Open Access

ARTICLE

Fracture behavior of plain concrete beams – experimental verification of one parameter model

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1 Department of Civil Engineering, Indian Institute of Science, Bangalore, 560012, India.

Structural Longevity 2009, 1(3), 135-154. https://doi.org/10.3970/sl.2009.001.135

Abstract

Several different models have been proposed to characterize mode-I crack propagation in concrete. The fictitious crack model proposed by Hillerborg et al. and the blunt crack band theory developed by Bazant & Oh are particularly well suited for a finite element analysis. The two-parameter fracture model proposed by Jenq & Shah is found to be applicable only for beams with s/w=4, where s=span & w=depth of the beam. The general applicability of the model for other testing configurations is not published. In the present study an experimental verification of a one-parameter model based on fundamental equation of equilibrium developed by Ananthan, Raghu Prasad, and Sundara Raja Iyengar to explain the mode - I fracture behavior of notched and un-notched plain concrete beams subjected to three or four-point bending, also called Softening Beam Model are reported and discussed in this paper. The influence of structural size in altering the fracture mode from perfect brittle fracture to plastic collapse is explained through the stress distribution obtained across the un-cracked ligament. The key factor affecting the stress distribution is found to be the strain softening modulus and is considered to dependent on structural size. Based on large number of experimental results available in the literature pertaining to the testing of plain concrete beams in either three-point or four-point bending, an empirical relationship for the determination of process zone length (L_p) has been developed. With the knowledge of L_p, the maximum load P_max can be obtained. It is demonstrated that the model can predict P_max quite accurately. Here the objective is to experimentally verify the predicted P_max. The comparison is valid within a range of errors, reasonable in the cementetious materials like concrete. In this model only an inelastic fracture mechanics parameter ‘L_p’ has been used. The parameter L_p has been obtained as a function of the size of the beam and also softening modulus in order to consider the effect of softening on the tensile stress-strain behavior of concrete. Further, the P_max predicted by the one parameter model as obtained for mode-I failure has been experimentally verified to see how far it is valid for mixed mode type of failure. Since a very few experimental investigations have been so far carried out to study the fracture behavior of concrete under mixed mode condition, the present experimental program is carried out, so as to obtain a wide range of test results pertaining the mixed mode fracture of concrete.

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