فهرست مطالب

علوم و مهندسی زلزله - سال پنجم شماره 4 (پیاپی 17، زمستان 1397)

مجله علوم و مهندسی زلزله
سال پنجم شماره 4 (پیاپی 17، زمستان 1397)

  • تاریخ انتشار: 1398/01/18
  • تعداد عناوین: 10
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  • محمدرضا عباسی *، لیلا مهشادنیا صفحات 1-19

    شهرستان های قم و ساوه از دیدگاه زمین شناسی در محل پیوند دو ایالت لرزه زمین ساختی ایران مرکزی و البرز قرار دارد. از گسله های فعالی که در این منطقه معرفی شده اند می توان به گسله کوشک نصرت اشاره کرد. در راستای این گسله تاکنون زمین لرزه دستگاهی و یا تاریخی گزارش نشده است. این گسله از دو روند نزدیک به خاوری- باختری و شمال باختری شکل گرفته است و بیشترین بخش آن از میان توده های سنگی با سن های مزوزوئیک و ائوسن می گذرد. بخش کوچکی از این گسله آبرفت های جوان (پلایستوسن بالایی) را متاثر می کند. برای مشخص شدن فعالیت زمین ساختی این گسله برای محاسبات خطر، افزون بر پیمایش های میدانی روش های دیگری به کار گرفته شده اند. بر اساس مطالعات وضعیت تنش به روش زمین ساختی و لرزه ای شاهدی بر فعالیت بخش خاوری- باختری گسله به دست نمی آید. برداشت های میدانی و مطالعه زهکش ها به طور مشخص نشان دهنده ی راستالغز بودن این گسله با مولفه راست بر است که با جهت تنش به دست آمده همخوانی ندارد. روش های دیگری چون شاخص های مورفومتریک (شاخص هیپسومتری و شیب رودخانه) نیز یافته بالا را تایید می کنند. پرسش بعدی که در ارتباط به بخش خاوری- باختری گسله کوشک نصرت مطرح می شود ارتباط احتمالی آن با پایانه شمال باختری گسله سیاه کوه است که در جنوب شهر تهران قرار می گیرد. با تکیه بر یافته های مورفوتکتونیکی و عکس های ماهواره ای به نظر می رسد که پیوندی میان این دو گسله وجود داشته باشد؛ هرچند که پیگیری این گسله به صورت یک خط واحد بر روی عکس های ماهواره ای مشخص نیست اما می تواند گسله از خطوط ناپیوسته همراه با تداخل دو روند گسلی خاوری- باختری و شمال باختری از گسله کوشک نصرت (بخش خاوری- باختری آن) تا گسله سیاه کوه تشکیل شده باشد.

    کلیدواژگان: ایران مرکزی، گسله کوشک نصرت، روش برگشتی، تنسور تنش، شاخص های مورفومتریک
  • پریسا اشجع ناس، افسانه نصرآبادی *، محمدرضا سپهوند، سید حسن موسوی بفرویی صفحات 21-36

    در این مطالعه پهنه بندی خطر زمین لرزه بر روی سنگ بستر برای بیشینه شتاب زمین به روش تعینی و احتمالاتی در استان فارس انجام گردید. فهرست نامه ی یکنواختی تا سال 2016 شامل زمین لرزه های تاریخی و دستگاهی با بزرگای بیشتر از 4 در مقیاس Mw تهیه شد. با توجه به روند گسل ها و زمین شناسی منطقه، 23 چشمه بالقوه زمین لرزه به صورت پهنه ای در این منطقه در نظر گرفته شده و پارامترهای لرزه خیزی محاسبه گردید. در روش احتمالاتی با استفاده از نرم افزار OpenQuake بیشینه شتاب و سرعت زمین برای دوره بازگشت های 50 سال و 475 سال و نمودارهای منحنی خطر PGA و PGV برای دوره 50 سال رسم شد. نتایج نشان می دهد که بیشترین سطح PGA برای دوره بازگشت های 50 و 475 سال به ترتیب g 23/0 و g 6/0 و به روش تعینی g 8/0 می باشد. در استان فارس، چهار منطقه پر خطر در شمال غرب، غرب، جنوب و جنوب شرق قرار دارد. این مناطق نزدیک به گسل های کازرون، قیر و زاگرس مرتفع می باشند که سابقه زمین لرزه های بزرگ تاریخی و دستگاهی را دارا هستند. به طورکلی می توان گفت که مناطق با تراکم جمعیت بالا و شهرهای مهم استان به دلیل نزدیک بودن به گسل های منطقه در مناطق با خطر بالا قرار دارند.

    کلیدواژگان: پهنه بندی خطر زمین لرزه، استان فارس، نرم افزار OpenQuake، رهیافت احتمالاتی و تعینی
  • سعید نعمتی نژاد، سید احسان سیدیحسینی نیا * صفحات 37-53

    اقتصاد تعداد زیادی از کشورهای صنعتی بر پایه واردات و صادرات کالا از طریق اسکله هاست. اسکله سازه ای است که کشتی ها را به خشکی ارتباط می دهد و یکی از مهم ترین بخش های بندرها محسوب می شود. در صورت گسیختگی و آسیب آن، فعالیت های مهم بندر به دلیل آسیب وارد به سازه های مجاور اسکله همچون جرثقیل متوقف خواهد شد. شمع های مستقر در خاک نیز یکی از این سازه هاست که در صورت خرابی آن، سازه قرارگرفته بر روی آن از بین خواهد رفت. به همین دلیل بررسی نحوه رفتار سازه های ساحلی در برابر عوامل خرابی همچون زلزله اهمیت بالایی دارد. مدل سازی های آزمایشگاهی زیادی بر روی شمع انجام شده است؛ اما به ندرت به بررسی رفتار آن در اسکله پرداخته شده است. یکی از این مدل های آزمایشگاهی، به بررسی رفتار شمع و دیوار در برابر روانگرایی با استفاده از میز لرزان و به صورت کوچک مقیاس پرداخته است. در این پژوهش به مدل سازی عددی این مدل آزمایشگاهی و صحت یافته های به دست آمده در مدل عددی به کمک مدل آزمایشگاهی پرداخته شده است. در این مقاله با کمک نرم افزار FLAC3D1 که دارای قابلیت تحلیل غیرخطی تنش موثر و تولید اضافه فشار آب حفره ای در محیط پیوسته خاک است، به شبیه سازی روانگرایی با کمک مدل رفتاری فین پرداخته شده است. اضافه فشار آب حفره ای، جابه جایی های خاک، لنگر خمشی و نیروی جانبی شمع، جابه جایی و خمش دیوار از جمله یافته های به دست آمده از طریق شبیه سازی است که با یافته های آزمایشگاهی مورد مقایسه قرار گرفته است. یافته های به دست آمده نشان می دهد که روانگرایی در خاک اتفاق خواهد افتاد و زمان آن مطابق با مدل آزمایشگاهی است. جابه جایی خاک در اثر این رخداد نیز استخراج شده و با مدل آزمایشگاهی مقایسه شده است. این مقایسه نشان می دهد که رفتار و روند افزایش جابه جایی در زمان های مختلف بارگذاری مطابق با یافته های آزمایشگاهی است. همچنین یافته های به دست آمده به کمک مدل عددی برای شمع تطابق بالایی با یافته های آزمایشگاهی به خصوص برای شمع های نزدیک به دیوار نشان می دهد. در نهایت نیز رفتار دیوار بررسی شده است که دیده می شود مکان حداکثر ممان خمشی در دیوار در مدل عددی مطابق مدل آزمایشگاهی است.

