Bending is where a good bar is most easily damaged on site. The rules are simple, and most of them are about what not to do.
Do
- Bend cold, at site temperature.
- Use a mandrel — the pin or roller the bar bends around — of the diameter the drawing or standard specifies.
- Use proper tools: a bar bending table or machine, not a hammer.
- Bend in one smooth motion.
- Follow the bar bending schedule for shapes and dimensions.
Don't
| Practice | Why it is harmful |
|---|---|
| Heating bars with a torch to bend | Destroys the heat-treated rim; leaves a weak zone |
| Bending sharply over an edge | Concentrates strain; can crack the bar |
| Rebending or straightening bent bars | Can crack or weaken the bar |
| Hammering bars into shape | Damages ribs and surface |
| Bending at a lap or weld | Weakens the joint |
Why Bend Radius Matters
A bar stretches on the outside of a bend. Too tight a radius stretches the outer fibres beyond what they can take, starting cracks you cannot see. Larger diameters need larger mandrels. Stirrups use smaller bars and smaller mandrels, but still need a proper former rather than a nail.
Starter Bars for Future Floors
When building G+1 now and the next floor later, column bars are left projecting above the roof. Common mistakes are bending them flat to keep them out of the way and straightening them years later. Leave them straight, protect them from rust, and plan their length for the lap they will need.
The Short Version
Cold, round a proper mandrel, once. No torches, no sharp edges, no straightening — and starter bars stay straight and protected.
