Steel fibres for the shear resistance of high strength concrete beams

Abstract

Available research on the use of steel fibres to increase the shear resistance of concrete structures shows that the effectiveness of this type of reinforcement increases with the increase of the concrete compressive strength, as long as the fibre rupture is avoided. Experimental research has also indicated that the effectiveness of the fibre reinforcement for the shear resistance is more pronounced in shallow beams than in deep beams. In terms of analytical research, some models have been proposed and, recently, RILEM TC 162 TDF recommended an analytical approach for the prediction of the fibre reinforcement contribution in terms of shear resistance of concrete beams. The present work has the purpose to contribute for this topic, discussing the performance of RILEM TC 162 TDF approach, by using the results obtained in an experimental program composed of three point bending tests with shallow beams of high strength concrete (HSC). Six different HSC compositions were developed, varying the dosage of steel fibres (0, 60 and 75 kg/m3) and concrete strength class. The experimental program also included tests to characterize the flexural behaviour of the developed high strength steel fibre reinforced concrete (HSSFRC). Using the force-deflection relationships obtained in the three point-notched beam bending tests, and performing an inverse analysis, the values of the fracture mode I parameters of the HSSFRC were determined. These values were used on the numerical simulation of the tests carried out with HSSFRC beams failing in shear, under the framework of the material nonlinear finite element analysis, in order to evince the influence of using a softening constitutive law for modeling the crack shear sliding. In the present work, the experimental program and the numerical research are described, and the main results are presented and discussed.