Structural and base materials · Metals
Structural Fixings and Anchors
Describes anchorage into concrete, masonry and steel as a product family in its own right, rather than as the coated metals the corpus currently names wherever a fixing is actually meant.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What structural fixings and anchors is
This entry covers the metal components that attach one thing to another by transferring load into a structural background. They divide into two routes. A cast-in fixing is placed before the concrete is poured and is held by the concrete that hardens around it: cast-in channels, anchor bolts and holding-down assemblies, sockets and inserts. A post-installed fixing goes into a hole drilled in the hardened material afterwards, and works either mechanically — an expansion or undercut anchor gripping the sides of the hole — or by bonding, with a resin or a cementitious mortar injected into a cleaned hole around a threaded element.
What decides whether a fixing works is mostly not the fixing. It is what it is fixed into: whether the concrete is cracked or uncracked at that point, how close the fixing sits to an edge or to its neighbour, whether the drill happened to find the web of a hollow block or the void beside it, whether the brick is solid or perforated, whether the hole was drilled to the depth the anchor was designed around, and — with bonded anchors above all — whether that hole was cleaned before the resin went in. The corpus already says this in its own words: the capacity of an anchorage depends on what it is fixed into as much as on the fixing itself.
That is why anchorage in a load-carrying position is designed rather than chosen. A designer establishes the load and its direction, identifies the background and its condition, works within the edge distances and spacings actually available, and then selects a particular anchor against the manufacturer's data for that background — with the manufacturer's installation procedure forming part of what was designed. Substituting an apparently similar anchor is a design change, because an anchor's data belongs to that anchor installed that way.
The boundaries matter here, because several neighbouring families are published separately. Wall ties connect the leaves of a cavity wall or restrain masonry to a frame and are their own component family. Timber-to-timber connector hardware — the straps, hangers, hold-downs and plates that join framed timber to itself — is a separate family from anchorage into concrete, masonry and steel and is covered elsewhere. Ground anchors and post-tensioning anchorages are designed and stressed structural and geotechnical systems and are not in this entry at all. And a cladding support bracket assembly is the support system; the anchor is only what holds that system to the structure behind it.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- Anchors
- Masonry and concrete anchors
- Post-installed anchors
- Cast-in anchors
- Resin-bonded anchors
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Cast-in channels, sockets and inserts positioned in formwork before concrete is placed.
- Holding-down assemblies and anchor bolts fixing baseplates, posts and column bases to concrete.
- Post-installed mechanical anchors into concrete for brackets, rails, plant and secondary steelwork.
- Bonded anchors, where a threaded element is set into a drilled hole with an injected resin or mortar.
- Fixings into masonry — solid, perforated and hollow units, which behave differently from one another and from concrete.
- Connections taking cladding support, balustrade and canopy components back to the primary structure.
- Restraint straps, ties and bars anchored into concrete or masonry as part of a designed arrangement.
Consideration
Where it is commonly considered
- Where a designer has established the load and its direction and has selected an anchor against manufacturer's data for the actual background.
- Where a cast-in solution can be positioned before a pour, which avoids drilling into reinforcement later.
- Where the background has been identified by opening up, surveying or scanning rather than assumed from the drawings.
- Where the manufacturer's installation procedure, including hole cleaning for a bonded anchor, can genuinely be followed in the position concerned.
- Where the exposure of the position has been considered in choosing the metal and its corrosion protection.
- Where on-site proof testing can be programmed if the design calls for it.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- In any load-carrying position where the anchorage has not been designed; this is the family where the difference between a design and a purchase matters most.
- Where the background is unknown, variable, cracked, rendered over, or of a masonry type nobody has identified.
- Close to edges, corners and other fixings, where spacing and edge distance govern what the background can do regardless of the anchor.
- Into hollow or perforated units, where assuming a solid unit is among the commonest and most consequential errors made.
- Where drilling may strike reinforcement, prestressing tendons or services and the structure has not been scanned.
- In positions affected by heat, vibration, fatigue or sustained load, each of which changes what the anchorage has to be.
- Where the fixing will be exposed or in contact with a dissimilar metal and the corrosion question has not been asked.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Substrate dependency
- The background is the subject: concrete condition, whether it is cracked at that point, masonry type, edge distance, spacing, member depth, and whether a unit is solid, perforated or hollow.
- Installation dependency
- Drilling method, hole diameter and depth, hole cleaning, setting torque and curing time for a bonded anchor are specified together, and the procedure is part of what was designed rather than advice.
- Documentation
- The manufacturer's data belongs to a particular anchor in a particular background installed a particular way, and the record of what was actually installed where is what makes any of that meaningful later.
- Weathering and exposure
- Exposed, semi-exposed and wet positions raise the corrosion question, including contact with a dissimilar metal or with treated timber, and the metal is chosen for the position rather than the range.
- Fire-related questions
- What happens to an anchorage in a fire depends on the type of anchor and belongs to the project's fire strategy and to the manufacturer's documentation; a resin-bonded anchor and a mechanical one are not the same subject, and neither is settled here.
- Repairability
- A failed or wrongly placed fixing leaves a hole in the structure, and remaking it nearby brings spacing and edge distance back into play immediately.
- Maintenance
- Fixings in critical positions may form part of an inspection regime; most are permanently concealed behind a finish and are never seen again after the day they went in.
Exposure
Exposure and environmental conditions
- Is the position internal, semi-exposed, fully exposed, coastal, or in a pool or plant environment?
- Is the fixing in contact with a dissimilar metal, or with treated timber, where the combination itself matters?
