CIVL1810 Chap.13 Drafting Structural Details in AutoCAD
Drafting Structural Details in AutoCAD
AutoCAD and Revit are the drawing tools of record here, backed by instructional videos and by weekly online consulting sessions for students wanting to draw better. AutoCAD comes from Autodesk, is in daily use across every engineering discipline, and produces both two and three dimensional drawings, with specialised extensions for structural detailing, advanced steel, civil engineering and architecture.
Every tutorial in the unit repeats the same opening sequence of drawing properties, units and layers before anything is drawn, and every drafting brief specifies its geometry completely, so what is assessed is whether the drawing says exactly that and nothing else.
What this chapter covers
- 01
AutoCAD as an Autodesk package producing two and three dimensional drawings across engineering disciplines
- 02
The four extensions the unit names for structural detailing, advanced steel, civil engineering and architecture
- 03
The interface split into the ribbon tool bar, the command line and the status bar
- 04
Starting a drawing and setting drawing properties so the file is unique and clear to collaborators
- 05
Setting units before drawing anything
- 06
Putting each kind of feature, each component and each trade on a layer of its own so unwanted things can be switched off
- 07
The architectural layer set of wall, dimensions, door, window and furniture
- 08
The structural layer set of concrete, dimensions, membrane, wall, sand, mesh and reinforcement
- 09
Draw commands from the ribbon and their command line shortcuts
- 10
The beam drafting brief with two beams fully specified by size, bar count and tie spacing
- 11
The structural plan brief converting an architectural plan with stated wall thicknesses and door widths
- 12
The steel connection brief with named sections, bolt standard, spacing, edge distance, plate thickness and gap
- 13
The concrete detailing brief regenerating edge and internal beam to raft foundation details
- 14
The isolated footing brief with stated footing dimensions, bar spacing in each direction and column size
Reading a reinforcement call up before drawing it
- +1Geometry and main bars. 450 by 300 gives the two cross sectional dimensions, and you must establish which is vertical before drawing. 4N24 bottom is four deformed bars of 24 millimetre nominal diameter in the bottom face, where a simply supported beam carries tension; 3N24 top is three of the same in the top face.
- +1Ties. N10 ties at 150 millimetres is a closed tie of 10 millimetre bar at 150 millimetre centres along the beam, closed with a 135 degree hook so that it cannot open once the surrounding concrete has cracked.
- +1Order of drafting, with the reason. Set drawing properties, units and layers first, then draw the outline on the concrete layer, then the tie offset from every face by the cover, then the main bars in the corners of the tie, then the dimensions on the dimension layer. The tie is drawn before the bars because it defines cover on all four faces at once, so every bar then has exactly one correct position.
Key terms
- Layer
- A named grouping in a drawing file for a feature, component or engineering discipline. Layers let unwanted components be hidden, so one file can present as an architectural plan, a formwork plan or a reinforcement plan.
- Drawing properties
- The file information set at the very start of a drawing so that the file is unique and clear for all collaborating companies. It matters because a drawing is passed between architect, engineer, detailer and fabricator.
- Command line
- The keyboard entry point for AutoCAD commands, an alternative to the ribbon. Short aliases start common commands, which is what makes drafting fast under time pressure.
- Shop drawing
- A drawing produced to fabricate a specific element, in which every clearance, edge distance and plate thickness is stated. Any deviation from the stated values is an error rather than a design choice.
- Edge distance
- The distance from a bolt centre to the edge of the plate, specified in a brief as a multiple of the bolt diameter.
- Erection tolerance
- A deliberate clearance drawn between members, such as a small gap between an incoming beam and a column, so that fabricated steel can be swung into position and adjusted on site.
Drafting Structural Details in AutoCAD FAQ
Why does every tutorial set units and layers before drawing?
Because neither can be fixed properly afterwards. Geometry entered under the wrong unit assumption is not corrected by changing the setting later, and geometry drawn on the default layer has to be selected and reassigned object by object. Setting drawing properties first also matters for a different reason: a drawing is exchanged between several companies, and an untitled file with no author is a liability.
What is the point of the layer set in a structural drawing?
It makes a drawing set reviewable. If dimensions always live on the dimension layer and reinforcement always on the reinforcement layer, a reviewer can switch to the reinforcement view across the whole set and compare like with like. If they are scattered across whatever layer happened to be current, that comparison is impossible and inconsistencies survive to site.
How does a structural plan differ from the architectural plan it is generated from?
The architectural plan shows everything the occupant sees; the structural plan shows only what carries or transfers load. Load bearing exterior walls stay and are drawn to their true thickness; non structural partitions come off, although their weight remains as a superimposed dead load in the notes.
Openings in load bearing walls become a structural question of lintels and trimming members, and the furniture layer is switched off entirely.
Why are the briefs so completely specified?
Because the exercise is not a design exercise. Every dimension, bar size, spacing, bolt standard and clearance is handed to you, so what is being assessed is whether the drawing you produce says exactly that. That is also why consistency between related drawings is the stated requirement: a value that appears in two places must be the same value in both.
Exam move
Practise the setup sequence until it is muscle memory, because it costs a minute and prevents most of the problems that appear later: start the drawing, set properties, set units, create every layer you will need, then draw. Learn the two layer sets the tutorials define and be able to say which layers you would switch off to turn one file into a different drawing.
For the briefs, read each specification aloud and turn it into a list of dimensions before touching the software, since the assessment is fidelity to the brief. Finally, connect each brief back to the chapter that defined it, because a question about a drawing is usually a question about the element the drawing shows.
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