Análise de viabilidade do uso de fibras metálicas em tubos de concreto: parte 1: campanha experimental

This is the first part of a research study focusing the viability analysis of metallic fibers application for concrete sewage and water rain systems pipes. In this work is presented the methodology, materials, and test procedures used in the study, together with some results obtained in tests carried out in Brazil. For the experimental program concrete pipes were produced with ordinary rebar reinforcement, together with others made with the same conditions but using steel fibers. Both test programs were accomplished with the intention of verify the technical feasibility of the ordinary reinforcement replacement by metallic fibers, depending on geometric characteristics of the pipe and the strength requirements. Other secondary objectives of the study are: (1) to demonstrate that the continuous three-edge-bearing test (TEBT) or crushing strength test provides reliable information for the fiber reinforced concrete pipes (the Brazilian NBR 8890:07 and European NBN-EN 1916 standards prescribe the cycled test with the intention to verify the post-crack performance of the fibers); (2) to confirm the possibility of fiber reinforcement to present similar performance to ordinary rebar reinforcement; (3) to produce results to calibrate a non-linear model Tubos de Hormigón (ATH) implemented in order to simulate the crushing test response of concrete pipes with fibers and/or with traditional reinforcement. Concrete pipes with conventional reinforcement and with steel fiber consumption of 40kg/m3 were produced at the same conditions to check if they meet the requirements of the class EA2. Crushing tests were performed with continuous loading together with the displacement control. It was found that the test of continuous crushing of pipes made with diametrical deformation monitoring of the component can be used as a reliable tool to control them. It was also observed that the performance of fiber reinforced concrete was higher than in conventionally reinforced concrete in the regions of initial cracking, surpassed by that for higher levels of displacement and cracking. The tubes were approved by wide margins left for the class EA2, and the pipes with conventional reinforcement could be classified as EA3. On the other hand, the use of the calibrated ATH model, with the constitutive equations to model the fiber reinforced concrete behavior under compression and tension stresses, turns possible to predict the pipe response under test loading. So, the ATH model could be used as an instrument to optimize the pipe reinforcement for each class of strength. Consequently, this experimental-numerical design approach provide a feasible instrument for reinforced concrete pipes design to feat the crushing test requirements, and taking into account the different materials and production conditions for each production plant