The analysis of crack width in flexural concrete members reinforced with polymer composite bars

Introduction. Rebars, made of fiber-reinforced polymers (FRP), have a number of distinguishing characteristics and disadvantages along with well-known strengths, such as high tensile strength, low specific density, high corrosion resistance, and low thermal conductivity. One of its principal strengths is the modulus of elasticity which is relatively low compared to steel. As a result, elements, having FRP reinforcement, feature higher deformability. In this regard, the requirements of serviceabi-lity limit states, applicable to structures, may become the main obstacle to the use of FRP as the reinforcement for concrete members. It is assumed that cracking patterns of members, having FRP reinforcement, may differ from those of traditional reinforced concrete structures. Materials and methods. Experimental studies were carried with regard for and in compliance with the provisions of National State Standard 8829-94. Tested samples represented concrete beams that were 1,810 mm long and had a cross section of 120 × 220 mm. Their tensile side was reinforced with two bars. Steel, glass fiber-reinforced polymer (GFRP) and basalt fiber-reinforced polymer (BFRP) bars were used to reinforce the beams. The value of the reinforcement ratio varied. Crack width calculation methods, applied according to Construction rules and regulations 63.13330.2012 and 295.1325800.2017 (Russia) and ACI 440.1R-06 (USA) were analyzed. Results. The results of the theoretical and experimental studies of the crack resistance of flexural members having FRP reinforcement are obtained. Discrepancies between the calculation methods are identified. Conclusions. Сracking patterns, typical for members having FRP reinforcement, are specified. They contest the applicabi-lity of methods, prescribed in the Construction Rules and Regulations. The methods, prescribed by Construction Rules and Regulations 63.13330.2012 and 295.1325800.2017, differ in respect of crack width calculations, and it leads to diverging calculation results.