Embedded Parts

What is an Embedded Part

An embedded part, also called a cast-in part, embed plate, or insert, is a prefabricated steel component placed in the mould before concrete is poured so that it becomes mechanically locked into the hardened structure. In its most common form it is a flat steel plate, the face plate or bearing plate, with anchor bars or headed studs welded to its back face. After the pour the plate sits flush with the concrete surface, presenting a clean steel face that later steelwork, brackets, rails, or equipment can be bolted or welded to. The anchors transfer the connection load back into the concrete by bond, by mechanical interlock at the head, and by the surrounding reinforcement.

The defining feature is the load path. Because the anchors are cast in while the concrete is plastic, there is no drilled hole, no expansion sleeve, and no adhesive bond line to fail. The concrete cures directly around the steel, so the joint behaves monolithically and carries the highest characteristic resistance available for a concrete connection. This is the fundamental distinction from a post-installed anchor, which is drilled and set into concrete that has already hardened and which is governed by a separate set of rules, including JGJ 145 in China and the post-installed clauses of EN 1992-4 in Europe. Where a fixing must be added after the pour, the alternatives are a bonded chemical anchor set in adhesive resin or a mechanical expansion anchor that grips by friction, rather than a cast-in part.

Embedded parts appear wherever steel meets concrete. Steel columns land on cast-in base plates; precast panels hang from cast-in anchor channels; composite floor slabs are tied to steel beams by headed stud shear connectors; crane rails, lift guides, pipe supports, curtain walls, and tunnel segment fixings all rely on cast-in steel. In a typical reinforced-concrete building, hundreds to thousands of embedded parts are scheduled, each detailed on a setting-out drawing that fixes its exact position, level, and orientation before the relevant pour.

The engineering of an embedded part is the engineering of two materials acting together. The steel side is sized so the plate does not yield in bending and the anchors do not rupture in tension or shear. The concrete side is checked so that the anchor head does not pull through, the concrete does not break out in a cone, and the edge does not spall. Standards such as 16G362, EN 1992-4, and ACI 318 Chapter 17 exist precisely to keep these two sides in balance, because an embedded part that is over-strong in steel but under-anchored in concrete fails just as surely as the reverse.

Historically, embedded plates with hand-welded anchor bars were the universal solution and remain dominant in cast-in-place concrete frames across Asia. From the 1950s the drawn-arc stud welding process, standardised today as part of AWS D1.1 and EN ISO 13918, allowed headed studs to be fired onto a plate in under a second, which industrialised both shear connectors for composite beams and headed-anchor embeds. From the 1980s, manufacturers such as Halfen, Jordahl, and Hilti productised the cast-in anchor channel, a continuous slotted profile with welded anchors that lets a fixing be positioned anywhere along its length, removing the tyranny of exact bolt setting-out for facades and rails.

Embedded Part Types

Embedded parts can be classified by the load they carry, by the anchor mechanism, and by whether they are bespoke fabrications or catalogue products. The Chinese standard design atlas 16G362 takes the load-based view and defines six standardised plate types, which is the cleanest framework for selection because it forces the engineer to name the governing action before choosing a detail. The table below summarises the six 16G362 types alongside the catalogue product families that compete for the same duties.

Axial tension and hanging-reinforcement embeds are the simplest case: the anchors are loaded almost purely in tension. Here the head detail matters most. A plain straight bar relies on bond length and may need a 90 or 135 degree hook, whereas a headed bar or a welded headed stud develops its full strength in a short embedment because the head bears directly on the concrete. 16G362 requires the anchor steel to be HRB400 or HPB300 and bans cold-worked reinforcement, because welding work-hardened bar can embrittle the heat-affected zone.

Shear and combined-action embeds introduce bending into the face plate. When a bracket transfers a vertical load offset from the plate, the plate sees tension on one anchor row, compression bearing on the opposite edge, and shear across the interface. The face plate must be thick enough not to yield in this bending before the anchors reach capacity; as a starting rule the atlas keeps plate thickness around 0.6 times the anchor diameter and never less than 6 mm. Compression-bending-shear column base plates additionally bear directly on the concrete or on a grout bed, sharing load between bearing and anchors.

