SER #294: Shear in Steel Fiber Reinforced Concrete without Stirrups

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  • Hooked end steel fibers were included between 0~1% by volume to provide enhanced shear resistance to three different types of steel fiber reinforced concrete (SFRC) namely, a regular concrete mix, a lightweight aggregate mix and a high strength mix. The test results at the material scale showed a substantial increase in the shear strength of regular and high strength concrete, but only limited enhancement in the case of the lightweight aggregate concrete. The steel fibers were most efficient in enhancing the post-peak shear performance in the regular concrete, where the cracks progressed around the coarse aggregate. The fractured surface of the specimens revealed that in the lightweight and high strength mixes, cleavage was through the aggregates. A total of 18 structural SFRC specimens were designed and constructed to capture the behavior of shear-critical SFRC members. The specimens contained longitudinal reinforcement but no stirrups, and utilized different mixes with 1% fiber content selected from the material scale testing phase. The specimens varied in overall height from 308 to 1000 mm with constant shear span to effective depth ratio of 3. The normalized shear stress at failure decreased with an increase in the specimen total depth, indicating that a size effect exists for SFRC specimens without stirrups. However, adding steel fibers into the concrete matrix considerably enhanced the shear capacity compared to the ACI 318-08 and CSA A23.3-04 predictions for RC members without steel fibers. An analytical shear capacity model was developed based on mechanical principles and empirical measurements of crack geometry observed in the current study for both normal weight and lightweight SFRC members without stirrups. The analytical model was then further simplified to be suitable for use in design. For validation, shear capacity predictions were examined for a large database and gave reliable and accurate predictions. The prediction quality of the proposed design model was also compared against published SFRC shear models from other researchers. Among the SFRC shear models studied, the proposed design model was the most accurate model in prediction quality and relatively the least sensitive model to different common design variables.

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    Attribution-NonCommercial 3.0 International