Learning how to read structural drawings is where most people give up. In a design package the architectural drawings are the easy part; the structural set is not. The reason is not that it is harder, but that it is a different language. Architectural drawings describe what you will see. Structural drawings describe what sits inside the concrete, using conventions nobody guesses on their own: what 4Ø16 means, why beams are drawn dashed, what the number in a150 is telling you.
This article explains how to read structural drawings for reinforced concrete, in the order an engineer actually works through a new package. From the general notes — the sheet that decides how every other sheet is read, and which almost no guide mentions — through to the bar schedule. It ends with seven common misreadings, and a short section for anyone facing a steel structure set.
What a structural drawing set contains
A structural set for an ordinary building is usually ordered from the ground up, matching the sequence of construction.
| Group of sheets | Content | Question it answers |
|---|---|---|
| General notes | Materials, conventions, cover, anchorage and laps | Under what rules is this whole set read |
| Foundation plan | Pile caps, tie beams, piles | What is the building standing on |
| Foundation details | Section through each foundation type, reinforcement | How much steel in each footing, arranged how |
| Framing plan per floor | Columns, beams, slabs on each level | Which members are on this floor, and where |
| Slab reinforcement plans | Bottom bars, top bars, hogging bars, extra bars | What steel goes in each panel, in which direction |
| Beam and column details | Sections and bar bending along the span | What is inside each member |
| Staircase | Stair flight, landing beams | How the stair spans, and where it anchors |
| Construction details | Lintels, wall ties, canopies, gutters, water tank, lift core | The small members the plans do not show |
| Bar schedule | Mark, shape, length, number of bars | How much steel to buy and cut |
The reading order runs against most people's instinct: do not open a detail sheet first. Read the general notes, then the plan, so you know where each member sits and what it is called. Only then look up the detail by name. Opening the beam details without knowing which grid line that beam is on leaves you with information you cannot place.
A full package also has architectural and services drawings alongside. How to read construction drawings covers the order for the whole package; this article goes deep on the structural part only.
General notes: the sheet that decides how the set is read
This is the most skipped sheet, and the one that causes the most misreadings. It usually sits at the front of the structural set, is all text with no drawings, so beginners flick past it. Yet every number on the sheets that follow is interpreted through it.
Four groups of information deserve careful reading.
Concrete. Written as B20, B22,5, B25 — the compressive strength class in current Vietnamese notation. Older packages and renovation drawings still use the grade form M250, M300. The two notations do not convert one-to-one, so when pricing the work, keep whatever the drawing says rather than converting it yourself.
Reinforcement grade. Written as CB240-T, CB300-V, CB400-V under TCVN 1651-2:2018. The letter T marks plain round bar, V marks ribbed bar, and the number is the yield strength in MPa. Older packages use AI, AII, AIII, which correspond roughly but not exactly to CB240, CB300 and CB400 — so any substitution has to go back to the designer.
Concrete cover. The distance from the outside face of the concrete to the outside face of the reinforcement, given in millimetres. The general notes usually give a small table by member type: foundations in contact with soil get more, internal slabs less. This number decides the true cut length of every bar, and it is the most common source of error in quantity take-off.
Anchorage and lap lengths. Written as 30d or 40d, meaning 30 or 40 times the diameter of that bar. For a Ø16 bar, 30d is 480 mm. On later sheets a lap is often noted only as "lap per general notes" — skip this sheet and you cannot work out the lap at all.
Beyond those four, the general notes set the unit of measurement and the rounding convention. Vietnamese structural drawings are almost always in millimetres. And this sheet carries the single most important sentence in any package: written dimensions govern over dimensions scaled from the drawing. When the number and the picture disagree, trust the number.
Reading the foundation plan: caps, tie beams and piles
The foundation plan is the first sheet with a drawing on it. Three families of objects appear.
Pile caps or pad footings are the concrete blocks under each column, marked M1, M2, Đ1 and so on. On plan they are rectangles under the column positions, with dimensions and a mark. That mark is what you use to find the matching detail sheet.
Tie beams connect the caps to each other, marked GM or DM. They keep the foundations from settling independently and carry the ground-floor walls. On plan they appear as narrow strips running between caps.
Piles, where used, are small squares or circles inside the outline of the cap, numbered and usually accompanied by a pile setting-out table. The number of piles under a cap governs the size of the cap, so these two must agree when you cross-check.
