An embed plate (or embedded plate) is a steel plate with anchors welded to its back that is cast into concrete so its face sits flush with the surface, giving steel a place to connect later. Beams, ledger angles, brackets, railings and equipment supports are welded or bolted to the exposed face once the concrete has cured. The plate itself is simple. What makes an embed work is the anchorage behind it, its position, and getting it into the forms before the concrete truck arrives.
What embed plates are used for
Concrete and steel meet all over a building, and embeds are one of the main ways to join them. Common uses include:
- Beam seats and connections where a steel beam frames into a concrete wall or core
- Ledger angles and shelf angles carrying floors, roofs or masonry along a concrete wall
- Stair and landing connections, where a steel stair stringer bears on or bolts to a concrete slab edge
- Railing and guard posts welded to plates at a slab or balcony edge
- Equipment supports, hangers, crane rail brackets and door frame anchors
- Edge angles cast along slab edges, pits and openings to protect the concrete corner
A related item is the steel angle embed: an angle with anchors on its back cast into the edge of a slab or curb, so one leg is flush with the top and the other with the face. It protects the edge and gives a weld point along its length.
Embeds are not the same as base plates. A base plate sits on top of the concrete and is held down by anchor rods cast below it, with grout between. An embed is part of the concrete pour itself. For posts, there is a third option, setting the steel directly in the concrete, compared in embedding steel posts in concrete vs base plates.
How an embed plate is anchored
The plate only works if the anchors on its back can carry the loads into the concrete. The usual anchor types are:
| Anchor type | How it works | Where it is used |
|---|---|---|
| Headed studs | Short round studs with a forged head, welded to the plate by stud welding | The most common embed anchor for shear and tension |
| Deformed bar anchors | Rebar welded to the plate, sometimes bent to hook into the concrete | Higher loads, or where the anchors must lap with the concrete's own reinforcement |
| Bent rods or straps | Plain bar or flat strap bent and welded to the back | Light embeds such as door frame and railing anchors |
| Angles or plates welded on edge | Steel lugs that bear on the concrete | Shear lugs for heavy horizontal loads |
Headed studs are welded with a stud welding gun, which welds the whole stud base in a fraction of a second. In the 2004 edition of CSA A23.3 we checked, a headed stud for this purpose is defined as one meeting CSA W59 or AWS D1.1, attached by stud arc welding. Welding rebar to a plate is a different matter: not every bar is suitable for welding, and the weld procedure has to suit the bar's chemistry. Our guide to weldable rebar in Canada explains the difference.
Anchorage to concrete is designed to the anchorage provisions of CSA A23.3, "Design of concrete structures" (the 2024 Ontario Building Code references the 2019 edition). The design checks several ways an anchor can fail:
- Steel failure of the stud or bar itself in tension or shear
- Concrete breakout, where a cone of concrete pulls out with the anchor, or a wedge breaks off toward an edge
- Pullout, where the head slides out without breaking a large cone
- Pryout, where short stiff anchors lever out a piece of concrete behind them under shear
- Side-face blowout for headed anchors close to an edge
Which one governs depends on the embedment depth, spacing, edge distance, concrete strength and whether the concrete is cracked. That is why embed design belongs to the engineer, not the shop.
Edge distance and spacing
Edge distance (the distance from the centre of an anchor to the nearest concrete edge) is the detail most likely to cause trouble on site.
In the CSA A23.3 method (we checked the 2004 edition), the concrete breakout cone around a tension anchor is taken to spread outward about 1.5 times the effective embedment depth from the anchor. When an edge cuts into that cone, the breakout resistance drops. So a stud that works in the middle of a wall may not work 50 mm from a corner, even though the plate looks the same.
Practical consequences:
- Do not slide an embed toward an edge, corner or opening to dodge a conflict without asking the engineer.
- Watch for adjacent embeds. Anchors close together share the same concrete, so two embeds placed side by side can have less capacity than two embeds apart.
- Think about reinforcement. Rebar near the anchors can help or can clash with them. Embeds and reinforcing are often detailed together for that reason.
- Mind the cover. Studs and bars on the back of the plate still need concrete around them, and the plate must not push the rebar out of position. Cover rules are covered in concrete cover for rebar.
