مطالعه عددی سیستم دال با تیرچه بتنی پیش‌تنیده تحت شرایط آتش

نوع مقاله : علمی - پژوهشی

نویسندگان

1 دانشیار، دانشگاه بوعلی سینا، همدان، ایران

2 دانشجوی کارشناسی ارشد، دانشگاه بوعلی سینا، همدان، ایران

چکیده

با توجه به آمار بالای آتش‌سوزی و هزینه‌های مالی و جانی ناشی از آن، جلوگیری از فروریزش سقف به عنوان یکی از اعضای اساسی در ساختمان، به هنگام آتش‌سوزی ضروری است. از آنجا که بتن دارای ضعف ذاتی در کشش می‌باشد، ترک خوردگی در ناحیه کششی دال‌ها اجتناب ناپذیر است. از طرف دیگر در سیستم دالهای با تیرچه پیش‌تنیده، معمولا ناحیه‌ی کششی بتن بکلی حذف و یا به صورت موثری کاهش می‌یابد و می توان انتظار داشت که عملکرد سقف تحت شرایط آتش بهبود یابد. در این پژوهش رفتارعددی دال بتنی ساده با سیستم تیرچه بتنی پیش‌تنیده یک طرفه تحت شرایط آتش بررسی شد. دمای بحرانی در 9 نمونه که در مقدار نیروی پیش‌تنیدگی، مقاومت و پوشش بتن و همچنین طول دهانه با یکدیگر تفاوت داشتند، به دست آمده و با یکدیگر مقایسه شد. بار حرارتی بر اساس پروتکل استاندارد ISO 834-1 به نمونه‌های مورد مطالعه اعمال شد. توزیع دما در سراسر دال به‌صورت یکنواخت و افزاینده اعمال شد و حالت‌های خرابی در مدل پیش‌بینی شده و با نتایج آزمایشگاهی مورد صحت‌سنجی قرار گرفت. نتایج نشان داد که نیروی پیش‌تنیدگی بیشترین تاثیر و طول دهانه کمترین تاثیر را بر کاهش و یا افزایش شاخص دمای بحرانی دارد. به این صورت که تغییر پارامتر میزان پیش‌تنیدگی از صفر به 600 و 1120 مگاپاسکال سبب افزایش شاخص دمای بحرانی به مقدار 20 و 43 درصد و تغییر پارامتر میزان طول تیرچه از مقدار اولیه 5/4 متر به 6 و 5/7 متر به ترتیب سبب کاهش شاخص دمای بحرانی به مقدار 1 و 2 درصد شده است. تغییر پارامتر میزان پوشش بتن از 20 میلی‌متر به 10 و 30 میلی‌متر به ترتیب سبب کاهش و افزایش شاخص دمای بحرانی به مقدار 11 و 9 درصدگردیده است. همچنین در تمامی نمونه‌ها مود شکست یکسان و به‌صورت خمشی در وسط دهانه تیرچه رخ داد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical Study of Prestressed Concrete Joist Slab System Under Fire Conditions

نویسندگان [English]

  • Freydoon Rezaie 1
  • Newsha Sayad Sedgh Herfeh 2
1 Associate Professor, BU-ALI SINA University, Hamedan, Iran.
2 M.Sc. Student, BU-ALI SINA University, Hamedan, Iran.
چکیده [English]

Due to the large number of fire and the resulting financial and human costs, it is necessary to prevent the roof from collapsing as one of the key members of the building during a fire. Because concrete has an inherent weakness in tensile stress, cracking in the tensile area of slabs is inevitable. On the other hand, in a system of prestressed concrete joist slab system, the tensile area of the concrete is usually completely eliminated or effectively reduced, and the performance of the floor can be expected to improve under fire conditions. The critical temperature was obtained and compared in 9 samples that differed in the amount of prestressing force, strength and concrete cover as well as the span length. The thermal load was applied to the studied samples according to the ISO 834-1 standard protocol. The temperature distribution across the slab was applied uniformly and incrementally and the failure states in the model were predicted and verified with laboratory results. The results showed that the prestressing force has the greatest effect and the span length has the least effect on decreasing or increasing the critical temperature index. Changing the prestressing parameter from zero to 600 and 1120 MPa, increases the critical temperature index by 20 and 43% and changing the beam length parameter from the initial value of 4.5 m to 6 and 7.5 m, decreasing the critical temperature index by 1 and 2%, respectively. Changing the parameter of concrete cover from 20 mm to 10 and 30 mm has caused a decrease and increase of critical temperature index by 11 and 9%, respectively. Also, in all samples, the same failure mode occurred in the middle of the joist in a bending manner.

کلیدواژه‌ها [English]

  • Fire
  • Numerical study
  • Prestressing force
  • Prestressed concrete joist. Critical temperature
  • Concrete cover
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