THEORY OF RCC DESIGN AND METHODS OF DESIGN ACCORDING TO THE IS:456-1978 (CODE FOR PRACTICE)

THEORY OF RCC AND DESIGN :--Two methods of design for RC structures are used ie the Working stress or elastic method and the load factor or ultimate load method. In the working stress method,the design is based on the working loads and the criterion for the strength of structure is its capacity to sustain the load and forces imposed on it .The load factor method of design is based on a determination of the load at which a structure fails and a certain factor of safety is adopted. The working stress method of design, which is the older and by for the still most commonly used by practicing Engineers .The factor of safety related with ultimate strength at failure and the permissible stress generally adopted 3 for concrete based on the cube strength Of crushing and 2 for steel based on the ratio of yield stress to permissible stress , and the modulus of elasticity is a measure of the elastic property of a material and is the ratio between the stress caused by an applied load and the resulting strain or deformation,which disappears on removal of the load in other words it may be represented Modular ratio ie stress in steel / stress in concrete .The modular ratio specified in the Indian code of practice is 2800/3fc where fc is maximum permissible compressive stress due to bending in the concrete in kg /sq cm . According to the code value 1978 said rounded -off value has been given and the Value of M100 grade concrete is 31 ,M 150 is 18.7,M 200 is 13.3 and M 250 is 11 .All this description made is based on IS:456-1978 .