Orlova O. The rigidity of reinforced concrete I-beam elements with normal cracks at torsion

In the dissertation, methods for calculating the rigidity and bearing capacity during torsion of reinforced concrete I-beam elements with normal cracks were developed. On the basis of theoretical and experimental researches, an important scientific and technical problem of determining the rigidity and torsional strength of reinforced concrete I-beam cross-sectional elements with normal cracks was solved taking into account the pin force in the longitudinal reinforcement, its number and location in the section. It is shown that the problem of determining the torsional stiffness of elements with normal cracks includes three stages: dissection of longitudinal reinforcement and determination of the mutual displacement of the sides of a normal crack; the determination of pin forces in longitudinal reinforcement; the calculation of torsional stiffness at the location of the crack and the element as a whole. It is shown that the first task is the most difficult. The problem of determining the mutual displacement of the faces of a normal crack is solved by various methods, including engineering, which allows the design of structures without the use of a computer. The results of determining the mutual displacement of the faces of a normal crack using the developed numerical and analytical and engineering techniques are compared with calcula-tions in software systems using volumetric finite elements. These results are shown to be in good agreement. At the same time, the use of the developed techniques makes it possible to abandon the use of cumbersome calculations with modeling by volumetric finite elements in real design, which greatly simplifies the design and saves labor costs. It is shown that the torque in an element with normal cracks is perceived due to the concrete zone without cracks and pin forces in the longitudinal reinforcement. A method for determining the pin forces in longitudinal reinforcement has been developed. In this case, the vertical and horizontal components of the pin forces, the location of the longitudinal reinforcement within the section, the number of longitudinal reinforcement rods are taken into account. The developed method for determining the thrust forces in longitudinal reinforcement does not require the use of computer technology. Experimental studies of rigidity and bearing capacity in torsion have been carried out on samples of reinforced concrete beams with normal cracks. The results of experimental studies are compared with theoretical proposals. They are shown to be in good agreement. Computer programs have been developed, in which all the proposed methods for determining the mutual displacement of the faces of a normal crack, the pin force and the torsional stiffness of elements with normal cracks are implemented.