اثر ارتفاع در مقاومت برشی تیرهای عمیق بدون آرماتور برشی با بتن معمولی و سبک

نوع مقاله : مقاله پژوهشی

نویسندگان

تهران-دانشگاه تربیت مدرس

چکیده

یکی از پارامترهای مهم در تعیین ظرفیت برشی تیرها، ارتفاع تیر میباشد. در این تحقیق به منظور بررسی اثر ارتفاع در مقاومت برشی تیرهای عمیق با بتن سبک و مقایسه با بتن معمولی دو سری تیر که شامل 8 تیر عمیق با نسبت دهانه برشی به ارتفاع 0/5 بود ساخته شد. سری اول شامل 4 تیر به ارتفاع 30 ،45 ،60 و 90 سانتی‑متر بود که در ساخت آنها از بتن سبک استفاده شد نمونه‌های سری دوم نیز شبیه سری اول بود با این تفاوت که در ساخت آنها از بتن معمولی استفاده شد. تیرهای به صورت دو نقطه‌ای و متمرکز از بالا تحت بار قرار گرفتند. نتایج نشان می‌دهد که مد ً مستقل از گسیختگی مستقل از ارتفاع و نوع بتن می‌باشد. الگوی گسترش ترک‌ها بیشتر تحت تأثیر ارتفاع است و تقریبا نوع بتن می‌باشد. مقاومت برشی نرمالیزه شده در هر دو گروه از تیرها با افزایش ارتفاع کاهش می‌یابد. مقایسه نتایج حاصل از آزمایش با روش‌های خرپایی موجود در آیین‌نامه‌ها نشان می‌دهد که تمام روش‌ها در تیرهای با ارتفاع کم محافظه‌کارانه بوده و با افزایش ارتفاع از حاشیه ایمنی کاسته می‌شود. نتایج آیین‌نامه CSA در مورد تیرها با ارتفاع cm 90 غیر محافظه‌کارانه است که این امر نیاز به تحقیق بیشتری دارد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Height effect on shear strength of deep beams without Shear Reinforcement with normal and lightweight concrete

نویسندگان [English]

  • abolfazl arabzade
  • amin noori
چکیده [English]

Failure in reinforced concrete deep beams is mainly in shear and in a brittle and sudden form, which this behavior can lead to destructive consequences. So determining shear capacity of these beams is an important issue. One of major parameters in determining shear capacity of beams is the height of beam. Researches show that with increase in beam’s height, normalized shear strength decreases which this phenomena is called size effect. In recent years due to advances in construction methods, the idea of using lightweight concrete deep beams has been proposed, this should be done with a full understanding of the behavior of lightweight concrete. Moreover, truss models are recently used for analysis and design of deep beams in codes which their validity for lightweight concrete should be investigated. In this research to investigating size effect in lightweight concrete deep beams and comparison with normal concrete, two series of beams including 8 deep beam with shear span to height ratio of 0.5 were built in lab. First series included 4 beams with height of 30, 45, 60 and 90 cm using lightweight concrete in their construction, specimens of second series were similar to first but normal concrete was used in there construction. Results show that failure mode is independent of height and concrete type. The pattern of crack propagation is more affected by height and almost independent of concrete type. Normalized shear strength in both groups of beams decreases with increase in height but the intensity of this decrease in lightweight concrete deep beams is more than normal concrete which shows that size effect in lightweight concrete is more than normal concrete. Results of Experiment were compared to truss methods in codes and some of proposed models in codes. Results indicate that all methods are conservative in low height beams and with increase in height, safety margin decreases. Results of CSA code is non-conservative for beams with 90 cm height which needs more study.

کلیدواژه‌ها [English]

  • Deep beam, Size effect
  • Lightweight Concrete
  • Truss method
  • Shear Capacity
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