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Improving Ductility and Design Methods for Reinforced HPFRCC Flexural Members

Graduate Researcher(s): 
Yi Shao (
Faculty Advisor/PI: 
Sarah Billington
Project Sponsor: 
John A. Blume Earthquake Engineering Center
Charles H. Leavell Graduate Student Fellowship

High-performance fiber-reinforced cementitious composite (HPFRCC) materials are a family of cement-based materials that under tension shows pseudo-strain hardening behavior. Numerous experimental studies have been conducted to investigate the flexural behavior of steel rebar reinforced HPFRCC members. An experimental database collected from the literature shows a large variation of drift capacity from 1.0% to 17.1% (Fig. 1). Based on a large-scale experimental program and literature review, two dominant flexural failure paths have been identified for reinforced HPFRCC flexural members (Fig. 2): (1) failure may occur after crack localization (i.e., the formation of a single, dominant crack), and the load capacity reduces because of the loss of fiber-bridging capacity that cannot be compensated for by the hardening of longitudinal reinforcing steel, or (2) failure may occur after crack localization, whereby the beam achieves a higher load capacity through gradual strain hardening of longitudinal reinforcing steel. These two failure paths represent distinct load-reduction mechanisms and ductility ranges. This research project aims at improving the understanding of flexural failure mechanisms of reinforced HPFRCC components, and develop methods that are able to predict the flexural failure path, strength, and ductility of reinforced HPFRCC flexural members.

By testing more than 20 steel rebar reinforced HPFRCC beams (Fig. 3), this study investigates the reinforced HPFRCC flexural behavior with different reinforcing ratios (from 0.53% to 2.10%), reinforcing types (A615 Grade 60 steel versus A1035 Grade 100 steel), matrix types (ECC with low tensile strength and high tensile ductility versus UHPFRC with high tensile strength and low tensile ductility), and loading conditions (monotonic versus cyclic loading). The experimental program results are used to validate a recently-developed numerical scheme, and then the numerical scheme is used to more systematically investigate the impact of multiple material properties on the reinforced HPFRCC flexural failure path and ductility, including HPFRCC tensile strength, tensile localization strain, tensile fracture energy, and steel rebar yielding strength and ultimate strength, and reinforcing ratios. After the experimental program and numerical program, a theoretical analysis facilitates the development of a model that predicts the flexural failure path, strength, and ductility of reinforced HPFRCC flexural members.