دانلود مقاله مهارگذاری آرماتورهای برشی در تیرها و دالها
چکیده
1. مقدمه
2. حالت پیشرفته در پاسخگویی و عملکرد خم ها و قلاب ها
3. برنامه آزمایشی
4. بحث در مورد نتایج آزمایش
5. تأثیر ظرفیت تغییر شکل خم ها و قلاب ها بر عملکرد لنگر
6. مدل مکانیکی و ملاحظات طراحی برای مقاومت لنگر خم ها و قلاب ها
7. نتیجه گیری
ضمیمه A. محاسبه مقاومت محلی خم ها و قلاب ها
ضمیمه B. جزئیات محاسبه مقاومت لنگر دم و مناطق منحنی
ضمیمه ج. مقایسه رویکرد پیشنهادی با شواهد تجربی
پیوست D. کالیبراسیون فرمت ایمنی برای مدل مقاومت لنگر
منابع
Abstract
1. Introduction
2. State-of-the-art on response and performance of bends and hooks
3. Experimental program
4. Discussion of test results
5. Influence of deformation capacity of bends and hooks on anchorage performance
6. A mechanical model and design considerations for the anchorage resistance of bends and hooks
7. Conclusions
Credit authorship contribution statement
Declaration of Competing Interest
Acknowledgements
Appendix A. Calculation of the local resistances of bends and hooks
Appendix B. Detail of the calculation of anchorage resistance of tail and curved regions
Appendix C. Comparison of proposed approach with experimental evidence
Appendix D. Safety format calibration for the anchorage strength model
References
چکیده
مهارگذاری آرماتورهای برشی مانند پیوندها یا رکاب ها را می توان با ایجاد قلاب، خم یا سر در انتهای آنها، با جوش آرماتورهای عرضی یا با بستن رکاب های باز با پین انجام داد. قلاب‌ها و خم‌ها، همچنین برای تقویت لنگر تقویت‌کننده خمشی در نواحی انتهایی تیرها و دالها، به دلیل تولید ساده و مقرون‌به‌صرفه ترجیح داده می‌شوند. با این حال، چنین لنگرگاه‌ها دارای چندین ویژگی هستند که باید در نظر گرفته شوند. آنها نسبتاً به جزئیات خود (قطر سنبه، طول بخش دم بین انتهای میله و ناحیه خم شده) و همچنین به حالت ترک خوردگی بتن اطراف حساس هستند. همچنین، شکست های شکننده می تواند به دلیل پوسته شدن پوشش بتنی در صورت وجود میله های نزدیک به سطح آزاد رخ دهد.
توجه! این متن ترجمه ماشینی بوده و توسط مترجمین ای ترجمه، ترجمه نشده است.
Abstract
Anchorage of shear reinforcement, such as links or stirrups, can be performed by providing hooks, bends or heads at their ends, by welding transverse reinforcement or by closing open stirrups with pins. Hooks and bends, also used to enhance the anchorage of flexural reinforcement at the end regions of beams and slabs, have often been preferred because of their simple and cost-effective production. Such anchorages present nevertheless several peculiarities that shall be accounted for. They are relatively sensitive to their detailing (mandrel diameter, length of the tail segment between bar end and bent region) as well as to the cracking state of the surrounding concrete. Also, brittle failures can occur due to spalling of the concrete cover in case of bars near to a free surface.
Introduction
Since the beginning of reinforced concrete construction, mechanical anchorage of the reinforcement in tension by means of bends and hooks has been extensively used in a large number of applications, such as beams, walls and slabs (Fig. 1a-f). Arrangement of hooks was first required for the anchorage of plain bars due to their poor bond performance. Such solution was observed to be efficient and was also adopted for the anchorage of various types of shear and punching reinforcement.
The first research works on hooks were performed for the anchorage of flexural reinforcement at the extremity of beams. On the basis of beam tests, Hyatt in 1877 [1] observed that flat reinforcing bars bent at 90° at their ends gave higher performances. As a result of this work, 90° bends became popular in the following years in the USA [2]. In Europe, in 1908 Mörsh [3] encouraged the use of hooks to enhance the performance of anchorages. He also proposed to use higher bend angles than 90°, in contrast to the practice in the USA. The reason for this was that 90°-angle bends caused failure issues in the case of too small concrete cover (as demonstrated by the tests of Wayss and Freytag [4], [5]). It was Considère in 1907 [6] who formally proposed a 180° hook bent with a mandrel diameter equal to 4 times the bar diameter to avoid failures due to concrete crushing. In addition to the use of hooks at beam ends, the hook anchorage of shear reinforcement (Fig. 1a-e) was also used in the early developments of reinforced concrete.
Conclusions
This paper presents the results of an experimental programme and a mechanical model allowing to better understand the behaviour and to predict the resistance of bends and hooks in tension. The case of the anchorage of shear reinforcement near to a free surface is investigated. In addition, the influence of bending cracks on the performance of shear reinforcement is also investigated. The main conclusions are listed below:
1. Three failure modes potentially govern the strength of a bend anchorage: (i) spalling of the concrete cover, (ii) pull-out (bond) failure and (iii) reinforcement yielding. The governing failure mode depends upon the size of the concrete cover, the transverse crack opening and the detailing of the region.
2. The mechanical response of bend anchorages is complex, with an interaction between normal, bond stresses and longitudinal steel stresses due to axial forces and bending. Such interaction is confirmed by means of an experimental programme performed with detailed fibre-optic measurements. Also, the experimental results presented in this paper show a significant influence of the state of cracking, consistently with previous researches on bond.
3. Spalling of the concrete cover is originated by a combination of the tensile stresses associated to bond and the uplift forces in the tail region of bends (lever effect). Such uplift forces allow, by equilibrium conditions, to develop an additional tensile force in the reinforcement at the end of the bend (enhancement of the anchorage capacity in case of pull-out failures).