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


The phenomenon of dowel action as a shear transfer mechanism across crackshas long been recognized as an important component of the overall shear resistancecapacity of reinforced concrete beams. The dowel contribution to shear dependsprimarily on the tensile resistance of concrete along the splitting plane and thebending resistance of the longitudinal bars. Fiber Reinforced Ultra HighPerformance Concrete (FRUHPC) is an advanced cementitious material consistingof a dense, high strength matrix containing a large number of evenly embeddedsteel fibers. Therefore, FRUHPC can be expected to improve dowel and frictionresistance to shear.This paper reports the experimental study of the components of shear forceapplied to FRUHPC beams, especially the effects of friction shear force and dowelaction. Six FRUHPC beams (120*150*1500)mm dimensions with and withoutpreformed cracks were made with three volume fractions of fibers: 1% , 1.5% and2%. The presence of steel fibers enhances the performance of shear transfermechanisms by friction or interface shear along the diagonal crack surface. Thusthe contribution of this mechanism to the total shear strength carried by the beamwas around 36.4% for FRUHPC beam with 2% fibers content. In the absence offriction or interface shear along the diagonal crack surface mechanism (preformedcracks beams) dowel action was the predominate contributor. However, thecontribution of this mechanism to the total shear strength carried by the beam wasaround 45.4% for HPRPC beam with 2% fibers content. Also, an expression forevaluating the dowel force is presented in this research. The coefficient of multipledetermination (R2) was (0.835).