Anchor channels are a different topology. Instead of a fixed bolt pattern, a continuous cold-formed or hot-rolled C-section is cast flush with the surface, its slot facing out. A later fixing is made with a hammer-head T-bolt dropped into the slot and turned 90 degrees so it engages the channel lips. This removes the need for precise setting-out: the fixing can sit anywhere along the channel, which is why anchor channels dominate the connections for a glass curtain wall, cladding, and rails where the supported element arrives later and to its own tolerances. The trade-off is that the load now passes through the channel lips, adding lip-flexure failure modes that a solid plate does not have.

Headed stud shear connectors form the third major family and are treated in detail in Chapter 3. They are not a connection to be bolted to later; instead they project from a steel beam flange into a concrete slab to make the two act compositely, so the beam and slab share bending as one section.

Headed Studs and Anchor Channels

Two catalogue families dominate the modern cast-in market: headed weld studs to EN ISO 13918 and cast-in anchor channels assessed under EN 1992-4 and EOTA TR 047. They solve different problems. A headed stud is a fixed-position, weld-on anchor used both as a shear connector for composite beams and as a headed anchor on embed plates. An anchor channel is a slotted profile that accepts a movable bolt. The table below compares the engineering parameters that decide between them and within each family.

Headed weld studs per EN ISO 13918 type SD are the workhorse shear connector for steel-concrete composite floors. They are supplied in standard shank diameters of 13, 16, 19, 22, and 25 mm; the dominant building sizes are 19 mm and 22 mm. The forged head spreads the bearing area: a 13 mm stud carries a 25 mm head, the 16 and 19 mm studs a 32 mm head, and the 22 mm stud a 35 mm head. The material is S235J2 + C450, a low-carbon steel cold-drawn to a minimum ultimate tensile strength of 450 N per square millimetre with at least 15 percent elongation, which keeps the stud weldable yet strong. In composite design to EN 1994-1-1, the design shear resistance per stud is the lesser of stud steel shear, governed by the 450 N per square millimetre UTS and shank area, and concrete crushing around the shank, governed by the concrete strength and the stud height-to-diameter ratio.

Studs are joined by drawn-arc stud welding: the stud welding gun draws a short arc that melts the stud tip and a pool on the plate, then plunges the stud into the molten pool and a ceramic ferrule shapes the weld collar. The process consumes part of the stud length, the burn-off, so studs lose roughly 4 to 5 mm between the as-supplied length and the after-weld length. Connectors are therefore ordered by the required length after welding, which must give the code-required head cover above the steel deck rib. Welding and inspection follow AWS D1.1 in North America and EN ISO 14555 in Europe, with bend tests on production studs to prove fusion.

Cast-in anchor channels reverse the logic by making the bolt movable. The channel is a C-profile with inturned lips and welded I-anchors or round anchors on its back; a hammer-head T-bolt is dropped through the slot and rotated to lock under the lips. Channels come in two manufacturing routes. Cold-formed channels are roll-formed from steel strip, are lighter and cheaper, and suit predominantly static facade and cladding loads. Hot-rolled channels, such as the Halfen HTA-CE range under ETA-09/0339, are rolled from a solid profile with thick lips and a deep root; their continuous grain flow gives high fatigue capacity, so they are mandatory for dynamic duties such as crane rails and bridge facade rails. Profile designations such as 28/15, 40/22, 52/34, and 72/48 state the channel height and width in millimetres, which scale with the bolt size and load.

Headed anchors on embed plates are the third use of the same studs. Rather than projecting into a slab, the studs are welded to the back of a face plate to replace bent anchor bars. The advantage is a short, predictable embedment that develops full head bearing without long bond lengths, and a clean fabrication with no hand-bent bars. ACI 318 Chapter 17 and EN 1992-4 both treat these as cast-in headed fasteners and require the same suite of concrete and steel checks as any other cast-in anchor.

Plate and Anchor Materials

An embedded part is a welded assembly of three material groups: the face plate, the anchors, and the corrosion protection. Each is chosen separately, but they must be compatible for welding and for the service environment. The starting point for Chinese practice is 16G362, which fixes the plate to Q235B or Q355B structural steel and the anchors to HRB400 or HPB300 reinforcing bar. European headed-fastener practice pairs an S235 plate with EN ISO 13918 studs, while US practice uses an ASTM A36 plate with ASTM A108 studs.

