Strength analysis of normal cross-sections of reinforced concrete structures in uniaxial bending by Wood-Armer method in LIRA SAPR software

Abstract

The Paper focuses on implementation of methodology stipulated in the valid regulatory documents of Ukraine for the strength analysis of RC structures by normal sections in uniaxial bending. The main attention is paid to atypical and practically not considered calculation cases, typical for automated algorithms in LIRA SAPR program. The purpose of the Article is to evaluate feasibility of methodology of the valid regulatory documents and provide recommendations that fit for computer-aided analyses. The study looks at rectangular cross-sections of RC structures with single and double reinforcement (in case of a significant increase in the area of reinforcement at the compressed zone) and with different values for concrete classes, the percentage of reinforcement and ratio of reinforcement areas. The stress-strain diagrams of concrete and reinforcement are bilinear with characteristic values set for ultimate limit states. The changes in the cross-sections diagrams ‘M - εc(1)’ are examined. For single-reinforced normal RC sections, the strain of the compressed concrete face εc(1) decreases in case the area of reinforcement decreases; for this strain, there is an equilibrium between internal and external forces. It will slow down the speed of the analysis of reinforcement in plate elements by the Wood-Armer method. For sections with double reinforcement and a relatively large ratio of the areas of reinforcement, the equilibrium of the section is at the max strain of the compressed fibre of concrete. The authors propose an approach to speed up the analysis of cross sections with single-reinforcement. This approach is based on using the ratio of the percentage (or area) of reinforcement to the strain of the most compressed face in a RC structure. Specific features of the analysis algorithms are implemented in LIRA-SAPR software. They are also applied to optimize existing algorithms for the analysis of RC structures.