IV. FEN BİLİMLERİ ARAŞTIRMA SEMPOZYUMU Yılmaz Öğünç TETİK, Osman KAYA EXPERIMENTAL ANALYSIS OF REINFORCED CONCRETE BEAMS’ BEHAVIOR WITH STEEL FIBERS UNDER PURE TORSION Yılmaz Öğünç TETİK, Osman KAYA yotetik@gmail.com ABSTRACT Reinforced concrete structural members especially columns are subjected to torsional effects during severe earthquakes. In real structure, shear and torsional forces act at the same time and the effects of torsional moments can not be observed alone. In TS500, which is Reinforced Concrete Design code of Turkey, there is no any requirements given about the pure torsional design. In order to understand the behavior of such members, 16 beams were produced with a dimension of 30x30x200 cm and with a same longitudinal reinforcement ratio. The main parameters that were investigated in this study were the spacing of transverse reinforcements (which means the volumetric ratio ) and volumetric ratio of steel fibers used in concrete mixture. The tests were done by fixing one end applying a force to the other end with lever arm. Results indicated that enhancement of steel fiber amounts up to a certain ratio increase the twisting level and energy absorbing capacity of the reinforced beams. Yet, the enhancement of the steel fiber ratio in addition to stirrup spacing was conducive to producing more ductile behavior unlike the brittle behavior of narrow stirrup spacing beams, owing to the attitude of steel fiber’s similarly with stirrup. ÖZET Betonarme yapı elemanları, özellikle kolonlar, güçlü deprem yükleri altında burulma kuvvetlerine maruz kalırlar. Gerçekte is burulma ve kesme kuvveti yapıya aynı anda etki eder ve burulma kuvvetinin etkileri tek başına gözlemlenemez. Betonarme yapı elemanlarını tasarımı hakkındaki yönetmelik, TS500, de yalın burulma momentine maruz elemanların tasarımları ile ilgili herhangi bir yöntem verilmemiştir. Bu sebeple, 16 adet 30x30x200 cm ebatında ve aynı boyuna donatı oranına sahip betonarme kiriş numuneleri üretilmiş ve kullanılan etriyelerin aralığı (etriye oranı) ile beton karışımının içine eklenen çelik fiberlerin oranı ana parametre olarak incelenmiştir. Deneyler elemanların bir ucu sabit tutularak, diğer uçtan moment kolu yarrdımıyla kuvvet uygulanarak yapılmıştır.. Sonuçlar, çelik liflerin lifsiz kiriş elemanlara göre yalın burulma momenti altında belli bir hacim oran değerine kadar dönme açılarını ve enerji yutma kapasitelerini arttırdığını göstermiştir. Fakat, birbirine daha yakın etriye aralığına sahip olan kirişlerde çelik lifin katkısıyla beraber, elemanlar daha gevrek bir davranış sergilemiştir. Aksine, yüksek orandaki çelik lif ve etriye aralığı fazla olan kiriş elemanlarda, lifler bir etriye gibi davranarak elemanı daha gevrek değil, tam tersi daha sünek hale getirmiştir INTRODUCTION The main objectives of this study is to determine the: Adequateness of TS-500 code in pure torsional design Response of beams under pure torsion Relationship b/w steel fibers and RC beams Comparison of SFRC beams considering torque- twist behavior and energy dissipation capacities TEST RESULTS For each specimen, maximum (Tmax), ultimate (Tu) and cracking (Tcr) torques are determined and shown in Table 2 with their corresponding ultimate angle of twist values. The identical specimens of S30V00 and S40V00 control were tested and all of them indicate identical behavior. Table 2: Determined test values METHODOLOGY Steel fiber type and test specimen details are given below. Steel fiber type : Figure 1: Geometry of steel fiber Specimen details : Figure 2: Dimensions of test specimens and reinforcement placement Table 1: Properties and fiber amounts of specimens Test Setup Figure 6: Comparison of energy dissipation capacities of the S30 and S40 group beams (i) S30V00 (iii) S30V15 The comparison of torque-twist curves of the whole S30 group of testing beams is illustrated in Figure 4. Among all, the S30V09 beam was clearly the reasonable option for steel fiber utilization. Torque-twist curves of the S40 group of testing beams is also shown in Figure 5. As can be easily seen, the S40V12 beam is the most logical selection of all. (ii) S30V09 Figure 7: Crack patterns of test beams In non-fibrous beams, failure occurred from a single crack, but in fibrous beams, many scatter cracks occurred and it was observed that fibers tried to envelop these cracks and improve the twisting qualification of beams. In spite of the fact that steel fibers showed good behavior under pure torsional moment for instance enhancing the ductility of the beams, energy absorbing capacity and maximum torque level, the validity of this affair was restricted by 0.9% volumetric ratio in the S30 group beams. The exceeding of the determined level caused brittle behavior. Subsequent to 0.9% volumetric steel fiber ratio, 1.2% and 1.5% levels were affiliated with more ductility in the S40 group of beams contrary to the S30 group. Due to the existence of lengthiness between stirrup spacings, fibers acted like stirrup. This incident leads to higher maximum and ultimate torsional capacities and better twisting behavior. It is observed that except from having 1.2 and 1.5% fiber ratios’ of S40 group of beams, other whole S30 group of beams showed better energy absorbing capacity. Due to ductile structure of S40 beams which have high amount of fiber, they exhibited good rotational movement. CONCLUSIONS Figure 4: Torque- twist curve of S30 group beams In the S30 group of beams, 0.9 % volumetric ratio was specified as optimum, but in the S40 group, 1.2% volumetric ratio was determined as optimum because, the fibers compensate for the position of the stirrup. Figure 5: Torque- twist curve of S40 group beams According to determined test results, all of energy dissipation capacities of specimens are illustrated in Figure 6. Considering the effect of the steel fibers, the number of cracks grown up compare to beams without fibers. The crack patterns of S30V00 as a fiberless specimen, S30V09 as a moderate or optimum fiber content specimen and S30V15 as an excessive fiber content specimen are indicated in Figure 7. Figure 3: Test setup, loading and measurement systems