This is also what session 2 of the drawing reading course starts with, because without the foundation plan you cannot trace the rest of the package.
The check to run on this sheet: match every pile cap against the column positions on the ground-floor framing plan. A column with no foundation under it means the package has a problem — and this is a real error, not a rare one.
Reading the framing plan: grid, columns, beams, slabs
Every floor has a framing plan. It is the sheet you use most, and the one to read slowest.
The grid is the coordinate frame of the whole building, numbered one way and lettered the other. Every member is located by grid reference, and every other sheet uses the same grid. Read a structural drawing without tracking the grid and you cannot cross-reference anything.
Columns appear as a cut section, usually solid or hatched, marked C1, C2 with the size as width by depth, for example 300×500.
Beams are drawn as two parallel lines, and the gap between them is the beam width. The line type tells you whether it is visible. What the slab hides is drawn dashed, which covers most internal beam faces. What can be seen is drawn solid: above all the outer face of the perimeter beams, because nothing covers it, so that line is the visible outline of the whole floor. Openings for stairs and services, and upstand beams above the slab, follow the same rule.
This is the single biggest source of confusion for anyone used to architectural drawings, where a dashed line means something else. Beams are marked D1, DP1 with the section, for example 220×400 meaning 220 mm wide and 400 mm deep, with the mark usually written along the beam.
Slabs are marked S1 (h = 120) — slab type 1, 120 mm thick. Panels with different reinforcement get different numbers.
On that one sheet, the marks are the route into the detail sheets. See D1 on the plan, look up D1 on the beam details. The full illustrated symbol tables are in Construction drawing symbols, in the structural section.
Reading a beam or column section: main bars against links
This is the core of a structural drawing, and the part that online material almost never explains.
In a beam or column section, reinforcement falls into two families with completely different jobs.
Main bars, also called longitudinal bars, run along the length of the member. On a section each one is cut through, so it shows as a solid dot. Count the dots and you have the number of bars. Main bars carry the principal forces: in a beam, the bottom bars take tension at mid-span, the top bars take tension over the supports.
Links, also called stirrups, are closed loops around the bundle of main bars, repeated along the member. On a section a link shows as a closed outline wrapped around the dots. Links hold the main bars in place and carry shear.
The loop must be closed: the two ends meet at one corner, and each is bent into a 135° hook turned into the concrete core. That small detail is what makes the link work — when the concrete cracks or spalls at the surface, the hooks are anchored in sound concrete inside, so the link cannot spring open. On a section the loop reads as closed, with two short diagonal strokes at one corner gripping the corner main bar on either side of it — one hook off the top leg, one off the side leg, both turned into the core. A link drawn as a plain closed rectangle with no hooks is a simplified sketch, not a construction detail.
The two are written in completely different ways, and this is the part to memorise:
| On the drawing | Read as | Applies to |
|---|---|---|
4Ø16 | Four bars, 16 mm diameter | Main bars — counted as a quantity |
2Ø18 | Two bars, 18 mm diameter | Main bars |
Ø8a150 | 8 mm bars at 150 mm centres | Links and slab bars — given as a spacing |
Ø8a100/200 | 100 mm spacing at the ends, 200 mm in the middle | Beam and column links |
The core distinction: main bars state how many bars, links state how far apart. The letter a is the spacing. Confusing the two notations causes most of the errors in steel quantity take-off.
Both Ø and ϕ mean diameter, used interchangeably depending on the office.
On standards, reinforcement presentation is covered by TCVN 6084:2012 – Construction drawings, representation of reinforcement, and working drawings for reinforced concrete by TCVN 5572:2012; both are current. In practice, though, most design offices draw to their own in-house conventions rather than following every line of the standard. The reason is simple: many of the standard symbols do not present well, and each office has its own habits. That is not wrong, as long as the package is consistent and has a legend.
The practical consequence: do not memorise one symbol set and apply it everywhere. The first thing to do with an unfamiliar package is find its legend and its general notes. What stays constant between offices is the structure — main bars counted, links spaced, plans pointing to details through member marks. What varies is the linework. Understand the structure and you can read anyone's drawings.
Slab reinforcement, stairs and construction details
These three groups are the ones beginners skip, and together they carry a large share of the total steel.
