فهرست مطالب

نشریه مهندسی عمران مدرس
سال یازدهم شماره 4 (زمستان 1390)

  • تاریخ انتشار: 1390/10/14
  • تعداد عناوین: 10
|
  • اسماعیل آیتی، احسان عباسی صفحه 1
    در این نوشتار به پژوهشی برای شناسایی عوامل موثر بر فراوانی و شدت تصادفات بزرگراه های درون شهری انجام شده پرداخته می شود و به عنوان مطالعه موردی از داده های تصادفات بزرگراه های شهری مشهد استفاده می شود. مدل های آماری که در این پژوهش استفاده شده، مدل های رگرسیون پواسن، دوجمله ای منفی، پواسن پرصفر و دوجمله ای منفی پرصفر است، از متغیرهای مربوط به جریان ترافیک و طرح هندسی راه به عنوان متغیرهای ناوابسته مدل ها استفاده شده است. کار ویژه ای که در این پژوهش انجام شده، جداسازی حجم کل ترافیک به حجم خودروهای سواری، خودروهای سنگین و خودروهای غیر سواری سبک است تا نقش حجم ترافیک در رخداد تصادفات به گونه ای ویژه و موشکافانه بررسی و روشن شود دقیقا کدام بخش از ترافیک نقش موثر یا موثرتری در رخداد تصادفات دارد.
    در این پژوهش کارایی مدل های رگرسیون پرصفر در برابر مدل های رگرسیون ساده پواسن و دوجمله ای منفی در مدل سازی تصادفات بزرگراه های درون شهری بررسی می شود. نتایج پژوهش نشان می دهد شمار راه های دسترسی و قوس های افقی در بخش های بزرگراه و حجم خوروهای غیرسواری سبک، نقش افزاینده ای در احتمال رخداد تصادفات دارد، همچنین مدل رگرسیون دوجمله ای منفی پرصفر بهترین و برازنده ترین مدل، هم برای مدل سازی تصادفات با زیان مالی و هم برای تصادفات با زیان جانی است و بر این اساس می توان کفایت مدل های رگرسیون پرصفر را در مدل سازی تصادفات بزرگراه های درون شهری مشهد تایید کرد.
    کلیدواژگان: تصادفات با زیان مالی، تصادفات با زیان جانی، بزرگراه های درون شهری، مدل سازی تصاد فات، مدل های رگرسیون پرصفر
  • رضا جمشیدی، رامین علومی صفحه 17
    یکی از تفاوت های مهم مصالح ژئومکانیکی با سایر مصالح مهندسی، تغییرات پارامترهای مرتبط با این مصالح در نقاط مختلف داخل مصالح است. این ویژگی که ناهمگونی نامیده می شود در این مطالعه بررسی شده است. برای بیان تغییرات پارامترهای مرتبط با مصالح ژئومکانیکی، توزیع های تصادفی مختلفی ارائه شده که در این بین توزیع قدر مطلق نرمال به عنوان توزیع مناسب در راستای افقی برای این پارامترها در نظر گرفته شده است. روند تغییرات میانگین این پارامترها در راستای قائم به صورت روندی مشخص معرفی و با کمک گرفتن از تئوری فضای تصادفی و تئوری حوزه های میانگین محلی و استفاده از نرم افزار MATLAB به تولید داده هایی با همبستگی متفاوت پرداخته شده است؛ و سپس با ترسیم تابع خودهمبستگی، رفتار این تابع به ازای مقادیر مقیاس نوسان مشخص ارزیابی و مشخص شده است که تابع خودهمبستگی تا رسیدن به فاصله مقیاس نوسان روند مشخصی را از خود نشان می دهد و نقطه انتهایی این روند، بیانگر مقادیر مقیاس نوسان داده ها است.
    کلیدواژگان: ناهمگونی، حوزه های میانگین محلی، فضای تصادفی، مقیاس نوسان، روند مشخص
  • نادر حیدری، محمد تقی احمدی صفحه 29
    بتن ماده ای است که ذاتا«در برابر کشش، ضعیف است و به دلیل تغییر حجم ناشی از تغییر دما، در آن تنش های کششی ظاهر می شود که در حالات بحرانی سبب بروز ترک می شود. به همین دلیل موضوع تنش های حرارتی و ترک های ناشی از آن در سدهای بتن غلتکی اهمیت ویژه ای دارد. از ویژگی هایی که در بررسی این مسئله بسیار مهم است ولی کمتر به آن توجه شده، لحاظ کردن تغییرات ضریب هدایت حرارتی و مدول الاستیسیته بتن نسبت به دما، تغییرات مقاومت بتن لایه ها نسبت به عمر آن ها، مدل سازی میزان تولید حرارت هیدراسیون سیمان به صورت متغیر با زمان، مدل سازی برنامه زمانی اجرای سد و در نظر گرفتن شرایط مرزی همرفت و تابش برای سطوح شامل تابش خورشیدی است. این پژوهش از موارد نادری است که در آن سعی شده به همه این ویژگی ها افزودن بر مسئله ی اثر حرارت محیطی، به طور هم زمان توجه شود تا با اعتماد بیشتری بتوان در مورد ساخت ایمن و اقتصادی این نوع سدها تصمیم گرفت. سرعت های مختلف اجرا، شروع اجرا در فصول گرم و سرد سال و توقف اجرا در ماه های سرد و گرم سال، پیش سرد کردن مصالح به عنوان پارامترهای موثر در نظر گرفته شده است. برای مدل سازی و تحلیل گذرا و همراه اندرکنش انتقال حرارت و توسعه تنش از نرم افزار المان محدود (انسیس 1/6) به گونه ای ویژه بهره گرفته شده است. از نتایج این پژوهش می توان به پایین بودن راندمان پیش سرد کردن، موثر بودن وقفه در ماه های گرم سال در کنترل ترک حرارتی و تاثیر ناچیز وقفه در ماه های غیر از فصل گرما در توزیع نهایی دما و بیشینه ی دمای بدنه سد اشاره کرد. همچنین اگر از یخ زدگی مصالح جلوگیری شود، شروع بتنریزی و اجرا در زمستان، نسبت به فصول دیگر مناسبتر است. بحرانیترین زمان شروع اجرای بتن ریزی،فصل گرما است.
