1) Working Stress Method (WSM)
This method is also know n as modular ration method or elastic methods. It is most popular and commonly used method for the design purpose. In this m,ethod the moment nad forces actin on a structure are obtained from the actial values of service loads but the stresses in concrete and the reinforcing steel are restricted to onlt a fraction of their true strenght in order to proved an sadquate safety factor. A factor of safety of 3n in concrete and 1.78 to 1.80 in steel is generally adopted.
2) Limit State Method
This method is also known as plastic method. In this method, the structures is designed to withstand safely all loads liable to act on it throughout its life. It should also satisfy the serviceability requirements such as prevention of excessive deflection, excessive cracking and excessive vibration. The acceptable limit for the safety and serviceability requirements before failure occurs is called limit state.
3) Ultimate Strength Method
This method is also known as load factor method. In this method of design, the true margin of safety is accurately known. The ultimate strength procedure is based upon the results obtained from the experimental investigation depicting the true behavior of the structures.