    کلیدواژگان: روانگرایی، تحلیل دیواره، تحلیل گروه شمع، FLAC3D
  • علی کاوند *، عباس قلندرزاده، فریبا کبیری صفحات 55-69

    در این مقاله به بررسی مقاومت روانگرایی ماسه مخلوط با شن با استفاده از آزمایش های سه محوری تناوبی پرداخته شده است. بدین منظور اثر افزایش درصد شن و تراکم نسبی (Dr)، بر مقاومت روانگرایی و سرعت موج برشی (Vs) مخلوط و همبستگی بین آنها بررسی شده است. نتایج نشان می دهد که افزایش تراکم نسبی مخلوط (Dr) در یک درصد شن ثابت موجب افزایش Vs و مقاومت روانگرایی نمونه ها شده و در یک Dr ثابت نیز افزایش میزان شن تا 50 درصد موجب افزایش Vs می شود. درحالی که در یک Dr ثابت، با افزودن شن به ماسه تا 10 درصد، مقاومت روانگرایی افزایش و سپس با افزایش بیشتر میزان شن تا 50 درصد، مقاومت روانگرایی کاهش می یابد. در ادامه افزایش بیشتر درصد شن تا 75 درصد، مجددا منجر به افزایش مقاومت روانگرایی مخلوط شده است. در توجیه رفتار مشاهده شده نتیجه گیری شده است که به منظور مطالعه رفتار روانگرایی خاک های ماسه ای مخلوط با شن بهتر است از پارامترهای نسبت تخلخل بین ذرات ریزدانه (ef) و نسبت تخلخل بین دانه ای (ec) به ترتیب در نواحی کنترل شونده توسط ذرات ماسه و شن به جای پارامترهای نسبت تخلخل کلی مخلوط یا تراکم نسبی مخلوط (Dr) استفاده شود.

    کلیدواژگان: خاک ماسه ای مخلوط با شن، روانگرایی، آزمایش سه محوری تناوبی، آزمایش المان خمشی پیزوالکتریک، سرعت موج برشی
  • جواد جلیلی *، صابر صفری صفحات 71-81

    مصالح مخلوط رس - سنگ دانه به صورت طبیعی در منابع قرضه یافت می شوند و همچنین به صورت مصنوعی ترکیب شده و در احداث سدهای خاکی و یا پوشش مدفن زباله به کار می روند. شناخت خصوصیات رفتاری این مصالح به جهت وفور آن در طبیعت و تشکیل دادن هسته نفوذناپذیر تعداد زیادی از سدهای خاکی کشورمان حائز اهمیت است. این مقاله برای نخستین بار به تاثیر فشار همه جانبه متناوب بر توزیع فشار آب حفره ای اضافی ناهمگن در این مصالح می پردازد. یافته های این مطالعه عددی نشان می دهد که در فواصل نزدیک سنگ دانه ها، با تغییرات تناوبی بار محوری و فشار همه جانبه به صورت هم زمان، امتداد برآیند بار اعمالی و جهت قرارگیری سنگ دانه ها در مصالح رسی بر میزان فشار آب حفره ای تاثیر می گذارد؛ به نحوی که با نزدیک تر شدن این دو امتداد به یکدیگر مقدار فشار آب حفره ای افزایش چشمگیر می یابد. این روند با افزایش فاصله سنگ دانه ها حفظ نمی شود و تاثیر میزان نوسان فشار همه جانبه بر افزایش فشار آب حفره ای در فواصل دورتر سنگ دانه ها بیشتر می شود.

    کلیدواژگان: مخلوط رس- سنگ دانه، فشار همه جانبه تناوبی، فشار آب حفره ای اضافی، نرم افزار اجزای محدود پلکسیس
  • الهه سادات هاشمی، علی خیرالدین *، محسن گرامی، عبدالرضا سروقدمقدم صفحات 83-98