    کلیدواژگان: سدبتن غلتکی، انتقال حرارت، شرایط محیطی، المان محدود، تنش کششی، ترک حرارتی، هیدراسیون سیمان
  • ارشیا خفاف، فریدون اربابی صفحه 43
    در زلزله های گذشته ساختمان های بنایی کلاف دار، برعکس ساختمان های بنایی غیرمسلح بدون کلاف، عملکرد مناسبی داشتتند؛ حتی وقتی خرابی در این ساختمان ها ایجاد شده، ریزش سقف و خسارت های جانی کمتری پیش آمده است. استفاده از کلاف سبب افزایش پایداری، یکپارچگی، مقاومت و شکلپذیری دیوارهای آجری در برابر زلزله میشود. با توجه به آیین نامه 2800 که استفاده از کلاف های افقی و قائم را الزامی دانسته، نیاز به مطالعه ی بیشتر درباره این ساختمان ها احساس میشود. در این مقاله، پس از تایید مدل سازی، دیوارهای آجری کلاف دار با ابعاد، شرایط تکیهگاهی و مشخصات مختلف مصالح بررسی شده است. از نتایج چنین برمیآید که در آنها دو مود شکست قطری و چرخشی معمول است. برای این دو مود شکست، الگوهای مختلف تقویت بررسی گردیده است.
    کلیدواژگان: دیوار آجری، کلاف، مقاوم سازی FRP
  • مجید ذبیحی طاری، محمود صفارزاده، مهدی شریف یزدی، علی عبدی صفحه 57
    صنعت حملونقل هوایی، به خاطر تاثیر زیاد بر توسعه اقتصادی و سطح رفاه جوامع، نسبت به سایر روش های حمل - ونقلی اهمیت ویژه ای دارد. شبکه پروازی یکی از اساسیترین اجزای بازار حملونقل هوایی است که تاثیر چشم گیری بر درامد شرکتهای هواپیمایی دارد. برای افزایش کارایی شبکه، وجود یک برنامه ریزی مدون ضروری است. شبکه قطب واقمار به دلیل کاهش هزینه عملیاتی، ایجاد زمینه برای توسعه شبکه پروازی و رقابت، نسبت به شبکه های مختلف، در حملونقل هوایی کاربرد گستردهای دارد. برای طراحی شبکه قطب و اقمار با توجه به تنوع پارامترها و متغیرهای تصمیمگیری و همچنین شکل های مختلف شبکه، مدلهای گوناگونی ارائه شده است.
    در این پژوهش، مدلی مناسب برای ارزیابی و طراحی شبکه قطبواقمار، تعیین مسیرهای بهینه پروازی و تخصیص ناوگان به این مسیرها ارائه شده است. در مدل طراحیشده، هر دو حالت ارتباط مستقیم و ارتباط از طریق قطب در نظرگرفته می شود و سرانجام، شبکه بهینه با تلفیقی از این دو حالت ارائه میشود. همچنین مدل برای الگوی تقاضای ایران با روش انشعاب و تحدید، حل شده که نتایج نشان میدهد این مدل جوابهای منطقی را درباره ی مسئله ارائه میدهد.
    کلیدواژگان: شبکه قطب و اقمار، حملونقل هوایی، مکان یابی قطب، مدل سازی ریاضی و فرودگاه
  • حمیدرضا فرشچی، عبدالرضا سروقد مقدم، روح الله احمدی جزنی صفحه 69
    قاب مهاربندی شده یکی از شکل های متداول اجرای سازه های فولادی در ایران است. در این سازه ها انواع مهاربندها به عنوان سیستم باربر کناری به کار می رود و در محاسبات، اتصالات تیر و ستون این قاب ها به شکل مفصلی فرض می شود. در اجرا سعی می شود با استفاده از اتصال ساده این فرض واقعیت یابد. واضح است چنین فرضی عملا اجرا شدنی نیست و اتصال تیر و ستون و مهاربند با مقداری گیرداری اجرا می شوند ولی برای محافظه کاری از این اثر چشم پوشی می شود.
