Fiberglass (GFRP) rebar corners, L-bars, hooks and stirrups are made at the factory, not bent on site. GFRP bars are made with a thermoset resin that cannot be re-bent once it has cured, so every bent shape has to be on the bar list, made to order at the manufacturer's fixed bend radius, and delivered ready to place. The bent portion is also much weaker than the straight bar, which is why bent shapes have their own strength values and their own test under CSA S807.
This post walks through the common bent GFRP shapes, what limits them, and how to detail and order them so they fit the first time.
Why GFRP bends are made at the factory
Steel rebar is bent cold on a bender. The steel yields and keeps its new shape, and a wrong bend can often be corrected. GFRP is different:
- The resin sets the shape. A bent GFRP bar is formed while the resin is still uncured and then cured in that shape. Once cured, the bar is rigid and brittle in bending. Trying to bend it cracks the resin and breaks fibres.
- Fibres on the inside of the bend are compressed and kinked. That makes the bent portion weaker than the straight length. One manufacturer's data sheet states the bent portion retains more than 50% of the straight bar's strength; others publish their own guaranteed values for bent bars and tell designers not to use the straight-bar strength for bends.
- Field forming is limited to large curves. Some manufacturers allow straight bars to be sprung into large-radius curves on site, for example around a circular tank or ramp, within published minimum radii. That is a gentle curve held by the concrete, not a corner.
For Ontario provincial work, the construction specification goes further: field bending is not permitted and bent bars must not be cut in the field. Our explainer on fiberglass rebar codes, CSA S807 and S806 covers those specifications.
Common bent GFRP shapes
Most of the shapes used in steel detailing have a GFRP equivalent, with some limits:
| Shape | Also called | Typical use | Notes |
|---|---|---|---|
| 90 degree corner bar | L-bar, elbow | Wall corners, slab-to-wall connections, footing-to-wall | The most common GFRP bent shape; two legs at one fixed radius |
| Hooked bar | 90 degree hook, J-hook (180 degree) | Anchoring bar ends where straight development does not fit | Tail length and radius set by the manufacturer |
| U-bar | Hairpin, U-bend | Slab edges, wall ends, barrier walls, and paired as closed stirrups | Inside width must suit the fixed bend radius |
| Stirrup | Tie, link | Beams, columns, barrier walls | Often supplied as two overlapping U-bars rather than a closed loop |
| Spiral | Helix, continuous spiral | Round columns and piles, and some square ties | Made as one continuous piece |
| Bent dowel | Bent starter | Connections between pours | Ordered like an L-bar |
Our comparison of GFRP stirrups and dowels vs steel rebar looks at the design side of stirrups and dowels in more detail.
Bend radius, leg length and other limits
The biggest surprise for steel detailers is that GFRP bend radii are fixed by the manufacturer's tooling, and they are generally larger, relative to bar size, than steel bends.
Some examples of what manufacturers publish:
- Fixed inside radii by bar size. One manufacturer's data sheet lists a single inside bend radius for each diameter, grouped so that, for example, its 10 mm and 13 mm bars share one radius and its 22 mm and 25 mm bars share a larger one.
- Minimum radius as a multiple of diameter. Another manufacturer gives a minimum bend radius of 5.5 times the bar diameter.
- Maximum leg lengths. One manufacturer limits stirrup legs to about 1.5 m (60 in.).
- Shapes that turn one way. Bends should continue in the same rotational direction. Shapes that reverse, like Z-bars or "gull-wing" offsets, are described by one manufacturer as not very economical.
- Closed squares as pairs. Closed rectangular stirrups are best supplied as two U-bars or as a spiral.
What this means in practice:
- Small U-bars may not be possible. A U-bar whose inside width is less than twice the fixed inside radius cannot be made. Some sizes fall between the available radii.
- Corner bars sit differently. A larger radius moves the bar away from the corner of the form, which can affect cover. The designer and detailer should check cover at bends.
- Steel shape codes do not transfer directly. A shape detailed to a steel bend diameter may need to be redrawn to the manufacturer's standard bends.
Because these limits vary between manufacturers, detail to the specific product that will be supplied, and check shapes against that manufacturer's published bends before the bar list is approved.
Strength of the bent portion
CSA S807, the Canadian material specification for FRP reinforcement, treats bent bars as a product with its own requirements. It includes a dedicated test method for the strength of the bent portion, and bent bars are produced and checked in their own production lots.
For the designer, this means:
- Bent bar strength comes from the manufacturer's bent-bar data, not the straight-bar strength.
- Design of GFRP-reinforced concrete, including hooks and bends, follows CSA S806 for buildings or CSA S6 for bridges, not the steel rules in CSA A23.3.
- The lap between a bent bar's leg and a straight bar is designed for GFRP, which typically needs different lengths than steel.
None of this is something to work out on site. If the drawings show a GFRP hook or corner, the dimensions on the bar list are the dimensions you get.
Detailing and ordering bent GFRP
Bent GFRP shapes are made to order, so the order has to be right before production starts. A few practices help:
- Use GFRP drawings, not steel drawings. Bar sizes, spacing, laps and bend details differ. A job designed for steel needs a GFRP redesign before shapes are ordered.
- List every shape with bar designation, leg lengths, bend angle and quantity, using the manufacturer's shape codes where they exist.
- State how dimensions are measured. Out-to-out leg lengths are usual; make sure the bar list and the manufacturer use the same convention.
- Check shapes against the manufacturer's standard bends before approval, especially U-bars and stirrups in thin members.
- Order bent shapes first. Straight bars are often easier to source than shapes made for your order, so the bent shapes usually set the delivery date.
- Talk about spares. A wrong or damaged corner cannot be fixed with a bender. Agree how replacements would be handled and how long they would take.
- Keep one product per element. Diameters, designations and properties differ between manufacturers, so do not mix bars from different makers in the same element without the engineer's approval.
On site, bent GFRP is handled like straight GFRP: store it supported and protected, tie it securely so it does not float during vibration, and use non-metallic or coated ties. Our GFRP buyer's guide for Ontario covers lengths, lead times and handling, and GFRP rebar price in Canada explains what drives the cost of straight and bent bar.
Ordering GFRP shapes with your rebar
We supply GFRP rebar alongside straight and fabricated steel bar, detailed from your drawings and delivered across the GTA and Ontario. Send us the GFRP drawings and bar list and ask which bent shapes, sizes and lead times we can supply for your job. Request a quote, or see our rebar products.
Frequently asked questions
Can you bend fiberglass rebar on site?
No. GFRP bar uses a thermoset resin that cannot be re-bent once cured, so corners, hooks and stirrups are made at the factory. Some manufacturers allow gentle large-radius curves to be formed in the field within their published limits, which is not the same as bending a corner.
Is there a 90 degree fiberglass rebar corner?
Yes. 90 degree corner bars, also called L-bars or elbows, are one of the most common GFRP bent shapes. They are made to order from a bar list with the leg lengths and bar size, at the manufacturer's fixed bend radius.
Are bent GFRP bars as strong as straight bars?
No. The bent portion of a GFRP bar is much weaker than the straight portion, and manufacturers publish separate strength values for bent bars. CSA S807 tests the bent portion separately, and the designer accounts for it.
How are closed GFRP stirrups made?
Usually as two U-shaped bars that overlap, or as continuous spirals, rather than as a single closed rectangle. Manufacturers note that shapes which reverse direction, like Z-bars, are hard to make and uneconomical.
