Use a bent or hooked rebar dowel when the concrete it starts in is too shallow for a straight bar to develop, or when the dowel has to turn a corner to anchor into the reinforcement on the other side. A standard 90° or 180° hook develops a bar in a fraction of the straight length, which is why footing dowels are almost always L-shaped. Straight dowels suit deep pours and drilled-in work, U-shaped dowels suit slab edges and wall ends, and threaded dowels suit joints where nothing can project through the formwork.
This post is about choosing the shape. For how long each part of a dowel needs to be, see how long rebar dowels should be, and for the footing to wall joint in detail, see footing to wall dowels.
The common dowel shapes
| Shape | What it looks like | Typical use |
|---|---|---|
| Straight dowel (dowel pin) | A plain length of deformed bar | Deep pours, drilled-in dowels into existing concrete, joints between thick elements |
| L dowel (90° hook) | One 90° bend, a short leg and a long leg | Footing to wall, pier or column; slab to wall |
| 180° hooked dowel (J) | A tight U-turn at the embedded end | Where there is no room for a 90° leg, or the design calls for it |
| U dowel (hairpin) | Two parallel legs joined by a bend | Slab edges, wall ends, ties across a construction joint |
| Cranked (offset) dowel | Two bends that shift the bar sideways | Where the bars above sit on a different line from the bars below |
| Bent dowel at a set angle | Legs at a fixed angle, often 90° | Anchoring a slab into the wall it bears on |
| Threaded dowel | Bar with a coupler or threaded end | Formwork savers, crane openings, vertical pour joints |
All of these are made from ordinary deformed rebar. A smooth dowel bar in a pavement or slab-on-grade joint is a different product that lets the joint move, and the two should not be confused.
When a straight dowel is enough
A straight dowel works when both pours are deep enough for the bar to develop on each side of the joint. Under the CSA A23.3 simplified method, a straight 15M bar in 30 MPa concrete needs about 430 mm of embedment to develop in tension, so the first pour needs at least that depth plus cover.
Straight dowels are the normal choice for:
- Drilled-in dowels set in adhesive in existing concrete, where a bent bar cannot be inserted. The adhesive system and the engineer set the embedment.
- Thick elements, such as deep pile caps, mat foundations and thick walls, where there is room for the full straight length.
- Compression dowels in some column bases. Hooks do not help a bar in compression, so A23.3 does not count them for compression development.
The main drawback is length. A straight dowel needs its full development length on the embedded side, which is more than most house footings are deep.
When to use L dowels and hooked dowels
Hooks are the answer to shallow embedment. A standard hook develops a bar in a much shorter length than a straight bar: for a 15M Grade 400 bar in 30 MPa concrete, roughly 300 mm instead of 430 mm, before modification factors. That makes hooked dowels the default in:
- Strip and pad footings. The hook sits on the bottom mat, the long leg projects up to lap with the wall, pier or column bars. Typical footings are not deep enough for straight dowels.
- Slabs tied into walls or beams. A dowel cast in the wall and bent into the slab, or a slab bar hooked down into the wall, anchors the slab edge.
- Structural slabs bearing on foundation walls. In the 2024 Ontario Building Code, the Part 9 rules for reinforced slabs over cold rooms require the slab to be anchored to the foundation walls with 600 mm by 600 mm 10M bent dowels at not more than 600 mm on centre (Article 9.40.1.4).
90° or 180°? A 90° hook is the default. A 180° hook is more compact in one direction and is used where the 90° leg will not fit, or where the designer specifies it. The standard hook dimensions for each size are in our guide to standard rebar hooks.
Hooks have their own limits. The hook must fit inside the concrete with full cover on every side, so a 25M hook in a 300 mm footing may not work at all. In tight spots, engineers sometimes use headed bars (a bar with a forged or welded head), which CSA A23.3 recognizes as a way to anchor bars, or change the bar size.
U dowels, cranked dowels and other bent shapes
U dowels (hairpins) are two legs joined by a bend. They show up where a bar needs to anchor on both faces of a joint at once, such as at slab edges, wall ends and construction joints in thick slabs. A U-bar placed around the end of a wall or slab confines the edge as well as tying the pours together.
