The rebar bend test is a mill test in which a sample of bar is bent 180 degrees around a pin of specified diameter and must show no cracking on the outside of the bend. Under CSA G30.18, the Canadian standard for steel reinforcing bar, every grade must pass it, with the pin size set by the bar size and grade. The result is reported on the mill test report for each heat, which is how fabricators, contractors and engineers know the bar can be bent into hooks, stirrups and ties without cracking.
This post explains what the test checks, how it differs from the other numbers on a mill test report, how to find the result for the bar on your site, and what people usually mean by "bending strength" and "bending capacity".
What the bend test actually checks
Reinforcing bar is bent constantly: hooks at the ends of bars, stirrups and ties, L-bars at footings and dowels. Bending stretches the outside of the bar well past its yield point. Steel with poor ductility, or with surface defects from rolling, cracks on the outside of the bend instead of stretching.
The bend test is a direct check of that behaviour:
- A sample is taken from the heat (the batch of steel melted and rolled together).
- It is bent 180 degrees around a pin whose diameter is a set multiple of the bar diameter for that size and grade.
- The outside of the bend is inspected. Any cracking on the outside of the bent portion is a failure.
It is a pass or fail test. There is no "bend test strength" number. A heat that fails does not get certified to the standard.
The pin sizes differ between grades. The weldable W grades (400W and 500W) are tested around tighter pins than the regular R grades for most sizes, and larger bars are tested around larger pins relative to their diameter. Our post on rebar grades in Canada has the pin and elongation table by size and grade.
The bend test alongside the other mill tests
A mill test report carries several results. Each answers a different question:
| Test or value | What it tells you | Reported as |
|---|---|---|
| Yield strength | The stress at which the bar starts to deform permanently; the number in the grade name | MPa, with a minimum (and a maximum for W grades) |
| Tensile strength | The stress at which the bar fractures | MPa, with a minimum |
| Elongation | How much a marked length of bar stretches before it breaks | % over a 200 mm gauge length |
| Bend test | Whether the bar can be bent tightly without cracking | Pass or fail |
| Chemistry | Carbon, manganese and other elements, plus carbon equivalent for W grades | % by weight |
Elongation and the bend test both measure ductility, but in different ways. Elongation measures how far the whole bar stretches in tension. The bend test checks the local, very high strain on the outside of a tight bend, where surface quality matters as much as the steel's chemistry.
The minimum elongation values in CSA G30.18, as summarized in the RSIC Manual of Standard Practice, show how much more ductility the W grades must have:
| Bar size | 400R | 500R | 400W | 500W |
|---|---|---|---|---|
| 10M | 10% | 9% | 13% | 12% |
| 15M, 20M | 10% | 9% | 13% | 12% |
| 25M | 9% | 8% | 13% | 12% |
| 30M, 35M | 8% | 7% | 12% | 10% |
| 45M, 55M | 7% | 6% | 12% | 10% |
These values are from the 2009 edition of G30.18 (reaffirmed in 2019) as reproduced by RSIC. If your specification names a different edition, the engineer will confirm which values apply. Our post on how rebar is made walks through where these tests sit in the production process.
How to find the bend test result for your bar
Every bundle of rebar from a mill or fabricator carries a tag. The tag links the bars to a heat number, and the heat number links to a mill test report. To check a delivery:
- Read the heat number on the bundle tag, or the fabricator's tag that references it.
- Match it to the mill test report supplied with the shipment or available from the supplier.
- Check the standard and grade on the report, for example CSA G30.18 grade 400W, against the grade on the drawings.
- Look for the bend test result. Reports usually show it as pass, OK or acceptable.
- For W grade bar, confirm the carbon equivalent is reported and within the limit, since that is what makes the bar weldable.
RSIC notes that mill test reports are provided for each shipment and include yield, tensile, elongation and bend test results, with reference to the standard the producer certified the bar to. If your specification calls for mill certificates as a submittal, this is the document that goes in the package.
The bar's rolled-on markings also help on site. Canadian bar carries rolled-on identification marks for the mill, the size and, for W grades, the grade, repeated every metre or so along the bar. R grade bar has no letter rolled on, so a missing W is itself a clue.
