Annotation

The deformation technique for calculating the moment of formation of normal cracks of bent fiber concrete elements is proposed. It considers the influence of fiber reinforcement and the limit deformations of concrete. For the first time, it was proposed to take into account the coefficient of fiber reinforcement by volume and the coefficient of orientation of fiber reinforcement for the calculation of the moment of formation of normal cracks.

According to the national Ukrainian design standards, the calculation of the formation of cracks normal to the longitudinal axis of reinforced concrete bent elements is performed taking into account both elastic and plastic deformations of the stretched zone of concrete. It is believed that cracks appear when the tensile deformations of the extreme fibers reach the limit values . Therefore, at the average tensile strength of concrete and the characteristic value of the modulus of elasticity of concrete , elastic and plastic deformations have the same values. In the national standard for the design and manufacture of dispersed reinforced structures, it is indicated that the calculation of the formation of cracks must be performed in the same way as for the reinforced concrete structures, but taking into account the tensile and compressive strength of fiber concrete. In this work, it is pointed out that this position has certain contradictions, since the formation of cracks should be associated with the ultimate deformations of concrete and the tensile strength of fiber concrete is higher than the stresses at which cracks are formed.

Integral equations of equilibrium of the external and internal forces related to the neutral axis for the formation of normal cracks and their developed solutions for combined reinforced fiber concrete bent elements were obtained. It allows considering both the influence of fiber reinforcement and the ultimate deformations of concrete under tension as a criterion for the formation of cracks.