    عملکرد ضعیف و فروریزش ساختمان های نامنظم سختی در ارتفاع، در طول زلزله های گذشته منجر به بروز خسارات مالی و جانی جبران ناپذیری شده است. از این رو ارزیابی دقیق تر این نوع سازه ها به ویژه در سطح عملکردی فروریزش، حائز اهمیت است. در این مطالعه قاب خمشی بتنی ویژه منظم شش طبقه، به عنوان مدل مرجع، مطابق با ضوابط آیین نامه های داخلی طراحی شده است. سپس 12 قاب نامنظم سختی در ارتفاع با مقادیر و محل های وقوع متفاوت در ارتفاع، ساخته شده است. جهت ارزیابی فروریزش، رفتار غیرخطی اعضا به روش پلاستیسیته متمرکز، در نرم افزار Opensees مدل سازی شده است. عملکرد احتمالاتی لرزه ای قاب های مورد مطالعه، مبتنی بر روش دستورالعمل FEMAP695 مورد مقایسه قرار گرفته است. در این ارزیابی، پارامترهای متداول طراحی از جمله ضریب رفتار، ضریب اضافه مقاومت و شکل پذیری و نیز نسبت حاشیه ایمنی فروریزش1 و همچنین منحنی های شکنندگی بررسی شده است. نتایج نشان داد که وجود نامنظمی باعث کاهش ضریب رفتار و ضریب شکل پذیری می شود. بیشترین کاهش در ضریب رفتار نسبت به قاب منظم، مربوط به مقدار فاکتور نامنظمی 4/0 واقع در طبقه اول می باشد که در حدود 24 درصد تخمین زده شده است. هنگامی که فاکتور نامنظمی برابر با 4/0 و در بخش پایینی سازه قرار گیرد، نسبت حاشیه ایمنی فروریزش اصلاح شده، در حدود 30 درصد نسبت به حالت قاب منظم کاهش و احتمال شکست در این قاب برای یک سطح مشخص از نیاز سازه، نسبت به سایر مدل ها، افزایش می یابد. لازم به ذکر است که تغییرات در نسبت حاشیه ایمنی اصلاح شده و احتمال شکست در مدل های با نامنظمی واقع در ارتفاع میانی سازه در مقایسه با سایر حالات کمتر است. وجود نامنظمی سختی2 در ارتفاع بنا بر مقدار فاکتور نامنظمی و محل وقوع نامنظمی، بر عملکرد احتمالاتی لرزه ای سازه ها در سطح فروریزش تاثیرگذار می باشد. بنابراین ضروری است در تعریف محدودیت های آیین نامه ای برای این نوع سازه ها علاوه بر فاکتور نامنظمی، محل اثر نامنظمی نیز به نحو مقتضی در نظر گرفته شود.

    کلیدواژگان: ارزیابی احتمالاتی3، قاب خمشی بتنی ویژه، نامنظمی سختی، تحلیل دینامیکی فزاینده4، منحنی شکنندگی، دستورالعمل FEMAP695
  • حسین کاظمی فرد، محمود حسینی *، مسعود نکویی، بهرخ حسینی هاشمی صفحات 99-113

    از فیوزهای سازه ای و سیستم الاکلنگی جهت کاهش پاسخ ساختمان در مقابل زلزله و هدایت آسیب استفاده می شود. در این سیستم ستون های ساختمان حذف شده و به جای آنها در مرکز از یک تکیه گاه و در پیرامون ساختمان از فیوزهای سازه ای غیرخطی استفاده می شود. هدف اصلی از ایجاد این سیستم این است که هنگام زلزله اجزای سازه ای به صورت الاستیک باقی مانده و تغییر شکل های غیرخطی در فیوز های سازه ای پیرامونی به وجود آید که پس از زلزله می توان در مدت زمان کوتاه و با هزینه کمتری نسبت به هزینه ساخت کل ساختمان، فیوزهای آسیب دیده را تعویض و از ساختمان بهره برداری نمود. در این تحقیق مشخصات نوعی از فیوز سازه ای مورد بررسی قرار گرفته و کاربرد آن در ساختمان با سیستم الاکلنگی تحت اثر زلزله حوزه نزدیک مورد مطالعه قرار می گیرد. به طوری که حداکثر شتاب مطلق بام و برش پایه به طور چشمگیری کاهش می یابد، اما میزان تغییر مکان جانبی نسبی طبقات در برخی از ساختمان ها افزایش یافته اما از حد مجاز کمتر است.

    کلیدواژگان: حرکت الاکلنگی، فیوز سازه ای، تحلیل غیرخطی دینامیکی، تاریخچه زمانی، آسیب پذیری لرزه ای، ساختمان تعمیرپذیر
  • جلال اکبری *، محمد میخی دوز صفحات 115-129

    یکی از روش های نوین طراحی سازه ها، طراحی بر اساس روش انرژی می باشد. در این روش با تعیین انرژی های ورودی، کارهای داخلی انجام شده توسط اعضای سازه و تعادل بین آنها تحت یک مکانیسم مطلوب از پیش تعیین شده برش پایه سازه محاسبه و طراحی مجدد سازه انجام می شود. انتخاب مکانیسم مطلوب از شروع طراحی و تعیین تغییر مکان هدف و حذف مکانیسم های گسیختگی نامطلوب از برتری های این روش می باشد. در این مقاله به طراحی قاب های خمشی بتنی ویژه به روش نیرو بر اساس آیین نامه بتن ایران و روش انرژی (مکانیسم تیر ضعیف- ستون قوی) پرداخته شده است. تفاوت اساسی دو روش در محاسبه برش پایه و توزیع آن در ارتفاع سازه می باشد. برخلاف روش نیرو که محاسبه برش پایه بیشتر بر ضریب رفتار سازه متکی است، در روش انرژی نیازی به اعمال مستقیم ضریب رفتار نیست. در این مقاله سازه های چهار، هفت و دوازده طبقه به روش های نیرو طراحی شده و سپس با طراحی مجدد سازه ها بر اساس مفاهیم روش انرژی، آنها تحت تحلیل های استاتیکی و دینامیکی غیرخطی قرار گرفته اند. نتایج نشان می دهد در سازه های طراحی شده به روش انرژی، جابه جایی نسبی طبقات یکنواخت تر و تشکیل مفاصل پلاستیک مطلوب تر بوده است. همچنین نتایج نشان می دهد که در سازه های طراحی شده به روش انرژی از تمام ظرفیت سازه برای استهلاک زلزله استفاده شده است.

    کلیدواژگان: روش انرژی، روش نیرو، مکانیسم مطلوب، تیر ضعیف- ستون قوی، استهلاک انرژی
  • لیلا ده بزرگی * صفحات 131-143