Slab reinforcement plans are usually kept separate from the framing plan, and split again into bottom steel and top steel — two sheets, or one sheet with two colours and two line types. Slab bars are given as a spacing, for example Ø10a200. Three things need attention: hogging bars over the supports, the top bars that run across the beam and stop, given with their extension length; extra bars around stair and service openings and where a wall sits directly on the slab; and the direction of the bars, because a two-way slab and a one-way slab are arranged quite differently.
The staircase has its own sheets: a stair plan, a section along the flight, and the flight detail. The flight is an inclined slab, so its bars run at that incline and anchor into the landing beams. Read this from the section along the flight, not from the plan, because the plan does not show the slope.
Construction details collect the small members the framing plan leaves out: lintels over openings, wall ties, canopies, roof gutters, the roof water tank, the lift core, and the details tying walls into columns. They are small but numerous, and together they are a significant part of the steel — missing this group is the most common error in a first take-off.
Reading the bar schedule
The bar schedule is the bridge between the drawing and the site, and the sheet an estimator uses most. It usually lists: bar mark, the shape of the bar after bending with the length of each leg, diameter, length of one bar, number of bars, total length, and mass.
Three things to do when reading it.
Match the mark to the drawing. Every bar in the schedule carries a mark, and that mark must be findable on a section or a bending diagram. A bar in the schedule that appears nowhere on the drawings, or the reverse, means the set is out of step with itself.
Check the length of one bar. The length in the schedule is the true length: cover deducted at both ends, hooks and anchorage added. If a length equals the overall size of the member, the schedule was compiled wrongly.
Check the total mass. Multiply total length by mass per metre for each diameter and add up, then compare with the total row. Fifteen minutes of arithmetic catches errors immediately.
For anyone pricing the work, the bar schedule is a direct input. What is quantity take-off? covers the mistakes made when carrying these numbers into a bill of quantities.
How steel structure drawings differ
Industrial buildings, pre-engineered steel structures and steelwork details use a separate set of conventions, so if what you are holding is a steel package, read it a different way.
Members are not described by a concrete section but by a steel section mark: I200 is an I-section 200 mm deep, H300×300 an H-section, L50×50×5 an angle with two 50 mm legs 5 mm thick, ☐100×50×2 a hollow section. In place of bars and links, the detail sheets concentrate on connections: gusset plates, bolts given as a count and a diameter such as 4M20, and welds with their own symbols for weld type and leg size.
A steel package also carries a layer that concrete work does not have: fabrication drawings, usually called shop drawings, produced for each individual member so the workshop can cut and drill it. Steel shop drawings from Tekla describes that layer.
Seven common misreadings
Skipping the general notes and the legend. You end up not knowing the cover, not knowing the lap length, and not knowing this office's conventions — every bar length you calculate afterwards is wrong.
Taking a dashed beam for an architectural hidden line. On a framing plan, a dashed line is almost always a beam under the slab.
Reading 220×400 the wrong way round. The convention is width by depth. Reversed, both the section and the concrete quantity come out wrong.
Confusing 4Ø16 with Ø16a4. The first is four bars, the second a spacing. This is the most expensive misreading in quantity terms.
Ignoring the closer link spacing at the ends. Taking only the wider mid-span spacing across the whole beam leaves out a significant amount of steel.
Not cross-checking between sheets. A column on the second floor needs a column below it and a foundation under that. A slab with a stair opening must show that opening in the same place on both the structural and architectural plans.
Trusting the picture over the number. A printed drawing may not be to scale after enlargement or reduction. In every package, the written dimension governs.
Frequently asked questions
If every office uses different symbols, which set should I learn?
Learn the structure, not the linework. Counted bars, spaced links, the way a plan points to a detail, the way a section is written — nearly every office shares these. For the shapes themselves, open the legend of the package in front of you.
Can someone without a construction background read structural drawings?
Well enough to understand what the building consists of and how the steel is arranged, yes, after a few guided sessions. Well enough to judge whether the design is correct, no — that needs structural analysis, not drawing-reading skill.
Is Ø8a150 different from Ø8@150?
No. The a form is common in Vietnam, @ comes from foreign documents. Both mean bars at 150 mm centres.
Why does the same beam show different sizes on different sheets?
Usually because several beams share a name on different floors, or because the package was revised and not all sheets were updated. Either way, ask the designer; do not pick a number yourself.
How long does it take to learn to read structural drawings?
To understand a package for an ordinary building, about six guided sessions plus a few packages of your own practice. To read quickly and spot contradictions between sheets takes real project work, usually measured in months.
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