    در این پژوهش رفتار تحلیلی-آزمایشگاهی اتصالات قاب فولادی مهاربندی با مقیاس 1/2 تحت بارگذاری چرخه ای بررسی و اعتبار سنجی می شود. این پژوهش با سه آزمایش قاب تشکیل شده از تیر و ستون، قاب همراه ورق های اتصال مهاربند در گوشه (Gusset Plate) و قاب همراه مهاربند ضربدری با مقطع ناودانی با شرایط یکسان بارگذاری، انجام شد. نتایج تحلیلی-آزمایشگاهی قاب نشان می دهد که اتصالات قاب در این سیستم حتی با چشم پوشی، در محاسبات دارای درصدی گیرداری است که با اضافه شدن ورقهای اتصال مهاربند در گوشه قاب (Gusset Plate) و متصل شدن آن به تیر و ستون، گیرداری بیشتری در این اتصالات به وجود می آید.
    کلیدواژگان: آزمایشگاهی، اتصالات، مهاربند، قاب فولادی Gusset Plate
  • رضا مهین روستا، حامد فرخ بروجردی صفحه 83
    در این پژوهش رفتار مکانیکی مصالح درشت دانه شنی با استفاده از شبکه عصبی چند لایه پرسپترون، که از پرکاربردترین شبکه های عصبی مصنوعی در مسائل ژئوتکنیکی است، شبیه سازی شده است. ابتدا اطلاعات دقیقی از آزمون های منابع مختلف در سراسر کشور تهیه و عوامل موثر بر مقاومت برشی خاک های درشت دانه بررسی شده است. پس از حذف اطلاعات نادرست، روند یادگیری، آزمایش و پیش بینی شبکه طی شده است. در آموزش شبکه از الگوریتم یادگیری پس انتشار خطا استفاده شده است. پارامترهای استفاده شده در آموزش شبکه شامل خصوصیات دانه بندی، چگالی خشک، چگالی نسبی، درصد سایش لس آنجلس، فشار همه جانبه، کرنش و تنش انحرافی است. برای تعیین چگونگی و مقدار تاثیر ورودی ها بر خروجی مدل، تحلیل حساسیت روی آن ها انجام شده و نتایج به دست آمده با قوانین مکانیک خاک مقایسه شده است. بررسی مدل گویای این واقعیت است که شبکه ارائه شده، توانایی لازم برای پیش بینی رفتار تنش_کرنش خاک های درشت دانه را دارد.
    کلیدواژگان: خاک های شنی، منحنی تنش، کرنش، شبکه عصبی مصنوعی، پرسپترون چندلایه، تحلیل حساسیت
  • محمد پیکانو، مصطفی زین الدینی، محمد دقیق صفحه 97
    قطع و وصل پیاپی جریان در خطوط لوله فولادی انتقال نفت و گاز فراساحلی، دوره های محوری کشش و فشار در خط ایجاد می کند که می توانند سبب چین خوردگی، کمانش غیر خطی موضعی یا خرابی خمیری پیش رونده در این خطوط شوند. این نوع کاهش مقاومت موضعی، بیشتر به وسیله ناراستی های اولیه و خرابی های موجود در خط لوله تشدید می شود. یکی دیگر از مسائل موثر بر روی مقاومت خطوط لوله دریایی، پدیده خوردگی است. این نوع آسیب به علت استقرار خط در محیط خورنده دریا و عبور سیال خورنده از داخل خط لوله ایجاد می شود. به طور کلی آسیب خوردگی که در عمق و اندازه از داخل و خارج سطح خطوط ایجاد می شود، می تواند بر مقاومت این خطوط تاثیر به سزایی داشته باشد. در این پژوهش پدیده خرابی پیش رونده در خطوط لوله های خورده شده تحت بارگذاری دوره ای محوری بررسی شده است. یک روش عددی برای بررسی این پدیده استفاده می شود.
    خواص غیر خطی مواد، به همراه رفتار سخت شوندگی غیر خطی ایزوتروپیک/کینماتیک برای نمونه بررسی شده در نظر گرفته شده است. درستی داده های مربوط به پارامترهای سخت شوندگی برای مدل سازی پدیده خرابی پیش رونده اهمیت زیادی دارد. این نتایج با استفاده از یک سری آزمایش روی نمونه هایی که در معرض دوره های زیاد کرنش متقارن قرار گرفته به دست می آید. مدل اجزای محدود استفاده شده در ابتدا با استفاده از نتایج به دست آمده از داده های آزمایشگاهی مربوط به آزمایش های یک سویه و دوره ای صحت سنجی شده است.