Face plate steel. Q235B is the default mild steel for general embeds, with a minimum yield of 235 N per square millimetre. Q355B (the former Q345) raises the yield to 355 N per square millimetre and is chosen when bending in the plate governs, for example on heavily loaded bracket or base-plate embeds, allowing a thinner plate for the same capacity. The B suffix denotes guaranteed impact toughness at 20 degrees Celsius, which matters because the plate carries welds. Plate thickness is sized so the plate does not form a yield-line mechanism before the anchors fail; the atlas keeps thickness near 0.6 times the anchor diameter and not less than 6 mm, with common plates from 6 to 20 mm and heavier for crane or column duties.

Anchor steel. HRB400 hot-rolled ribbed reinforcing bar, with a 400 N per square millimetre yield, is the standard anchor, developing bond through its ribs and full tension through a welded head or hook. HPB300 plain round bar is used for lighter constructional anchors. The atlas prohibits cold-worked or cold-drawn reinforcement for anchors, because the welding heat needed to fix them to the plate removes the cold-work strength and can crack the brittle heat-affected zone. The anchor-to-plate weld is itself dimensioned: 16G362 sets the fillet leg of a T-joint anchor weld at a minimum of 0.5 times the bar diameter for HPB grade and 0.6 times the diameter for HRB335 and HRB400, so the weld is never the weak link.

Welding method. Anchors are attached by one of three methods. Drawn-arc stud welding, to AWS D1.1 or EN ISO 14555, fires headed studs onto the plate in under a second and is the production standard for studs. Perforated plug welding sets the bar through a hole in the plate and fills it, used where a flush back face is needed. Manual fillet T-joint welding, accepted to JGJ 18 in China and GB 50661 for structural steel, attaches anchor bars or angle anchors by hand and is checked by the weld-height rules above. Whichever method is used, galvanizing must come after welding so the weld zone is also protected.

The table below maps service environments to recommended materials and protection. It is for initial selection; verify chloride level, exposure class, and design life against the project specification and the manufacturer ETA before issue.

Corrosion protection. Inside sound, dry, uncracked concrete the high alkalinity passivates the steel and no coating is needed, so most interior structural embeds ship bare or shop-primed. Exposed faces and aggressive environments take batch hot-dip galvanizing to EN ISO 1461, which gives a metallurgically bonded zinc layer in the order of 45 to 85 micrometres depending on the steel thickness; the coating thickness sets the maintenance-free life. For high chloride, splash zones, and architectural finishes, stainless steel grade A4, type 1.4401 (316) or 1.4571 (316Ti), is used for channel, bolt, and often anchor. Mixed assemblies of a stainless channel with carbon-steel welded anchors are permitted where the anchor sits deep in passivating concrete.

Key Specification Parameters

An embedded part datasheet or ETA lists many numbers, but only a handful drive the connection. The same part may be described by its geometry, its steel grades, and a table of characteristic resistances per failure mode; the engineer must read all three and check the lowest resistance against the design action. The parameters below are the ones to extract and verify on every selection.

Characteristic resistance per failure mode. This is the heart of any cast-in design. EN 1992-4 and ACI 318 Chapter 17 require the part to be checked for every relevant mode, with the lowest resistance governing. The catalogue or ETA gives a characteristic value N or V for each mode, which is then divided by a partial safety factor. Do not read a single headline capacity; read the table and find which mode controls for your edge distance, spacing, and concrete strength.

Tension failure modes that must each be checked are listed below; for anchor channels the last three are additional to the headed-fastener set.

• Steel failure of the anchor: tensile rupture of the anchor bar or stud, governed by anchor steel area and ultimate strength.
• Pullout: the head pressing through the concrete, governed by head bearing area and concrete strength.
• Concrete cone breakout: a cone of concrete pulling out, governed by embedment depth, edge distance, and spacing.
• Concrete blow-out: spalling of the side cover near an edge for deeply embedded anchors.
• Concrete splitting: the member splitting due to insufficient member thickness or edge distance.
• Channel lip failure: local flexure of the channel lips under the T-bolt (anchor channels only).
• Anchor-to-channel connection failure: the welded or forged joint between anchor and channel (anchor channels only).
• Bolt steel failure: tensile rupture of the T-bolt itself (anchor channels only).

Shear failure modes to be checked are steel failure of the anchor or T-bolt, concrete pryout (a wedge levering out behind the anchor under shear), and concrete edge failure toward a free edge. Edge failure usually governs near a slab or beam edge and is highly sensitive to the edge distance, which is why setting-out tolerance directly affects capacity.

