What Is Steel Detailing? Meaning, Decisions and an Example

Steel detailing is the work of turning a structural engineer's design into the exact information a fabricator needs to build every piece of a steel structure: the length of each member, every hole, cope, plate, bolt and weld, and a mark that says where each piece goes. The engineer decides what size the beams and columns are and what the connections must do. The detailer works out how each piece is actually made and how it fits to its neighbours, and records it on shop drawings the shop builds from and the erector installs from.

This is an introduction for builders, contractors and anyone new to the trade. If you are buying detailing or comparing fabricator quotes, our guide to steel detailing services in Canada covers the deliverables, review process and how to get a quote.

Steel detailing in plain terms

Three different jobs sit behind a finished steel frame, and the word "detailing" is easiest to understand by separating them:

• Design. The structural engineer sizes members and connections for the loads, under CSA S16 in Canada, and issues structural drawings and a specification. Those drawings show a beam as a single line with a size, such as W310x39, and an elevation.
• Detailing. The detailer takes that single line and turns it into a real piece of steel: its cut length, the holes at each end, the plates welded to it, the bolts that join it to the column, and the mark painted on it in the shop.
• Drafting. Drafting is producing the drawings themselves. Every detailer drafts, but detailing also needs trade knowledge: how a shop cuts and fits steel, how an erector lands a beam, and what clearances let it slide into place.

Put simply, design says what the structure is, and detailing says how each piece is made. Structural drawings never contain enough information to fabricate from, which is why detailing exists. The difference between the design drawings and the detailer's output is covered in shop drawings vs construction drawings.

What a steel detailer actually decides

Within the limits of the design, a detailer makes hundreds of small decisions on every job. The main ones:

• Member lengths. Grid dimensions run centre to centre. The detailer works back to the actual cut length of each beam, allowing for the column it frames into and a small erection clearance so it can be swung into place.
• Connection layout. For each connection shown or designed, the detailer sets out the plates, the number and spacing of bolts, gauge lines and edge distances, staying within the limits of the design and the standards.
• Copes and blocks. Where a beam frames into another beam at the same top elevation, the top flange has to be cut back (coped) to clear the supporting beam. The detailer sizes the cope.
• Shop vs field work. Most welding is better done in the shop, so the detailer usually arranges connections as shop-welded plates with field bolts. Where field welding is needed, it is shown clearly so the erector plans for it.
• Piece marks. Every shipping piece gets a unique mark that appears on the erection plan and on the steel itself.
• Shipping and handling. Long or heavy members may need a field splice, and the detailer locates it where the design allows. Lengths also have to suit trucking; see standard steel beam lengths and delivery limits.
• Interfaces. Anchor rods in concrete, embedded plates, openings for mechanical work, stair and railing supports, and connections to masonry or wood all have to line up with other trades' drawings.

Every one of those decisions is checked against the design drawings. Where the drawings are silent or contradict each other, the detailer does not guess: they send a request for information (RFI) to the design team.

A worked example: detailing one floor beam

Take a single floor beam on a small commercial building. The structural drawing shows a W310x39 spanning between two columns on a gridline, top of steel at a given elevation, with a note for shear connections to the column flanges.

Here is what the detailer turns that one line into:

1. Confirm the geometry. Check the grid dimension, the column sizes and their orientation (is the beam landing on a flange or a web?), and the top of steel elevation against the architectural floor build-up.
2. Choose the connection detail. Following the design, a shear tab is welded to each column flange in the shop, and the beam web is bolted to it on site. The detailer lays out the tab size, bolt count, bolt type (typically high-strength ASTM F3125 Grade A325 bolts on Canadian work), hole spacing and edge distances.
3. Work out the cut length. From the face of one column flange to the other, less the erection clearance at each end, gives the beam length to the millimetre.
4. Locate the holes. Holes in the beam web are dimensioned from the end of the beam and from the top flange, so they line up with the holes in the tab once the beam is at the correct elevation.
5. Add everything else on that beam. Holes or clips for framing beams coming in from the side, camber if the engineer specified it (see when to specify pre-camber), shear studs if the slab is composite, and the coating.
6. Mark it. The beam gets a piece mark, the shear tabs are shown on the column's own assembly drawing, and the erection plan shows exactly where that mark goes.

Multiply that by every beam, column, brace, plate and angle on a job, and you have a detailing package. The same thinking applies to a single basement beam and posts in a house: the detailer still has to land the beam at the right height, size the cap and base plates to the design, and make the posts the right length.

What a detailer is responsible for, and what they are not

Clear lines between the detailer, the engineer and the erector prevent most arguments on a steel job:

The key point is that a detailer is not a connection engineer, however good the software is. If a project delegates connection design to the fabricator, an engineer has to design those connections and the detailer draws them. Whether that engineer also seals anything is a separate question, covered in do shop drawings need an engineer's stamp in Ontario?

How steel detailing is done today

Most structural steel is now detailed in a 3D model of the whole structure rather than drawn sheet by sheet. Specialist detailing software lets the detailer place members and connections in the model, check for clashes, and then generate the 2D drawings, lists and machine files automatically. When a design change comes in, the model is updated and the affected drawings regenerate.

The outputs are broadly the same whatever the tools:

• Anchor rod (setting) plans for the concrete contractor.
• Erection plans and elevations showing every piece mark.
• Assembly drawings for each shipping piece.
• Single-part drawings for plates and fittings.
• Bolt lists and bills of material for purchasing and shipping.
• Machine files for automated cutting and drilling, where the shop uses them.

Those drawings go through review by the engineer and architect before the shop cuts any steel. The full submittal and review loop is described in steel detailing services in Canada, and how to check a set yourself is in how to review steel shop drawings.

Structural, miscellaneous and rebar detailing

"Detailing" is used for three related trades, and it helps to know which one someone means:

• Structural steel detailing covers the primary frame: columns, beams, bracing, joist and deck supports, and their connections. It is the subject of this post.
• Miscellaneous steel detailing covers stairs, railings, ladders, lintels and supports. The geometry is often fussier than the main frame and has to suit architectural finishes and building code rules for stairs and guards. See miscellaneous steel detailing.
• Rebar detailing produces placing drawings and bar lists for reinforcing steel in concrete. It works to different standards and produces different documents; see what is rebar detailing?

Why detailing matters to the person paying for the steel

Detailing is a small part of the total cost of a steel package, but it controls almost everything that follows it. A hole in the wrong place is found on site, with a crane and a crew waiting. A beam detailed short cannot be stretched. A missed connection for another trade becomes a field weld or an extra.

Good detailing shows up as:

• Fewer RFIs late in the job, because questions were asked early.
• Shop drawings that pass review with minor comments rather than a resubmission.
• Steel that goes together on site without reaming holes, cutting or shimming beyond normal tolerances.
• Anchor rod drawings delivered early enough that the concrete is not held up.

For a builder, the practical lesson is to send the detailer a complete, current set of drawings and answer their questions quickly. Drawings that arrive in pieces, or design changes after detailing has started, are the most common causes of delay. Our guide to the shop drawing process from IFC to fabrication walks through the timeline.

Detailing and fabrication under one roof

Procut Steel prepares shop drawings in-house, detailed so every piece fits the first time, and then fabricates, marks and delivers the steel to match. Engineering services are available for projects that need them, so ask us how connection design will be handled on yours. Send us your structural or architectural drawings and we will prepare a detailed take-off and quote, free of charge.

Send your drawings for a quote, or see our shop drawing and fabrication services.