Steel structure design has three methods of design which are as under:
Plastic design
Elastic design
Limit sate design
Plastic design is a design criterion in analysis of a design structure considering the final load of the structural design. The expression plastic is derived from the final load that is created from the strength of steel in the range of plastic.
This is a fast method providing a rational method for the study of the steel structure design that helps to provide a striking economy as against the weight of steel since the sections needed by this approach are comparatively small in size than those needed by the elastic analysis method. It is better to know that plastic analysis and steel structure design have its main application in the design and analysis of statically undefined framed structures.
Elastic design - is a traditional design method. Majority of steel is elastic up to the given point and elastic theory is a superior method on which ton base design. Elastic theory analyzes structures and sections are sized so the tolerable stresses do not increase. Design is in accordance with BS 449: plastic theory which is developed to take into account of behavior past the yield point dependent on finding the load that cases the steel structure design to collapse. Then work load collapses divided by a load factor. This too is permitted under BS449.
Limit sate design It is the primary duty of a Civil Engineering Designer to ensure that the amenities he designs or are prepared by steel design services are fit for its purpose; are safe, economic as well as durable. Ensuring safety is one of the major duties of the designer. Though, it is not easy to assess primarily that how safe a proposed design will really be. There is a great deal of uncertainty about a few factors that influence safety as well as economy. Uncertainties that may affect the safety of a structural design are caused due to the following:
Loading
Material strength
Structural dimensions plus behavior
Together these uncertainties make it difficult for any designer to ensure that a design structure provided by the structural design services will be completely safe. The designer can just confirm about the risk involved or failure despite the uncertainties.