The shape of the stirrup follows the layout of the vertical bars: round columns and piers, where the bars sit on a circle, get circular ties (hoops) or spirals, and square or rectangular columns get rectangular ties. CSA A23.3 (2004 edition) allows a complete circular tie where the bars are arranged around a circle, provided its ends are lap welded, bent at least 135 degrees around a longitudinal bar, or otherwise anchored within the core. A square tie in a round pier is a poor fit unless the engineer has detailed it that way, because it pulls the bars toward the centre and leaves uneven cover.
Strictly, the bars wrapping a column are ties, and stirrups are the shear bars in beams. On site and in searches the words are used interchangeably, so this post uses both. Our post on stirrups vs ties explains the difference.
The options at a glance
The RSIC Manual of Standard Practice gives each common shape a type code that appears on bar lists:
| Shape | RSIC type | Used in | How it closes |
|---|---|---|---|
| Square or rectangular tie | T1 (135° hooks) or T2 (90° hooks) | Square and rectangular columns, pilasters, piers | Hooks at a corner |
| Circular hoop, lapped | T3 | Round columns, sonotube piers, caissons | Lap equal to a Class B tension splice |
| Circular tie with hooks | T3A | Round columns and piers | 135° hooks around vertical bars |
| Spiral | SP, SP1 | Spirally reinforced columns and piles | Continuous, with extra end turns |
| Crosstie | T5, T9 | Larger rectangular columns, to support middle bars | Hooks at each end |
Our guide to rebar bending shape codes covers the full list.
What CSA A23.3 asks of each
The column tie rules in CSA A23.3 apply whatever the shape. In the 2004 edition (the version in our reference library; your engineer designs to the edition the project uses):
- Tie size. Longitudinal bars 30M and smaller are enclosed by ties at least 30% of the diameter of the largest longitudinal bar. Bars 35M, 45M and 55M, and bundled bars, need ties of at least 10M.
- Tie spacing. The spacing may not exceed the smallest of 16 times the smallest longitudinal bar diameter, 48 tie diameters, the least dimension of the column, and 300 mm where bars are bundled. It is reduced further for concrete above 50 MPa.
- Lateral support of bars. In tied columns, every corner bar and alternate longitudinal bar must sit in the corner of a tie with an included angle of no more than 135°, and no bar may be more than 150 mm clear from a supported bar. This is why wide rectangular columns need crossties or extra ties.
- Circular ties. Where bars are around the periphery of a circle, a complete circular tie may be used with its ends lap welded, bent at least 135° around a longitudinal bar, or otherwise anchored in the core.
- Minimum number of bars. Four bars within rectangular or circular ties, three within triangular ties, and six within a spiral.
- Spirals. A minimum spiral bar diameter of 6 mm, a pitch no more than one sixth of the core diameter, and clear spacing between turns of 25 mm to 75 mm, with the amount of spiral steel set by a formula in the standard.
A circular tie has a structural advantage that falls out of these rules: because every bar on the circle bears against a continuous curve, there are no "unsupported" bars between corners. A rectangular tie only gives full lateral support at its corners, which is why bars in between need crossties once the 150 mm rule is exceeded.
Square ties in round piers: why it's a poor fit
It is tempting on a residential job to put square ties in a sonotube pier, because square ties are easy to bend. The geometry works against it:
- The bars move inward. A square that fits inside a circle has its corners on the circle and its sides well inside it. Vertical bars held in the corners of a square tie end up closer to the centre than they would on a circular tie of the same outside size.
- Cover is uneven. The corners of the square set the cover, so the sides of the tie sit deep inside the concrete and the cover around the pier varies.
- Less confinement. A square tie confines a smaller, square core instead of the full round core.
- Harder to place. A square cage can rotate in a round tube and catch on the form.
If the drawings show square ties in a round pier, place what is shown, because the engineer may have reasons. If they show circular ties, do not substitute square ones without written approval. Our post on rebar in sonotubes covers how typical piers are laid out and how to work out tie diameter from the form size and cover.