    کلیدواژگان: خرابی پیش رونده، بارگذاری تناوبی، لوله های دارای خوردگی، چین و چروک
  • لیلا خان محمدی، جواد واثقی امیری، بهرام نوایی نیا صفحه 107
    برای فرمول بندی محیط سیال در سیستم سد-پی-مخزن از دو دیدگاه اویلری و لاگرانژی می توان استفاده کرد که هر کدام ویژگی های خاص خود را دارد. در این مقاله فرمول بندی این دو دیدگاه در محیط مخزن سد با در نظر گرفتن اثر اندرکنش سد- پی-مخزن به روش اجزای محدود و اعمال شرایط مرزی مناسب برای سدهای بتنی وزنی ارائه شد؛ سپس این دو روش برای براورد پاسخ سد دراثر زلزله های مختلف بررسی شد. نتایج به دست آمده برای دو روش مدل سازی مخزن با تغییر پارامترهای مختلف [مانند نسبت مدول الاستیسیته جسم سد به پی، شرایط مرزی مخزن، شیب کف و عمق آب مخزن و نیز تاثیر رسوبات کف مخزن در جذب امواج الاستیک] از جنبه های مختلف مانند دقت و کاهش حجم محاسبات با هم مقایسه شد. نتایج به دست آمده گویای آن است که دو روش مدل سازی مخزن از جنبه های مختلف مزایا و معایبی دارند؛ اما در مجموع اختلاف قابل توجهی در پاسخ سد به دست نمی آید.
    کلیدواژگان: اندرکنش سد، پی، مخزن، سدهای بتنی وزنی، روش های اویلری و لاگرانژی، زلزله
  • سیروس یوسفی خاتونی، حسین شوکتی*، محمد شیخ بگلو صفحه 117

    دیوارهای برشی فولادی (ssw) برای مقابله با نیروهای جانبی زلزله و باد در ساختمان ها به ویژه در ساختمان های بلند در سه دهه اخیر مورد توجه قرار گرفته است. این پدیده نوین که در جهان به سرعت رو به گسترش است در ساخت ساختمان های جدید و همچنین تقویت ساختمان های موجود به ویژه در کشورهای زلزله خیزی مانند آمریکا و ژاپن به کار گرفته شده است. از نظراجرایی، سیستمی بسیار ساده است و پیچیدگی خاصی در آن وجود ندارد. از مزایای اصلی این دیوارها می توان به شکل پذیری بالا و مقاومت زیاد آن ها اشاره کرد. در این مقاله رفتار دیوار برشی فولادی ساخته شده از ورق های صاف و موج دار بررسی و منحنی های over_ push و دوره ای آن ها تحت بارگذاری چرخه ای ارزیابی شده است. طبق بررسی های انجام شده در این مقاله، دیوارهای برشی فولادی موج دار شکل پذیری پایین تری نسبت به دیوارهای برشی با ورق صاف دارد. در این پژوهش همچنین معلوم شد با این که در جابجایی های پایین، ورق موج دار مقاومت بالایی دارد؛ ولی رفتار دیوار برشی با ورق صاف نسبت به دیوار برشی موج دار پایدارتر است. جذب انرژی دیوار برشی صاف نسبت به دیوار برشی موج دار بیشتر است. بنابراین استفاده از دیوار برشی با ورق صاف در مناطق با خطر زلزله خیزی زیاد توصیه می شود.

    کلیدواژگان: دیوار برشی فولادی موج دار، روش اجزای محدود، شکل پذیری، منحنی پوش اور، منحنی دوره ای
|
  • A. Ayati, A. Abbasi Page 1
    We handle in this paper, the research that have been performed to recognize the factors that affect crash frequency and severity in urban highways and use crash data of Mashhad urban highways as a case study. Statistical models that have been used in this research include Poisson, Negative binomial, Zero-inflated poisson and Zero-inflated negative binomial regression models. Traffic flow related variables and road geometric related variables have been used as independent variables of models. We are interested in this study, to inspect the efficiency of Zero-inflated models against simple Poisson and Negative binomial regression models in modeling accidents on urban highways. Special task that have been done in this research, is separation of total traffic volume into passenger cars, heavy vehicles and light non-passenger vehicles volume. Through this special, Researcher intend to have an especial look at the role of traffic volume in accident occurrence to see precisely, which part of traffic have effective role or more effective role in crash occurrence. Accident data are two-level data, the first level is road segments i.e. highway is divided into several segments. The segmentation is based on total traffic volume i.e. each segment has a constant volume. The second level is daily hours; peak hour traffic considered as the first sublevel, day non peak hour traffic the second and night non-peak hour traffic as the third sublevel. SAS 9.1 software has been used to fulfill statistical computations. It turns up, after statistical analyses, which factors affect crash occurrence and which do not have much effect. Comparisons between obtained results and other researchers’ results have been made then. The main object of researcher is to assess the efficiency of Zero-inflated models against Poisson and Negative binomial regression models in modeling urban highways crashes. This aim is followed by, with evaluating goodness of fit and making comparison between models. The Results of study show that the presence and number of access roads and horizontal curves on highway segments increase the likelihood of accidents, both no injury and more severe. Also increment of speed and number of lanes increase the likelihood of no injury accidents, but not more severity ones. The conclusions also demonstrate that the volume of passenger cars and light nonpassenger car vehicles increase the likelihood of no injury accidents, but heavy vehicles volume does not have much effect on occurrence of no injury accidents, also light vehicles increase the likelihood of more severe accidents, but passenger cars and heavy vehicles volume does not have much effect on occurrence of severe accidents. Finally, the results of research indicate that Zero-inflated negative binomial regression model is best fitting the modeling of accidents, whether no injury or more severe and consequently, the efficiency of zero-inflated models in modeling accidents on urban highways is approved.
