Article describes methods and results of experimental research for strain behavior, crack formation and fracture of concrete beams reinforced with fiber reinforced polymer (FRP) bars during bending moment action. 18 beams (3+3 series) reinforced with glass FRP (GFRP) and basalt (BFRP) 6, 10 and 14 mm in diameter were tested. Deflection in the middle of the beam, concrete and bars strain and ultrasonic transmission time for 4 routes were measured during tests besides visual inspection. Main crack formation occurred at 8-20% of the ultimate load for all beams. Crack formation was transition border to linear (elastic) straining at low bending stiffness. More than 15 times decrease in bending stiffness was seen for beam reinforced with two types of bars 6 mm in diameter compared to initial values. Existence of main cracks and major deflections is not allowed during design of bending elements. However small bending stiffness at linear elastic straining is a positive factor in case of «hard» loading and impact (pulsed) loading. It is possible to prevent structures collapse and people deaths at impact loading and cyclic «hard» loading by permitting crack formation in load bearing structures.

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The article discusses the effect of transverse reinforcement spacing for the strength and deformation characteristics of beams with glass fibre reinforced polymer. The bending tests results of reinforced concrete specimens are presented (GFRP) with different concrete strength and reinforcement spacing. Force-deflection, force-GFRP bars deformation and force-concrete compressed zone deformation dependencies are given in the article. Based on ultimate force and beams destruction pattern it is established that increasing transverse reinforcement spacing reduces the beams strength and leads to destruction in oblique section. With narrow-mashed transverse reinforcement fracture occurs in the compressed zone of concrete. A computational analysis for different types of beams fracture is presented. It is established that transverse reinforcement spacing doesn’t affect the parameters determined by service limit state: crack formation load, crack width and beam deflection. A comparative analysis of maximum permissible deflection based on test results and theoretical calculations was carried out. The numerical values of bending stiffness parameter are obtained at the loading stages with linear deformation before and after first crack formation.

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