"Bending strength" and "bending capacity": three different things
Searches for rebar bending strength or bending capacity usually mean one of three things, and they get mixed up:
1. Can the bar be bent without damage? That is the bend test and the minimum bend diameters. A bar bent once, cold, around at least the minimum bend diameter in CSA A23.1 is not weakened in any way that matters to the design. Bending too tightly, rebending or straightening is what causes damage, which our post on whether bending rebar weakens it covers in detail. The finished bend diameters by size are in our metric rebar bending chart.
2. How much load can a reinforced beam or slab carry in bending? That is the member's flexural capacity. It is calculated by the structural engineer under CSA A23.3 from the concrete strength, the depth of the member, the area of steel and its yield strength. It is a design question, not a property of the bar, and no field test or chart replaces it.
3. How big a bar can a bending machine handle? That is the bender's rated capacity, set by the manufacturer for a maximum bar size and strength. Shops run machines sized for the bars they bend. If you are renting a bender, check the rating against both the bar size and the grade; our post on renting a rebar bender vs ordering pre-bent bar covers what to check.
When bend testing happens after the mill
In normal practice nobody repeats the bend test after the bar leaves the mill. The mill test report is the evidence. Extra testing comes up in a few situations:
- Unidentified bar. Bar with no tag or no traceable certificate, such as material left over from another job, cannot be shown to meet the standard. The engineer may reject it or require samples to be tested by an independent laboratory.
- Imported or substituted bar. Bar made to a different standard, such as ASTM A615 or A706, has its own grades and bend test requirements. Substituting it for G30.18 bar is the engineer's decision, not the supplier's.
- Cracking during fabrication. If a shop sees cracks on the outside of correctly made bends, the heat is set aside and the supplier and mill are involved. Bends made to the correct diameter on certified bar should not crack.
- Investigations. After a failure or a dispute, a testing lab may run tension and bend tests on samples taken from the structure or from stock.
Do not confuse any of this with the bend tests in welding certification. Welder qualification tests bend a welded coupon to check the weld for defects. That is a test of the welder and procedure, not of the reinforcing bar; our post comparing CWB and AWS certification explains those.
What it means on site
The bend test is the reason a properly made bend is trustworthy. It is not a licence to bend bar any way you like:
- Bend around the right diameter. The test pin is a test condition. The bend diameters you fabricate to come from CSA A23.1 and the drawings.
- Bend once. Straightening and rebending a bar is not covered by the test and can crack it.
- Do not heat bar to bend it unless the engineer has approved a procedure.
- Watch the temperature. CSA A23.1 limits bending in cold conditions; ask the engineer before bending outdoors in an Ontario winter.
- Keep the paperwork. Mill test reports and tags are the only record of what is in the concrete once it is poured.
Certified bar, bent to your bar list
We supply rebar from 10M to 55M, sheared and bent in our shop to the shapes on your bar list, tagged and bundled by mark. If your specification calls for mill certificates as a submittal, tell us when you request the quote. We also prepare bar lists and placing drawings from your structural drawings and supply GFRP bar. Send your drawings or bar list for a free quote, or see our rebar products.
Frequently asked questions
What is the bend test for rebar?
A sample of bar from the heat is bent 180 degrees around a pin of a specified diameter. It passes if there is no cracking on the outside of the bent portion. The pin size depends on the bar size and grade, and the result is reported on the mill test report.
Who does the rebar bend test?
The producing mill tests samples from each heat as part of certifying the bar to CSA G30.18 (or ASTM for US bar). Fabricators and contractors do not normally repeat it; they rely on the mill test report traced through the heat number on the bundle tag.
Is the bend test the same as bending strength?
No. The bend test is a pass or fail check of ductility, showing the steel can be bent tightly without cracking. The bending strength of a concrete beam or slab is a design value worked out by the engineer from the concrete, the bar area and the yield strength.
Do W grade bars have a different bend test?
Yes. Under CSA G30.18 the weldable W grades are tested around tighter pins than the R grades for the same bar size, and they also have higher minimum elongation, because they are intended for uses where bending and ductility matter.
