Reading a structural steel drawing
Grids, marks and revisions. Enough to follow a steel drawing and know when you are looking at the wrong one.
Steel drawings are dense, but they are built from a few consistent conventions. Knowing them makes site conversations much faster.
The grid
Letters one way, numbers the other. Every column sits on a grid intersection, and every position on the job is described by it. "Column B4" is unambiguous in a way that "the one near the door" is not.
Piece marks
Every fabricated member carries a mark, painted or tagged, matching the erection drawing. Marks are how the right member reaches the right place. Two members that look identical may differ in hole position or plate thickness, which is exactly the kind of difference that is invisible until it will not fit.
Levels
Usually given relative to a project datum rather than as absolute heights. Steel levels are often stated as top of steel, which is not the same as the finished floor level above it — a routine source of confusion between trades.
Connection details
Usually drawn separately and referenced from the general arrangement. The GA shows where members go; the details show how they join. Both are needed, and a site working from only the GA is guessing at bolt counts.
The revision box
The most important part of the sheet. Revision letter, date, and what changed. A superseded drawing on site is worse than no drawing, because it looks authoritative. Before anything is fabricated or erected, confirm the revision in hand is the current one — and take old revisions away rather than filing them nearby.