Influence of Sectional Design and Fibre Type and Dosage on Cracking Behaviour of Reinforced Beams Made with FRC Under Prolonged Loading

Fibre-reinforced concrete is a material under continuous research even though it has been in use for many years. Much effort continues to be devoted to quantifying its contribution to serviceability limit state response. The effects of fibres in the calculation of crack opening and mean crack spacing have been included in the fib Model Code for Concrete Structures 2010 and in Annex L of the new Eurocode 2. The aim of this paper is to analyse the influence of different factors on the occurrence and pattern of cracks. A statistical design of experiments has been proposed to rigorously analyse the effect of the variables normally considered. The experimental programme is carried out on fibre-reinforced concrete beams tested in bending. In this study, the results of 18 beams, each 3.70 m long, are presented. These beams were tested until reaching the service deformation in the main reinforcements, and their condition of cracking was maintained for one year. The beams were retested to the same load level, sustained for 24 h, to assess short-term delayed deformations. Finally, they were loaded until failure. With the results obtained for crack spacing and crack opening, the influence of the different factors was determined by statistical analysis. Results have been obtained for an instantaneous load, for a prolonged load and for failure. Finally, using the statistical results obtained, a formulation has been developed to calculate the average crack spacing and has been compared with the existing formulation in the draft Eurocode 2, Annex L and Model Code 2010.