The most common bent rebar shapes have site names that describe what they look like: a U-bar is bent into a U with a flat back, a hairpin is a U with a tight rounded bend, a Z-bar has two bends in opposite directions, and a J-hook ends in a 180° hook. Each one does a specific job in footings, walls, slabs and beams, and each has a standard type on a Canadian bar list, so the shop bends it from a few leg dimensions rather than a sketch.
This guide covers what each shape is for and what to put on the order. For the numbering system behind the shapes, see our guide to rebar bending shape codes.
Why rebar gets bent at all
Straight bars do most of the work in concrete. Bends exist for three reasons:
- Anchorage. A bar that cannot run far enough past a critical point to develop its strength gets a hook or a bent leg instead.
- Continuity. Corners, intersections and changes in level would break the steel if every bar stopped. A bent bar carries the reinforcement around or through them.
- Confinement and position. Stirrups, ties, U-bars and standees hold other bars in place or wrap around them.
The engineer decides where bends are needed and shows them on the structural drawings. The detailer turns those details into bar marks with a shape type and dimensions, and the shop bends to that list. Under RSIC (Reinforcing Steel Institute of Canada) standard practice, all bent bar dimensions are measured out to out of the bar, and if a hook is called for without saying which kind, a 90° hook is assumed. Our post on standard rebar hooks covers the hook shapes in detail.
The common shapes at a glance
| Site name | What it looks like | Typical uses |
|---|---|---|
| L-bar | Straight bar with one 90° bend | Corner bars, footing dowels with a foot, top bars ending at a slab edge |
| U-bar | Two parallel legs joined by a straight back with square corners | Wall ends, slab edges, openings, two-piece closed stirrups |
| Hairpin | A U with a tight rounded bend | Edge confinement, open stirrups, anchoring bars at slab edges where detailed |
| Z-bar | Two bends in opposite directions, ends parallel | Step footings, slab drops, offsets in walls |
| J-hook | Straight bar ending in a 180° hook | Anchorage in short lengths, bars hooked over other steel |
| Offset (crank) | Two small bends that jog the bar sideways | Column bars lapping into a smaller column above |
| Standee | Bar bent in more than one plane to stand on the bottom mat | Holding up the top mat of thick slabs and mat footings |
Site names vary between crews, regions and countries. "Hairpin" on one job is "U-bar" on another, and a "Z-bar" to one crew might be called an offset or a step bar by the next. That is why the bar list uses type numbers, not names.
U-bars and hairpins
U-bars are the most common bent shape after L-bars, and they show up in several places:
- Free ends of walls and slab edges. A U-bar wraps the end of a wall or the edge of a slab, lapping with the horizontal bars on each face so the two layers act together at the edge.
- Around openings. Where a wall or slab opening interrupts bars, U-bars and extra straight bars are often detailed around it.
- Two-piece closed stirrups. The RSIC manual shows two lapped U-bars as one way to form a closed tie in a beam. Placing a U, then dropping the longitudinal bars in and closing it with a second piece, avoids springing a closed stirrup open, which can crack the bar.
- Grade beams and pile caps. U-shaped bars commonly wrap the top and bottom steel at the ends.
A hairpin has a rounded bend instead of square corners, so its legs usually sit closer together. The RSIC typical bar bends table lists hairpin-shaped stirrups as their own shapes, separate from the square-cornered U. If your drawings say "hairpin", check whether the detail shows a rounded or a square bottom, because the two shapes are dimensioned differently on the bar list.
The minimum bend diameter limits how tight any U or hairpin can be. Bend diameters grow with bar size, so a 20M hairpin is a much wider shape than a 10M one. The values are in our rebar bending chart.
Z-bars, offsets and step bars
A Z-bar has two bends turned in opposite directions, so the ends point away from each other and the bar looks like a Z on its side. Its main job is carrying reinforcement through a change in level:
- Step footings. Where a strip footing steps up or down a slope, the longitudinal bars are bent or lapped through each step. In Part 9 houses, the 2024 Ontario Building Code limits each step to a 600 mm rise with at least 600 mm between risers (Article 9.15.3.9), which keeps the step bars to a manageable shape.
- Slab drops and depressions. Bars run down into a depressed area, such as a recessed shower pan or a thickened slab edge.
