Traditionally, it used careful placement of coordinate axis to simplify complex equations associated with tensor quantities such as stress and resulting displacements of structural elements, such as beams. This simplification was essential to being able to solve problems. A successful engineer must design a structure to withstand the loads specified to be placed upon it. As long as the design loads were not exceeded the structure should spring back when the load was lifted or hold steady indefinitely.
The advancement of computer software has allowed many of the more complicated calculations to be carried out more accurately and quickly, freeing up time for the engineer. This is obviously economically advantageous.
Typically, apprentice structural engineers may design simple beams, columns, and floors of a new building, including calculating the loads on each member and the load capacity of various building materials (steel, timber, masonry, concrete).
An experienced and respected engineer would tend to design more complex structures, such as multi-storey buildings (including skyscrapers), or bridges.