فهرست مطالب
مجله مهندسی عمران شریف
سال سی و سوم شماره 4 (زمستان 1396)
- تاریخ انتشار: 1396/12/27
- تعداد عناوین: 14
-
- پژوهشی
-
صفحات 3-12
امروزه استفاده از دیوارهای برشی فولادی به عنوان یک سیستم باربر جانبی لرزه یی کارآمد، در افزایش مقاومت جانبی و سختی ساختمان ها در برابر زلزله، در نوسازی و بهسازی لرزه یی سازه های بتنی و فولادی مورد توجه قرار گرفته است. در نوشتار حاضر، ظرفیت و سختی برشی دیوار برشی فولادی تحت آرایش های مختلف سخت کننده، اعم از: افقی، قائم و افقی قائم، به کمک روش اجزاء محدود بررسی و درنهایت، روابط نیمه تجربی مرتبط ارائه شده است. نتایج حاکی از پیش بینی مناسب سختی و مقاومت برشی دیوار برشی با سخت کننده بوده است، لیکن افزایش تعداد سخت کننده از حدی خاص، تاثیر محسوسی در افزایش سختی و مقاومت نخواهد داشت.
کلیدواژگان: دیوار برشی فولادی تقویت شده، سختی، ظرفیت برشی -
صفحات 13-23
در پژوهش حاضر، سیاست قیمت گذاری تراکم با عوارض متغیر نسبت به وقت از روز، به عنوان سیاست مدیریتی دفعی و بهبود سیستم اتوبوس رانی از طریق اعمال دو سیاست کاهش زمان سفر اتوبوس و کاهش فاصله ی ایستگاه اتوبوس تا محل کار، به عنوان سیاست های تشویقی بررسی شده اند. با استفاده از رجحان بیان شده، 231 نفر از شاغلان محدوده ی زوج فرد شهر تهران نسبت به سیاست های موردنظر، مدل لوجیت آشیانه یی انتخاب وسیله ی سفر ساخته و اثرات مستقل و ترکیبی سیاست ها برآورد شده است. نتایج نشان داده اند که سیاست قیمت گذاری تراکم در ساعات 30:6 تا 9 صبح، اگر به صورت ترکیبی با سیاست کاهش فاصله ی ایستگاه اتوبوس تا محل کار اعمال شود، می تواند تا 0٫49 سهم گزینه ی خودروی شخصی در ساعات مذکور را کاهش دهد. همچنین می توان به سیاست های پیشنهادی پژوهش حاضر به عنوان جایگزینی برای طرح زوج فرد شهر تهران توجه کرد.
کلیدواژگان: قیمت گذاری تراکم، بهبود سیستم اتوبوس رانی، انتخاب وسیله ی سفر، آزمایش رجحان بیان شده -
صفحات 25-35
در پژوهش حاضر، نتایج تحلیل لرزه یی غیرخطی سدهای بتنی وزنی با احتساب اندرکنش سد و مخزن با استفاده از مفاهیم مکانیک شکست، به منظور مقایسه ی مدل سازی ترک در جسم سد به دو روش ترک اندود چرخشی و غیرچرخشی چندجهته ی عمود ارائه شده است. سیستم سد مخزن به روش لاگرانژی مدل سازی و تحلیل به روش اجزاء محدود صورت گرفته و پاسخ های تغییر مکان تاج سد و نیز تنش در جسم سد پاین فلت تحت شتاب زلزله ی تفت ارائه شده است. از روش انتگرال زمانی بوساک برای حل معادلات دینامیکی حرکت استفاده و تحلیل غیرخطی به روش نیوتن رافسون اصلاح شده انجام شده است. نتایج به دست آمده نشان می دهند که هر دو روش مدل سازی ترک اندود، ضمن اینکه تا حدی وابسته به پارامترهای مدل سازی ترک است، در بسیاری از نقاط آسیب دیده ی جسم سد به طور مناسبی بر هم منطبق هستند. همچنین هر دو الگوی ترک ثابت و چرخان در تعداد نقاط ترک خورده و نیز مسیر رشد ترک، اختلاف اندکی با هم دارند.
کلیدواژگان: سد بتنی وزنی، تحلیل دینامیکی غیرخطی، ترک اندود چرخشی، ترک اندود چند جهته ی ثابت -
صفحات 37-45
در نوشتار حاضر با استفاده از روش های تحریک طبیعی، تبدیل ویولت پیوسته و تبدیل هیلبرت، مشخصات دینامیکی یک قاب برشی 3 طبقه تحت تحریک نوفه ی سفید ناایستا شناسایی شده است. همچنین روشی برای تبدیل سیگنال های ناایستا به سیگنال های ایستا پیشنهاد شده است، تا بتوان از روش تحریک طبیعی استفاده و ارتعاشات آزاد درجات آزادی سیستم را استخراج کرد. در روش مذکور، ارتعاشات آزاد استخراج شده به کمک تبدیل ویولت پیوسته به ریزسیگنال های مودی سیستم تجزیه و با استفاده از تبدیل هیلبرت ریزسیگنال ها، مشخصات دینامیکی سیستم نظیر: بسامدهای طبیعی، میرایی های مودی و ماتریس های میرایی و سختی شناسایی می شوند. در نوشتار حاضر، به کمک روش پیشنهادی مشخصات دینامیکی (بسامدهای طبیعی، شکل های مودی، ماتریس میرایی و سختی) یک سیستم قاب برشی 3 طبقه ی خطی و یک قاب 2 بعدی فولادی تحت ارتعاش نوفه ی سفید ناایستا شناسایی شده است.
