A structural drawing set compresses an entire building’s skeleton into a dozen sheets of lines, marks and abbreviations. Once you know the conventions, every sheet reads the same way. Here is the decoder.
The typical sheet set
- Footing / foundation layout — footing sizes, depths, and centreline dimensions.
- Column layout plan — every column’s position, orientation and mark (C1, C2…), on the structural grid.
- Plinth beam layout, then floor-wise beam & slab layouts.
- Column schedule — sizes and reinforcement of each column, floor by floor.
- Beam schedules / beam elevation details.
- Typical details — laps, stirrup hooks, staircase sections, sunken slabs.
- General notes — grades, cover, codes, and instructions that override everything else. Read this sheet first, not last.
Grids and marks: the addressing system
Structural plans are organised on a grid — letters one way, numbers the other. A column “at B-3” sits at the intersection of grid B and grid 3. All dimensions are to grid lines or member centrelines (c/c), not to finished wall faces — a routine source of site set-out errors when the architectural and structural sheets are mixed up.
Reading a column schedule
The column schedule is a table: one column mark per row (or column), one storey band per level. A typical cell reads:
Beam notation decoded
- “3-16Φ” = three bars of 16 mm. “Φ” (or #) = diameter.
- “THROUGH” bars run the full length; “EXTRA” bars are curtailed where marked.
- “2L” = two-legged stirrup; “@ 100 C/C” = spaced at 100 mm centre-to-centre.
- Closer stirrups near supports reflect higher shear there — do not “average them out” on site.
Sections, details and the abbreviation glossary
A section marker (X-X, Y-Y, A-A) on a plan means: cut here and look in the direction of the arrows; the corresponding section drawing shows what you would see. Detail bubbles (a circle with a number/sheet reference) zoom into a junction.
| Abbreviation | Meaning |
|---|---|
| C/C | Centre to centre |
| Ld | Development length |
| T & B | Top and bottom |
| EF | Each face |
| THK | Thick / thickness |
| FFL / SFL | Finished / structural floor level |
| PCC | Plain cement concrete (lean levelling course) |
| GFC | Good For Construction (the only revision you may build from) |
Three habits that prevent expensive mistakes
- Check the revision block first — building from a superseded sheet is the classic site disaster. Only GFC drawings are for construction.
- Cross-check structural against architectural at every opening, level change and sunken portion.
- When a dimension is missing or two sheets disagree, ask the engineer — never scale off the print.
Frequently asked questions
What does 2L-8Φ@150 C/C mean?
Two-legged stirrups of 8 mm diameter, placed at 150 mm centre-to-centre spacing along the beam.
What is a GFC drawing?
“Good For Construction” — the issued revision that has been cleared for building. Earlier revisions (tender, “for approval”) must not be used on site.
Why do stirrup spacings change along a beam?
Shear force is highest near the supports, so stirrups are closest there (e.g., 100 mm c/c) and relax toward midspan (e.g., 150–200 mm c/c). The spacing zones on the drawing follow the shear diagram.