در این مقاله، استفاده از روش پیشنهادی کاشت میلگرد پیش تنیده در ارتفاع مقطع جهت تقویت تیر های دارای کمبود آرماتور برشی بصورت آزمایشگاهی مورد بررسی قرار گرفته است. بمنظور بررسی اثرپذیری روش تقویت پیشنهادی، 10 نمونه تیر بتن‌آرمه به ابعاد 1700×200×200 میلی‌متر با ضعف مقاومت برشی در یکطرف ساخته شده و با شرایط تقویت مختلف بصورت دهانه ساده با بار دو نقطهای در وسط دهانه مورد آزمایش قرار گرفتند. درکلیه تیرها قبل از تقویت با پیش بارگذاری ترک برشی ایجاد گردید. نیمی از نمونه‌ها پس از بار برداری و بقیه تحت بار ثابت مورد تقویت قرار گرفتند. بر اساس نتایج حاصله، روش کاشت میلگرد پیش تنیده بطور موثری میتواند جهت تقویت برشی تیرها حتی در مواردی که تیر دارای ترک خوردگی برشی قابل توجه شده باشد، با باربرداری و یا بدون باربرداری از تیر، بکار رود.
Experimental investigation of Shear Strengthening of R.C. Beams by Pre-stressed Embedded through Section Bars
نویسندگان [English]
reza morshed؛ ehsan tavasoli؛ mehrbod barzegar
Assistant Professor, Faculty of Civil Eng., Yazd University
چکیده [English]
In this paper, shear strengthening of R.C. beams with insufficient shear reinforcement by a new proposed method, Prestressed Embeded Through Section Bars (PETSB), was studied experimentally. This method consists of boring holes through beam web and embedding steel bolt and tightening the bolt to pre-determined pre-stressing force. In order to investigate the influence of the proposed strengthening method, a test program, including 10 RC Beams with dimensions of 1700 × 200 × 200 mm, was planned. The beams were tested and simply supported by two points loading at the midspan and a shear span of 600 mm on each side. The beams were fully shear reinforced at one side and poorly shear reinforced at the shear span on the other side (no shear reinforcement in 5 beams, 0S Beams, and only one middle stirrup in 5 beams, 1S Beams). The strengthening bolts were one No.10 steel bolt or two No.6 steel bolts, pre-stressed or non-prestressed. To simulate the actual load conditions, an initial load was applied before strengthening to make initial shear cracks. Strengthening was performed in two loading statuses: under constant load or after load removal. After strengthening, each specimen was loaded to failure and the load vs deflection at midspan was recorded and drawn. Failure mode for most of specimens was shear failure, but it changed in two of specimens strengthened by prestressed steel bolts to bending failure. These two specimens also had the maximum ductility and energy dissipation.
Based on the results, embedding steel bolts effectively increased shear strength of beams in all test conditions, prestressed or non-prestressed bolts, and constant load or load removal before strengthening, but better results were obtained in prestressed bolts, especially under constant load strengthening. Ductility and energy dissipation were also investigated. Prestressed bolts were considerably more effective in ductility and energy dissipation improvement.
کلیدواژه‌ها [English]
Shear strengthening, R.C. Beams, Prestressed Bolt, Embeded Through Section
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