjected to inertial loading due to earthquake ground motion, the foundation may undergo sliding, settling and rocking movements. If the capacity of the foundation is mobilized, the soil-foundation interface will dissipate significant amounts of vibrational energy, resulting in a reduction in structural force demand. This energy dissipation and force demand reduction may enhance the overall performance of the structure, if the settlement or bearing failure potential is considered. In this paper, the effect of soil and shallow foundation types, and variation of safety factor are studied to assess the seismic response of steel buildings. For this purpose, five stories special steel moment frames with two different soil types (II and IV) have been considered. The footing and strip shallow foundations have been designed for these buildings with safety factors of 2, 3 and 4. The finite element models are developed using OpenSees software. The structural members such as beams and columns are modeled by nonlinear beam–column elements and fiber sections. The soil–foundation interface is modeled using Beam-on-Nonlinear-Winkler foundation. In this procedure, an array of vertical q–z springs is used to capture vertical and rotational resistance of the foundation, while two springs, namely p–x and t–x, are placed horizontally to capture the passive and sliding resistance of the foundation, respectively. The constitutive relations for the q–z, p–x, and t–x springs are represented by nonlinear backbone curves that have been constructed from the pile-calibrated backbone curves developed by Boulanger. The independent p-x and t-x springs are connected to identical end nodes with zero distance between them. The seismic performance of these special steel moment frames with various foundation and soil type are evaluated using nonlinear static pushover and nonlinear dynamic time history analyses through seven far–fault ground motions. The numerical results for each case of soil-foundation-structure systems and rigid base conditions are then presented and compared in terms of maximum base shear and maximum inter–story drifts. These results are shown that in the soil type IV, the steel moment frames with the footing foundations have lower structural capacity and maximum base shears than structures with the the strip foundations or rigid bases, but the maximum inter-story drifts in the strip foundation bases are higher than others. It is also observed that by enhancing the safety factor, the structural capacity, the maximum base shear and the maximum inter-story drifts in the models with the footing foundations are increased, but changing in the safety factors do not influence in the structural response of models with the strip foundation. On the other hand, the safety factor and foundation types have not any effect on the structural capacity and the seismic responses of the structures that located on the soil type II.
    Keywords: Soil-foundation-structure interaction, Soil, foundation types, Low-rise Special steel moment frame, Safety factor
  • Davood Zarei, Abbas Ali Tasnimi* Pages 131-141
    Reinforced concrete shear walls are frequently used as lateral load resisting systems because of their ductile response and very good energy dissipation. When openings in RC shear walls are used due to architectural requirements, coupling beams are forming to connect two adjacent walls. The behavior of coupled shear walls is governed by coupling beams and they are the most vulnerable parts of coupled shear wall systems and were seriously damaged due to severe past earthquakes. To avoid construction difficulties and huge size of the RC coupling beams and better seismic performance an ductility, steel coupling beams in reinforced concrete shear walls have been mostly used during last years. Steel coupling beams connections to concrete shear walls are vulnerable and it is practically difficult and economically waste to repair damaged coupling beams, which would cause the building life cycle cost increasing. Therefore, it is necessary to transform traditional design approach to a design method in which some important parts would be replaceable rather than repairable. In this paper a building with special shear walls with steel coupling beams as lateral force resisting system is designed based on Iranian Standard 2800 and Iranian National Building Code. One of the 5th to 8th floor steel coupling beams section considered as fuse element and side beams and stiffeners of I-shaped beams designed based on eccentrically braced frames link beam criteria of Iranian National Building Code (part 10). Experimental specimen containing two RC shear walls that connected to each other with designed replaceable steel coupling beam in 1 to 3 scale is constructed and assembled in strong floor lab. For providing one degree of freedom movement of load wall four TBI Motion Company TRH65VE linear supports used. Cyclic displacement history of experiment calculated based on story drift and amplitudes of loading determined using Iranian Standard 2800 limit for story drift. Based on experimental results side beams remained in the border of elastic range and inelastic behavior of system concentrated in fuse element so the goal of system is satisfied. The side beam section is stronger and different with that was obtained from link beam criteria of Iranian National Building Code (part 10) because of available steel sheet size and since the side beam force is almost equal to elastic capacity of beam, the criteria for designing side beams is modified. Total system stiffness and fuse beam stiffness that obtained from experiment are fewer than analytical stiffness of system and fuse beam. Stiffness degradation of system occurs due to partially fixed performance of steel coupling beam connection to RC shear wall and micro cracks of wall in the connection zone. Different between real and analytical stiffness of system is very important and it is necessary to repeat the building design with modified stiffness and recalculate story drifts and distributed forces in structural elements. In this paper modifying method of stiffness is developed with moving fixed end point of steel coupling beam and increase of beam length. Effective fixed point of beam is defined by adding a portion of embedment length of steel beam in RC shear wall to both steel coupling beam ends.
