It is a method or tool by which we find out safe and economical specifications of a structure or a member of the structure sufficient to carry the load.
In other words finding out cross-sectional dimension, grade of material, amount of reinforcement etc. necessary to withstand the internal forces that we have got from structural analysis.
Structural design is the first design stage. Feasibility studies and options appraisals that the consultant team or independent client advisers may have previously carried out do not involve ‘design’ as such. They are preliminary studies whose purpose is to establish whether the project is viable, to assist in the development of the project brief and to aid the identification of feasible options.
The preferred option is then be developed into a Structural design which is a response to the project brief. The project brief will continue to develop as the Structural design is prepared.
Before starting design, the structural engineer must determine the criteria for acceptable performance. The loads or forces to be resisted must be provided. For specialized structures this may be given directly, as when supporting a known piece of machinery, or a crane of known capacity. For conventional buildings, building codes adopted on a municipal, county, or state level provide minimum design requirements for live loads.