    در این مقاله با استفاده از نتایج دو سری آزمون، مدل کردن آشوبناکی سیگنال بر اساس نویزها و تشخیص ناهنجاری های قبل از زلزله مورد مطالعه قرار گرفته است. ابتدا تعدادی ویژگی مانند ویژگی های فرکانسی، آماری و آشوب از سیگنال لرزه استخراج شد، سپس ماتریس ویژگی حاصل توسط شبکه پرسپترون چند لایه مورد بررسی قرار گرفت. شبکه پرسپترون توانایی تشخیص آشوبناکی بر اساس نویزها در فاصله زمانی 5 دقیقه قبل از وقوع زلزله با دقت قابل قبول 1404/81 درصد برای زلزله های 5-7 ریشتری ثبت شده سال های 2004-2010 برای 21 ایستگاه ایران را دارا می باشد. سیگنال های ثبت شده لرزه نگار ایستگاه قیر نیز با این روش مورد بررسی قرار گرفت، که شبکه آشوبناکی قبل از وقوع زلزله را با دقت قابل قبول 8696/60 درصد برای آن ایستگاه تشخیص داد. در مقاله حاضر تلاش می شود تا ویژگی های غیر وابسته به زمین شناسی از سیگنال های لرزه نگاشت یک ایستگاه و 21 ایستگاه استخراج شود، سپس نتایج شبکه پرسپترون در تشخیص ناهنجاری و آشوبناکی سیگنال بر اساس نویزها در فاصله زمانی 5 دقیقه قبل از زلزله برای هر دو حالت مورد مقایسه قرار گیرد. نتایج نشان می دهد که استفاده از تعداد بیشتر داده های ثبت شده هر ایستگاه و افزودن ویژگی های غیر زمین شناسی آنها به ویژگی های زمین شناختی هر منطقه می تواند در نتیجه شبکه پرسپترون برای مدل کردن آشوبناکی سیگنال بر اساس نویزها تاثیرگذار باشد.

    کلیدواژگان: زمین لرزه، شبکه پرسپترون چند لایه، تبدیل ویولت، مدل کردن آشوبناکی بر اساس نویزها، نمای لیاپانوف
  • حسن استاد حسین *، سید محمدحسین کامل، مجتبی حنطه صفحات 145-163

    امروزه روش های طراحی بر اساس عملکرد با دو رویکرد مستقیم و غیرمستقیم انجام می شوند. در رویکرد مستقیم، ویژگی ها و مشخصاتی مثل مکانیسم مطلوب، میزان دوران مفاصل، تغییر مکان نسبی طبقه هدف و محدودیت کرنش مصالح که متناظر با سطح عملکرد مورد نظر هستند از همان ابتدا در فرآیند تحلیل و طراحی گنجانده شده اند. یکی از روش های طراحی بر اساس عملکرد با رویکرد مستقیم، طراحی مستقیم بر اساس تغییر مکان است که در آن سازه با فرض مکانیسم و عملکرد مطلوب تحلیل و طراحی می شود. در این پژوهش ابتدا مبانی روش طراحی مستقیم بر اساس تغییر مکان بیان شده و سپس قاب های خمشی بتنی 4، 8، 12 و 16 طبقه با روش طراحی بر اساس نیرو و این روش، طراحی شده اند که مقایسه ی آنها نشان می دهد ستون قاب های روش تغییر مکان ابعاد بزرگ تر یا مساوی و آرماتور خمشی بیشتری نسبت به ستون قاب های روش نیرو دارند. علاوه بر این میزان آرماتور وسط دهانه ی تیرهای قاب های روش تغییر مکان نسبت به دو انتهای آن (محل های احتمالی تشکیل مفاصل پلاستیک) بیشتر است. همچنین در ستون قاب های طراحی شده با روش طراحی مستقیم بر اساس تغییر مکان نسبت به طراحی بر اساس نیرو وزن کل بتن به کار رفته تا 28 درصد و وزن آرماتور به کار رفته 45 تا 82 درصد بیشتر است، حال آن که در تیرها وزن بتن به کار رفته تا 18 درصد کمتر و وزن آرماتور به کار رفته 3 تا 31 درصد بیشتر است.

    کلیدواژگان: طراحی مستقیم بر اساس تغییر مکان، طراحی بر اساس نیرو، قاب خمشی بتنی، برش پایه، مکانیسم مطلوب
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  • Mohammad Reza Abbassi*, Leyla Mahshadnia Pages 1-19

    The studied area lies in the Central Iranian plate. Two reasons for the lack of knowledge concerning the recognition of active faulting in this region could be summarized as following: 1- faults with pure vertical motion are difficult to recognize on aerial photos, 2- especially those cutting through rock units. The mapped active fault, Kushk-e Nosrat is an example of uncertain knowledge of its activity. The existing evidence to prove its activity such as seismicity and geologic data are yet unclear, and concerning morphological aspects it contradicts the present-day stress direction. The present-day stress direction dictates a left lateral deflection of drainages, however the drainage pattern is in accordance with NW-directed paleostress. Therefore, it was necessary to examine the activity of Kushk-e Nosrat fault. The current investigation focuses on two specific issues: 1- The characterization of changes in the Plio–Quaternary state of stress using inversions of slip vectors measured on fault planes with a broad range of displacement values; 2- The identification of present- day stress field by inversion of seismically determined by fault slip vectors (focal mechanism of earthquakes); and 3- The verification of the coherence and mechanical compatibility of the inversion results with the geological and structural characteristics of the region illustrating the kinematic significance of each fault system. The central part of Kushk-e Nosrat trending (N100E) is a dormant fault. The evidence for the inactivity are reflected in prevailing stress direction, drainage pattern and Quaternary deposits. The stress direction measured directly on several station on this fault show a NW-directed stress (σ1), which explains the right lateral deflection of drainage pattern crossing this fault. The last evidence of inactivity of these faults is delivered by mapping of geomorphic surfaces. The young alluvial deposits such as Holocene and late Pleistocene in age are not affected by Kushk-e Nosrat Fault. The deflection of drainage pattern crossing the fault is compatible with a NW-directed stress direction. The inversions of slip vectors measured on fault planes has shown the states of paleostress existing on the faults and the inversion of focal mechanisms revealed the present day stress direction as following: The present day state of stress deduced form focal mechanisms is characterized by a transpressional tectonic regime consistent with the ongoing stress state (N20°E trending σ1); The paleostress field was characterized by a regional mean of N140±10°E trending horizontal compression (σ1), and a transtensional tectonic regime. The change from paleostress to modern stress states has occurred through an intermediate stress state. Characterized by a mean regional N-S trending σ1. According to the obtained results, the assessment of earthquake hazard based on Kushk-e Nosrat fault must be revised in term of considering them as active faults; therefore, caution must be paid by taking them into any calculation. Under the influence of NW-directed paleostress, the faults trending nearly E-W acted as dextral faults, thus the present landscape must be interpreted as the result of a relatively recent reversal of stress direction.