    Keywords: RC shear wall, Steel coupling beam, Fuse element, Effective fixed point
  • Ali Zarei, Abolfazl Hassani* Pages 143-153
    In this research, 0, 5, 10, 15 and 20 percent of crumb rubber mix was used as a fine grained substitute for concrete pavement. Also, in another state, half percent of the steel fibers recovered from worn tires were added to these samples. The results of this study indicate that the compressive strength of samples with 5, 10, 15 and 20% crumb rubber in comparison with the control sample was reduced by 1.6, 36.9, 49.9% and 63.1%, and samples with 0, 5, 10, 15 and 20% crumb rubber and 0.5% steel fibers, respectively, decreased by 0.3, 11.2, 33.7, 5 / 41% and 44.3% respectively. Therefore, it is observed that the compressive strength of concrete containing crumb rubber and steel fibers is better than specimens with crumb rubber. Also, by replacing 5%, 10%, 15% and 20% of crumb rubber in concrete, its indirect tensile strength would be reduced by 7.5%, 15.3%, 41.4% and 31.2% , and by adding 0.5% of the steel fibers to the concrete by replacing 0, 5, 10, 15 and 20% of crumb rubber in concrete, Indirect tensile strength increased by 67.8%, 46.7%, 32.4%, 17.8% and 3.5%, respectively, and it is concluded that the tensile strength of concrete increases due to the addition of steel fibers.
    Keywords: worn tire, compressive strength, indirect tensile strength, concrete pavement, recycling
  • Mohammad Alembagheri*, Reza Sheikhzadeh Shayan Pages 155-167
    The Seismic analysis of concrete dams had been considered in an ideal form by means of two dimensional Monoliths in analyse and design procedures and structures had been subjected to ground motions with defining seismic coefficient. Lately, the research focus, however, has been more on linear time history analytics and fracture analysis of concrete dams in 3D space. With the advancement of knowledge in the field of earthquake engineering and the development of more precise methods for estimating the intensity of possible earthquakes, The methods of analyzing and evaluating the seismicity of the structures have been improved and the effects of more parameters can be considered in assessing the risk of each structure. In the present study, the seismic response of a concrete arch-gravity dam under the influence of earthquake stimulation is investigated in a three dimensional finite element analysis. The effects of dam-reservoir-foundation interactions are considered and the nonlinear behavior of the concrete and also the different patterns of the arc radius of the dam are studied. Finally, the contribution of response of each of the sustainability factors to seismic stimulation is evaluated. The Seismic analysis of concrete dams had been considered in an ideal form by means of two dimensional Monoliths in analyse and design procedures and structures had been subjected to ground motions with defining seismic coefficient. Lately, the research focus, however, has been more on linear time history analytics and fracture analysis of concrete dams in 3D space. With the advancement of knowledge in the field of earthquake engineering and the development of more precise methods for estimating the intensity of possible earthquakes, The methods of analyzing and evaluating the seismicity of the structures have been improved and the effects of more parameters can be considered in assessing the risk of each structure. In the present study, the seismic response of a concrete arch-gravity dam under the influence of earthquake stimulation is investigated in a three dimensional finite element analysis. The effects of dam-reservoir-foundation interactions are considered and the nonlinear behavior of the concrete and also the different patterns of the arc radius of the dam are studied. Finally, the contribution of response of each of the sustainability factors to seismic stimulation is evaluated. The Seismic analysis of concrete dams had been considered in an ideal form by means of two dimensional Monoliths in analyse and design procedures and structures had been subjected to ground motions with defining seismic coefficient. Lately, the research focus, however, has been more on linear time history analytics and fracture analysis of concrete dams in 3D space. With the advancement of knowledge in the field of earthquake engineering and the development of more precise methods for estimating the intensity of possible earthquakes, The methods of analyzing and evaluating the seismicity of the structures have been improved and the effects of more parameters can be considered in assessing the risk of each structure. In the present study, the seismic response of a concrete arch-gravity dam under the influence of earthquake stimulation is investigated in a three dimensional finite element analysis. The effects of dam-reservoir-foundation interactions are considered and the nonlinear behavior of the concrete and also the different patterns of the arc radius of the dam are studied. Finally, the contribution of response of each of the sustainability factors to seismic stimulation is evaluated.
