Bearing Capacity of Reinforced Concrete Beams with Initial Cracks Reinforced with Polymer Composite Materials

The use of polymer-composite materials for strengthening the reinforcing of concrete structures represents a current scientific trend. The article is devoted to experimental studies of the strength of inclined sections of bent concrete elements, reinforced with transverse polymer reinforcement with initial inclined cracks, with different shear spans and transverse reinforcement options. The characteristics of reinforced concrete specimens with initial inclined cracks and the test results of 22 experimental beams, each of which was tested twice, are given. A significant influence of all eight variable factors was established: three spans of the section, equal to 1.5 h0; 2 h0 and 2.5 h0; two types of compound clamps and their layout; and opening width of oblique cracks from 0.6 to 0.9 mm. It is shown that the strengthening of the beams supporting sections with external polymer reinforcement using three-sided U-shaped and vertical double-sided stirrups significantly changes their stress-strain state (SSS) and the form of destruction. SSS transforms from the classical destruction of the compressed zone above the end of the inclined crack to the destruction of the beam zone of average height at α = 2.0 and brittle crushing of concrete in the tension zone. Unfavorable combinations of force and geometric factors are revealed. Recommendations are proposed that can be used for structures operated in all weather conditions.