A steel structure is an assembly of structural elements (beams, columns, floor, plates, roof members, side wall covering members etc) It contains Melbourne steel Fabrication members of various sizes and shapes and they are all connected to each other by bolting or welding.
The design engineer in his design drawing indicates the sizes of the members, the orientation, the member location in 3D space, and how they are to be connected to each other. He also indicates the exact material specification from among options available. He gives the overall bay / aisle dimensions of the building, the floor levels etc. He also indicates the paint specification.
This design drawing enables the contractor/fabricator/erector to assess the total volume of work, assess the material quantities for each member size, the time to execute the job, the difficulties and the complexities of execution and the resources and time required so that he can quote a fair price to execute it.
Once the contract is awarded, the contractor proceeds to execute the job but the engineer’s drawings are not good enough for him to start cutting the material to exact size, length, shape, and drill the bolt holes in the correct places to enable assembly with other connected members. He needs to “detail the structure”. He must prepare a fresh set of drawings for each structural element, indicating the shape, size, exact cutting length, the exact diameter and location of the connecting bolt holes, the details of the fixtures and locations, the detailed bill of materials listing all the materials required. Such a drawing is called a shop drawing, or a fabrication drawing, or manufacturing drawing. He then assigns a unique identifying tag (called erection mark) to each assembled piece and then ships them to the construction site where these fabricated pieces are unloaded with the identifying marks punched or painted on them. A new drawing called GA drawing (general arrangement drawing) also called Marking Plan, or Marking Elevation is prepared that indicates where each fabricated piece goes at the site and to which other fabricated member it is connected to.
These drawings are prepared by the contractor (in his drawing office) or offloaded to specialised agencies. During the past, they were painstakingly prepared by expert draftsmen but now Modelling software produces these drawings.
This entire process is called Structural Steel detailing and it is an essential and important part of the structural steel construction activity. It is time consuming, strenuous and accuracy is very important. A mistake in these drawings will cause difficulties at site in assembling them and will boost up the cost as the members may have to be prefabricated if there was a mistake in the drawing. These drawings are required urgently and those responsible for producing these drawings are always under tension as everybody will be putting pressure on them to hurry up, as hundreds of skilled workmen at site are waiting for the drawings with expensive equipment which cannot be kept idle.
In steel detailing, the detailer’s drawings covering the making of these steel pieces are called shop drawings. They identify the precise specifications for fabricating each member/piece of a structure.
The steel fabricator uses these drawings, (also called detail drawings) to produce these members. With steel detailing, comprehensive shop drawings may include for each piece:
Special fabricating instructions.
With steel detailing, once the steel fabricator produces the steel members, the steel detailer steps in again and produces the drawings for the erection of the steel members in the field. These are called erection drawings.
It is the construction site steel erector who refers to these drawings in the steel detailing process, in order to know how and where to build with the fabricated steel pieces. Included in the erection drawings are dimensional plans to identify the steel members, in addition to all work required on the site including welding, bolting, and installing masonry anchors.
Additional Duties and Responsibilities
For the detailer in the steel detailing process:
- Observes design drawing parameters and with industry standards like those of the American Institute of Steel Construction (AISC) and the American Welding Society (AWS).
- Presents his drawings to the structural engineer and/or architect for evaluation before their release to the fabricator.
- In cases where structural drawings have inadequate information, offers links subject to the sanction of the structural engineer.
- If the detailer is uncertain about any information which prevents him from completing the drawings, they send a request for information (RFI) to the relevant parties before continuing.
- Sends his drawing to another steel detailer (labeled the “checker”) for completeness and accuracy.
- To monitor changes during the drawing creation process, identifies the revisions by assigning an associated number or letter code in the drawing revision block.
- Must resolve any comments which may have come out of the checking and approval process.
Computer-aided drafting (CAD) has replaced manual drafting for the most part in steel detailing. The detailer using these systems generates his drawings on the computer, employing software designed for this purpose, and then prints them. Accordingly, in the skills needed for steel detailing, the detailer needs proficiencies in the use of computers and comprehension of the particular CAD software he will utilize.
The extensive steel detailing would include the following details for each part:
- Surface specifications
- Material requirements
- Manufacturing instructions
- Fabrication instructions
- Painting specification