  • R. Jamshidi Chenari, R. Oloomi Dodaran Page 17
    One of the main distinctions between geomaterials and other engineering materials is the spatial variation of their properties in different directions inside them. This characteristic of geomaterials (so- called as heterogeneity) is studied herewith. Almost all natural soils are highly variable in their properties and rarely homogeneous. Soil heterogeneity can be classified into two main categories. The first is lithological heterogeneity, which can be manifested in the form of thin soft/stiff layers embedded in a stiffer/softer media or the inclusion of pockets of different lithology within a more uniform soil mass. The second source of heterogeneity can be attributed to inherent spatial soil variability, which is the variation of soil properties from one point to another in space due to different deposition conditions and different loading histories. Inherent spatial variability of geomaterials is itself devided into the random component, which is attributed to different depositioaln conditions, and the deterministic trends, which are attributed to the variation in soil properties, such as increase in soil strength with depth due to increase in confining pressure. Different elements of soil inherent spatial variability such as mean, variance, and spatial correlation characteristics were introduced with the main focus on the importance of spatial correlation distane and the way to handle it. Several spatial distributions introduced to describe the probabilistic variation of geotechnical properties of soils. Among all, absolute normal distribution was adopted as appropriate distribution, which best presents these properties in horizontal direction. Variation of geotechnical parameters in vertical direction is, however, conceived to follow a deterministic trend. Using random field theory, local average subdivisions (LAS) formulation and MATLAB Mathworks, virtual data with different correlations was produced, and by employing autocorrelation function, a trend for this function was invoked for different predetermined values of the scale of fluctuations. It was found that autocorrelation function has a deterministic trend as far as the scale of fluctuation has not been exceeded. It is clearly concluded that, for distances farther than the specific scale of fluctuation, the behavior is chaotic and this can be an index to calculate the scale of fluctuation of the experimental data.
  • N. Heydari, M.T. Ahmadi Page 29
    Mass concretes including roller-compact concrete are materials with poor tensile behavior. When subjected to shrinkage or heat in their very early ages such concretes may easily crack. Thus for controlling and minimizing the risk of thermal cracks, it is crucial to study the effects of such parameters as the rate of concrete pouring in construction layers, seasons of start, pause of construction, and the extent of pre-cooling of concrete materials. Therefore, thermal stresses and probable cracks should be controlled based on a sound construction schedule. In practice, most cases are dealt with using a simple one-dimensional analysis pertaining only internal concrete evolution and thus disregarding the surface concrete story. At the same time, the induced surface stresses are not accounted for in such analyses. However, as a minimum requirement, a two dimensional model of the dam body across its vertical section is needed to account for the main effects mentioned above. Despite that many analyses have been carried out by others so far, in this research, concrete thermal conductivity coefficient is considered as a function of concrete temperature throughout a transient heat conduction analysis. The material is assumed as isotropic in both thermal and mechanical senses. The topology of model as well its top boundaries are continuously updated according to the construction schedule. Furthermore, accounting for the dam construction schedule, heat generation due to both ambient and cement hydration phenomena, as well as inclusion of convection and radiation boundary conditions due to solar effects are considered. In addition, when dealing with stress analyses and safety evaluation against cracks, the dependencies of concrete elasticity modulus on time and temperature, and concrete compressive as well as tensile strengths on time (i.e., the ages of layers) are all considered. Indeed, the thermal analyses are carried out after performing each single layer. Also after every 10 layers are performed, a full stress analysis is conducted under the current thermal and gravity loads. Safety factors are calculated considering the material properties and strength available at the same instance in each layer. To study the effect of these parameters on heat generation, and the subsequent thermal stresses in the body of RCC dam, "THA-DAN" dam in Thailand was chosen as a benchmark introduced by ICOLD. This dam has been built of 160 layers of 30 centimeter thickness. Program ANSYS-6.1 was employed in a special manner to allow such a coupled transient
  • A. Khaffaf, F. Arbabi Page 43
    Masonry buildings with confined walls have performed well during the past earthquakes. The same cannot be said for unreinforced masonry walls. In the former buildings, even when damage occurs, falling roofs and losses of life do not usually follow. This is because confined masonry walls have higher strength ductility and are more stable. The Iranian Seismic Code (Standard 2800) makes the use of horizontal and vertical ties mandatory for masonry buildings. In spite of this, such confined walls have not been studied sufficiently. In this study, the nonlinear behavior of masonry walls is examined using finite element discretization. From the two types of modeling that are commonly used for the study of masonry material, namely macro- and micro- modelings, the latter are employed here. This is because such a model can provide more detailed information. Micro- models are the best tools available for understanding the behavior of masonry structures. They can depict all the failure mechanisms of the system. The behavior of mortar joints and masonry unit-mortar interface is lumped into a set of discontinuous elements. In this way, each joint, consisting of mortar and two unit-mortar interfaces, is modeled by a zero-thickness interface element. In other words, the masonry structure is modeled by a set of elastic blocks bonded together with potential fracture/slip lines at the joints. The composite interface model includes a tension cut-off for mode I failure, a coulomb friction envelope for mode II failure and a cap mode for compressive failure. For modeling the behavior of concrete, a model suggested by Thorenfeldt and Hordijk is used. For the longitudinal reinforcing bars, the failure criterion is that of Von Mises. The hardening of steel is also considered. The interface between the reinforced concrete members and the masonry units panel is modeled by the coulomb friction model including a tension cut-off mode. A parametric study is conducted for confined masonry walls by changing with different dimensions, boundary conditions and loading patterns. The results indicate that failure has one of the two failure modes: diagonal tension or rocking. In cantilever walls with rather large heights compared to their length, the failure mode is rocking. In the other cases, diagonal tension failure mode occurs. The use of tie also affects the capacity of the wall. This can be considered in the design of masonry structures. The results of nonlinear analyses show that deboning does not occur between the ties and the body of masonry walls. Therefore, in analytical studies, the adjoining nodes for the two parts can be merged. Upon determination of failure modes, different patterns of FRP were investigated for the dominant mode in order to select the most suitable pattern. The FRP configuration patterns considered for strengthening the wall were: 1. FRP in vertical direction; 2. FRP at both ends in vertical direction; 3. FRP in diagonal direction; 4. FRP covering the whole surface of the wall. The last pattern was considered only for reference as it cannot be justified because of the increased cost. In confined masonry walls with diagonal tension or rocking mode, the best strengthening configuration is diagonal. The increase in the capacity of strengthened walls with rocking and diagonal tension failure modes depends directly on the amount of FRP. In fact, the capacity increases from 1.2 to 2 for the walls with rocking mode. For the walls with diagonal tension mode, this increase is from 1.5 to 3.
