3 Structural Design Methods

The following three methods are considered to be construction industry standards to approaching structural design.

Working Stress Method

The Working Stress Method was the traditional method of design not only for reinforced concrete, but also for structural steel and timber design. The method basically assumes that the structural material behaves as a linear elastic manner, and that adequate safety can be ensured by suitably restricting the stresses in the material induced by the expected “working loads” on the structure.  As the specified permissible stresses are kept well below the material strength, the assumption of linear elastic behavior is considered justifiable. The ratio of the strength of the material to the permissible stress is often referred to as the factor of safety.

Ultimate Load Method

The Ultimate Load Method method is sometimes also referred to as the load factor methods are the ultimate strength. In this method, the stress condition at the site of impending collapse of the structure is analyzed, and the non linear stress-strain curves of concrete and steel are made use of.

Limited State Method

The LSM philosophy uses a multiple safety factor format which attempts to provide adequate safety at ultimate loads as well as adequate serviceability at service loads, by considering all possible ‘Limit State’.