    Keywords: Active Faulting, Central Iran, Geomorphology, Present-Day Stress, Paleostress
  • Parisa Ashjanas, Afsaneh Nasrabadi *, Mohamad Reza Sepahvand, Seyed Hasan Mousavi Bafrouei Pages 21-36

    In this study, Seismic Hazard zoning was probed by studying seismogenic zones and earthquake data in a 150 km radius around the Fars province boundaries in the Zagros seismotectonic zone. Zagros is one of the most seismically active parts of Alpine-Himalayan seismic belt. Fars province located at latitude of 27.2° – 31.42° and longitude of 50.42° – 55.36°, respectively. In this study, seismotectonic zone was determined based on the location of interest, faults strikes, seismic records, and geological structure. In the first step of process, an earthquake catalogue of the instrumental and historical earthquakes was prepared by assimilating them to a uniform magnitude type (Mw) from 8th century until September 2016. Then, by using the Uhrhammer (1986) and Gardner and Knopoff (1974) methods in 1974, aftershocks and foreshocks were eliminated from the catalogue to have main earthquakes only. After the elimination of aftershocks and foreshocks, 2181 earthquakes remained as the main earthquakes in catalogue and their completeness magnitude was calculated by ZMap software. Afterwards, it was tried to recognize all the active faults around the sites; therefore, 23 area sources were introduced within the studied area from faults, historical and instrumental earthquakes. After introducing area sources, seismic parameters such as beta and lambda were calculated for each part using Kijko software. Similarly, space distribution function portion of each source was calculated. In addition, the results of six magnitude studies utilizing step method carried out by Mousvai et al. (2014) was used in this paper. In the deterministic approach, Pick Ground Acceleration (PGA) over bedrock was computed using two attenuation equations, Campbell and Bozorgnia (2008) and Boor and Atkinson (2008), using a MATLAB software for Fars province. Besides, in the probabilistic approach, PGA and pick ground velocity, PGV, were calculated using the same values in the attenuation equations that were used in the deterministic method using OpenQuake, one of the distinguished programs in seismic hazard analysis to determine the PGA on bedrock. The probabilistic approach was carried out on a grading area using a 10 km zonation map. PGA was calculated and covered 63% and 10% probability of exceedance in one life cycle of 50 and 475 years were presented, and hazard curves were calculated for 50 and 475 years using OpenQuake software. Probabilistic study resulted maximum PGA values in the periods of 50 and 475 years to be 0.23 g and 0.6 g respectively .These maximum PGA values centered on Kazeroon. After Kazeroon, Shiraz and Lamerd have the highest levels of hazard risk of cities in Fars province. Moreover, using the deterministic approach and the two attenuation equations, the obtained maximum PGA values fell between 0.68 g and 0.75 g. Finally, the results were compared with previous studies like Hamzeloo (2005), Ghafory-Ashtiany (1999) and Mousavi (2014).

    Keywords: Hazard Analysis, Zagros, Fars Province, Seismogenic Zone, Pick Ground Acceleration, Openquake Software
  • *Saeed Nematinejad, Ehsan Seyedi Hosseininia Pages 37-53

    The economy of a large number of industrialized countries is on the basis of import and export goods through waterfronts. The waterfront is a marine structure that links the ship to the land and is one of the most important parts of the port. In case of waterfront damage, adjacent structures such as cranes will be damaged and important activities of the port will be stopped. Piles inside the soil are also one of these structures that in case of pile failure, the structures over it will be lost. Because of this, the behavior of offshore structures against damage factors such as an earthquake is very important. Numerous experimental modeling has been done with the pile, but its behavior in the waterfront has rarely been studied. One of these experimental models was presented by Motamed and Towhata in 2010. This experimental model presents results of 1-g shaking table model tests on a 3×3 pile group behind a sheet-pile quay wall. The main purpose was to understand the mechanisms of liquefaction-induced large ground deformation and the behavior of the pile group subjected to the lateral soil displacement. The sheet-pile quay wall was employed to trigger the liquefaction-induced large deformation in the backfill. Furthermore, distribution of maximum lateral force within the group pile was thoroughly studied. In this study, the experimental test has been modeled numerically, and the accuracy of the results in the numerical model has been investigated using experimental tests. Numerical simulation has been done using Flac3D software that is a three-dimensional explicit finite-difference program for engineering mechanics computation. The Software is able to simulate the behavior of three-dimensional structures built of soil, rock or other materials that undergo plastic flow when their yield limits are reached. Besides, it simulates the excess pore pressure and liquefaction with the help of Finn constitutive model. Using this software, the pile group behind the quay wall has been loaded dynamically using shake table and the possibility of liquefaction has been studied in the model. The lateral displacement of the soil flow in the numerical model has been compared with experimental results and these displacements have been analyzed. Moreover, the bending moment and the lateral force of the piles and bending moment and lateral displacement for quay wall obtained from numerical simulation have been compared with experimental results. The results show that liquefaction in the soil has occurred and its time is consistent with the experimental model. The soil liquefaction behind the quay wall and the pile group causes the lateral spreading of the soil. The maximum lateral displacements are formed on the surface and behind the quay wall, which decreases with distance from the quay wall and by moving toward the free surface of the soil. The behavior of the pile in this research is similar to a cantilever beam whose maximum bending moment occurs at the bottom of the pile. The results show that the piles near the quay wall can tolerate bending more than the other piles, the reason of which is the greater displacement of the soil in the place of these piles. Comparison of the bending moment of the piles in the numerical model with the experimental model shows that the matching of the results is very good for the piles near the quay wall and is acceptable for other piles. The lateral force of the liquefied soil flow exerted on the piles was obtained by two different methods including back-calculated and software outputs. The total force on the piles was compared in different scenarios, including the JRA (Japan Road Association) design code, the model of the experimental, the numerical model using back-calculated and the numerical model using the software output. The JRA instruction proposes non-conservative values, so that experimental results and numerical model provide more values. The sheet-pile quay wall was modeled as a floating type quay wall without any constraint at the bottom, so that quay wall moves completely with the surrounding soil and its lateral displacement is similar to the displacement of the soil. The maximum bending moment on the wall is well suited to the experimental result, which indicates the accuracy of numerical modeling.