The plate's own edge distance matters too: weld lines and bolt holes need room from the plate edge, and studs need room from the plate edge for the stud weld. The engineer or detailer sets all of these on the embed drawing.
Embed plate details on drawings and shop drawings
Embeds usually appear on the structural drawings as typical details, with a mark (E1, E2, and so on), a plate size and thickness, the anchor type, size, length and number, and a finish. The fabricator's shop drawings then show each embed type, the quantity, and where it goes.
A good embed shop drawing package includes:
- A piece drawing for each embed type, with plate size, thickness, grade, stud or bar layout, and any holes or threaded studs on the face
- A placement plan showing every embed by mark, with dimensions to gridlines and elevations, tied to the concrete pour sequence
- Orientation marks where the embed is not symmetrical, such as a plate with studs off-centre or an angle embed with a top leg
- Finish: bare steel for interior embeds that will be welded, hot-dip galvanized for exterior or wet locations, as specified
Because embeds go in early, they are often detailed and submitted as their own package ahead of the rest of the miscellaneous steel. Waiting until the stair and railing drawings are ready usually means the walls are already poured.
Setting embeds in the forms
Embeds are fabricated in a shop and set on site by the concrete contractor, usually after the rebar is placed and before the pour. A few practices make the difference between an embed that is usable and one that needs a field fix:
- Fix the plate to the form, not just to the rebar, with nails through holes in the plate, screws, or bolts through the formwork, so the face ends up flush and in position.
- Tie the anchors to the reinforcement so the plate does not float or rotate when concrete is placed and vibrated.
- Seal the edges so paste does not run behind the plate face.
- Consolidate around the plate. Air pockets under a large horizontal embed reduce bearing and can hide a void. Large plates sometimes have vent holes for that reason.
- Survey before the steel arrives. Check location, elevation and plumb against the placement plan, and send any misses to the engineer and fabricator.
A missing or misplaced embed is usually fixed with a surface-mounted plate and post-installed anchors, which needs engineering and costs more than doing it right in the first place.
Welding to embed plates
Most embeds are made to be welded to later. Two points matter:
- Heat. A large weld puts heat into the plate and the concrete behind it. Very thin plates can distort or break the bond with the concrete. The plate thickness and weld size on the design account for this.
- Weld quality. Field welds to embeds are structural welds and should be made by qualified welders to CSA W59. See our overview of the CSA W59 structural welding code.
Galvanized embeds need the coating removed at the weld area and the area repaired afterward, so plan finishes with the welding in mind.
Embed plates made to your drawings
Embeds are small pieces with a big effect on the schedule. We cut plates and fabricate structural and miscellaneous steel, including plates, angles and connection pieces, in our shop with CWB certified welding and shop drawings prepared in house. Engineering services are available for projects that need them, and deliveries can be phased to match your pour schedule across the GTA and Ontario. We can prime or galvanize embeds to suit the job; ask us about stud-welded embeds for your project.
Send your structural drawings and embed details for a free take-off and quote, or see our services for fabrication, shop drawings and delivery.
Frequently asked questions
What is an embed plate?
An embed plate is a steel plate with anchors welded to its back, cast into a concrete wall, slab, beam or column so the face sits flush with the concrete. Steel members such as beams, angles, ledgers or brackets are later welded or bolted to the exposed face.
How is a steel plate anchored into concrete?
Usually with headed studs welded to the back of the plate, or with deformed bars or bent rods welded on. The anchors transfer tension and shear into the concrete. Their size, number, length and spacing come from the engineer's design.
How close to the edge of concrete can an embed plate be?
There is no single number. Anchors close to an edge lose capacity because the concrete can break out toward that edge, so the engineer sets the minimum edge distance for each embed. Moving an embed toward an edge on site should always be checked with the engineer first.
Who installs embed plates?
Embeds are usually fabricated by the steel or miscellaneous metals fabricator and set in the formwork by the concrete contractor before the pour. The contract should say who supplies them, who sets them and who checks their location.
Can you weld to an embed plate after the concrete is poured?
Yes, that is what most embeds are for. Heavy welding heats the plate and the concrete behind it, so the weld size and procedure should come from the design, and the welding should be done to CSA W59 by qualified welders.
