Short-term and long-term testing of beams made of high-strength concrete with different types of reinforcement

The object of research is the nature of deformation of flexural elements made of high-strength concrete, reinforced with classical bar and sheet reinforcement, under long-term loads. The relevance of the work is determined by the lack of data on the deformation characteristics of such structures in regulatory documents and scientific literature; this applies both to short-term loads and especially to long-term ones. Such experiments have not been conducted previously in our country, and they are also rare abroad. Method. Comprehensive experiments were carried out on beam specimens of the same cross-section, reinforced in three different ways — external sheet reinforcement (Type A), classical bar reinforcement designed for the same failure load (Type B), and bar reinforcement for twice the load (Type C). The experiment included short-term tests to failure and long-term tests with step-by-step loading; part of the beam specimens was loaded to 50% of the failure load before the long-term tests. During the testing, beam deflections and the nature of crack formation were investigated. Results. It was found that with the same load-bearing capacity and similar nature of deformation, significantly fewer cracks form in beams with external sheet reinforcement, but with a crack width an order of magnitude greater. Under long-term loading conditions, beams with external sheet reinforcement and initial cracks showed a smaller reduction in stiffness at the reloading stages compared to beams reinforced according to the classical scheme. The work confirmed the applicability of standard calculation methods for the first group of limit states to flexural elements with external sheet reinforcement. To increase crack resistance, the installation of additional structural bar reinforcement is recommended in them. The obtained data reveal the features of deformation of structures with external sheet reinforcement and determine the necessity for further research for other types of cross-sections and classes of concrete.