The paper investigates the formation and propagation of flexural cracks in beams made of ultra-high performance steel fiber reinforced concrete (UHPFRC). A comprehensive series of laboratory tests was carried out on seventeen beams of rectangular and T-shaped cross-sections, varying in longitudinal reinforcement ratios, fiber volume contents, and fiber types (straight and wave-shaped). The results demonstrate that the inclusion of steel fibers significantly enhances the crack resistance of the beams, promotes a more uniform crack distribution, and improves their load-bearing capacity. In under-reinforced UHPFRC beams, failure typically occurs due to fiber pull-out localized within one or more dominant cracks. Prior to the onset of deformation localization in the tensile zone – which coincides with the yielding of the longitudinal reinforcement – the crack widths in fiber-reinforced specimens remain below 0.25 mm. This behavior ensures that even under service-level loads (65–70% of ultimate), the crack openings stay within the allowable design limits (0.3–0.4 mm). The experimental findings contribute to a better understanding of the cracking mechanisms in UHPFRC beams and provide a valuable foundation for refining numerical models and optimizing design approaches for flexural members made of advanced high-performance cementitious composites.

Keywords: ultra-high performance concrete, beams, bending moment, steel fibers, flexural cracks

The article provides information about method of sustainability calculation of compressed polymer rods taking into account nonlinear creep . As the law of the relationship between stress and strain is used nonlinear equation of Maxwell-Gurevich. Derived from the analysis of the resolving equations with time tends to infinity, we obtain an expression for a long critical force in the case of constant rigidity of the rod.

Keywords: nonlinear creep, rod, stability, Maxwell-Gurevich, finite difference method, long critical force, relaxation viscosity, viscoelasticity, high elasticity modulus.

The technique of determining the stress-strain state of the polymer thick cylindrical shells in flat tension conditions with effects of temperature and creep deformation. As the law of the relationship between stress and strain is used nonlinear equation of Maxwell-Gurevich. Solution is performed numerically by finite element method.

Keywords: nonlinear creep, cylinder, the Maxwell-Gurevich equation, finite element method, relaxation viscosity, viscoelasticity, high elasticity modulus, plane stress and temperature.

Solved the inverse problem for a thick-walled cylinder, experiencing temperature and force action, under the plane of the axisymmetric problem of elasticity theory. By the variation of the modulus of elasticity, in which the cylinder is equally stressed by the Mohr's theory of strength. The problem is reduced to a differential equation of the first order. This equation was solved numerically, using the Runge-Kutta method of fourth order.

Keywords: thick-walled cylinder, optimization, heterogeneity, method, Runge-Kutta, temperature, flat axisymmetric problem