Reinforced Cement Concrete Questions and answers

The strength of materials below which not more than 5% of the test results are expected to fall is known as the characteristic strength of the material and it is denoted by fck.

The acceptable limit for the safety and serviceability requirements before failure occurs is called limit state. This structure is so designed that it carry the loads with sufficient degree of safety and serviceability and structure will not become unfit for use for which it is to be designed.

Latest code for RCC is IS 456:2000 and for steel code is IS 800:2000.

Cement concrete is a mixture of binding material (cement), fine aggregate (sand), coarse aggregate, water and admixture in proper proportion to achieve concrete of desired properties at fresh state and hardened state.

There are mainly two types of limit state, one is limit state of collapse and second is limit state of serviceability.

As per IS 456:2000, maximum percentage of reinforcements in column is 6%.

Modulus of elasticity of steel is 2 x 105.

As we know that the tensile strength of concrete is very much less as compared to its compressive strength and also the tensile strength of concrete does not contribute towards enhancement of moment of resistance of the section except providing bod between concrete and steel for developing tensile strain and thus stress in steel.

The limitations of this method are:

  1. It assumes stress strain relation for concrete is constant, which is not true.
  2. It gives the impression that “factor of safety times the working load” is the failure load, which is not true. This is particularly so in case of indeterminate structures. In these structures there will be redistribution of forces as plastic hinges are formed at critical sections.
  3. And this method gives uneconomical sections.

Advantages of this method are:

  1. It is simple.
  2. Reasonably reliable and,
  3. As the working stresses are low, the serviceability are automatically satisfied and there is no need to check them.

In this method ultimate load is used as design load and the collapse criteria used for the design.

Structures have to carry dead load and live loads. The maximum working load that the structure has to withstand and for which it is to be designed is called characteristic loads. As per the code the characteristic loads means the value of the load above which not more than 5% results are expected to fall.