    Keywords: Arch-gravity dam, seismic response, dam-reservoir-foundation interaction, nonlinear behavior
  • Mehdi Ghassemieh*, M. Taheripour Pages 169-180
    This study investigated the effect of combined loading on end-plate moment connection considering the interaction of bending moments, axial forces and twisting moments. In some cases, beam-to-column joints can be subjected to the simultaneous action of bending moments, axial forces and twisting moments. Current specifications for steel joints do not take into account the presence of axial forces (tension and/or compression) or twisting moments in the joints. Although the axial force or twisting moments transferred from the beam is usually low, it may, in some situations attain values which can lead to a considerable effect on the connections behaviour and significantly reduce the joint flexural capacity. Unfortunately, few studies considering the bending moment versus axial force interactions have been reported and there aren’t any reports considering bending moments versus twisting moments interactions or combination of all the mentioned cases of loads at the same time. The lack of knowledge for understanding the performance of end-plate moment connection under combined loads may lead to unreasonable or even unsafe design. Thus in this study a combination of different loads being applied simultaneously on the end-plate moment connection have been examined. Therefore two extended End-Plate connections with different behaviour modeled using finite element method of analysis. The interactions between connection components (bolts, members and endplate) were accurately modelled to simulate the actual behaviour of connections. Material nonlinearity as well geometric nonlinearity were considered in the analysis including the effect of contact. At first the behavior of the end-plate models are investigated in pure bending application. The numerical results were validated against experimental data. Due to the lateral loads and because of the existence of axial force in the moment resisting frames, the combination of bending and axial force in beams should be considered. An example of having bending and axial action is when the structures are subjected to fire which the effects of beam thermal expansion and membrane action can induce significant axial forces in the connection is a common condition. The results show that even in small amount of axial force the mode of failure and moment capacity of connection can change. Axial tensile forces decrease the initial stiffness of connection and axial compressive forces increase the stiffness. In many applications beams are eccentrically loaded and as a result experience twisting loads in combination with bending. The interaction effects due to torsion acting in combination with bending can reduce the capacity of the beam and initial stiffness of connection. Finally axial forces were added to the previous models so they experienced a combination of axial force, bending and twisting moment. The results indicated that the level and direction of axial force significantly modified the connection response. It was observed that compression forces significantly decrease the bending capacity of the models and lateral-torsional buckling of beam occures in all models. Tension forces can reduce the effect of torsion and in many cases they caused the bolts ruptured. Moreover, interaction diagram for predicting the bending capacity considering interaction of bending, torsion and axial forces are proposed based on the results from finite element analysis.
    Keywords: Moment Connection, End-Plate, Combined Loading, Torsion, Lateral Torsional Buckling
  • Sajedeh Farmani, Mahnaz Ghaeini, Hessaroeyeh*, Saleh Hamzehei, Javaran Pages 181-192
    In this paper, the Navier-Stokes and Laplace equations are solved using the Finite Element Method (FEM) based on complex Fourier elements. The FEM is considered by two types of shape functions: Lagrange shape functions and new complex Fourier functions. The proposed interpolation functions are derived using enrichment of complex Fourier radial basis functions in the form of . The present functions have properties of Gaussian and real Fourier radial basis functions. These useful properties have provided the robustness of the proposed method. Also, these functions have the simultaneously functions field such as trigonometric, exponential, and polynomial; while the classic Lagrange functions satisfied only polynomial functions field. In other words, these features provide an improvement in the solution accuracy with number of elements which are equal or lower than the ones used by the classic finite element method. Solving the Navier-Stokes and Laplace equations is the important challenge in the fluids mechanics problems. The most problems cannot be solved by the analytical methods. For this reason, the numerical methods are developed. Generally, the numerical methods are divided to two classes: the methods based on the mesh and meshless methods. In the first class, the computational domain are meshed and the governing equations are solved based them the finite element method, Finite Difference Method (FDM) and finite volume method (FVM) are placed in this category. While, in the second category methods, the computational domain is divided to moving particles. In these methods, there is no needed to any grid and the equations are solved on the particles. The smoothed particles hydrodynamic (SPH) method, Moving Particles Semi-implicit method and Discrete Least Squares Meshless method are in this class. The FEM is capable to solving the problems with complicated geometry. Also, the Neumann boundary conditions are applied properly.     Generally, the numerical methods such as finite element and finite difference methods are based on the mesh for solving the equations. For obtaining the results with high accuracy, it is needed to have enough elements. On the other side, when the number of elements (or number of degrees of freedom) is enhanced, the CPU time and storage space are also increased. For this reason, in this paper, the complex Fourier shape functions have been developed, which using them, both the number of elements can be reduced and also the suitable results can be obtained. In the present paper, at first, the governing equations and boundary conditions are expressed. Then, the FEM formulation and solution procedure are stated. Next, the complex Fourier shape functions and their enrichment process are described. Finally, three benchmark numerical examples are used in solving the Navier-Stokes and Laplace equations for the application of the proposed functions in the finite element method. These tests include Couette flow, flow of a viscous lubricant in a slider bearing and steady state heat transfer in rectangular region.  In order to show the efficiency and accuracy of the present method, the results of the proposed method are compared with the classic functions and also the analytical solutions. The results of this comparison indicate the high accuracy of the proposed method.
