Dowel bars in a column are the bars cast into the footing, pedestal or slab below that stick up to lap with the column's vertical bars. They tie the two pours together and carry the column's force across the joint. Their length is two parts: an embedment into the footing, at least the compression development length of the bar, and a projection above the footing, at least the lap splice length on the drawings. Under CSA A23.3, the dowels crossing the joint must have an area of at least 0.5% of the column's gross area, and they cannot be more than one bar size larger than the column bars.
This guide explains how column dowels are sized, how their length is worked out, the common types, and how they are set so they end up where the column needs them. It applies to cast-in-place concrete columns. Steel columns sit on base plates and anchor rods instead; see setting steel columns on footings and pedestals.
What column dowels do
A concrete column is almost never cast in one pour with its footing. The footing goes in first, then the column is formed and poured on top. That leaves a cold joint at the base, and the vertical bars cannot simply run through it unless they were placed full length before the footing pour, which is rarely practical.
Dowels solve that. They are placed in the footing before it is poured, and the column bars are later lapped to them. Through the dowels, the joint can carry:
- Compression beyond what the concrete can carry in bearing at the joint.
- Tension, where wind, earthquake or uplift can pull on part of the column.
- Moment at the base, where the column is designed as fixed.
- Shear, together with friction and keying at the joint.
CSA A23.3 deals with this in its rules for transfer of force at the base of columns, walls and pedestals (Clause 15.9 in the 2004 edition we checked against; confirm the clause in the edition your engineer uses). In plain terms:
- The bars across the joint must transfer any compression that exceeds the bearing resistance of the concrete, plus any calculated tension.
- For cast-in-place columns, pedestals and pile caps, the bars across the joint must be at least 0.005 times the gross area of the supported member, even where calculations need less. For a 400 × 400 mm column, that is 800 mm² of dowels: four 20M (1,200 mm²) would satisfy it, though in practice the dowels usually match the column bars.
- Dowels may not exceed the size of the vertical bars by more than one bar size.
- At footings, 45M and 55M column bars in compression only may be lapped to dowels no larger than 35M, with special length rules. Normally 45M and 55M bars cannot be lap spliced at all.
How long column dowels should be
Embedment into the footing
The part of the dowel inside the footing has to develop the bar, so it can transfer its force into the footing concrete. For a column in compression, that means the compression development length. CSA A23.3 calculates it from bar size, steel grade and concrete strength, with a minimum of 200 mm. The RSIC Manual of Standard Practice tabulates it. For Grade 400 bar in 30 MPa concrete:
| Bar | Compression development length |
|---|---|
| 15M | 280 mm |
| 20M | 340 mm |
| 25M | 440 mm |
| 30M | 530 mm |
| 35M | 630 mm |
Two consequences matter for anyone building the footing:
- A hook does not count in compression. A23.3 says hooks are not effective in developing bars in compression, so the straight vertical leg inside the footing must provide the length on its own. A footing that is too thin for that straight length is a design problem, not something the hook fixes.
- Tension changes the answer. Where the dowel must carry tension, the tension development length applies, and that is generally longer. A hook does help in tension, which is one reason engineers detail hooked dowels at columns with uplift or base moment.
Projection above the footing
Above the footing, the dowel laps with the column bars. In a column carrying compression, the lap is a compression lap splice. CSA A23.3 sets it at 0.073 × fy × bar diameter for Grade 400 bar (a longer formula applies above 400 MPa), and never less than 300 mm. The RSIC tables give, for Grade 400:
| Bar | Standard compression lap | With qualifying ties (×0.83) | Within a spiral (×0.75) |
|---|---|---|---|
| 15M | 440 mm | 370 mm | 330 mm |
| 20M | 590 mm | 490 mm | 440 mm |
| 25M | 730 mm | 610 mm | 550 mm |
| 30M | 880 mm | 730 mm | 660 mm |
| 35M | 1,030 mm | 850 mm | 770 mm |
The reductions only apply where the ties through the lap meet a minimum area in A23.3, or where the bars sit inside a spiral. Where the column bars can see tension, the lap becomes a tension lap: Class A or Class B depending on the stress and how many bars are spliced at one location. Those are longer, sometimes much longer. Seismic frames add their own rules about where laps can go. Our post on lap length and splice zones for beam and column rebar covers those cases.
Bottom line on length: dowel length = footing embedment + lap length (plus any hook). The engineer's drawings should state both the lap and the embedment. If they don't, ask before the bar list is made, because RSIC practice is that the detailer does not assume reinforcing that is not shown.
