Effects of prestress parameters of fiber reinforced polymer rebar on the stiffness and crack resistance of bending concrete elements. Experimental studies

Introduction. In contrast to steel reinforcement, high tensile strength and relatively low elasticity modulus of fiber reinforced polymer rebar (FRP) determine the feasibility of its prestressing. However, the issues of its prestressing technology and the design of structures with its application are insufficiently studied. The current regulatory documentation contain no exhaustive scope of provisions and requirements in relation to the conditions and parameters of FRP prestressing and their account in the design and calculation of structures. In this regard, conducting a set of clarifying studies on this topic appears to be relevant and represents a considerable practical interest.Aim. To assess the effect of various FRP prestressing parameters on the stiffness and crack resistance of bending concrete elements.Materials and methods. As a part of the study, an experimental research program was developed and implemented, including the manufacture and bending testing of six concrete sample series with various FRP prestressing parameters.Results. The destructive loads were determined; patterns of deformation, cracking and destruction of bending concrete elements for various FRP prestressing parameters were established. The prerequisites for improving the system of urban planning activities in terms of clarifying and supplementing the existing regulatory documents for the design of FRP-reinforced concrete structures were established.Conclusion. The technology of FRP mechanical tensioning was laboratory successfully tested. Nevertheless, an adaptation of tensioning devices and grippers is required for its implementation at contemporary production enterprises. FRP prestressing was concluded to be an effective way of increasing the crack resistance and stiffness of bending concrete elements. Within the framework of the study, increase in the time of crack formation (relative to structures without prestressing) and a decrease in deflections in the middle of the span of up to 2.25 and 0.5 times, respectively, was recorded.