CIVL1810 Chap.7 Reading Reinforced Concrete Drawings
Reading Reinforced Concrete Drawings
A drawing set is a system of cross references, and the Week 3 tutorial makes the point directly by asking for a numbered set of sections that must be consistent with each other. The plan is the most important drawing, usually at 1 to 100 and varying from 1 to 500 down to 1 to 50; grids are usually set by the architect and everything else is positioned relative to them.
A solid line marks the top of the slab stepping and the slab edge, a dashed line marks the soffit stepping, and the legend fixes the meaning of every other annotation. Reinforcement is not on the plan at all: columns carry a mark that points into a schedule, and the notes block carries the values that govern the whole sheet.
What this chapter covers
- 01
What a reinforced concrete drawing tells you, and which parts the architect normally sets
- 02
The structural plan as the most important drawing, and its usual and possible scales
- 03
Grid lines and grid dimensions as the positioning framework
- 04
Solid lines for the slab edge and for the top of the slab stepping
- 05
Dashed lines for the bottom of the slab, the soffit, stepping up or down
- 06
Beam annotations by depth and width
- 07
The legend: concrete thickness, slab step, wet area setdown, and penetrations requiring trimmer bars
- 08
Column and wall marks with over, under and over and under suffixes
- 09
Precast walls referred to the wall elevations
- 10
Suspended slab design notes: exposure classification, live loads, superimposed dead load
- 11
Serviceability limits expressed as span over 250 total and span over 500 incremental
- 12
Concrete strength specified as a minimum at 28 days unless noted otherwise
- 13
The column schedule: mark, size, vertical reinforcement, ties, type and concrete strength
- 14
General notes on formwork stripping at 80 percent of specified 28 day strength, or back propping after five days
Turning one plan annotation into a site instruction
- +1CW1/U is a load bearing concrete wall under the level shown, so it stops at this slab and continues below. The formwork carpenter forms a slab over it rather than a wall starter above it, and the steel fixer places no starter bars there.
- +1A dashed line marks a change in the bottom of the slab, the soffit, stepping up or down. That is a formwork instruction: the deck is built at two heights along that line, and any section drawn through the bay must show the step.
- +1Exposure classification B1 external is a durability requirement. It governs the concrete grade and the cover required, so it constrains both the concreter, who supplies the specified mix, and the steel fixer, who must achieve the cover with chairs and spacers.
Key terms
- Structural plan
- The most important drawing in a set, usually drawn at a scale of 1 to 100 and varying from 1 to 500 to 1 to 50 depending on what is being shown.
- Solid and dashed line convention
- A solid line marks the slab edge and a change in the top of the slab; a dashed line marks a change in the bottom of the slab, the soffit, stepping up or down.
- Over and under suffix
- A mark such as CC1 over, under, or over and under states whether a column or wall continues above the level shown, stops at it and continues below, or passes through.
- Trimmer bars
- Additional reinforcement placed around a penetration or void in a slab. The legend attaches the instruction to the void symbol, so a section cutting a void that shows no trimmers is drawing an element that would be rejected.
- Column schedule
- The table that lists, against each column mark, the size, the vertical reinforcement, the ties, the type and the concrete strength, so the plan need only carry the mark.
- Incremental deflection
- The movement of a slab after a chosen point in its life, typically after brittle finishes are installed, commonly limited to span over 500. It is a different limit from the total long term deflection limit of span over 250.
Reading Reinforced Concrete Drawings FAQ
Why do the tutorial sections have to be consistent with each other?
Because a drawing set is a system of cross references rather than a folder of pictures, and an inconsistency between two sections is a real defect. Two sections cutting the same beam must show the same depth, the same reinforcement and the same relationship to the slab. The reliable way to achieve it is to read the general notes first, write the governing values once, and check by cross reference rather than by eye.
What is the fastest way to get the line convention right?
Ask which surface is moving. A solid line means the top of the slab is stepping, so it is struck by the concreter and sets the finished floor level; a dashed line means the bottom is stepping, so it is built by the formwork carpenter and sets the deck. Getting the convention backwards makes every section drawn from that plan wrong in the same way, which is exactly what the tutorial task is designed to expose.
Which numbers live in the notes block rather than on the drawing?
The ones that govern everything on the sheet: exposure classification, live loads and superimposed dead load, the serviceability deflection limits, and the concrete strength specified as a minimum at 28 days unless noted otherwise. General notes also carry construction instructions, including when formwork may be stripped, which is a structural rule hiding in a notes block.
Why is column reinforcement not shown on the plan?
Because repeating it at every column would make the sheet unreadable and would create many places for the same value to disagree. The plan carries a mark, and the schedule carries the size, vertical reinforcement, ties, type and concrete strength against that mark. A steel fixer then works from one authoritative table rather than from dozens of annotations.
Exam move
Practise reading before you practise drawing. Take any structural plan and write out, in order, the governing values from the notes block, then the marks on the plan, then what the schedule says about each mark.
Learn the line convention with a physical cue, such as the deck is dashed because you cannot see the underside, and drill the over and under suffixes by sketching a section from a plan and checking which side of the slab the element lands on.
When you work the sections task, resolve every step before drawing anything and check by cross reference, comparing one beam that appears in two sections digit by digit rather than trusting your own earlier drawing.
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