BI-AXIAL BENDING IN R.C. COLUMNS

Abstract

The principal function of the columns is to carry compressive loads. However, whenever unequal spans or unequal loadings occur even interior columns becomes subjected to biaxial moments. The common examples are exterior columns in a framed building, bridge piers, shear walls, air supply ducts, elevator shafts etc. While the analysis and design of such columns are based upon the familiar and simple assumptions common to most reinforced concrete solutions, the inclination of the neutral axis makes it impossible to derive equations from which simple design aids could be produced. Consequently, unlike rectangular columns subjected to uniaxial moments there is no simple and generally accepted method. of analysing and designing columns with biaxial moments. Problem of biaxial bending is complex mainly because of position of neutral axis. Some time it may be within the section and at small eccentricity it may be outside the section. Each position of neutral axis gives a complex shape of concrete compression block. It is not easy to determine geometrical properties of such areas. In present work, all the five possible cases of neutral axis have been taken and required geometrical properties have been presented in proper manner for the development of the computer program. Basic analysis steps for both working stress method as well as ultimate load method based on the principles of strain compatibility and equilibrium have been presented to suit the development of the computer program. With the introduction of the computers in the design processes, task of design and analysis can be made easy with varied options of shapes of cross-sections, reinforcement pattern, material properties etc. In present work computer programs have been developed to eliminate handicaps associated with the present design aids and to provide more accurate and speedy solutions to biaxial problems. Number of columns have been analysed and designed using developed computer programs. A categorical discussion on each program results have been presented by comparing it with available approaches.