کلیدواژگان: شناسایی سیستم، روش تحریک طبیعی، تبدیل ویولت پیوسته، تبدیل هیلبرت، نوفه ی سفید ناایستا -
صفحات 47-59
در نوشتار حاضر، تاثیر فاصله ی زمانی بیشینه ی پاسخ مولفه های افقی و قائم زمین لرزه در رفتار لرزه یی ساختمان های بتن آرمه ارزیابی شده است. از این رو، ساختمان های منظم بتن آرمه با تعداد طبقات 4، 7، 10، 13، 16 و 20 با سیستم قاب خمشی به کمک نرم افزار O p e n S e e s تحت 7 رکورد زلزله ی حوزه ی نزدیک، تحلیل استاتیکی و دینامیکی غیرخطی شدند و تاثیر مشخصه ی مذکور در نیروی محوری ستون ها، تغییر مکان جانبی، برش پایه، زمان تناوب افقی، ترتیب و الگوی شکل گیری مفاصل خمیری بحث و بررسی شد. نتایج نشان دادند که فاصله ی زمانی بیشینه ی پاسخ مولفه ی قائم و افقی زلزله، تاثیر قابل ملاحظه یی در نیروی محوری ستون ها دارد و این تاثیر در ستون های داخلی بیشتر از بقیه ی ستون هاست و می توان بیان کرد که تاثیر فاصله ی زمانی در ساختمان های کوتاه مرتبه بیشتر از ساختمان های میان مرتبه و بلندمرتبه است؛ به گونه یی که در ساختمان 4 طبقه، مقدار افزایش 43\٪ به مقدار 28\٪ در ساختمان 20 طبقه کاهش می یابد. تاثیر مولفه ی قائم زمین لرزه در تغییرات بارمحوری با افزایش فاصله ی زمانی میل به کاهش دارد، اما در تغییر مکان جانبی و برش طبقات ناچیز است.
کلیدواژگان: مولفه ی قائم زمین لرزه، فاصله ی زمانی، نیروی محوری ستون، ساختمان بتن آرمه -
صفحات 61-69
در مطالعات پیشین، رابطه های تحلیلی متعددی برای تخمین باربری ستون های محصور شده با F R P تحت بار فشاری ارائه شده است، اما عملا ستون ها تحت اثر توام بار فشاری و لنگر خمشی قرار می گیرند. روابط کمی برای تعیین باربری ستون ها تحت بارگذاری خارج از مرکز ارائه شده است و در بعضی موارد، مدل های ارائه شده در تناقض با یکدیگر هستند. در مطالعه ی حاضر، ابتدا به اصلاح ضریب عامل موثر کرنش F R P در مدل لام\پانویس{L a m} و تنگ\پانویس{T e n g} برای نمونه های تحت بارگذاری هم مرکز که با توجه به نوع F R P متفاوت است و سپس به بررسی ضریب تصحیحی برای اعمال خروج از مرکزیت در مدل های موجود و مقایسه ی آنها با نتایج آزمایشگاهی موجود پرداخته شده است. در مطالعه ی حاضر، ضرایب مذکور با استفاده از الگوریتم ژنتیک با بهینه کردن اختلاف بتن نتایج آزمایشگاهی و مدل تئوری محاسبه شده اند. با مقایسه ی نتایج آزمایشگاهی و نتایج مدل های اصلاح شده نشان داده شده است که مدل های اصلاح شده در مطالعه ی حاضر، تخمین بهتری برای ستون های دورپیچ شده تحت بارگذاری خارج از مرکز و هم مرکز ارائه می دهند.
کلیدواژگان: مقاوم سازی، بار خارج از مرکز، بار هم مرکز، ستون، محصور کننده ی F R P -
صفحات 71-79
در نوشتار حاضر، اتصالات خارجی تیر به ستون بتنی تحت اثر بارهای چرخه یی آزمایش شده اند. پس از ایجاد آسیب اولیه در نمونه ها، تقویت با ورقه های F R P انجام و اتصالات مجددا آزمایش شدند. سپس اتصال مبنا و اتصالات تقویت شده با استفاده از نرم افزار O p e n s e e s مدل سازی و نتایج با رفتار آزمایشگاهی آنها مقایسه شده است. سپس یک قاب 3 طبقه مدل سازی شده و روند ایجاد آسیب تحت اثر تحلیل بارافزون بررسی و با توجه به شدت آسیب، قاب ها مشابه روند آزمایش مقاوم سازی شدند. در انتها، قاب ها تحلیل غیرخطی تاریخچه ی زمانی شدند و اندیس خسارت پارک و انگ به دست آمد. با توجه به نتایج، سطح ترمیم پذیری سیستم قاب خمشی تقویت شده با ورقه های F R P معادل سطحی است که تمامی تیرها در سطح عملکرد آستانه ی فروریزش قرار گیرند. با بررسی پاسخ دینامیکی قاب ها و محاسبه ی اندیس خسارت پارک، سطح ترمیم پذیر برای قاب مورد مطالعه در دریفت طبقه ی 1٫03\٪ ایجاد می شود.
کلیدواژگان: اتصالات خارجی بتنی، مقاوم سازی، ورقه های F R P، سطح عملکرد، تحلیل غیرخطی -
صفحات 81-90
سازه های فولادی سرد نورد شده در مقایسه با سایر انواع سازه های ساختمانی، از قبیل: سازه های فولادی معمولی، سازه های بتن آرمه و سازه های سنتی، محاسن قابل توجهی از جمله: سبکی قابل توجه وزن و سرعت بالای ساخت دارند. یکی از سیستم های مقاوم در مقابل نیروهای جانبی در ساختمان های فولادی سبک، دیوار برشی با پوشش صفحه ی سیمان فایبری است. در نوشتار حاضر، رفتار لرزه یی دیوار برشی سرد نورد شده ی فولادی با پوشش صفحه ی سیمان فایبری بررسی شده است. برای این منظور از تحلیل المان محدود غیرخطی با استفاده از نرم افزار A N S Y S استفاده شده است که در آن تاثیر برخی از مشخصات هندسی قاب ها، مانند: نسبت عرض به ارتفاع، ضخامت ستونچه ها، ضخامت صفحه ی سیمان فایبری و فاصله ی ستونچه های قاب ها بررسی شده است. پارامترهای بیشترین ظرفیت باربری دیوار و شکل پذیری آن، از جمله پارامترهای اصلی مورد استفاده جهت مقایسه ی قاب ها هستند و ضریب رفتار قاب های بررسی شده با مقادیر آیین نامه های موجود مقایسه شده است.