    Keywords: Waterfront, Liquefaction, Analysis of Pile Group, Flac3D
  • Ali Kavand *, Abbas Ghalandarzadeh, Fariba Kabiri Pages 55-69

    Most of the previous studies on liquefaction of soils have been concentrated on sandy soils since it was traditionally believed that only clean sandy soils are prone to liquefaction and those containing fine or coarse portions are unliquefiable. However, the evidences during past earthquakes have shown that sandy-gravel composites can also liquefy under certain circumstances. Although a number of recent laboratory studies have considered the liquefaction behavior of sand-gravel mixtures, some aspects of this behavior have not fully been understood yet. In this study, a series of undrained cyclic triaxial tests was performed to characterize the liquefaction behavior of sand-gravel mixtures with different gravel contents (GC) and relative densities (Dr). The tested soils comprised of Firoozkooh silica sand (no. 161) mixed with different amounts of a river gravel obtained from Tehran. In order to characterize the behavior of the mixtures in small strain range, shear wave velocity (Vs) of all tested specimens was measured using bender element tests. Combining all testing data, the effects of GC and Dr values on the liquefaction resistance and shear wave velocity of the samples were quantified. The tested samples had a diameter of 100 mm and a height of 200 mm and were prepared according to the wet tamping technique. The tests were performed on samples with three different Dr values of 10%, 30%, and 50% and five different GC values of 0%, 10%, 30%, 50% and 75%. In addition, for any combination of Dr and GC values, the tests were repeated with three different cyclic stress ratio (CSR) values, namely, 0.1, 0.15 and 0.2. The testing procedure included sample preparation, saturation, consolidation under a confining stress of 100 kPa, Vs measurement with bender elements and application of a cyclic deviatoric stress at the desired CSR value. The results of bender element tests show that for a constant GC value, Vs of the sample increases with its relative density. In addition, at any constant Dr, Vs increases as the GC value in the mixture increases up to 50%. In order to quantify the liquefaction behavior of the mixture, the variation of cyclic stress ratio (CSR) versus number of cyclic stress cycles (N) required to cause initial liquefaction in the samples defined by a double amplitude strain value of 5% or an excess pore pressure ratio (ru) of 1.0 were also scrutinized. The results demonstrate that N decreases with increasing CSR values. For all GC values, as the relative density of the mixture increases, the liquefaction resistance increases accordingly. The variation of liquefaction resistance of the mixture at a constant Dr value with gravel content shows that as GC increases up to 10%, the liquefaction resistance increases as well; however, with further increasing GC to 50%, the liquefaction resistance decreases and further increase in GC up to 75% increases the liquefaction resistance of the mixture. In other words, the highest liquefaction resistance is observed for a GC value of 75%. It should be added that at higher Dr values, the effect of GC on liquefaction resistance was found to be more significant. To interpret this behavior, it was further showed that the liquefaction behavior of the mixture can be well illustrated by dividing its behavior into two distinct parts, i.e. the sand-controlled and the gravel-controlled parts. For a sand-controlled part, the interfine void ratio (ef) can be used to characterize the liquefaction behavior of the mixture while within the gravel-controlled portion, the interangular void ratio (ec) is better to be adopted. These two definitions of void ratios can be substituted for Dr, which was conventionally used to quantify the liquefaction behavior of the soils. Finally, the correlation between the liquefaction resistance of the mixtures with their Vsvalues was evaluated. The observations describe that for a constant GC value, as Vs of the mixture increases, the liquefaction resistance increases as well whereas for a constant Vs value, with increasing GC up to 50%, the liquefaction resistance decreases. The reason is that in order to keep Vs constant during increasing the GC value, the sand matrix of the mixture should be kept looser and therefore, the mixture whose behavior in this case is profoundly controlled by the sand matrix, shows a lower liquefaction resistance.

    Keywords: Sand-Gravel Mixture, Liquefaction, Cyclic Triaxial Test, Bender Element Test, Shear Wave Velocity
  • Javad Jalili *, Saber Safari Pages 71-81

    This paper describes findings of a series of numerical studies to investigate the effect of Variable Confining Pressure (VCP) on Excess Pore Water Pressure (EPWP) distribution in a mixture of gravelly inclusions floating in matrix of clay, called “mixed clay” material. Mixed clay material has frequently been used as core of embankment dams in seismically active areas of Iran. The mixture naturally exists in rainfall active areas and also is made manually. The matrix provides sealing while the inclusions increase strength and deformation modulus. Previous studies reveal noticeable increase of EPWP among inclusions under cyclic or dynamic loadings, keeping the initial confining pressure constant. The confining pressure is usually held constant based on the triaxial testing routine. However, recent studies have discovered evident variation of confining pressure in different locations of the shaking embankment-core during an earthquake. After reviewing the literature of analytical and experimental studies regarding the magnitudes of VCP caused by different input motions on an embankment, and also those regarding mixture behavior especially in terms of EPWP variation caused by cyclic loads, results of the conducted semi-coupled dynamic analyses on models of triaxial specimens having limited inclusions inside are presented herein. Making use of PLAXIS 2D 2016, specimens with different inclusion sizes and inclusion distances, experiencing VCP are analyzed. The geometry of a triaxial specimen is modelled in PLAXIS environment in an axisymmetric mode. The inclusions are modeled by half-circle geometry at the center of the specimen. The material behavior is undrained, capable of liquefaction resembling, which means that the degradation of the soil is also modeled. Calibration of the model is based on experiments of previous studies on similar materials, taking into account slight modifications to postpone liquefaction generation. This would clarify EPWP generation caused by VCP variation in pre-liquefaction stage; the UBC model is not precise enough in post-liquefaction stage. The bulk modulus of the soil and water are combined and the consequent slight volumetric strain multiplied by the huge bulk modulus of the water provides the excess pore water pressure, while the relatively slight soil skeleton modulus (compared with that of water) leads to nearly zero effective stress. To assure providing of enough precision, two types of calculations were compared: dynamic semi-coupled and static fully-coupled analyses were conducted and results were compared. It was evident that giving permission to EPWP to redistribute in a coupled analysis was not conservative. The parameter that defines VCP effect is the ratio of the confining pressure cycle amplitude to that of deviatoric stress, called “h”. The results of this study shows that cyclic variation of confining and deviatoric stress at the same time would cause the increase of EPWP within inclusions of the matrix. By decrease of inclusion distance to diameter, EPWP increase among inclusions is dominant, which weakens as the distance increases. The EPWP increase is maximum at the minimum h (0.3), which represents the constant confining pressure situation. This shows that neglecting the increase of h as the consequence of VCP is conservative regarding the stability of structures made up of such mixtures during strong ground motions. Findings of this study is in agreement with those of previous ones: increase of EPWP among inclusions affected by loading direction relative to inclusions locations and geometry was evident. Further studies are required to reveal the effect of loading frequency on the results.

