In the presented paper, the effectiveness of steel fiber use on the shear and flexure behaviors of ultra-high performance concrete (UHPC) beams and the feasibility of steel fibers in place of shear reinforcement were investigated experimentally. In this framework, a total of four I-shaped UHPC beams were produced for a high tensile reinforcement ratio of 2.2%. While two of them were non-fiber UHPC beams with and without the shear reinforcement to show the contribution of steel fibers, the remaining beams were made from the ultra-high performance steel fiber-reinforced concrete (UHP-FRC) having the short straight fibers with 1.5% and 2.5% by volume. The shear and flexural parameters, such as the load–deflection response, cracking pattern, failure mode, deflection, and curvature ductilities were discussed based on the four-point loading test results. While the reference beam without fiber and shear reinforcement failed by the shear with a sudden load drop before the yielding of reinforcement and produced no deflection capability, the inclusion of steel fibers to the UHPC matrix transformed the failure mode from shear to flexure through the fibers’ crack-bridging ability. It might be deduced that the moderate level of steel fiber use in the UHP-FRC beams may take the place of shear reinforcement in practical applications.

Steel fibers are frequently used in ultra high-performance concrete (UHPC) due to their superior properties, but they also have disadvantages, such as corrosion exposure, high specific gravity and high cost. Although synthetic fibers have emerged as an alternative, the focus has generally been on hybrid use with steel fibers in UHPC. This study investigates the applicability of macro-polypropylene (PP) fibers for UHPC in terms of mechanical properties. An experimental campaign was conducted for UHPC mixtures containing macro-PP fibers with varying volumetric ratios. The effects of macro-PP fiber on the mechanical properties of UHPC were investigated in terms of compressive strength, splitting tensile strength and flexural behavior. The two-dimensional digital image correlation (2D-DIC) method was adopted to examine the cracking behavior. In addition, tensile constitutive law for UHPC mixtures was obtained with inverse analysis based on Model Code 2020 (MC2020). The results showed that the use of macro-PP fibers had no significant impact on compressive and splitting tensile strength. However, residual flexural tensile strength and fracture energy increased by up to 2.8 and 2.5 times, respectively, compared to UHPC without fiber. It was determined that macro-PP fibers could exhibit effective crack control in UHPC.

En tr This study investigates the flexural behavior of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with hybrid steel fiber referencing the ASTM standard C 1609. Two types of end-hooked fibers in macro fiber concretes and one type short straight fiber in micro fiber concretes were used in mono and hybrid forms. In order to determine the flexural response of UHPFRC, a series of prismatic beam specimens with a dimension of 100 x 100 x 400 mm were tested under the four-point loading and following parameters were compared and evaluated in terms of the first cracking loads and patterns, flexural strengths, deflection capacities, toughness and residual strength capacities under bending loads. The test results showed that as the fiber amount of specimens with mono steel fiber increases, in general, better flexural behavior may be ensured. The specimens with hybrid steel fiber showed better performance in terms of the flexural behavior regarding the macro fiber specimens. This study investigates the flexural behavior of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with hybrid steel fiber referencing the ASTM standard C 1609. Two types of end-hooked fibers in macro fiber concretes and one type short straight fiber in micro fiber concretes were used in mono and hybrid forms. In order to determine the flexural response of UHPFRC, a series of prismatic beam specimens with a dimension of 100 x 100 x 400 mm were tested under the four-point loading and following parameters were compared and evaluated in terms of the first cracking loads and patterns, flexural strengths, deflection capacities, toughness and residual strength capacities under bending loads. The test results showed that as the fiber amount of specimens with mono steel fiber increases, in general, better flexural behavior may be ensured. The specimens with hybrid steel fiber showed better performance in terms of the flexural behavior regarding the macro fiber specimens.

In the present study, the impacts of variety of fiber types and amounts on shear dominant Ultra High Performance Fiber Reinforced Concrete (UHPFRC) beams and the feasibility of fully replacement of stirrups by the steel fibers were investigated. Fifteen UHPFRC beams containing five different fiber types and three volume fractions were prepared without stirrup and were loaded under four-point loading. The influences of steel fiber were discussed in terms of the load-deflection behavior, cracking behavior, collapse modes, ultimate shear strength, nominal moment capacity and deflection ductility. The steel fiber use prominently increased the post-cracking stiffness and load capacity of the UHPFRC beams with the help of the fibers’ crack-bridging ability. Conversely, the steel fibers in different types didn’t have an importance on the collapse mode of the shear dominant UHPFRC beams. The use of straight steel fibers in the UHPFRC beams, even at very low volume fractions of 0.5 percent, changed the collapse condition from shear to flexure resulting in a ductile behavior. But the hooked fiber inclusion by 1.5 vol percent percent at least is needed to guarantee the flexural behavior regardless of hooked or multi hooked-end form.

Bu çalışmada, Deprem Bölgelerinde Yapılacak Binalar Hakkında Yönetmelik’te (DBYBHY) betonarme elemanlar için öngörülen şekildeğiştirme esaslı hasar sınırları deneysel olarak incelenmiştir. Bunun için, düşük beton dayanımına sahip ve sargı donatısı yetersizliği bulunan dört adet betonarme konsol kolon eleman test edilmiştir. Testlerde kolonlara sabit düşey yük ve tersinir artan yatay yük protokolü uygulanmıştır. Çalışmada öncelikle DBYBHY’de verilen hasar sınırlarını tanımlayan birim şekildeğiştirme değerleri kolon tepe yatay yerdeğiştirmesine dönüştürülmüştür. Bunun için DBYBHY’de verilen prosedür ve yapı mekaniğinin temel ilkelerinden yararlanılmıştır. Daha sonra ilgili yerdeğiştirme taleplerine karşılık gelen kolon hasarları gözlenmiş ve hasar sınırları değerlendirilmiştir. Testler sonucunda incelenen tüm elemanlarda, yönetmelikteki minimum hasar sınırına (MN) karşılık gelen performans düzeyinde kalıcı hasarların olmadığı gözlenmiştir. Güvenlik ve göçme hasar sınırlarında (GV ve GÇ) benzer şekilde kalıcı hasarların oluştuğu, ancak yük taşıma kapasitelerinde önemli azalmaların meydana gelmediği görülmüştür. İncelenen elemanlarda, kabuk betonu dökülmeleri vb. büyük hasarlar ve taşıma kapasitesindeki önemli dayanım azalmalarının göçme hasar sınırından sonra başladığı gözlenmiştir. Çalışmadan elde edilen sonuçlar ışığı altında, DBYBHY’deki değerlendirme yönteminin düşük beton dayanımına sahip ve sargı yetersizliği bulunan kolon elemanlar için hasar sınırlarını belirlemede güvenilir sonuçlar verdiği söylenebilmektedir.