Influence of Fatigue Loading in Shear Failures of Reinforced Concrete Members without Transverse Reinforcement

Shear fatigue of reinforced concrete members without transverse reinforcement has been observed to be potentially governing for the strength of some structural members subjected to large live loads of repetitive nature (as traffic, wind or wave actions). Although extensive experimental programmes have been performed in the past and a rational approach to the problem can be performed on the basis of Fracture Mechanics, most design codes still ground shear fatigue design on empirical equations fitted on the basis of existing data. These empirical formulas show inconsistency amongst them and some neglect potentially relevant parameters as the ratio of maximum and minimum fatigue load levels. In this paper, a consistent design approach is presented, by using the principles of Fracture Mechanics applied to quasi-brittle materials in combination with the Critical Shear Crack Theory. This approach leads to a simple, yet sound and rational, design equation incorporating the different influences of fatigue actions (minimum and maximum load levels) and shear strength (size and strain effects, material and geometrical properties). The accuracy of the design expression is checked against available test data in terms of Wöhler (S-N) and Goodman diagrams, showing consistent agreement to experimental evidence. In addition, the estimate of the number of cycles until failure is shown to be significantly more accurate and with lower scatter than current empirical shear fatigue formulations of Eurocode 2 or fib-Model Code 2010.