کلیدواژگان: دیوار برشی، رفتار لرزه یی، قاب سرد نورد شده ی فولادی، ضریب رفتار، صفحه ی سیمان فایبری -
صفحات 91-98
در نوشتار حاضر با استفاده از روش های تحریک طبیعی، تبدیل ویولت پیوسته و تبدیل هیلبرت، مشخصات دینامیکی یک قاب برشی 3 طبقه تحت تحریک نوفه ی سفید ناایستا شناسایی شده است. همچنین روشی برای تبدیل سیگنال های ناایستا به سیگنال های ایستا پیشنهاد شده است، تا بتوان از روش تحریک طبیعی استفاده و ارتعاشات آزاد درجات آزادی سیستم را استخراج کرد. در روش مذکور، ارتعاشات آزاد استخراج شده به کمک تبدیل ویولت پیوسته به ریزسیگنال های مودی سیستم تجزیه و با استفاده از تبدیل هیلبرت ریزسیگنال ها، مشخصات دینامیکی سیستم نظیر: بسامدهای طبیعی، میرایی های مودی و ماتریس های میرایی و سختی شناسایی می شوند. در نوشتار حاضر، به کمک روش پیشنهادی مشخصات دینامیکی (بسامدهای طبیعی، شکل های مودی، ماتریس میرایی و سختی) یک سیستم قاب برشی 3 طبقه ی خطی و یک قاب 2 بعدی فولادی تحت ارتعاش نوفه ی سفید ناایستا شناسایی شده است.
کلیدواژگان: شناسایی سیستم، روش تحریک طبیعی، تبدیل ویولت پیوسته، تبدیل هیلبرت، نوفه ی سفید ناایستا -
صفحات 99-110
طراحی لرزه یی مناسب و ایمن بر پایه ی درک واقعی و دقیق تر از رفتار سازه صورت می گیرد که مستلزم شناخت دقیق تر از نحوه ی رفتار سازه در هنگام وقوع زلزله است و با درنظر گرفتن معیارهای مختلف آیین نامه یی تحقق می یابد. لذا در پژوهش حاضر، قاب های خمشی فولادی منظم با شکل پذیری و ارتفاع متوسط انتخاب و با معیارهای مقاومت (روش نیرو)، تغییر مکان مستقیم، انرژی و رخداد مفصل خمیری طراحی و ارزیابی شده است. پس از ارزیابی مدل ها، رابطه یی جدید برای بیشینه ی تغییر مکان جانبی مجاز بام (جهت کنترل رفتار سازه پس از طراحی) ارائه شده است. نتایج به دست آمده نشان می دهند که رابطه ی مذکور، اجازه ی تغییر شکل های بیشتری را نسبت به استاندارد 2800 به سازه می دهد. همچنین روش های تغییر مکان مستقیم و نیرو به ترتیب بیشترین و کمترین مقدار برش پایه و روش های رخداد مفصل خمیری و انرژی نیز به ترتیب بیشترین و کمترین مقدار دوره ی تناوب را ارائه می دهند.
کلیدواژگان: اب خمشی فولادی متوسط، روش نیرو، روش تغییر مکان مستقیم، روش انرژی، روش رخداد مفصل خمیری، بیشینه ی تغییر مکان جانبی مجاز بام -
صفحات 111-119
در پژوهش حاضر، عملکرد دینامیکی پل چند دهانه تحت تحریک وسیله ی نقلیه ی متحرک شتاب دار مطالعه شده است. مدل نوسان گر متحرک به منزله ی مدلی از یک سیستم متحرک که با درنظر گرفتن اثرات سیستم تعلیق و فنربندی وسیله ی نقلیه، مدل کامل تری نسبت به مدل های سنتی نیرو و جرم متحرک است، در پژوهش حاضر به کار رفته است. با مطرح شدن اندرکنش نوسان گر متحرک و سازه ی تیر چند دهانه، فرایند تحلیل در برگیرنده ی مدل های نیرو و جرم متحرک در دو حالت مجانبی نسبت بسامدی نوسان گر متحرک به بسامد سازه و علاوه بر آن شامل طیف وسیعی از حالات میانی خواهد بود. بررسی تاثیر شتاب حرکت نوسان گر متحرک در پاسخ دینامیکی تیر نشان می دهد که در نسبت سرعت های پایین، کمینه ی میزان پاسخ دینامیکی تیر به وقوع پیوسته و با افزایش یافتن پارامتر شتاب حرکت نوسان گر متحرک، بیشینه ی پاسخ دینامیکی نرمالایز شده بین دهانه ها در یک تیر چند دهانه به شکل محسوسی افزایش می یابد.
کلیدواژگان: پل چند دهانه، تیر چند دهانه، نوسان گر متحرک، حرکت شتاب دار، پاسخ دینامیکی - یادداشت فنی
-
صفحات 121-129
با توجه به روند شتابان واگذاری بخش اعظم فعالیت ها به شرکت های پیمانکاری، نرخ شاخص های مرتبط با حوادث شغلی، رشد نگران کننده یی به خود گرفته و موجب شده است تا بحث ارزیابی و انتخاب پیمانکاران صنعت ساخت و ساز از نظر بهداشت، ایمنی و محیط زیست حائز درجه اهمیت بالایی شود. الگوی ارائه شده از طریق تحلیل مطالعات کمی و نیز تکمیل پرسش نامه ی اختصاصی و برداشت های میدانی انجام و حجم نمونه با سطح اطمینان 95\٪ و احتمال خطای 5\٪، 252 نفر تعیین شد. روش آزمون با استفاده از آزمون کامئو و بارتلت و تحلیل عاملی تاییدی صورت گرفت. نتایج پژوهش حاضر بیانگر آن است که بالاترین شدت تاثیرگذاری مربوط به معیار منابع انسانی و کمترین شدت مربوط به معیار طرح ریزی است. الگوی پیشنهادی می تواند نیاز روزافزون سازمان ها را به یک الگوی جامع ارزیابی و انتخاب پیمانکاران برآورده سازد.