    Keywords: Navier-Stokes&Laplace equations, Finite Element Method, Complex Fourier Elements, Classic Lagrange Functions
  • Parviz Ghoddousi, Ali Akbar Shirzadi Javid*, Behnam Bozorgmehr Pages 193-206
    Several studies have been done on the rheological properties and setting time of cementitious mixes, but the relationship between these two important features has not been studied so far. Therefore, the aim of this study is to investigate the relationship between rheological properties and setting time in self-consolidating concrete mixtures. In this study, six self- consolidating concrete mixture proportions were considered, in which the effect of water-cement ratio changes, silica fume and slag was used. The electrical resistivity method has been used in determining its setting time, and the performance of this method has been evaluated in determining the rheological properties. Since the electrical resistivity method is not standardized in determining the setting time, therefore, to verify the results, the standard penetration resistance method is also used according to the ASTM-C403. In the study of rheological properties, the studies have been done in two sections of efficiency and rheometer analysis. From the results, it was found that mixtures that have higher slump flow have recorded less time to take. It was also found that concrete mixtures that have higher yield stress (static and dynamic)  have shorter setting time. In this way, the relationships between these two important variables (rheological properties and setting time) were evaluated by the relationships.
    Keywords: rheology, setting time, electrical resistance, self-consolidating concrete
  • Mohammad Yaghobi Sarbisheh, Mohammad Taghi Ahmadi* Pages 221-231
    Gravity dams are vital structures whose proper design and evaluation for stability are quite important. Effective issues on the stability of gravity dams are the uplift force and its distribution below the dam base. The uplift load pattern and distribution according to common codes are influenced by some factors such as head and tail water, assuming a segmented linear load distribution below the dam. In this research, to investigate the sensitivity of the load pattern to dam height, a number of gravity dams of Pine Flat type with different heights and their foundations are modeled. Coupled p-u finite element analysis is performed accounting for the seepage and stress field simultaneously. Dam body is considered to be completely impervious. The foundation rock is assumed as homogeneous and uniform, in terms of elasticity and permeability. The stresses generated in the dam interface for each case of the coupled hydro-mechanical analysis is compared against that of the conventional load pattern according to the USACE regulation for the same dam model. It was found that the error magnitude due to the conventional pattern has a direct relationship with the dam height. As the dam height increases, the amount of error of calculated stress increases. In particular, the error at the critical zones of the foundation such as at the dam heel, may raise even up to 40%. In the group of dams studied, the error increases even up to 12 times in respect to the expected error in the shorter dams. The deficiency could in some cases completely affect the safety of the dam. This research indicates the necessity of using more accurate methods of estimating uplift load under high gravity dams. Gravity dams are vital structures whose proper design and evaluation for stability are quite important. Effective issues on the stability of gravity dams are the uplift force and its distribution below the dam base. The uplift load pattern and distribution according to common codes are influenced by some factors such as head and tail water, assuming a segmented linear load distribution below the dam. In this research, to investigate the sensitivity of the load pattern to dam height, a number of gravity dams of Pine Flat type with different heights and their foundations are modeled. Coupled p-u finite element analysis is performed accounting for the seepage and stress field simultaneously. Dam body is considered to be completely impervious. The foundation rock is assumed as homogeneous and uniform, in terms of elasticity and permeability. The stresses generated in the dam interface for each case of the coupled hydro-mechanical analysis is compared against that of the conventional load pattern according to the USACE regulation for the same dam model. It was found that the error magnitude due to the conventional pattern has a direct relationship with the dam height. As the dam height increases, the amount of error of calculated stress increases. In particular, the error at the critical zones of the foundation such as at the dam heel, may raise even up to 40%. In the group of dams studied, the error increases even up to 12 times in respect to the expected error in the shorter dams. The deficiency could in some cases completely affect the safety of the dam. This research indicates the necessity of using more accurate methods of estimating uplift load under high gravity dams.
    Keywords: Uplift, High Gravity Dam, US-ACE, Finite Element