Types of dowel bars in columns
| Type | What it looks like | Where it fits |
|---|---|---|
| Hooked (L) dowel | 90° hook at the bottom, sitting on or tied to the footing mat | The most common column dowel; easy to support and tie |
| Straight dowel | No hook, held by a template or ties | Deep footings and pile caps where straight embedment is ample |
| Offset (cranked) bar | Bent to step inward so the bar above can lap | Column bars carried up through floors, with small changes in face |
| Separate dowel at a column change | Straight dowel added where the column face steps in more than 75 mm | RSIC detailing practice: the bars below stop and new dowels lap the bars above |
| Mechanical splice or dowel bar substitute | Coupler cast in, column bar threaded or connected later | Congested joints, or where protruding bars are a problem |
| Post-installed (drilled) dowel | Bar set in a drilled hole with an adhesive | Adding a column to existing concrete, by engineered design only |
Mechanical splices trade lap length for hardware; see rebar couplers vs lap splices. Post-installed dowels depend on the adhesive system, hole cleaning and embedment the engineer specifies; our guide on how long rebar dowels should be covers drilled-in dowels.
Note that "dowel bar" also means something different in pavement work: smooth, greased bars that let slabs slide at joints. Column dowels are deformed bars that are meant to bond.
Setting column dowels before the pour
Column dowels are small in number but expensive to get wrong. A dowel that ends up 75 mm out of position can mean a column that cannot be formed, bars bent on site, or a drilled-in fix the engineer has to design. Good practice:
- Use a template. The RSIC manual defines a template as a device used to locate and hold dowels. A simple plywood or bar frame at the top of the footing, matching the column's bar layout, holds every dowel at the right spacing and cover while the concrete goes in.
- Tie the hooks to the footing mat. Hooked dowels should sit on and be tied to the bottom mat, oriented the way the drawings show, with the vertical legs plumb.
- Add ties around the dowels. One or two column ties tied around the projecting dowels at the top of the footing keep them from spreading. In the finished column, A23.3 requires the first tie no more than half a tie spacing above the footing or slab.
- Check cover and orientation. Dowels are set to the column's cover, not the footing's. For rectangular columns, confirm which face is which before the pour.
- Check projection. Measure the projection against the lap length on the drawings. Short dowels are the most common column dowel problem, and they are hard to fix after the pour.
- Protect the ends. Exposed vertical bars are an impalement hazard; cap or cover them where Ontario's occupational health and safety requirements and your site safety plan call for it.
The same thinking applies to dowels from footings into walls, which are spaced along the wall rather than grouped; see footing to wall dowels.
Ordering column dowels
On a bar list, column dowels are their own marks, separate from the column verticals: bar size, grade, quantity, hook type and the two leg lengths. RSIC practice is to detail footing dowels at the same size and spacing as the vertical bars they connect to, unless the drawings say otherwise, and to bend offsets in the shop.
Because each dowel combines a footing embedment, a hook and a lap, they are a good item to have shop fabricated. A dowel bent on site with a short leg or the wrong hook is hard to fix once the footing is poured.
Getting column dowels detailed and bent
We detail bar lists and placing drawings from your structural drawings, then cut, bend and tag dowels, column verticals and ties in our shop, in sizes from 10M to 55M. Send us your drawings for a free take-off and quote, or see our rebar detailing and fabrication services.
Frequently asked questions
What are dowel bars in a column?
They are bars cast into the footing, pedestal or floor below a concrete column that project up to lap with the column's vertical bars. They carry the column's force across the joint between the two pours.
How long should column dowels be?
Two lengths add up: the embedment into the footing, at least the bar's compression development length, and the projection above it, at least the lap splice length the engineer specifies. For Grade 400 bar, the RSIC compression lap table gives 440 mm for 15M, 590 mm for 20M and 730 mm for 25M before any reductions.
Do column dowels need hooks?
Hooks are common because they sit on the footing mat and help hold the dowel in position, and they help where the dowel must carry tension. CSA A23.3 does not count hooks as effective for bars in compression, so the straight part still needs enough embedment.
Should column dowels be the same size as the column bars?
Usually. RSIC practice is to detail footing dowels at the same size and spacing as the vertical bars unless noted. CSA A23.3 also limits dowels to no more than one bar size larger than the vertical bars.
Can dowels be drilled in after the footing is poured?
Sometimes, using an approved adhesive anchoring system, but only where the engineer designs it. Cast-in dowels set before the pour are the normal approach for new columns.