  • M. Zabihi Tari, M. Saffarzadeh, M. Sharifi Yazdi, A. Abdi Page 57
    Air transportation has an important position among the other modes of transportation due to its significant impact in the economy and welfare of a society. Within the several components of air transportation market, flight network plays a fundamental role and considerably affects the airlines revenue. Improvement of the network system requires an accurate plan and programming. Hub-and-spokes are of further interest; as such networks reduce the operational costs, create proper ground for flight network development and extension, and help in competition. However, several models have been introduced for hub-and-spokes design purposes based on the diversity of the effective factors, decision-making variables and different forms of the network. Generally speaking, hub-and-spokes are categorized into two principal sectors: single allocation and dual or multiple allocations. Within a single allocation, traffic is accumulated in a single hub and then distributed to the destinations, while within a dual-allocation network, the gathered traffic at the first hub is again distributed to another hub before directing it to the final destination. This research presents a linear model for hub-and-spokes evaluation and planning, determining optimum flight routes and fleet assignment. The model considers both direct flights and hub connections, and outputs an optimum network based on the mixture of these two options. Sets of airport connections are so designed to well cover all the necessary inter-airport trips. This particular is done by utilizing hub-and-spoke system as the airport networks. To fulfill the requirements of the study location (Iran), in this paper, single allocation was selected to develop the models, meaning that just one hub has been considered in the modeling process. Inter-airport demands of the passengers were inputted in the network and the model works only for passenger transportation. The objective was to design the hubs so as to obtain an optimum network. In other words, the model is to suggest the best option with which the demand is handled cost-effectively. Trips are planned to be either direct or meeting a one-hub maximum. As the model is to minimize the cost, such variables as demand for variety of routes and type and quantity of the available aircrafts were included. The model was developed in two stages to ease the process.
  • H.R. Farshchi, A.S. Moghadam, R. Jazany Page 69
    SCBF (Special Concentrically Braced Frame) is a common structural system for steel construction in Iran. This system could be used where increasing of strength and stiffness is the main concern for a structural system over the ductility. In SCBF, it is assumed that most of stiffness and strength are provided by the brace element. The contribution of gusset plates in total stiffness and strength values is even overlooked in the structural analysis and design. Ignoring these effects is conservative for controlling of seismic responses and is on the safe side. But, in practice, this hypothesis is not valid since this extra portion of stiffness and strength values is not included in the design of gusset plates and the connections. The importance of this phenomenon will be more noticeable when the brace element material behavior significantly enters the nonlinear phase. Based on previous descriptions, experimental and analytical study of this kind of structural system under seismic loading seems necessary in order to evaluate the contribution of stiffness and strength of each mentioned element i.e. gusset plates and double- seat angle connections. Three test specimens were built in half scale and designed regarding the AISC seismic provisions (2005); the first test specimen consisted of one-by-one story frame with simple connection, i.e. double seat angle connections, known as simple frames. The second specimen was simple frame with gusset plate connections without brace elements. The third specimen was braced frame; the specimens were tested cyclically and companion Finite Element (FE) analysis was then conducted. Verification of FE models in ANSYS finite element program using “Solid 45” element with proper mesh dimensions, obtained by sensitivity analysis, showed good agreement between the analytical and experimental responses. The experimental results showed that the stiffness value of simple frame and simple frame with gusset plates reached 60% to 65% and 86% to 98% of stiffness values of the braced frame, respectively. Also energy absorption values of simple frame and simple frame with gusset plate reached 4 % and 10% of the energy absorption value of braced frame, respectively. Moreover, ultimate strength value for simple frame and simple frame with gusset plate reached 11% and 25% of the ultimate strength values of braced frame. As a result, it could be mentioned that gusset plates and double seat angle connections have significant contribution in the total stiffness values of a braced frame whereas their contributions in strength value of a braced frame are insignificant. The results of FE analysis also confirmed the above-mentioned results with a definite low tolerance.
