COMPARISON OF CALCULATIONS OF THE SECTION AREA OF LONGITUDINAL REINFORCEMENT IN BENDING ELEMENTS OF THE BRAND PROFILE

Abstract

Reinforced concrete bending elements of the T-profile are widely used in buildings and structures. In connection with the introduction of new building codes, it became necessary to develop modern methods for calculating such elements based on a deformation model, taking into account two possible cases of the neutral line in the cross-section, and to determine the effectiveness of the adopted methods based on a comparison with the calculation results according to previous regulatory documents. The developers of the currently valid regulatory documents proposed to calculate bending elements based on a deformation model using a full or simplified concrete deformation diagram, in particular, for T-profile and I- profile elements, four cases of the neutral line in the cross-section of the element are considered. The authors proposed a practical method for calculating bending elements of a rectangular profile, while the calculation is performed by the method of successive approximations relative to the height of the compressed section zone, given by the deformation of the extreme compressed concrete fiber, which corresponds to the maximum bearing capacity of the element. Such calculation prerequisites make it possible to easily determine the required cross-sectional area of the reinforcement, especially when using computer technology. The task is set to calculate the cross-sectional area of the longitudinal working reinforcement in the T-section element according to the new standards and compare the calculation results with those obtained according to the previous regulatory document. According to the method of Babich V.E. – Savitsky V.V., we take the maximum value of the coefficient of completeness of the stress diagram in compressed concrete. To determine the position of the neutral line, we find the bearing capacity of the cross-section of the element, provided that the neutral line passes on the border of the shelf and the wall (rib) of the T-section element. In this case, the bearing capacity is  defined as the sum of the moments of internal forces in the compressed shelf and the tensioned reinforcement, relative to the neutral line. Using the method of successive approximations, we find the height of the compressed zone of concrete at which the ratio of the moment from internal forces in the cross section to the bending moment from the external design load will be as close to unity as possible. This task is conveniently performed in the Excel software environment. The obtained calculation results are compared with the results according to the previous design standards. The initial data for the calculation will be the same. To determine the position of the neutral line, we find the moment that the concrete of the compressed shelf can perceive relative to the center of gravity of the stretched reinforcement. We will calculate the cross-sectional area of the longitudinal reinforcement according to the current standards with the same initial data. We determine the value of the relative deformation of the compressed concrete at the level of the lower edge of the shelf according to the hypothesis of flat sections. We find the value of the bending moment from the internal force in the compressed concrete of the shelf overhangs. We determine the value of the bending moment from the internal force in the compressed concrete of the wall. We will perform a comparative calculation according to the previous design standards. The obtained calculation results and the magnitude of the difference with the results according to the canceled standards indicate the acceptability of both methods, the advantage of the canceled method is greater simplicity, especially when using manual calculations, the advantage of the new method is versatility due to the elimination of empiricism when calculating more complex structures and the possibility of widespread use of computer technology.