Question

By sketching the stress-strain curves for concrete and reinforcement steel, explain the philosophy of idealization the characteristic strength for concrete and reinforcement steel so to be used in reinforced concrete design. Elaborate the importance of such idealization in design.

Answer 1

From the stress-strain curve of Concrete and steel we can easily idealize the characteristic strength of concrete and steel. In the graph, characteristic strength i.e yield strength of steel (fy) is shown and ultimate tensile strength of steel is shown by its yield strength. It is the maximum stress that a steel can sustain before elongation. Where characteristic strength of concrete (fc') is shown and it is the maximum compressive strength of concrete after that concrete brittles.

So, from the graph we can say, the steel is ductile in nature where concrete is brittle in nature. There is a yield point in steel so that before failure of steel the steel gives alert in the structure, but there is no yield point in concrete, after reaching to permissible limit the crack generates in concrete and fails. So this concept is used in design and the structural designer wants first steel reaches its permissible limit to safe the design. That's why most of design is made with under reinforced ( where percentage area of steel is less than concrete).