    Keywords: Clay-Aggregate Mixture, Cyclic Confining Pressure, Cyclic Triaxial, Excess Pore Water Pressure
  • Elahesadat Hashemi*, Ali Kheyroddin, Mohsen Gerami, Abdoreza, S. Moghadam Pages 83-98

    The use of aesthetic parameters in the architecture of the building as well as the existence of various applications in different stories of a building will lead to irregularities in the structure. Non-uniform distribution of dynamic characteristic, e.g. mass, stiffness and strength of these structures causes the focus of nonlinear deformation, and consequently, the global or local destruction of the structure during an earthquake. For this reason, many current world-wide codes have provided definitions and limitation for irregular buildings. One common type of irregular structures that is important to investigate its seismic behavior is stiffness irregular structures. ASCE 7-16 defines stiffness irregularity as: Stiffness-Soft Story Irregularity: Stiffness-soft story irregularity is defined to exist where there is a story in which the lateral stiffness is less than 70% of that in the story above or less than 80% of the average stiffness of the three stories above (ASCE 7-16). Stiffness-Extreme Soft Story Irregularity: Stiffness-extreme soft story irregularity is defined to exist where there is a story in which the lateral stiffness is less than 60% of that in the story above or less than 70% of the average stiffness of the three stories above (ASCE 7-16). It should be noted that this definition is based on the irregularity magnitude and the effect of the location of irregularity in height of structures has not been mentioned, which can be expressed as a defect in the definition of the stiffness irregularity. The major previous researches on the seismic response of the structures with vertical irregularity have been deterministic that they generally have aimed to calculate the mean values of peak responses. The seismic behavior of the structure due to available uncertainties is probabilistic rather than deterministic. It should be noted that research on the effect of irregular structures on the seismic capacity of structures is less than the effect of irregular structures on the seismic demand of structures. In order to assess the collapse capacity of irregular structures, the use of a collapse behavior model of the elements with respect to the probabilistic process as well as Incremental Dynamic Analysis (IDA) can be effective. Various methods have been developed to evaluate the probabilistic response of structures. In this study, the effect of the stiffness irregularity on the probabilistic seismic performance of RC moment resistant frames has been studied according to the FEMAP695 (2009) procedure. To do so, nonlinear static analysis and the Incremental Dynamic Analysis (IDA) are conducted. According to the fragility curves, the collapse capacity of the structure is calculated for each model. The CMR for the models is compared to the acceptance collapse criteria based on the FEMAP695 (2009) guideline. The obtained results show that the irregular structures have different seismic performance than regular one. The results show that both the level of irregularity and the location of irregularity in height affect the seismic responses of these structures. It seems that the reconsideration of seismic code requirements for stiffness irregularities needs to be necessary to provide more accurate for structures with stiffness irregularities especially for those with an irregularity in the critical stories.

    Keywords: Probabilistic Assessment, Special Concrete Moment Frame, Stiffness Irregularity, Fragility Curve, FEMA-P695
  • Hossein Kazemifard, Mahmood Hosseini *, Masoud Nekooei, Behrokh Hosseini Hashemi Pages 99-113

    Preventing the collapse of buildings during major earthquakes by using the capacity of plastic deformations of their structural members is regarded as the main philosophy behind most of the present seismic design codes. However, regarding large, especially near-source earthquakes, the amount of these plastic deformations may be so large that the building may lose its performance, and its demolishing may become inevitable. As a result, some adverse consequences are imposed to the stricken community. First, it is necessary to evacuate and shelter thousands, even hundreds of thousands of people who have lost their living or working spaces. Second, demolishing the severely damaged (but not collapsed) buildings is a very difficult and time consuming task since the considered ductility in design may not result in losing their integrity easily, and the common demolishing techniques may not be used for those buildings. Third, the debris removal of the demolished buildings, whose weight may be over millions of tons in case of large cities is very time consuming and costly. Finally, plenty of time and cost as well as a large number of skilled work forces are needed to construct the new buildings to replace the demolished ones. Based on the above-mentioned issues, it is recommended to design and construct the buildings in such a way that they can be easily and quickly repaired with little cost, even after major earthquakes. Buildings that are created in this way can be called repairable or resilient buildings. Employing a structural system with seesaw motion is considered as one of the ways for creating earthquake-resilient buildings. In seesaw buildings, all circumferential columns at the lowest story are equipped with energy dissipating devices or structural fuses, all internal columns at that story are omitted, and a central mega hinge support with a grid of orthogonal strong girders are used to keep the integrity of the upper stories and transfer their gravity loads to the mega hinge support and the circumferential columns at the lowest story. In this research, the specifications of a kind of yielding-plates structural fuse, namely the initial stiffness and the yielding displacement, have been investigated and its application in a set of buildings with seesaw structural systems has been studied subjected to near-source earthquakes by performing a series of nonlinear time history analyses (NLTHA) using the scaled accelerograms of a set of selected earthquakes. Results of the conducted NLTHA indicate that the IO seismic performance level is mostly achieved in seesaw buildings by using the appropriate values for the aforementioned behavioral parameters of the structural fuses, while the conventional buildings with the same geometry mostly fail subjected to the same applied earthquakes. The maximum absolute acceleration of the buildings’ roofs and their base shear are significantly reduced by using the seesaw system; however, the roofs maximum displacements in some seesaw buildings are increased comparing to the conventional buildings, but they are still in the range of seismic design code limitations.

    Keywords: Seesaw Motion, Structural Fuses, Nonlinear Time History Analysis, Seismic Vulnerability, Repairable Buildings
  • Jalal Akbari *, Mohammad Mikhidoz Pages 115-129

    One of the novel methods for design of civil engineering structures is energy based design approach. In this method, by determining the input energy and balancing between the accomplished works by the members of structures under a pre-determined mechanism, the base shear is calculated, and structures are re-designed. From the beginning of the design, selection of the appropriate mechanism and determining the target drift are the main advantages of this approach. Furthermore, compared with forced-based design method, removing the undesirable mechanisms is the superiority of this method. In this paper, reinforced concrete frames have been designed using Iranian concrete code (ABA) and energy method (weak beam-strong column). The main difference between two approaches is the calculation of base shear of structures. Unlike the force-based method, energy method does not directly use the force reduction factor (R). In this research, 4, 7 and 12-story special reinforced concrete frames have been designed using force-based and energy-based methods, and then for seismic evaluation of the frames; nonlinear static and dynamic analyses have been conducted. The results show that for designed structures using energy method, the relative displacements of the stories are uniform, and the plastic hinges have been appeared in the beams. For frames designed by energy method, whole structural capacities are participated in the earthquake energy dissipation process.

