2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference

Investigation on the Flexural Capacity of Ultra-High Performance Fiber Reinforced Concrete Beams

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Mr. Jamil Madanat, Ryerson University (Presenter)
Ms. Hesham Othman, Ryerson University
Dr. Hesham Marzouk, Ryerson University

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a relatively new generation of cementitious material that exhibits exceptional mechanical and durability characteristics in comparison to its traditional counterparts. Despite the obvious advantage of UHPFRC, its structural application is not widespread. One of the main reasons that has delayed the extensive use of UHPFRC has been the lack of widely accepted design guidelines. Additionally, the flexural (moment) capacity of UHPFRC beams is an ongoing task for researchers. This task is complicated due to the presence of steel fibers in the specimen which shifts the neutral axis location within the rectangular stress block. The inclusion of these fibers is not incorporated into traditional reinforced concrete design guidelines. Thus, international codes could not provide an accurate estimation of the moment capacity of UHPFRC structural members. This investigation examines the applicability moment capacity equations of different design standards to estimate the flexural capacity of UHPFRC beams.

To achieve this goal, 8 beam specimens are tested under four-point loading to estimate the flexural capacity. All test specimens have the same cross-sectional area of 305x178 mm. The design variables are: the span (945, 1890 mm); and steel reinforcement ratio (1.27%, 2.54% and 4.02%). UHPFRC of this study is a commercial product widely used in North America. This UHPFRC is self-consolidating concrete, which does not require special mixing or curing techniques. This UHPFRC mix has a nominal 28-day compressive strength of 150 MPa and contains a typical 2 % by volume steel fibers. The testing setup is equipped with calibrated instrumentation to measure applied load, reaction forces, mid-span displacement, and the reinforcement strain at the central point. The specimens have been loaded gradually by applying monotonic load at 5.00 kN increments to monitor the crack initiation, damage state, and marking the crack pattern. The beam testing has been accompanied by material investigation; this material testing is motivated mainly by the lack of a general mathematical formula that can be used to model the behaviour of UHPFRC. Compression, splitting tensile and elastic modulus tests of concrete are conducted on 100×200 mm cylinders. Modulus of rupture tests are conducted on 100×100×400 mm prisms.

The flexural capacities of all tested specimens are estimated analytically using different design standards (ACI, CSA, French, and Japanese) to examine the applicability of code equations to estimate the flexural capacity of UHPFRC beams.  Later, it proposes a method for determining the moment capacity for UHPFRC beams.