Generalized Design Aids for Reinforced Concrete Columns

Abstract

Design Aids in the form of interaction curves are an inevitable requirement for Design of Reinforced Concrete Columns subjected to Axial Load & Moment. Design Aids are available for Fe-415 & Fe-500 grades of steel in many Text Books and Handbooks (Design aids for reinforced concrete to IS:456-1978 (1980), Torsteel design handbook for reinforced concrete members with limit state design, Torsteel Research Foundation in India, Mumbai, (1990), Handbook of reinforced concrete design, Tata-McGraw Hill Publishing Company Ltd., New Delhi, (1996)) and (Design Aids for Limit State Design of Reinforced Concrete Members, Khanna Publishers, Nai Sarak, Delhi (2005)). Design Aids published by Bureau of Indian Standards has been very useful for the designers from past four decades. However, the Design Aids in the form of Interaction Curves for columns with high strength steels like Fe-550 & Fe-600 grades are scarce. With the availability of high strength steels, the usage of the same is increasing. Considering this requirement, an attempt is made in this paper to derive the required mathematical formulae and suggest a systematic step by step procedure to formulate interaction curves for any grade of steel. Mathematical expressions have been derived for Rectangular column with reinforcement equally distributed on all the four sides. As the procedure suggested involves iterative computations using a systematic approach, it is well-suited to be developed as a computer program. The typical output of such a program has been validated and presented for rectangular section with reinforcement equally distributed on all the four sides for HYSD Fe-600 grade of steel and d′/D = 0.05 in the form of interaction curves. Typical interaction curves for rectangular section with reinforcement equally distributed on two opposite sides for d′/D = 0.05 with HYSD Fe-600 steel is also presented. The mathematical formulae and the step by step procedure suggested can be easily modified for Rectangular column with reinforcement equally distributed on two opposite faces, circular columns and even members subjected to Axial tension and moment. The formulae and step by step procedure presented here are so general in nature that, once the design stress–strain curve of steel is known, interaction curves can be plotted for any grade of steel including Mild Steel, High Yield Strength Deformed bars and TMT bars.