No abstract

Experience gained in design, erection and operation of span reinforced concrete structures has proved that practically all of them are subject to complex stress-strain state. At that, the researchers pay considerable greater attention to calculation of strength, deformation analysis and determination of crack resistance in normal cross-sections than to calculation of their support zones, including oblique sections, which results are generally taken into account for determining the section dimensions and the quantity of the cross reinforcement.

Experimental data of strength, deformability, and crack resistance of 2,000×200×100 mm reinforced concrete and basalt-concrete beams are given. Longitudinal reinforcement consisted of 2 Ø14 A500C for reinforced concrete beams and 2 Ø14 BFRP (AKB800) for basalt-concrete beams. Transverse reinforcement consisted of 2 Ø3, 4, 5 ВрI for reinforced concrete beams and 2 Ø4, 6, 8 BFRP (АКБ800) for basalt-concrete beams. Beams were made of heavy concrete of C16/20, C30/35, and C40/50 classes. The experimental beam specimens were tested according to a four-point scheme as loosely supported beams loaded with two concentrated forces. Loading in the series of tests was stepwise increasing, static and low-cycle repeated at high levels of 0.50, 0.65, and 0.80F ult. Distance from supports to concentrated forces (shear span), a/h 0 , varied within 1, 2, 3. Experimental beam specimens were made and tested according to the theory of experimental design according to the Box B4, optimal plan D. Comparative analysis of main performance parameters of reinforced concrete and basalt-concrete beams under the action of abovementioned loads was performed. The necessity of these studies was determined by the unsatisfactory convergence of experimental and calculated values of bearing capacity of oblique sections of basalt-concrete beams determined according to existing standard methods. The studies have established the influence of design factors and loading nature on basic parameters of the working capacity of basalt-concrete beam elements in a form of experimental-statistical dependences. These results will form a basis for a physical model of resistance of oblique sections in such structures to external loads. The presented results will significantly supplement the existing database of the operation of beam basalt-concrete structures and will be used in the development of an analytical method for calculating strength, deformability, and crack resistance

To investigate and to analyze the behavior of the areas near supports of reinforced concrete beam elements under the action of low-cycle loads of constant sign and repeated alternating loadings taking into account the influence of constructive factors and factors of external action for the future using of obtained results for improvement of calculated engineering technique. Methodology. Three series of experiments were performed to research this problem. Test specimens are reinforced concrete beams of rectangular cross section with sizes 200100 mm,

In order to study the cracking of prestressed reinforced concrete T-shaped beam structures, the authors planned and carried out a full-scale experiment with five variable factors. The following factors were chosen as variable factors: the relative span of the shear, the ratio of the table overhang width to the thickness of the beam rib, the ratio of the table overhang thickness to the working height of the beam section, the coefficient of transverse reinforcement, the level of prestressing in the working reinforcement. The article describes the cracking process and the destruction of test beams. It was found that the loading level of an opening of inclined cracks is 53% larger than the loading level of a normal crack opening. Mathematical models of bending moments and transverse forces of cracking were built using the “COMPEX” software. Also, the mathematical models of the crack opening width and the projection length of a dangerous inclined crack were obtained. These models are based on the experimental data. Analysing the obtained models, the complex influence of variable factors on the main parameters of crack formation and crack resistance was established. In particular, it was found that the prestress level in the working reinforcement has the greatest effect on the bending moment of cracking. In this case, the value of the shear force of cracking significantly depends on both the prestressing level in the reinforcement and the relative span of the shear. On the basis of the experimental data, the empirical expression is obtained for determining the projection of a dangerous inclined crack for prestressed reinforced concrete T-shaped beams. The resulting equation can be used to calculate a shear reinforcement.