کلیدواژگان: ارزیابی عملکرد، انتخاب، پیمانکاران، صنعت ساخت و ساز، بهداشت، ایمنی، محیط زیست -
صفحات 131-139
در پژوهش حاضر، از توابع پتانسیل مختلط استیونسون برای تنش در محیط اطراف حفره ی بیضی شکل در داخل صفحه ی فلزی کشسان استفاده شده است. توابع پتانسیل مذکور برای تونل های طولانی و با فرض کرنش صفحه یی قابل استفاده هستند. ضرایب توابع پتانسیل با توجه به شرایط مرزی و فرضیات مسئله به دست آمدند و سپس با به کارگیری مشتقات متوالی و جزء به جزء توابع مرتبط، تنش های محوری و برشی در اطراف تونل بیضی شکل محاسبه شدند. از شرایط تنش های برجای یک محوری و دومحوری برای حل مسائل مربوط استفاده شده است. با استفاده از نگاشت همدیس، منطقه ی اطراف تونل بیضی شکل به قلمرو اطراف تونل دایره یی شکل تبدیل یافت. نتایج به دست آمده از تنش های محوری و شعاعی، هماهنگی مناسب با روش و مدل ارائه شده ی ماش خلیشویلی بر روی سطح تونل دارد.
کلیدواژگان: توابع پتانسیل، نگاشت، همدیس، کشسان، هارمونیک، بی هارمونیک -
صفحات 141-146
خاک های متورم شونده در مناطق زیادی از جهان وجود دارند و یکی از روش های اصلاح آنها، اضافه کردن آهک است. در نوشتار حاضر، اثر نوع آهک و روش افزودن آن بررسی شده است. پس از تعیین درصد بهینه ی آهک، با آزمایش بر روی نمونه های یک نوع خاک با درصد آهک متفاوت، دو نوع آهک شامل آهک دولومیتی و آهک خالص استفاده و در هر مورد سعی شده است تا خاک با افزودن آهک به صورت شکفته و مرده تثبیت شود. نتایج به دست آمده نشان داده که درصد آهک بهینه، 3\٪ وزنی خاک است. از طرفی آهک خالص در مقایسه با آهک دولومیتی، تورم آزاد کمتر، ولی فشار تورم بیشتری دارد. همچنین آهک های شکفته نسبت به آهک های زنده، تورم آزاد بیشتر و فشار تورم کمتری دارند. در نهایت، بهترین روش اختلاط آهک، تثبیت آن در درصد رطوبت بهینه ی خاک و به صورت دوغاب تعیین شده است.
کلیدواژگان: خاک متورم شونده، تثبیت، آهک
-
Pages 3-12
The use of steel plate shear walls (SPSW), as an efficient lateral seismic resistant system for buildings, has recently received much attention, both in new and rehabilitated structures of concrete and steel. Shear panels play an important role in improving the seismic behavior of structures. They generally occur as unstiffened or stiffened steel plate shear walls. This paper focuses
on stiffened steel plate shear walls and endeavors to investigate the shear behavior of this kind of panel as there are many theoretical and experimental studies on these systems without stiffeners, for which different analytical methods have been presented, and are mostly applicable to very thin steel plate shear walls, and also, as there is no simple mathematical equation which correlates the amount of increase in shear strength and stiffness of stiffened panels with the number of stiffeners. In order to achieve this purpose, the shear capacity (strength) and stiffness of stiffened shear wall panels have been studied with the aid of a series of finite element analyses under different stiffener configurations, including horizontal and vertical stiffeners and a combination of both, using ANSYS. The aim of the present numerical research is to study the effect of stiffening upon the ultimate shear strength and stiffness of stiffened shear panels; finally, to find a mathematical relationship (if any) between the increase of strength and stiffness of the wall and the number of vertical and horizontal stiffeners used. At the beginning, the unstiffened panel was modeled, by comparing the results of the analysis with the related classical equations and experimental tests. Having calibrated the errors, the process of stiffening went on for up to four vertical and horizontal stiffeners, and, finally, the corresponding
equations for the percentage of increase in strength and stiffness of the panels were obtained. Consequently, a domain of the number of stiffeners was introduced, and the addition of more stiffeners to the upper boundary of the proposed domain did not have considerable effect on the increase in strength and stiffness. Ultimately, the validity of the proposed equations was examined by some re-modeling within that a related domain was introduced, and the results confirmed the proposed equations in a very favorable manner.Keywords: S?T?I?F?F?E?N?E?D S?T?E?E?L P?L?A?T?E S?H?E?A?R W?A?L?L, S?T?I?F?F?N?E?S?S, S?H?E?A?R C?A?P?A?C?I?T?Y -
Pages 13-23
Today,transportationdemandmanagement(TDM)policy tools are accepted as practical solutions for decreasing the costs of congestion in urban regions, and more ecient using of transport infrastructures. This paper investigates the role of a \time-of-day congestion pricing scheme" as a pull TDM policy and two push TDM policies including \bus travel time reduction" and \bus access time reduction" in user's car use behavior. The main goal of this research is to estimate the impacts of these policy-tools on the probability of choosing car at morning peak, when they are applied separately or simultaneously. The analysis is based on the results of a stated preferences survey developed through the experimental design approach and was completed by 231 users, who travel intoTehranseven-oddzoneforworkbycar. Theadvantage of data gathering in even-odd zone was that these commuters were familiar with the boundaries of pricing area and so, they could make a more realistic decision(forexample, decisionaboutchoosingpark-and-ride mode). For considering a time-of-day congestion pricing policy, we introduced a cordon pricing scheme from 6:30 AM with a discount on entering after peak period (in this case study, between 6:30 AM to 9 AM). Like other policies, the discount policy has three levels containing 50%, 25% and 0% of peak period tolls. The independent and interaction e ects of these policies are assessed by developing a two-level mode choice nested logit model and estimating marginal e ects. This model has 8 alternatives, three of which are related to driving a car: drive before 6:30, drive between 6:30 and 9, and drive after 9 AM. Results show that cordon pricingschemefrom6:30AMhasthelargeste ectandcould decrease share of drive between 6:30 and 9 AM by 0.408. Congestion charging scheme at 6:30-9 AM and bus access time reduction, are also the most e ective policytools with a 0.49 decrease in car share when applied simultaneously.