- Wall offsets. Where a wall face steps, bent bars carry the vertical or horizontal steel through.
An offset or crank is a gentler cousin. It jogs a bar sideways so column bars can lap inside a smaller column above. Offsets have their own design limits in CSA A23.3, so they must be shown on the drawings.
RSIC advises designers that standard bending equipment bends bars in one plane. A shape that needs bends in two planes is costly to make, so it is often better to detail two simpler bars spliced together. If a step or offset detail produces a three-dimensional bar, expect your detailer to ask whether it can be split.
J-hooks, L-bars and standees
J-hooks end in a 180° hook. They are used where space for a straight anchorage is short, or where a bar hooks over another bar to hold it. Do not confuse them with J-bolts, which are threaded anchor rods for base plates and sill plates and are ordered as anchors, not rebar.
L-bars are the workhorse bend: one 90° leg. They are the corner bars in footings and walls, the feet on footing dowels, and the hooked ends of top bars at slab edges. In walls, RSIC notes that corner bars are the same size and spacing as the horizontal steel they splice with unless the drawings say otherwise. Our post on footing rebar laps and corner bars shows how the corner arrangements work.
Standees are bent in more than one plane so they stand on the bottom mat and support the top mat in thick slabs, rafts and mat footings. They are ordered on the bar list like any other bar, so they must be counted in the take-off.
Stirrups and ties are bent shapes too, with their own series of type numbers. They are covered in our guide to custom rebar stirrups and ties,, and circular hoops and spirals have their own tie and spiral types.
Ordering bent shapes so they fit
Most bent bar problems on site come from the order, not the bending. Before a bar list goes to the shop:
- Give every bent bar a type. Use the standard type that matches the shape, with each lettered dimension filled in. Anything non-standard needs a sketch.
- Dimension out to out. Leg lengths are measured to the outside of the bar. Dimensioning to the centreline or inside face makes U-bars and hairpins too small to fit around other steel.
- Allow for cover. A U-bar wrapping a 200 mm wall with cover on both faces has a back much shorter than 200 mm. Work back from the concrete dimensions and the cover shown on the drawings.
- Check the bend diameter. A tight hairpin in a large bar may not be possible at the minimum diameter, and a bigger bend changes the leg positions.
- Flag critical dimensions. If a shape has to fit inside a tight space, mark the dimension as critical so it is bent to a closer tolerance. Standard bending tolerances apply to everything else.
- Think about shipping and handling. Large U-bars and long Z-bars take up room on a truck and can be awkward to lift. Say if the site has access limits.
Field bending is possible for small bars with proper benders, but consistency suffers, and bars should not be heated to make a bend easier unless the engineer approves a procedure. Bending bars that are already cast into concrete needs the engineer's approval.
Get bent shapes cut and tagged to your bar list
Procut details bar lists from your structural drawings, then cuts and bends 10M to 55M bar to all standard shapes in our shop, tagged and bundled so your crew can place without sorting. We also supply fabricated dowels and stirrups.
Send us your drawings or bar list for a free take-off and quote, or see our rebar products and services for detailing, fabrication and delivery across the GTA and Ontario.
Frequently asked questions
What is a U-bar in rebar?
A U-bar is a bar bent into a U with two parallel legs joined by a straight back. It is used to wrap the free end of a wall or slab edge, to close a beam stirrup in two pieces, and to tie top and bottom layers together where the engineer shows it.
What is the difference between a U-bar and a hairpin?
On site the names are often used for the same bar. Strictly, a U-bar has square corners and a flat back, while a hairpin has a tight rounded bend, which is why hairpin-shaped stirrups have their own entries in the RSIC typical bar bends table.
What is a Z-bar used for?
A Z-bar has two bends in opposite directions so its ends point opposite ways. It carries reinforcement through a change in level, such as a step in a footing or a drop in a slab, where the drawings detail it that way.
What is a J-hook in rebar?
A J-hook (or J-bar) is a bar ending in a 180° hook, so it looks like the letter J. It is used where a bar needs anchorage in a short length. A J-bolt anchor rod is a different product and is not ordered as rebar.
Can U-bars and hairpins be bent on site?
Small bars can be bent on site with the right bender, but shop bending gives consistent bend diameters and leg lengths. Bars should not be heated to bend them, and bending partly embedded bars needs the engineer's approval.
