The design engineer starts with a design drawing which defines the sizes of the steel members, the orientation, the location of a particular member in 3D space, and how they are meant to be connected to each other. He gives the dimensions of the aisle or overall bay of the building and the floor levels besides indicating the paint specifications. He also specifies the exact material from the available options.
After the design drawing is complete, it is what the contractor/fabricator/erector uses to evaluate everything from the total volume of work, the quantities of material required for each member size, the time and resources needed to execute the job, the possible problem areas and the complexities of execution, so that he can quote a fair price for execution of the project.
Once the contractor is awarded the project, the next step is to move towards executing it. The earlier design drawing is now no longer useful for specific jobs like cutting the material to exact size, length, shape, and drilling the bolt holes in the correct places for connecting with other members. The contractor needs detailed plans and needs to prepare a new set of drawings for each structural element, specifying the exact shape, size, cutting length, diameter and location of the connecting bolt holes. The new drawing has to specify accurate details of the fixtures and locations and have the detailed bill of materials with the list of all the materials required. This new drawing is called a shop drawing or fabrication drawing, or manufacturing drawing. There is a unique identification tag, called erection mark, allotted to each assembled piece after which they are shipped to the construction site where they are unloaded with the identifying tags punched or painted on them.
At this point, a new drawing called GA drawing (general arrangement drawing) or Marking Plan, or Marking Elevation is prepared to show where the fabricated pieces go at the site and to which other member they are connected to. These drawings are expertly prepared by specialized steel detailing agencies which today use advanced Modeling software. However, earlier they were painstakingly prepared manually by expert draftsmen.
The process of Structural Steel Detailing is time consuming and strenuous, with accuracy being of utmost importance.
A small mistake in these drawings & data files can lead to complications at the site while assembling and will also blow up the cost if any steel member needs to be re-fabricated / field modified due to a mistake in design or due to a detailing error.
With hundreds of skilled workmen waiting for the drawings with expensive equipment at the site, the drawings are always required urgently, creating immense pressure and tension on those responsible for producing the drawings.