Keywords: Congestion Pricing, Bus System Enhancement, Mode Choice, Stated Preference Experiment -
Pages 25-35
Seismic evaluation of concrete dams due to some considerations is very important. The effects of fluid-structure-foundation interaction, nonlinear behavior of dam material due to crack, and earthquake loading are some of these considerations and should be considered in modeling and analysis of the system.The nonlinear seismic response of concrete gravity dams is presented when the effect of the dam-reservoir interaction is included using Lagrangian-Lagrangian approach of the finite element method. Nonlinear fracture mechanics, based on the smeared crack concepts, is used to study the cracking profile and response of the dam. In this study, a comparative study between the coaxial rotating crack model and orthogonal multi-fixed smeared crack models is carried out. Based on the presented formulation, Pine Flat concrete gravity dam is analyzed and its crest response and stresses within the dam body are founded. Bosak's time integration and corrected Newton-Raphson method are used for solving nonlinear dynamic equations.Results show that the two crack approaches have negligible difference in terms of the number of cracked gauss points and the crack profile. Tensile principal stresses based on fixed crack concept are greater than those of the rotating crack concept, but for compressive principal stresses the results are vice versa. The differences are due to unloading-reloading path and shear retention factor, but crack propagating path remains the same. Displacements of dam crest in nonlinear cases are greater than those of linear ones and show the same result in two crack models. This phenomenon depended on internal damping of system in both linear and nonlinear cases. Permanent displacement of dam crest based on fixed crack concept is greater than that of the rotating crack concept, and this phenomenon depends on cracking intensity of dam body. Results show that the fixed crack concept have better convergence than that of the rotating crack concept and the number of iterations in the time steps are low.
Keywords: C?O?N?C?R?E?T?E G?R?A?V?I?T?Y D?A?M, N?O?N?L?I?N?E?A?R D?Y?N?A?M?I?C A?N?A?L?Y?S?I?S, R?O?T?A?T?I?N?G S?M?E?A?R?E?D C?R?A?C?K, N?O?N-R?O?T?A?T?I?N?G M?U?L?T?I?D?I?R?E?C?T?I?O?N?A?L S?M?E?A?R?E?D C?R?A?C?K -
Pages 37-45
Different approaches are presented for systems identification in the literature. Benchmark problems for the system identification and damage detection of civil engineering structures are established, and different methods are illustrated by international participants. In this paper, the dynamic characteristics of a three story shear frame, subjected to nonstationary white noise excitation are identified by the use of Natural Excitation Technique (NExT), Wavelet and Hilbert transforms. Because the ambient vibration imposed on the system is nonstationary, the response acceleration of the system is also nonstationary. Therefore, a method is used to turn nonstationary signals into stationary ones. Natural Excitation Technique is applied to extract free vibration responses of the system from the available stationary signals.Continuous Wavelet Transform (CWT) of free vibration decay decomposes the signals to a set of sub-signals corresponding to natural vibration modes. The mother wavelet used is modified complex morlet wavelet. Analytical complex signals are extracted from the mentioned sub-signals using Hilbert Transform. The Hilbert transform is applied to each modal response to obtain the instantaneous phase angle and amplitude as functions of time t. Then, a linear least-square fit algorithm is used to fit the instantaneous phase angle and the log of instantaneous amplitude. From the slopes of these linear least-square lines, the natural frequency and damping ratio of each mode can be identified. Based on a single measurement of the free vibration time history at a proper location of the MDOF linear system, all natural frequencies and damping ratios can be identified. When the responses at all degrees of freedom are measured, the complete system dynamic characteristics can all be identified, including the mode shapes, damping and stiffness matrices. The applications of the proposed method are illustrated in detail using a linear three degrees of freedom shear frame. Simulation results show that the accuracy of the method in identifying the system characteristics is remarkable.
Keywords: S?Y?S?T?E?M I?D?E?N?T?I?F?I?C?A?T?I?O?N, N?A?T?U?R?A?L E?X?C?I?T?A?T?I?O?N T?E?C?H?N?I?Q?U?E, C?O?N?T?I?N?U?O?U?S W?A?V?E?L?E?T T?R?A?N?S?F?O?R?M, H?I?L?B?E?R?T T?R?A?N?S?F?O?R?M, N?O?N?S?T?A?T?I?O?N?A?R?Y W?H?I?T?E N?O?I?S?E -
Pages 47-59
One of the main characteristics of the near-fault ground motions is low time interval between horizontal and vertical ground motion peaks, which can be coincidental when the source distance is less than 5 km. Generally, vertical peak ground motion occurs earlier than the horizontal one, thus has a significant effect on the response of the structures. In this paper, the effect of time interval between peak response in the horizontal & vertical components of ground motion is evaluated on the seismic behavior of RC Buildings. In this regard, regular RC buildings (in plan and elevation) with 4, 7, 10, 13, 16, and 20 stories and moment-resisting frame system in the ground type II are analyzed by OpenSees code. Then, the nonlinear static and dynamic analyses were done under the seven near-fault records, accordingly. These records were selected from the various parts with different magnitudes and frequency contents. The effect of vertical component of ground motion as well as time interval between horizontal and vertical ground motion peaks has been explored on the seismic behavior of RC buildings including column axial forces, lateral displacement, base and story shear force, horizontal period as well as order and pattern of plastic hinge occurrence. Results showed that time interval between horizontal and vertical ground motion peaks has considerable effect on the columns axial force; this effect is higher on the internal columns rather than perimeter columns. It can be explained that the effect of time interval between horizontal and vertical ground motion peaks on low-rise buildings is higher than those of medium- and high-rise buildings. The effect of vertical component of ground motion on the column axial force variation tends to decrease with the increase of time interval, which, nevertheless, has small effects on the lateral displacement and story shear.