- Is the position wet, subject to freezing, or exposed to de-icing salts?
- Will the anchorage see vibration, repeated loading or sustained load?
- Does heat reach this position, from a process or from sun on dark cladding?
- Will the fixing stay accessible for inspection, or be permanently concealed?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- The background material and its condition govern everything, and it is identified rather than assumed.
- Edge distances, spacings and member depth limit what the background can carry whatever anchor is chosen.
- Reinforcement, prestressing tendons and services within the structure decide where drilling can happen at all.
- Renders, finishes and insulation between the fixture and the structure change the load path and the embedment the fixing needs.
- Where a fixing passes through insulation, the thermal question and the structural question arrive together.
- Cast-in items depend on the formwork, on being held in position during the pour, and on the concrete that ends up around them.
Appearance
Appearance and finish considerations
- Most anchorage is concealed; what is seen is the fixture, plate or bracket it holds.
- Where heads, nuts and plates are exposed, the metal and its protection become a visible choice rather than only a technical one.
- Rust staining from an exposed fixing marks whatever sits below it, and is often the first sign that anything is wrong.
- Drilled holes, cores and made-good patches in exposed concrete or fair-faced masonry remain visible permanently.
- A resin-bonded anchor leaves material at the mouth of the hole unless it is cleaned off while still workable.
- Where a fixing is set into a finished surface, the made-good patch around it rarely matches and rarely ages the same way.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- What is the background, and what evidence is there of its condition at the actual fixing positions?
- Was each hole drilled to the required depth and cleaned as the manufacturer's procedure requires?
- Were setting torques applied, by whom, and with what?
- What corrosion protection does this position call for, and is that what was supplied?
- Were any fixings tested on site, and was the result recorded?
- What happens to this anchorage if the fixture is removed and refitted later?
Upkeep
Maintenance and repair considerations
- Is there a record of which anchor was installed where, and to which specification?
- Are any of these fixings part of an inspection regime, and who holds it?
- If a fixing has to be removed, can it be replaced in the same position at all?
- Is there any sign of staining, movement or cracking around a fixing position?
- Who is called if a fixture becomes loose, and what do they look at first?
- Does anyone hold the manufacturer's data for what was used, years after the work?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- The manufacturer's installation procedure is part of the design rather than a suggestion: hole diameter, depth, cleaning, curing and torque are specified together.
- Hole cleaning is the step most commonly skipped for bonded anchors, and its absence cannot be seen afterwards or detected for years.
- The drilling method — hammer, rotary, diamond — changes the hole itself and is specified alongside the anchor.
- The structure is scanned or otherwise investigated before drilling wherever reinforcement, tendons or services may be present.
- Cast-in items are surveyed and held in position before and during the pour, because they cannot be moved once the concrete has set.
- Where on-site proof testing forms part of the design, it has to be programmed into the sequence rather than added at the end.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The manufacturer's technical data for the anchor in the actual background it is going into.
- The designer's fixing schedule or detail, including load, position and any testing required.
- The installation procedure covering drilling, cleaning, curing and torque.
- Records of any on-site testing that was carried out, and by whom.
- Corrosion protection information for the position and for the material actually supplied.
- For cast-in items, a record of what was set and where, made before the pour.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Who has designed this anchorage, and against what load and direction?
- What is the background here, and how has it been identified?
- What edge distances and spacings are available, and do they govern the design?
- Is there reinforcement or a service where the drill is going, and how is that being established?
- Could a cast-in solution be used here instead of drilling into the structure later?
- What corrosion protection does this position call for?
- What installation procedure applies, and who verifies that it was followed?
- Is on-site testing required, who carries it out, and what is recorded?
Blind spots
Commonly overlooked points
- The fixing is usually the smallest variable in the problem; what it is fixed into decides most of the outcome.
- Solid and hollow masonry units take entirely different fixings, and which is which is rarely obvious from the feel of a drilled hole.
- Hole cleaning for a bonded anchor is invisible once the resin is in, and its absence stays invisible until something moves.
- An apparently identical substitution is a design change, because the data belongs to the anchor as installed rather than to the shape of it.
- Wall ties, timber-to-timber connector hardware, ground anchors and post-tensioning anchorages are separate families, and nothing in this entry covers them.
- A fixing through insulation arrives with a thermal question attached as well as a structural one, and the two are usually answered by different people.
What this page does not do
- Anchorage in any load-carrying position is designed by a qualified engineer against the actual background. Nothing in this reference states a capacity, a spacing, an edge distance, an embedment or a load.
- Ground anchors, post-tensioning anchorages and timber-to-timber connector hardware are separate families with their own design disciplines and fall outside this entry entirely.
- Drilling into a structure without establishing what is inside it risks cutting reinforcement, tendons or services; investigation comes before the drill.
- The manufacturer's installation procedure is part of what was designed, and departing from it turns the anchorage into something no data describes.
Component forms
Building components commonly formed from this material
Elements this material is commonly used to make, named by the position they occupy in an assembly rather than by what they are bought as. This states common practice only — it is not a statement that this material suits any of these components in a particular building.
Related entries
Common comparisons
Entries met at the same decision but which behave differently, so the comparison is about the difference rather than a swap.
Related entries
Often used alongside
Entries commonly encountered together with this one. Co-occurrence only — never a claim that any combination is compatible or suitable.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Metals in Construction
Reference entries for the metals used in building — structural and light-gauge steel, galvanised and stainless steel, aluminium, copper, zinc, lead and reinforcement.
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