Embedment depth. The effective embedment, the depth from the concrete surface to the load-bearing head, controls the concrete cone capacity, which scales roughly with the embedment depth to the power of 1.5. Doubling embedment more than doubles cone resistance, so deepening the anchor is often cheaper than thickening the plate. The datasheet states minimum and design embedment for each profile.

Edge distance and spacing. The characteristic edge distance and characteristic spacing are the distances beyond which a free edge or a neighbouring anchor no longer reduces the concrete cone resistance. Below them the resistance is reduced by published factors. These geometry limits are as important as the steel grade, because a strong anchor too close to an edge fails the concrete first.

Steel grades and partial safety factors. Confirm the plate grade (Q235B, Q355B, S235, A36), the anchor grade (HRB400, S235J2 + C450, A108), and the bolt grade (commonly 8.8 or stainless A4). For steel failure, ACI 318 uses the ultimate strength futa, capped at the lesser of 1.9 times the yield and 125,000 psi; EN 1992-4 applies a material partial factor to the characteristic steel resistance. Read these so the design value, not the headline characteristic value, is compared to the factored action.

Supplementary reinforcement. Where the concrete cone or edge mode governs and cannot be satisfied by geometry alone, hairpins or stirrups looped around the anchors can be designed to take over the concrete tension and edge loads, transferring them into the main reinforcement. The datasheet states whether the published resistances assume plain concrete or rely on supplementary reinforcement, which must then be detailed on the drawing.

Selection Decision Factors

To turn the preceding chapters into a specified part, follow the decision sequence below. Most embedded-part failures trace not to a wrong steel grade but to a missed concrete failure mode, a too-thin plate, or a setting-out error, so the sequence deliberately checks geometry and concrete before steel. These steps double as a fixed RFQ template.

1. Define the action and the type: name the governing load (axial tension, shear, combined tension-bending-shear, compression-bending-shear, suspended, or movable facade fixing) and pick the matching type from the 16G362 set or the anchor-channel family. A movable later fixing points to a channel; a fixed bolted joint points to a plate with headed studs.
2. Locate the connection in the concrete: fix the edge distances, spacing, member thickness, and concrete strength class. These geometry inputs control the concrete cone, edge, and splitting modes and often govern the whole design, so settle them before sizing steel.
3. Size the anchors and embedment: choose anchor diameter, number, and effective embedment so steel resistance and concrete cone resistance are balanced. Deepening embedment is usually cheaper than adding anchors because cone capacity scales with embedment to the power of 1.5.
4. Size the face plate: set plate thickness so the plate does not yield in bending before the anchors reach capacity, starting near 0.6 times the anchor diameter and not less than 6 mm, and choose Q235B or Q355B per the bending demand.
5. Check every failure mode: run the full tension and shear mode list from Chapter 5 and confirm the lowest design resistance exceeds the factored action. Add supplementary reinforcement if the concrete cone or edge mode governs.
6. Specify materials and corrosion protection: match plate, anchor, and bolt grades for weldability, then choose bare, hot-dip galvanized to EN ISO 1461, or stainless A4 per the exposure class and design life. Confirm galvanizing is applied after welding.
7. Specify connection and tolerances: state the later connection method (bolt size and grade, or weld), the slot or hole pattern, the surface flushness, and the position and level tolerances. For channels, require the foam filler strip and a fixing-position survey.
8. Verify standards and documentation: require the relevant approval (16G362 detailing, an ETA for catalogue channels and studs, ACI 318 or EN 1992-4 calculations), weld procedure and inspection records to AWS D1.1, EN ISO 14555, or JGJ 18, and galvanizing certificates to EN ISO 1461.

One last dimension is often overlooked: buildability and serviceability on site. An embedded part is only as good as its position when the concrete sets, so the specification must address how the part is fixed to the formwork or cage, how it is protected from concrete laitance, and how its position and level are surveyed before and immediately after the pour while correction is still possible. Established suppliers such as Halfen, Jordahl, Hilti, and Nelson provide setting templates, foam slot fillers, and as-built survey support; for bespoke 16G362 plates, the fabricator and the site team must agree these controls in advance, because a mispositioned cast-in part can only be remedied by core-drilling and post-installed repair, at far higher cost than getting the pour right the first time.