Keywords: V?E?R?T?I?C?A?L C?O?M?P?O?N?E?N?T O?F G?R?O?U?N?D M?O?T?I?O?N, T?I?M?E I?N?T?E?R?V?A?L, A?X?I?A?L F?O?R?C?E, R?C B?U?I?L?D?I?N?G -
Pages 61-69
Wrapping reinforced concrete columns with composite materials is among the new methods of repairing and strengthening at the moment. There are several analytical relationships for load capacity prediction of strengthened columns with this method under compressive load in the literature, but, columns that are on the border of buildings are usually subjected to combined axial-flexural loading in practice. According to strain gradient in the columns under eccentric loading, the FRP confinement effect is different and changing with the load eccentricity. A few relationships for load capacity calculation of strengthened columns under eccentric loading are presented, some models in the literature are in contradiction with each other. This paper presents constant factor, FRP strain efficiency factor in the model, proposed by Lam and Teng, which is modified for specimens under centric loading, varying according to the type of FRP. It has been shown in this study that the constant factor is not only dependent on FRP type, but it also depends on the FRP elastic modulus to unconfined concrete compressive strength ratio. With this modification, total error value of 76 specimens under centric loading will decrease from 10.63 to 9.5 percent.Then, correction factor is analyzed to apply the load eccentricity to the existing models and compare them with available experimental results. This correction factor shows that compressive strength of confined concrete under eccentric loading increased by increasing in the load eccentricity. By applying this coefficient to the model by considering the load eccentricity and calculating the load carrying capacity of specimens, the total error of specimens under eccentric loading decreases from 11 to 6 percent. This factors is determined using Genetic algorithms by optimizing the difference between experimental results and theoretical values. Comparison of results of tests with modified model, demonstrates that modified models in this study provide a better prediction for wrapped columns under concentric and eccentric loadings.
Keywords: S?T?R?E?N?G?T?H?E?N?I?N?G, E?C?C?E?N?T?R?I?C L?O?A?D, C?O?N?C?E?N?T?R?I?C L?O?A?D, C?O?L?U?M?N, F?R?P C?O?N?F?I?N?E?M?E?N?T -
Pages 71-79
The scope of this study is the investigation of the rehabilitation of structures retrofitted by use of carbon-u{fb01}bre-reinforced plastics (CFRPs) to achieve a safe, economic and practicable level of seismic damage. This paper investigates analytically the efficiency of the strengthening technique for improving the seismic behavior of damaged structures. 4 beam-column connections are tested under reversed cyclic load. The connections have none-seismic detailing of rebars, i.e., no transverse rebar and seismic stirrups are used in the joint core and beam and column critical end zones. The joints are damaged in different levels and then retrofitted by CFRP sheets. The strengthened joints are tested again to reach the ultimate drift capacity. Then, the tested joints, such as reference joint and retrofitted joints, are analyzed by Opensees nonlinear software. The results of joint analysis are compared with experimental behavior of specimens. The hysteresis curves of the modeled joints had a high level of accuracy in terms of stiffness degradation, moment carrying capacity, capacity degradation and energy dissipation. In the following, a multi-story/multi-bay moment-resisting frame is selected for assessment of seismic response of damaged frames. So, a step-by-step pushover analysis is done in order to find the plastic hinge positions and the level of plasticity on the moment resisting frame. The plastic hinges are developed on the beam ends and middle length of the frame beams. As the analysis progresses, the damaged frames are categorized in 7 levels according to performance levels defined by FEMA 356. The damaged Frames are retrofitted by CFRP sheets, considering the level of damage similar to the tested joints mentioned above. At the end, the retrofitted frames are subjected to El-Centro base acceleration. The root mean square parameter of roof displacement is also calculated for nonlinear time history response of frames. The retrofitting of the plastic hinges improved the RMS of the responses and compensated the lost capacity and stiffness. The results show that reparability level of frames retrofitted by CFRP sheets is equal to the level that the hinges on all of the beams are formed in collapse-preventing performance level. This level for specific frame investigated in this study is equal to 1.03% storey drift. Also, the results show that structures could be retrofitted by external bonding of FRP sheets to a limited level. If the damage level of structures is higher than this reparability level, other rehabilitation methods may be useful.
Keywords: B?E?A?M-C?O?L?U?M?N C?O?N?N?E?C?T?I?O?N, R?E?H?A?B?I?L?I?T?A?T?I?O?N, F?R?P S?H?E?E?T?S, N?O?N?L?I?N?E?A?R A?N?A?L?Y?S?I?S, P?E?R?F?O?R?M?A?N?C?E L?E?V?E?L -
Pages 81-90
In recent times, the use of cold formed steel (CFS) structures in housing industry has increased worldwide due to its great advantages, such as their light weight and high speed construction. In addition, the possibility of mass production and industrialization, quality control of construction and performance are other advantages of this type of structures. Although CFS walls are not new and have been used as non-structural components for many years, their application as the main load-bearing structural frames is relatively new, and as a result, appropriate guidelines that address the seismic design of CFS structures have not yet been fully developed. In addition, the lateral design of these systems is not adequately detailed in the available standards of practice. One of the currently-in-use lateral resistant systems for light steel buildings is steel shear walls sheathed by fiber cement boards (FCB). Fiber cement board sheathed panel lateral resistant system is already being used in housing industry though there are very few studies on the structural performance of these systems. In this paper, the seismic behavior of shear cold formed steel walls sheathed by fiber-cement board panels is investigated. For this purpose, finite element nonlinear analysis is employed using ANSYS software. The impact of some structural characteristics on the behavior of frames, including geometric imperfections and residual stresses are also studied. In addition, the ratios of height to width, studs thickness, fiber cement boards thickness, and studs spacing are investigated. Of particular interest are the specimen's maximum lateral load capacity and deformation behavior as well as a rational estimation of the seismic response modification factor. The study also looks at the failure modes of the system and investigates the main factors contributing to the ductile response of the CFS walls. A discussion on the calculated response factors in comparison to those prescribed in the relevant codes of practice is also presented.
