How to read a structural steel drawing
Homeowners and builders are regularly handed a steel drawing and expected to act on it. Once you know the conventions, most of it is readable.
Section callouts
A note like 254x146x31 UB S355 gives you almost everything: a universal beam 254mm deep, 146mm wide, 31kg per metre, in grade S355 steel. UC means universal column, PFC a parallel flange channel, SHS and RHS square and rectangular hollow sections, and EA or UA equal and unequal angle.
S275 and S355 are steel grades. S355 is stronger, so a design using it cannot be substituted with S275 of the same size.
Levels and datums
Steelwork drawings work from a datum, often finished floor level of the ground floor, with everything else given as a level relative to it. Soffit level means the underside of the beam, which is normally what determines your ceiling height.
Confusing structural and finished levels is the single most common error, because floor build ups can be 100mm or more.
Connections, bolts and welds
Bolt callouts give quantity, diameter, grade and length, for example 4 no. M20 grade 8.8. Weld symbols sit on a reference line with the symbol shape indicating the weld type and the number indicating the leg length, with a flag meaning a site weld.
You do not need to interpret these to a fabricator's level, but knowing that a symbol means a specific, sized weld explains why connections are priced the way they are.
Notes are part of the design
General notes usually carry the padstone requirements, the corrosion protection specification, the fire protection requirement and the execution class. These are frequently skipped and they are where the cost drivers hide.
If anything on your drawing is unclear, send it to us. We read these every day and will tell you what it means before you order.
Want this priced for your own job? Send us your drawings or a photo and we will come back with a fixed price, usually within one working day.
Common questions
Need this done properly? Talk to the workshop.
Send us drawings, a sketch or a site photo. We come back with a fixed price and a firm lead time, usually within one working day.