Improving methods of strength design of normal sections of flexural concrete members reinforced with fiber-reinforced polymer bars

Abstract

Theoretical and experimental studies of the strength of normal sections of flexural concrete members reinforced with FRP bars have been conducted. The test specimens were concrete beams 1810 mm long, with a rectangular section of 120×220 mm, reinforced with two bars in the tensile area. The beams were reinforced longitudinally with steel, glass fiber-reinforced polymer (GFRP) and basalt fiber-reinforced polymer (BFRP) bars. The design methods of guidelines of Russia, the USA, Canada and the European Union have been considered. There are two approaches to the strength design of normal sections – the European and the North American. The approach used in the design method of the Russian guideline SP 295.1325800.2017, when all partial safety factors are used in calculating the design characteristics of materials, causes an overestimation of the boundary values of relative depth of the compressed region ξR . It leads to an inaccurate determination of the failure mode and possible over-reinforcement of the construction. Some corrections have been brought about to the design methods of the Russian guideline SP 295.1325800.2017. Factor β has been introduced, which takes into account prestressing of the reinforcement. As a result, the deviation of the theoretical evidence from the experimental values of failure moments decreased from 30.44 % to 13.2 %. Changes have been made to the approach for the application of safety factors, which allowed increasing the accuracy of determining the failure mode and bring the safety factor for members C to the value of 1.6 adopted by the authors.