Keywords: Shear Wall, Cold-Formed Steel Frame, Seismic Behavior, Response Modification Factor, Fiber Cement Board -
Pages 91-98
Much attention has been given to structural damage detection in recent decades in order to assess the reliability of structures during their service time. To detect damage in structures, one method, among different ones, is considered the most important i.e. the vibration-based methods. Because the modal parameters of structures like frequency and mode shape are so sensitive to structural properties like stiffness, it can therefore be used for detecting damage in structures.This paper presents a novel approach for structural damage detection and estimation using expanded mode shapes and extreme learning machine (ELM). One of the problems in damage detection is the compatibility between the number of sensors and Degree of Freedoms (DOFs) in the finite element model of structures, in which the number of sensors, installed to structure, is usually less than the number of DOFs in the finite element model. So, the model reduction method should be used to match incomplete measured mode shapes or the measured mode shapes should be expanded to the dimension of the analytical mode shapes. In this study, the second option is adopted, using the improved reduction system (IRS) transformation matrix and used as input parameters to the ELM for damage identification. The proposed method uses the first two expanded mode shapes and natural frequencies as the input parameters and damage states as output to train the ELM model. Also, noise effect on the measured modal data has been investigated. The present method is applied to three examples consisting of a four span continuous beam, plane steel truss and four story plane frame. The obtained results demonstrated the accuracy and efficiency of the proposed method using incomplete modal data. Also, the results obtained indicate that the proposed method is a promising procedure for damage identification in spite of use of noisy modal data.
Keywords: D?A?M?A?G?E D?E?T?E?C?T?I?O?N, E?X?P?A?N?D?E?D M?O?D?E S?H?A?P?E, E?X?T?R?E?M?E L?E?A?R?N?I?N?G M?A?C?H?I?N?E -
Pages 99-110
Appropriate seismic design is based on real understanding of structural behavior. This requires precise perception of structural behavior during earthquakes which will beachieved by considering various code's criteria. In other words, an ideal seismic design is a method which directly considers non-linear behavior and designs frames in a way that they experience their maximum capacity, it means plastic hinges occur in frames. The plastic hinge locations should be far from joints between beams and columns. In this way, local instability does not occur. Actually, more accurate recognition of structural behavior during earthquakes is the main issue of this research. For this purpose, regular steel- moment frames with medium ductility and height were designed based on resistance (force), direct displacement, energy and plastic hinge methods. All the models were developed in OpenSees computer program, and they were analyzed through non-linear time history. Three records, according to record magnitude, fault distance, and soil type, were used from Pacific Earthquake Engineering Research Center (PEER) (Kobe, Northridge, and Tabas). Ultimately, these records were coordinated based on Iranian Standard No. 2800. Then, frames were evaluated with various code's criteria in order to represent a new formula for maximum roof allowed displacement (for the purpose of controlling structural behavior after design).This formula is based on maximum displacement that frames have experienced during different earthquake records in non-linear time history analysis. The result indicates that the new formula allows more displacement to structures in comparison to Iranian Standard No. 2800. According to displacement time history of designed frames, at the beginning of the earthquake, the structures experienced severe impact and their nonlinear behavior was started. The transient displacement occurred when the first impact was applied to structure, and it was a displacement which happened along with the first plastic hinge occurrence. It makes sudden shock in displacement time history curve. With the passage of time, structures experienced variable displacements, and finally, a permanent displacement remained which is for the sake of nonlinear analyzing. Also, it can be inferred from the results that direct displacement and force methods present maximum and minimum base shears, respectively. In addition, in all frames, plastic hinge method provides maximum period value in comparison to other methods. It reveals that those frames which have been designed with plastic hinge method are more flexible. According to the results, the difference between direct displacement and energy methods period values is low, and period value of energy method is the minimum, as well.
Keywords: M?E?D?I?U?M S?T?E?E?L M?O?M?E?N?T F?R?A?M?E?S, F?O?R?C?E M?E?T?H?O?D, D?I?R?E?C?T D?I?S?P?L?A?C?E?M?E?N?T M?E?T?H?O?D, E?N?E?R?G?Y M?E?T?H?O?D, P?L?A?S?T?I?C H?I?N?G?E M?E?T?H?O?D, M?A?X?I?M?U?M R?O?O?F A?L?L?O?W?E?D D?I?S?P?L?A?C?E?M?E?N?T -
Pages 111-119
Vibration of structures under moving loads has been extensively dealt with by numerous researchers. In particular, this problem is of importance to bridge engineers. In this regard, there are a great number of studies on vibration analysis of single - span thin beams under moving loads. It is noteworthy to highlight that there is lack of research on the dynamic behavior of multi-span beams under moving inertial loads. Moreover, most of these studies neglect the inertia of the moving vehicle and consider the moving force approach. However, several investigations using moving mass approach highlighted the considerable contribution of load/structure inertial interaction for heavy masses moving at high speeds. In moving mass simulation framework, a solid mass is considered to slide on the base structure while remains directly in contact with the base structure. Therefore, the transverse acceleration of the moving object corresponds to that of the beam beneath the traveling load and the effects of vehicles flexibility are neglected. Moving oscillator model is composed of a mass supported by a spring-damper system in order to allow for the vehicle suspension system. Hence, moving oscillator can capture a wider range of possible structural behaviors with regard to the variation of vehicle stiffness. In this research, dynamic behavior of a multi-span continuous beam subjected to the excitation of an accelerated moving oscillator is studied to simulate vibration of a multi-span bridge acted upon by the accelerated movement of a vehicle. Euler-Bernoulli beam theory is employed as the governing equation for each span of the beam. The proposed solution is applicable to general beam fixity conditions. Moving oscillator model, as a reduced order model of a moving system, is of higher accuracy rather than old-fashioned methods of moving force and moving mass due to importing suspension system effects on the corresponding computational model. The solutions are verified and very close agreement is observed with published results via other methods in the asymptotic states of moving oscillator, where soft and rigid springs correspond to moving force and moving mass, respectively.
