A formulation integrating the code recommendations for the design of steel fiber reinforced concrete (SFRC) beams with redundant supports

Abstract

An experimental program was conducted to evaluate the effectiveness of replacing conventional reinforcement by steel fiber reinforcement in the hogging region of continuous shallow beams (with redundant supports). Seven groups of steel fiber reinforced concrete (SFRC) continuous shallow beams were tested under flexural loading, simulating a strip of a slab supported by three aligned piles or columns. The tests also aimed to assess the influence of different ratios of conventional reinforcement in both sagging and hogging regions, under serviceability and ultimate limit state conditions (SLS and ULS, respectively). The results of this experimental program are used to assess the predictive performance of an analytical model for the design of SFRC beams of redundant support conditions. This model is based on the flexibility method and considers the moment‐curvature relationship to derive the flexural stiffness during the loading process of a SFRC beam. The moment‐curvature is determined by using the recommendations of the Model Code 2020 (MC2020) and the Eurocode 1992‐1‐1 (EC2). The predictive performance of the developed approach is assessed on the serviceability and ultimate limit design verifications considering the results from the experimental program. When using average values for the material properties, the analytical model using both the MC2020 an EC2 provided overpredictions in terms of load carrying capacity for SLS and ULS design verifications (up to 57% and 38%, respectively, in terms of normalized error). When using characteristic values, the overprediction was limited to 31% with the MC2020, while over‐ and under‐predictions were obtained with EC2, limited to 25%. By applying the Estimation of the Coefficient of Variation method, safe predictions were obtained using MC2020 and EC2 formulations. It was verified that normalized error of the average crack width was less than 18% when using MC2020 and EC2 formulations. Finally, numerical studies were conducted on statically indeterminate shallow beams to assess the influence of both beam scale and the replacement of conventional tensile reinforcement by fibers at the intermediate support on the ULS and SLS design verifications.