Cranked or offset dowels shift sideways between the two pours. They are used where the wall above is thinner than the one below, where a column changes size, or where the bars above sit on a different line. If the offset is large, the designer may prefer separate dowels instead of cranking the bars.
Dowels in more than one plane are hard to bend and hard to place. The RSIC Manual of Standard Practice notes that standard equipment bends in one plane, and recommends splicing separate bars where bends in more than one plane would be needed. If a dowel detail looks like it needs a three-dimensional bend, ask before it goes on the bar list.
Threaded dowels and formwork savers
Sometimes the problem is not anchorage but the formwork. A dowel projecting through a form means drilling the form for every bar, and projecting bars can get in the way of the next stage of work. The RSIC manual describes dowel bar substitutes and formwork savers for these cases, giving crane openings and vertical pour joints in walls as typical examples.
A formwork saver is a coupler fastened to the inside of the form, with its anchoring bar cast into the first pour. When the form is stripped, the coupler face sits flush with the concrete, and the continuing bar is threaded in when needed. Threading is a specialty item under RSIC practice, not part of standard fabrication, so tell your supplier early if your drawings call for threaded dowels.
Couplers and lap splices each have their place; our comparison of rebar couplers vs lap splices covers the trade-offs.
Field bending: when it is and is not acceptable
Bending dowels on site is common practice and common trouble:
- Bending cast-in dowels down and back up to clear formwork or traffic is something many specifications prohibit without the engineer's approval. Bending a bar that is already embedded in concrete can damage the bar and crack the concrete around it.
- Wet-setting, pushing bent dowels into fresh concrete after it is placed, often leaves them out of line, short of embedment and poorly consolidated. Set dowels before the pour unless the engineer approves otherwise.
- GFRP dowels cannot be field bent at all. Bends in glass fibre bars are made by the manufacturer before the resin cures. If your job uses GFRP, order every bent dowel as a factory shape; see GFRP stirrups and dowels vs steel rebar.
Shop bending to the RSIC bend diameters gives every dowel on a mark the same shape, so it lands where the drawing puts it.
Ordering bent and hooked dowels
Dowels are easy to get wrong on a bar list because the shape matters as much as the length. When you order:
- Give the shape and every leg, using the RSIC bend type and out-to-out dimensions, not just "L-bar 600 by 900".
- Show which leg is embedded and which projects, and the hook direction where it matters.
- Separate marks for different projections, such as walls of different heights or footings at different steps.
- Note coating with the prefix letter, such as C for epoxy-coated, because coated bars use larger bends.
- Tag by location so the right dowels end up in the right footing.
We fabricate rebar dowels, L-bars, hooks, U-bars and other bent shapes from 10M to 55M in our Erin shop, cut and tagged to your marks along with the rest of the order, and we supply GFRP rebar for jobs that need it. Send us your drawings for a free take-off and quote, or see our cut and bend services.
Frequently asked questions
When should rebar dowels be bent or hooked?
When the first pour is too shallow for a straight bar to develop its strength, such as a footing or slab, or when the dowel has to turn a corner to anchor into the reinforcement, such as a slab tied into a wall. A hook develops the bar in a much shorter embedment than a straight bar.
What is an L dowel?
An L dowel is a rebar dowel with a 90 degree bend at one end. The bent leg sits in the first pour, usually on the bottom mat of a footing, and the straight leg projects up to lap with the bars in the next pour.
What are threaded rebar dowels used for?
Threaded dowels, often called dowel bar substitutes or formwork savers, use a coupler cast flush with the form so nothing projects. A matching bar is threaded in after the forms are stripped. They suit places where cutting holes in forms is uneconomical or where projecting dowels would get in the way.
Can you bend a rebar dowel on site after it is cast?
Only where the engineer allows it. Project specifications commonly prohibit field bending of reinforcement without approval, and bending bars partly embedded in concrete can damage both the bar and the concrete. GFRP dowels cannot be field bent at all.