Circular ties vs spirals
Both suit round members, but they are not interchangeable:
| Circular ties (hoops) | Spirals | |
|---|---|---|
| Form | Separate rings at a spacing | One continuous helix at a pitch |
| Confinement | Good | Highest; used in spirally reinforced column design |
| Code basis | Tie rules for spacing and size | Spiral rules for pitch, clear spacing and steel ratio |
| Placing | Rings tied to verticals at marked spacing | Opened to pitch and held with spacers or ties |
| Splices | Each ring lapped or hooked | Spliced only where needed, as detailed |
| Common in | Ordinary round columns, sonotube piers, caissons | Columns and piles designed as spirally reinforced |
A spiral is chosen at the design stage, because a spirally reinforced column is designed differently from a tied one. Swapping a spiral for hoops, or the reverse, is the engineer's call.
RSIC practice for spirals includes making the spiral 80 mm smaller than the column's outside diameter unless shown otherwise, adding one and a half extra turns at the top and bottom, and splicing with a tension lap of at least 50 bar diameters plus a 90° hook around a vertical bar at the free end. Our post on bending rebar into circles, hoops and spirals covers spiral fabrication, minimum diameters and tolerances.
How each is fabricated and ordered
Rectangular ties are bent from straight bar on a stirrup bender: four bends plus hooks. They are ordered by out-to-out dimensions, the hook type (90° or 135°) and the bar size. Getting the out-to-out size right is the main source of errors; our guide to calculating stirrup cut length shows how dimensions turn into a bar length.
Circular ties are rolled to a diameter in the shop. They are ordered by outside diameter, bar size and whether they close with a lap (T3) or 135° hooks (T3A). Small hoops are limited by the minimum bend diameter for the bar size, so very small diameters in larger bar may not be practical. Bending accurate hoops by hand is slow, and inspectors check diameter, lap and spacing.
Spirals are ordered by outside diameter, pitch, height or number of turns, bar size and any spacers the engineer has specified.
For all three, put the member mark on the order so ties for different columns or piers are bundled separately. Our post on custom rebar stirrups lists what to include.
Which shape for which member
| Member | Usual tie shape | Notes |
|---|---|---|
| Square or rectangular column | Rectangular ties, plus crossties as needed | Corner and alternate bars supported |
| Round column | Circular ties or spiral | Spiral if designed as spirally reinforced |
| Sonotube pier (deck, porch, post) | Circular ties, where ties are specified | Follow the drawings; some small piers have no ties |
| Caisson or drilled pier | Circular hoops or spiral in a prefabricated cage | Cage lifted in as a unit |
| Pilaster or wall end | Rectangular ties | Often tied into the wall steel |
Ties and hoops bent to your drawings
We bend rectangular ties, circular hoops and other stirrup and tie shapes in our shop from your bar list or drawings, tag them by member and deliver them with the vertical bars and dowels across the GTA and Ontario. If you do not have a bar list, we can prepare one from your structural drawings. Send your drawings for a free quote, or see our services.
Frequently asked questions
Can you use square stirrups in a round column or pier?
Only if the engineer has detailed it that way. Round columns and piers normally use circular ties or spirals because the vertical bars sit on a circle. A square tie inside a round form pulls the bars toward the centre and leaves uneven cover, so follow the drawings and ask before substituting.
What is the difference between a circular tie and a spiral?
A circular tie is a single closed ring, repeated at a set spacing up the column. A spiral is one continuous helix at a set pitch. Spirals give more confinement and are used in spirally reinforced columns designed for them; circular ties are simpler to place in ordinary round columns and piers.
How are circular rebar stirrups closed?
Either with a lap, where the two ends overlap by a tension splice length, or with 135 degree hooks around a vertical bar. CSA A23.3 (2004) allows a complete circular tie where the ends are lap welded, bent at least 135 degrees around a longitudinal bar, or otherwise anchored in the core.
How many vertical bars does a round column need?
Under CSA A23.3 (2004), at least four longitudinal bars within rectangular or circular ties, and at least six within a spiral. The engineer sets the actual number and size.