    Keywords: Energy Method, Force Based Method, Desirable Mechanism, Weak Beam - Strong Column, Energy Dissipation
  • Leila Dehbozorgi * Pages 131-143

    In this paper, using two experimental results, chaotic signal modeling based on noise and detection of anomalies before an earthquake has been studied. First, a number of features such as frequency, statistical, entropy and FFT of the seismic signal were extracted, then the property matrix was investigated by multi-layered perceptron network (MLP). MLP can detect anomalies based on noise at a time interval of 5 minutes before an earthquake with an acceptable accuracy of 81.1404% for the magnitude 5-7 on the Richter scale from 21 earthquake recording stations in Iran (between 2004 and 2010). The recorded GHIR station signals were also investigated by this method, so MLP network determined the chaotic before an earthquake with an acceptable accuracy of 60.8696% for GHIR station. In this paper, it is tried to extract non-geologic properties from seismic signals of GHIR station and 21 stations. Then, the results of the MLP network are compared in terms of chaotic detection based on noise five minutes before an earthquake for each case. The results demonstrate that by using more recorded data of each station, MLP network is more capable for diagnosis of the chaotic based on noise before an earthquake. The actual recorded seismic data is much better than simulated signals to detect seismic signal abnormalities before an earthquake and simulate the signal, in order to investigate the recorded signals of seismicity. In the recent study, recorded seismic signals were investigated. The purpose of this study is to determine the most desirable characteristic matrix for detecting anomalies within five minutes before the earthquake. Chaotic signal modeling based on noise and detection of anomalies before an earthquake using MLP network process contains four main stages: (1) Separate earthquake and slice signal, (2) The signals were processed using a high pass filter to reject the baseline drifts in signals, (3) Different types of features were extracted from the filtered signals and the feature vector was constructed, (4) The feature vector were fed to a neural network. Our database contains 760 records for 21 stations and 148 records for GHIR station of IRAN earthquakes, from the International Institute of Earthquake Engineering and Seismology. The sampling frequency was 50 Hz. . Fourth Order High Pass Butterworth Filter was used to annihilate low frequency (fc=0.04), and then the signal was normalized. The features were extracted from the filtered signals. Then the classifier was trained and tested. 70% of the data were randomly selected for training purposes and the rest 30% were used for testing for each experiment. MLP networks were successfully trained using MATLAB (for both condition) and the results were presented for both conditions. The networks had one output in which every value at output uniquely representing each categories (1: earthquake, 0: no earthquake). In this study, by using the results of two series of experiments, chaotic signal modeling based on noise and detection of anomalies before an earthquake has been investigated and the features matrix has been constructed for the following two conditions: By using seismic signals in different geographic regions of the country (IRAN). By using seismograph signals at a specific station (GHIR station). The results show that MLP network produced better accuracy for 21 stations compared with GHIR station. Because the number of data was different in two ways or the features are non-geological. To achieve better results, the following suggestions are presented: noise reduction and use of more frequency features. We are now going to collect more and more earthquake data from all around the world, adding more chaos dependent parameters to the feature vector, using committee machines to increase the accuracy of classification and increasing prediction length from five minutes before to ten and more as well.

    Keywords: Earthquake, Multilayer Perceptron Network, Wavelet Transform, Chaotic Modeling Based on Noise, Lyapunov Exponent
  • Hassan Ostadhossein *, Seyed Mohammad Hossein Kamel, Mojtaba Henteh Pages 145-163

    Considering the performance of a structure in design procedure as an initial explicit and primary assumption is a valuable achievement, which enable the client to decide about acceptable cost and risk. In traditional Force Based Design (FBD) method after limitation of internal forces to the strength limits of members, performance of a structure will be checked as a secondary goal of design procedure. While actually it is the damage level that is defined by desired performance, it is the main concern of design as well. Performance based design methods are categorized into direct and indirect approach. In direct approach, in spite of indirect one, structure features and characteristics are predefined such that the desired mechanism, rotation of hinges, target story drift and material strain limits correspond to the desired performance level, have been included from the beginning of the analysis and design process. Direct Displacement Based Design (DDBD) is a direct performance method in which desired mechanism of inelastic deformation and optimal performance for frames are considered as initial and essential assumptions of the design procedure. According to predefined acceptable total drift of the structure as an index of performance, base shear will be determined by using displacement spectra considering nonlinearities and damping effects. After that, the calculated base shear will be distributed throughout the stories of structure according to predominant mode shapes. Internal forces of structural members will be calculated based on a plastic analysis considering assumed mechanism. In this paper, four concrete special moment frames with two 5 m bays and 4, 8, 12 and 16 stories with height of 3 m were designed by direct displacement based method and were compared with force based design method results. According to base shear calculation relation of DDBD, it is required to predefine the total drift as a performance indicator. The total drift for life safety performance level is suggested to be 2% in FEMA 356 for concrete moment resistant frame. It was observed that DDBD base shear was greater than FBD one. Besides, by increasing the height of the structure, the difference of base shear in DDBD and FBD become greater. It was concluded that columns dimensions and longitudinal reinforcement of DDBD are equal or greater than FBD. As a general conclusion, it has been understood that the issue of weak ductile beam against strong column that is the main design topic in special moment frame design is more feasible in DDBD approach. In fact, in direct displacement based design procedure, plastic hinges are assumed to be formed in beams ends, explicitly. This consideration leads DDBD columns to have more concrete volume and longitudinal reinforcement weight compared to FBD columns. Moreover, beams of DDBD have longitudinal reinforcement weight more than FBD beams but they have less concrete weight. In addition, it was observed that in DDBD method, obtained reinforcement arrangement in columns and beams and section dimensions are such that the formation of hinges in columns or beams mid span is prevented. Finally, it is concluded that DDBD leads to a more efficient design.

    Keywords: Direct Displacement-Based Design (DDBD), Force-Based Design (FBD), Concrete Moment Frame, Base Shear, Favorable Mechanism