تحليل رفتار تيرهاي عميق با بتن مقاومت بالا تحت بار گسترده

INVESTIGATION OF EXPERIMENTAL AND ANALYTICAL OF REINFORCED CONCRETE DEEP BEAMS WITH CONCRETE OF HIGH-STRENGTH UNDER DIDTRIBUTED LOADNG

در اين مقاله رفتار تيرهاي عميق بتن مسلح با مقاومت بالا به صورت آزمايشگاهي بررسي شد. بدين منظور 5 نمونه تير عميق بتن مسلح با مقاومت فشاري 60 مگاپاسكال تحت اثر بار گسترده مورد آزمايش قرار گرفت. تيرهاي آزمايشگاهي در دو انتها داراي تكيه گاه ساده و با آرماتورهاي برشي قائم به فواصل مساوي تقويت شده بودند. آرايش آرماتورهاي برشي نمونه ها يكسان ولي قطر آنها متفاوت بود. در طول آزمايش رفتار كلي نمونه هاي آزمايشگاهي مورد بررسي قرار گرفت. مشاهدات آزمايشگاهي شامل تغيير شكل وسط دهانه، وضعيت شكست، حالت هاي گسيختگي و مقاومت فشاري نظير ترك خوردگي اوليه و شكست نهايي نمونه تير عميق بود. گسيختگي هر 5 نمونه به صورت شكست ترد برشي بود. بر اساس نتايج حاصله، آرماتورهاي قائم جان بر ظرفيت برشي تيرهاي عميق تاًثيرگذار بوده و نمونه ها تحت بار گسترده عموماً مقاومت برشي بالاتري در مقايسه موارد مشابه تحت بار متمركز از خود نشان مي دهند. نتايج آزمايشگاهي با نتايج به دست آمده از روش Strutandtie (مدل خرپايي) مقايسه گرديد. نتايج حاصله از مقايسه حاكي از انطباق رضايت بخش مدل STM ارائه شده براي تيرهاي عميق بتن مسلح تحت بار گسترده با نتايج آزمايشگاهي مي باشد .

Reinforced concrete deep beams have useful applications in many structures, such as tall buildings, foundations, offshore structures, and several others. The reinforced concrete deep as important structural elements having small spantodepth ratio. The investigation of their behavior is a subject of considerable interest in RC structures researches and some studies on the shear strength of reinforced concrete deep beams have been carried out over the last fifty years. In deep beams, according to shear spantodepth ratio and web reinforcement the ultimate strength is generally controlled by shear rather than flexure, if the sufficient amount of longitudinal reinforcement is used. Several different failure modes have been identified from experimental studies, due to variability in failure, the determination of their shear strength and identification of failure mechanism are very complicated. In this paper the influence of effective parameters on the behavior of highstrength RC deep beams was investigated. For this purpose, an experimentalanalytical investigation was conducted a total of five reinforced concrete deep beams with compressive strength in range of 60 MPa were tested under uniform contributed top loading. The tested specimens were simply supported and reinforced by vertical steel bars in various spacing. The general behavior of tested beams was investigated. Observations were made on midspan vertical deflections, cracks form, failure modes and shear strengths. All the beam specimens showed a same response up to failure. The test results indicated that vertical web reinforcement are efficient in shear capacity of deep beams, all the specimens were failed at abrupt shear mode. According to the test results, the shear capacity is affected by amount of web reinforcement and the test specimens are stronger in comparison with those were tested under twopoint loading. Elastic solutions of reinforced concrete deep beams provide a good description of the behavior before cracking, but after cracking, a major redistribution of stresses occurs and hence the beam capacity must be predicted by inelastic analysis. Due to their geometric proportions, the capacity of reinforced concrete deep beams is governed mainly by shear strength. Deep beams behave differently from shallow beams and have been identified as discontinuity regions where the strain distribution is significantly nonlinear and specific strutandtie models need to be developed, whereas shallow beams are characterized by linear strain distribution and most of the applied load is transferred through a fairly uniform diagonal compression field. Strutandtie method is one of the most simple and applicable methods which can be used to simplify analysis and design of deep beams. Strutandtie modeling is the most rational and simple method for designing no flexural members currently available. At least, the experimental strength of specimens was compared with predicted results of strutandtie method (STM). The performed comparison indicates that the STM to provide acceptable estimates of shear capacity of deep beam loaded under uniform loading.