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Ultra-high-performance fiber-reinforced concrete (UHPFRC) is a novel cementitious material with enhanced strength in tension and compression, and significantly high energy absorption in the post-cracking region. The application of UHPFRC for the earthquake strengthening of existing structures could considerably improve the performance of existing structures due to its superior properties. There are published studies where the direct tensile and the flexural behaviors of UHPFRC have been investigated and the superior tensile strength and post-crack energy absorption have been highlighted. However, there are not any published studies on the performance of UHPFRC under cyclic loading. In this paper, the results of an extensive experimental program on UHPFRC under direct tensile cyclic loading are presented and a constitutive model for the response of UHPFRC under cyclic loading is proposed. The accuracy of the proposed model is validated using experimental results from various loading histories and for different percentages of fibers, and the reliability of the proposed model is highlighted.
Keywords: constitutive model; cyclic loading; direct tensile tests; ultra-high-performance fiber-reinforced concrete (UHPFRC).
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INTRODUCTION
Ultra-high-performance fiber-reinforced concrete (UHPFRC) is a relative new material with high strength and durability. Some of the main characteristics of UHPFRC are the high compressive strength (normally in the range of 150 to 200 MPa [21.8 to 29 ksi]), the high tensile strength that can reach values more than 15 MPa (2.2 ksi), the ductile behavior, and finally, the durability and the significantly high energy absorption in the post-cracking region.
There are published studies where the behavior of UHPFRC under static loading has been investigated.1-5 The effect of the steels fiber amount was examined by Kang et al.1 and Yoo et al.,4 and it was found that the flexural strength was considerably increased as the fiber volume ratio was increased, while the ductility was decreased. Inverse analysis1 was used to determine the direct tensile fracture model of UHPFRC, and a trilinear tensile fracture model of UHPFRC with a softening branch was proposed. Another important parameter in case of UHPFRC is the orientation and the distribution of steel fibers in the mixture. This parameter can considerably affect the post-cracking behavior, but the effect on the precracking elastic phase is negligible.2
All these studies are focused on the mechanical properties of UHPFRC...