  • R. Mahin Roosta, H. Farrokh Page 83
    Prediction of stress-strain behavior of geotechnical material is one of the major efforts of engineers and researchers in the field of geomechanics. Experimental tests like tri-axial shear strength tests are the most effective apparatus to prepare the mechanical characteristics of gravelly material; but due to difficulties in preparing test samples and costs of the tests, only several tests will be donein a new project. Artificial neural network is a kind of method, in which engineer could judge the results based on numerous data from other similar projects, which enable the engineer to have a good judgment on the material properties. In this research, the behavior of gravelly material was simulated by use of multi-layer perceptron neural network, which is the most useful kind of artificial neural networks in the field ofgeotechnical engineering. For instance, first exact information was provided from laboratory tests of various barrow areas of embankment dams in the country and effective parameters on shear strength of coarse-grained material were studied. After omitting incorrect or weak data, 95, 20 and 23 sets of data were used for learning, testing and evaluating data, respectively. Input parameters for the model were as follows: particle-size distribution curve, dry density, relative density, Los-angles abrasion percent, confining pressure, axial strain; and outputs were selected as deviator stress. In order to reach a steady state in the model and force the model to behave homogenous to the all inputs, data wasnormalized to the value between. 05 and 0.95. In the simulation, back-propagation algorithm was used for learning or error reduction. The aim of the simulations was defined to reduce error between realdata and predicted values; for instance root mean square error (RMS) was used to be minimized through simulation and predicted versus real graphs were used to observe the global error of the model. After modeling the data based on some criteria, it was shown that curves of stress-strain from simulation tests were in good agreement with those from laboratory. These close coherencies were observed in all training, testing and evaluation data, in which the RMS errors were 0.038, 0.037 and 0.026, respectively. To reach this ultimate step, a 10*19*1 multilayer perceptron was used via trial and error. In order to determine quality and quantity of the effect of inputs on outputs, and prove that the results were in good agreement with soil mechanic principles, sensitivity analyses were done on the average data of the inputs. Results show that confine pressure, uniformity coefficient and relative density of the material were the most effective parameters on the stress-strain curves; thus the model has enough capability to predict the stress-strain behavior of gravelly soils.
  • M. Peykanu, M. Zeinodini, M. Daghigh Page 97
    Plastic axial strain, local buckling, wrinkling and plastic buckling of pipeline are caused by cyclic compression and tension loadings. This kind of local buckling is amplified by initial defect, heat affected zone and circular welding. Progressive plastic failure or ratcheting is caused by frequent periods of cyclic loading. On the other hand, life time of the offshore pipelines is decreased by the corrosion effect caused by fluids inside the pipeline and the sea Environment. This kind of corrosion can be found with variable size and depth in the inner or/and the outer surface of the pipeline. Corrosion can effect on the strength of pipeline. In the current study, an advanced finite element program has been used to simulate the ratcheting response of carbon steel tubes. The numerical model has been applied to reproduce a series of laboratory tests on small-scale tubes. These tests were carried out by the authors on intact and defected tubes, in which wrinkling and ratcheting behaviour of tubes under axial monotonic and cyclic loads were studied. A nonlinear isotropic/kinematic hardening model has been employed torepresent the cyclic behaviour of the material. The verified model has then been used for a parametric study on ratcheting behaviour of the defected tubes under cyclic axial loading. Several stabilized cycles of specimens that are tested experimentally under symmetric strain cycles are used to obtain stress-strain data and hardening parameters of the material. The numerical model has then been used to investigate the effect of mean stress, stress amplitude and geometrical defects on the ratcheting response of steel tubes. It has been noticed that: a) The ratcheting strain rate was governed by (a) the initial non-linear strain in the tube, (b) by the stress amplitude and (3) by the mean stress, respectively. b) The ratcheting strains in the defected tubes had significantly higher rates in comparison to those in the intact tubes and very rapidly turned exponential. c) In defected tubes the local wrinkling first initiated from the damaged part. This local buckling then gradually proceeded to the entire circumference. The ratcheting strains in the defected area very rapidly turned exponential, while the ratcheting strains in the perfect zone still remained linear trajectory. d) It showed that surface corrosion imperfections had a very pronounced effect on theratcheting response of the defected tubes, as compared to their monotonic response. e) The wrinkles in the defected tubes were non-axisymmetric and initiated from the damaged part of the tube.
