Investigation of the Dowel and Friction Forces in Fiber Reinforced Ultra High Performance Concrete Beams

Abstract

The phenomenon of dowel action as a shear transfer mechanism across cracks has long been recognized as an important component of the overall shear resistance capacity of reinforced concrete beams. The dowel contribution to shear depends primarily on the tensile resistance of concrete along the splitting plane and the bending resistance of the longitudinal bars. Fiber Reinforced Ultra High Performance Concrete (FRUHPC) is an advanced cementitious material consisting of a dense, high strength matrix containing a large number of evenly embedded steel fibers. Therefore, FRUHPC can be expected to improve dowel and friction resistance to shear. This paper reports the experimental study of the components of shear force applied to FRUHPC beams, especially the effects of friction shear force and dowel action. Six FRUHPC beams (120*150*1500)mm dimensions with and without preformed cracks were made with three volume fractions of fibers: 1% , 1.5% and 2%. The presence of steel fibers enhances the performance of shear transfer mechanisms by friction or interface shear along the diagonal crack surface. Thus the contribution of this mechanism to the total shear strength carried by the beam was around 36.4% for FRUHPC beam with 2% fibers content. In the absence of friction or interface shear along the diagonal crack surface mechanism (preformed cracks beams) dowel action was the predominate contributor. However, the contribution of this mechanism to the total shear strength carried by the beam was around 45.4% for HPRPC beam with 2% fibers content. Also, an expression for evaluating the dowel force is presented in this research. The coefficient of multiple determination (R2) was (0.835).

Keywords

• dowel action
• friction force
• high performance
• fibers
• reactive powder concrete