Seismic Considerations

Confinement Reinforcement for Under-Reinforced UHPC Beams under Flexure

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Abstract

Ultrahigh-performance Concrete (UHPC) flexural members with high compression strengths need large amounts of steel confinement to meet the current code confinement requirements. This study investigated the impact of different steel confinement amounts on the flexural behavior of longitudinally reinforced UHPC beams. Four small beam specimens with different steel confinement reinforcement amounts and grades were tested under monotonic three-point loading until failure. Steel confinement reinforcement grades varied from Grade 60 to Grade 120. The confinement volumetric ratios of the four specimens were 50%, 110%, 30%, and 50% of the minimum requirement of ACI 318-14. All specimens were under-reinforced longitudinally. The specimen with the least amount of confinement failed due to excessive shear cracking. The other specimens failed under flexure in the form of longitudinal reinforcement fracture, and exhibited similar flexural strength and ductility levels regardless of the confinement amount. These results indicated the need for re-evaluating ACI 318-14 requirements on the confinement for UHPC flexural members, especially when the longitudinal reinforcement ratios are low. A numerical analysis based on section equilibrium was conducted and evaluated using the test results. The constitutive tensile model of UHPC was obtained through material tests. Several unconfined and confined concrete compression models in the literature were examined. Compared to the compression models developed for normal concrete, the existing models for fiber-reinforced high-strength concrete significantly improved the predictions of flexural moment strength and failure mode for UHPC.

Keywords: Ultrahigh-performance concrete, Fiber reinforced concrete, Flexure, Constitutive model, Ductility

How to Cite:

Yang, C., Bhargava, A., Bhuralal Purohit, M. & Okumus, P., (2019) “Confinement Reinforcement for Under-Reinforced UHPC Beams under Flexure”, International Interactive Symposium on Ultra-High Performance Concrete 2(1). doi: https://doi.org/10.21838/uhpc.9722