  • L. Khan Mohammadi, J. Vaseghi Amiri, B. Navayi-Nia Page 107
    Hydrodynamic pressure on the upstream face of the concrete dams under the effect of earthquake is one of the most important parameters, in planning dam's structure in earthquake zone. Because of the reservoir effect, dynamic analysis of concrete dams is more involved than other common structures. This problem is mostly sourced by the differences between reservoir water, dam body and foundation material behaviors. As a result, researches in this case must be able to evaluate the response of dam with consideration of dam’s interaction with reservoir and its foundation. This problem has been studied vastly by different researchers. The first research on the analysis of concrete gravity dam has been done by Westergaard in 1930 and hydrodynamic pressure on the dam face was obtained by some simplifications. There were a lot of other researches which studied the seismic behavior of the dam-reservoir system, including nonlinear behavior of the dam under pressure and also cavitation. In each research, different modeling methods are presented which are divided into two main groups. In first method which is called Eulerian method, pressure is the main unknown variable in reservoir nodes. In the second method that its main unknown variable is displacement of nodes is called lagrangian method. Each of the methods contain some advantageous and disadvantageous. The purpose of this paper is to evaluate possible advantages and disadvantages of both methods. Specifically, application of the above methods in the analysis of dam-foundationreservoir systems is leveraged to calculate the hydrodynamic pressure on dam faces. Within the frame work of dam- foundation-reservoir systems, dam displacement under earthquake for various dimensions and characteristics are also studied. To achieve this purpose, visual C#.NET 2003 computer programming language is used in this investigation that produces possibility of dynamic analysis of concrete dams under earthquake with system modeling by both methods. Nine node elements for reservoir and eight node elements for dam and foundation are used for both methods. Also newmark average acceleration method is used for solving dynamic’s equilibrium equation. Modares Civil Engineering Journal (M.C.E.L) Vol.11, No.4, Winter 2011 131 In this paper the response of the tallest, non-overflow monolith of Pine Flat dam in California, which is 122 m high, to horizontal and vertical component of earthquake is computed. A water depth of 116 m is considered in full reservoir condition, and the water has the following properties: unit mass,  1000 kg /m3, bulk modulus, K  2.07*109 kg/m2, and pressure wave velocity, w c 1440m/ s. The finite element model of reservoir consists of 12 isoparametric elements and it extends upstream a distance of 366 m, three times the dam height. The dam consists of 20 isoparametric elements. The concrete of dam has the unit mass of  2500kg /m3, young’s modulus ofE  2.275*1010kg /m3, and poisson`s ratio of   0.25. The concrete of foundation has the unit mass of, young’s modulus ofE 4.45*1010 kg / m3 f , and poisson`s ratio of  0.25 f . The peak acceleration of S69E and vertical components are 0.18g and 0. g, respectively. The results of both Lagrangian and Eulerian methods for Pine Flat dam are quantitatively evaluated and compared in different condition and following results are achieved: 1- In Lagrangian Method, there is only one variable in equilibrium equation and mass and stiffness matrixes are symmetric. But there is not such a condition in Eulerian method. Also, the numbers of unknown parameters are different in two methods. By considering these differentiations, needed time for analysis of Pine Flat Dam under Taft earthquake, with mentioned characteristics, by Lagrangian method is 1.17 times more than needed time for Eulerian method. 2- The effect of material on reservoir's bottom in absorbing energy and `reducing system's response was considerable especially under vertical component of the earthquake. Results indicate that this case is not affected by reservoir modeling method. By applying this effect, the response will decrease about 15% under horizontal component and 60% under vertical component of the earthquake. 3- By evaluating the effect of reservoir bottom's slope, it is concluded that in the case of rigid foundation, the response by Lagarngian modeling is about 10% more than Eulerian one. With the increase of slope, the response will decrease under horizontal component of earthquake but it will decrease or increase about 13% under vertical component of the earthquake. In other words, reservoir bottom slope has little effect on response of the system under both vertical and horizontal component of earthquake. But this effect is not negligible. 4- It is included from the analyses that by decreasing the depth of reservoir the response will decease up to 50 percent under horizontal component of earthquake. This amount is 80 percent under vertical component. Also in the case of decreased depth, response of Lagarngian method is about 10% more than Eulerian method. 5-In all analysis, the assumption of rigid foundation results in greater answers than the cases of flexible foundation.
  • S. Yousefikhatoni, H. Shokati, M. Shaikhbagloo Page 117

    Steel shear walls has been noticed against wind and earthquake lateral loads about high buildings in the last three decades. This modern phenomenon is growing rapidly worldwide so that system have been employed highly in construction of new buildings and seismic upgrading of existing buildings in some countries such as USA and JAPAN. That is a very simple system from viewpoint of implementing and there isn’t particular complexity. High strength and ductility are main advantages of these systems. Current paper has investigated comparatively behavior of steel shear walls made of smooth and corrugated sheets. Also the paper has assessed push-over curves and cyclic binding. According to this result of the research, corrugated steel shear walls have lower ductility than smooth shear walls. The research also founded that despite the high strength of corrugated sheets in low displacement, behavior of flat shear walls is more stable than corrugated shear walls. On the other hand flat steel shear walls attract energy more than corrugated shear walls. Therefore using of flat shear walls is recommended in high seismic regions. In this research, 18 samples of flat steel shear walls and corrugated shear walls were modulated. In all models, panels height were 3 m and panels span were 3, 4 and 5 m. the thickness of sheets in the samples were 3, 4 and 5mm. According to results of the research: 1- Corrugated sheets are unstable and unpredictable in high thinness. In the low displacements occurs a mutation state, so it distinguishes the corrugated and flat shear walls behavior. 2- At low displacement, a corrugated sheet bears greater load than a flat sheet. 3- In a constant thickness for thinner corrugated sheets is increased the mutation rate and its behavior becomes more non-uniform. 4- Despite of the fact, pynchyng phenomenon appears in all samples, but all samples behavior is stable and significant energy attraction is observed.