What is ultimate load method?

Answer 1

In ultimate load method, the working loads are increased by suitable factors to obtain ultimate loads. These factors are called load factors. The structure is then designed to resist the desired ultimate loads. This structure is then designed to resist the desired ultimate loads. This method takes into account the non-linear stress-strain behavior of concrete.

The term safety factor has been used in the working stress method to denote the ratio between the yield stress and the permissible stress. It had little meaning as far as the ratio between collapse loads and working load was concerned. The team load factor has been traditionally used to denote the ratio between the collapse or ultimate load to the working load. The knowledge of load factor is more important than the knowledge of factor of safety.

Several ultimate load theories have been proposed in the past. In each of these theories and idealized stress-strain curve has been adopted for concrete which is the only difference among them. This theory is based on the assumption that ultimate strain in concrete is 0.3% and the compressive stress at the extreme edge of the section corresponds to this strain. Whitney replaced the actual parabolic stress diagram by a rectangular stress diagram such that the centre of gravity of both diagrams lies lat the same point and their areas are also equal.