Keywords: Multi-Span Bridge, Multi-Span Beam, Moving Oscillator, Accelerated Movement, Dynamic Response -
Pages 121-129
According to assignment of most activities to contractingcompaniesandneglectingstrictenforcementof safety, health, and environment in companie's contractions, ratesofrelatedindexesoccupationalaccidentshavebeen growing disturbingly, and thus increasing the importance of evaluating health, safety, and environment (HSE)performanceofbuildingindustrycontractors. The mainpurposeofthisstudyistoprovideanoptimumpattern for evaluation and selection of construction industry contractors by HSE view. This research determines the main and secondary criteria which a ected evaluating and selecting contractors by quantitative studies and special questionnaires and surveying perceptions. Sample size of 95% con dence level and margin of error of 5 percent by 252 peoples, including 4 Group executives and managers, employers, contracting companies and experts in health, safety and the environment were determined by the employer and contractor. KMO and Bartlett's test and con rmatory functional analysis (CFA) were used as testing methods. Validity of this questionnaire was obtained as 0.863 by Cranach's Alpha coecientandreliabilityofquestionnairewascon rmed. This article tries to determine intensity of these criteria in patterns of a model. Results show that human resources criteria are with the most e ectiveness and planning criteria are of little e ect. Suggested pattern can ful ll a continuous increase to a comprehensive pattern for evaluation and selection contractors. According to the proposed model, organizations can simply evaluate theircontractorsintermsofHSEperformance. Contractors can also use this model to assess and identify their own weaknesses in the eld of Health, Safety and Environment (HSE) of the model, which in turn "reduces accidents and improves awareness of contractors in the eld of HSE Management System, and so, Standards HSE will be the scope of its activities.
Keywords: Evaluation, Selection, Contractors, Construction Industry, Health, Safety, Environment -
Pages 131-139
A powerful method for analysis of stress and deformation around underground structures is the analytical method. Among the analytical models the one that utilizes complex potential functions for the solution have the advantages of applicability and accuracy. Most of the governing solutions are applied to the circular shape tunnels or simple cross-section tunnels with one- or two-dimensional in-situ normal stresses conditions. For the elliptical shape tunnels, there are three methods of solution based on the complex potential analysis. They are Stevenson method, Mushkelishvilli method, and Series method for approximation of the complex potential functions. In the above models, the solutions are not unique in details, but all satisfy the boundary conditions on the tunnel surface and far field stress situation. The interested readers to these analytical method's solutions to tunnels with different shapes can refer to the papers and books governing Timoshenko and Goodier, Savin, and Muskhelishvilli. In the above models, the Stevenson one is a powerful and robust model for analysis of stress and deformation on and around the elliptical tunnels. Therefore, in this research, the complex potential and conformal mapping functions of Stevenson model are applied to obtaining the stress around those openings. The analysis is a two-dimensional plane stress or plane strain conditions. Therefore, the solution can be used for stress concentration around long tunnels. The parameters of the governing complex potential functions are obtained by satisfying the boundary conditions and the problem hypothesis. Then by applying the sequence differentiations of the potential and conformal complex functions to the formulation the normal and shear stresses around the tunnel are calculated. The stress field, which is considered around tunnel, is uniaxial and biaxial compressive stresses. The results from three solved problems show the similarity between the calculated stresses on the tunnel surface with the Muskhelishvilli model. The solution can also be used for the situation of in-situ shear stress boundary condition around tunnel. It is suggested that the formulation be developed for the deformations on the surface and around the elliptic tunnels.
Keywords: P?O?T?E?N?T?I?A?L E?Q?U?A?T?I?O?N?S, M?A?P?P?I?N?G, C?O?N?F?O?R?M?A?L, E?L?A?S?T?I?C, H?A?R?M?O?N?I?C, B?I?H?A?R?M?O?N?I?C -
Pages 141-146
Expansive soils are generally found in many parts of the world, especially in arid and semi-arid areas. Because of the ability of volumetric changes in response to seasonal fluctuations of moisture content, these soils are known as a harmful phenomenon in geotechnical engineering. Such soils swell when the moisture content is increased and shrink when the moisture content is decreased. Consequently, expansive soils cause detrimental damage to the structures founded on them. Clay soil can be stabilized by the addition of small percentages, by weight, of lime, thereby enhancing many of the engineering properties of the soil and producing an improved construction material.In this study, in order to find an optimum percentage of the lime to stabilization of expansive soil, the expansive soil was stabilized with various amounts of dolomite quick lime. Next, in order to find the effective type of lime to reduce the swelling potential, the expansive soil was stabilized with two types of lime such as Dolomite lime and Calcite lime that are used as quick lime and hydrated lime. Finally, in the last step, the soil was stabilized with lime by different methods to find the best method of adding lime to the soil.The results show that the optimum percentage of adding lime is 3% of the total weight of expansive soil. However, the results indicate that the use of calcite quick lime shows a lower free swell, but a higher swelling pressure than the use of dolomite quick lime. It is also expressed that stabilization of expansive soils with hydrated lime has higher free swell and lower swelling pressure, in comparison to the stabilization with quick lime. The experimental results also show that adding lime in the optimum moisture of soil is the most effective method of stabilization of expansive soil.
Keywords: E?X?P?A?N?S?I?V?E S?O?I?L, S?T?A?B?I?L?I?Z?A?T?I?O?N, L?I?M?E
©2000-2025 magiran.com All Rights Reserved.