Material Behavior

Experimental and Numerical Characterization of Pullout Behavior of Hooked Steel Fibers in Ultra-High Performance Cementitious Matrix

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Abstract

Steel fiber is the most common type used to reinforce concrete. Although a large number of research studies have been conducted to investigate the pullout mechanism of straight steel fibers, experiments have shown that to improve the compressive concrete strength, flexural strength, and shrinkage, deformed steel fibers are more effective than straight fibers due to mechanical anchorage created by the deformed shape. While interface debonding and frictional sliding are the two main mechanisms controlling the pullout of straight fibers, additional mechanism due to fiber straightening during the pullout process must be taken into account for mechanically deformed fibers, which introduces additional complexity on the pullout response, and thus the analytical and numerical modelling of the pullout mechanism of deformed fibers has been a difficult task. There still exist no models in which the heterogeneous nature of the concrete is considered to characterize the pullout process of mechanically deformed steel fibers. As first proposed by Cusatis, fiber reinforced concrete is analyzed by a multi-scale model, called LDPM-F, in which the fine-scale fiber matrix interaction is solved independently and the overall response is analyzed in a 3D meso-scale framework based on the recently formulated lattice discrete particle model (LDPM). LDPM is a realistic 3D model of concrete meso-structure developed by Cusatis et al., which has been extensively calibrated/validated under a wide range of quasi-static and dynamic loading conditions, showing superior capabilities in predicting qualitative and quantitative behavior of concrete. As a natural extension for this discrete model to include the effect of dispersed fibers as discrete entities within the meso-structure, LDPM-F incorporates this effect by modeling individual fibers, randomly placed within the framework according to a given fiber volume fraction. In this study, LDPM-F is herein extended to simulate fibers with hooked ends which, up to the present, represent the most widely used steel fibers' geometries used in concrete reinforcement. To calibrate and validate the proposed model, a tensile fiber pullout test has been designed and conducted on CORTUF, an ultra-high-performance concrete recently developed and characterized at the Geotechnical and Structures Laboratory (GSL), United States Army Engineer Research and Development Center (ERDC), which was designed to develop ultra-high compressive strength while maintaining workability and production economy.

Keywords: steel fiber, hooked fiber, numerical simulation

How to Cite:

Cusatis, G., Jin, C., Du, M., Feng, J. & Zhou, X., (2016) “Experimental and Numerical Characterization of Pullout Behavior of Hooked Steel Fibers in Ultra-High Performance Cementitious Matrix”, International Interactive Symposium on Ultra-High Performance Concrete 1(1). doi: https://doi.org/10.21838/uhpc.2016.14