How to choose the right chemical anchor
12 בJuly 2026
Why use a bad plug when you can use a good one?
12 בJuly 2026How to choose the right chemical anchor
12 בJuly 2026Why use a bad plug when you can use a good one?
12 בJuly 2026How Anchors Behave Under Blast Loading
Anchors do not behave the same way under static and dynamic loads. Under an explosion, some anchors weaken dramatically while others actually get stronger — and choosing the right type can be the difference between a protection system that saves lives and one that fails at the worst possible moment.
It has long been known that anchors respond differently to static loads and to dynamic loads such as seismic action, explosion, or long-term load cycling. In the 1970s the problem was handled crudely, by applying a safety factor of 3 to any dynamic load — a 1 kg load was simply designed as 3 kg because it was dynamic. We have moved on since then: laboratory studies (borne out in the field) show that some anchors actually perform better under blast loading than under static loading. Choosing the right anchor type is at least as important as calculating the load itself.
How the four common anchors compare
We compared the four most common construction anchors in laboratory tests, static loading against dynamic (explosion / shock) loading:
| Anchor type | Capacity: dynamic vs static | Failure mode | For explosions |
|---|---|---|---|
| Wedge anchor | 30% less (sometimes only a third) | Sudden, no energy absorption | Not recommended |
| Heavy-duty (dynamic) anchor | 0% to 80% more | Sudden, but at a higher load | A suitable option |
| Chemical anchor | 0% to 80% more | Gradual, some energy absorption | Good, esp. weak/cracked concrete |
| Concrete screw | 0% to 80% more | Very gradual, high energy absorption | Best of the four |
The four anchor types in detail
1. Wedge anchor
The most standard anchor in construction, found on almost every site — but under dynamic loading it is the weakest of the four. Even the best wedge anchors hold 30% less under dynamic loading than under static; ordinary ones hold, on average, only a third of their static load. There is no meaningful energy absorption before failure, and the failure comes suddenly. On these figures, the wedge anchor is not recommended for blast loading.
2. Heavy-duty (dynamic) anchor
A heavy expansion anchor designed specifically to withstand shock and vibration. Under dynamic loading it holds between 0% and 80% more than its static capacity — a big improvement on the wedge anchor — because its heavy expansion sleeve distributes the forces better within the borehole. Failure under explosion is still sudden, but it occurs at a significantly higher load. It is particularly suited to continuous vibration and fatigue loading, not only one-off shocks, and is a sound option where resistance to seismic action or prolonged vibration is required.
3. Chemical anchor
The chemical anchor relies on an adhesive (epoxy or vinylester) rather than mechanical expansion, so it transfers load along the length of the bond rather than at a single point. Under dynamic loading it holds 0% to 80% more than its static capacity, and it fails gradually, with some energy absorption. It is an especially good choice where the concrete is weak or cracked.
When is a chemical anchor the right choice?
A chemical anchor performs particularly well in cracked or low-quality concrete, where expansion-based mechanical anchors such as the wedge anchor struggle to develop the grip they need. The adhesive layer forms a continuous bond along the whole length of the borehole, rather than a single point of contact.
4. Concrete screw
The concrete screw is threaded directly into the concrete, with no separate plug, and it shows the best behaviour of the four types tested. Under dynamic loading it holds 0% to 80% more than its static capacity. Failure comes from a gradual increase in slip along the thread as the pull-out force rises: this partial release absorbs a very large amount of energy and produces a very gradual failure — exactly what an energy-absorbing element in a blast-protection system should do. On our analysis, the concrete screw is the best of the four for explosions.
Why this is exactly the behaviour we want
This is exactly what an energy-absorbing element in a blast-protection system is meant to do: fail gradually, so that the structural element takes up part of the energy before the anchor lets go entirely. On our analysis the concrete screw is the best of the four anchor types for blast loading.
Why this matters to the design
An anchor failing under blast loading can fail suddenly and without warning, or gradually while absorbing energy — and the difference between the two is sometimes the difference between a protection system that saves lives and one that fails at exactly the moment it is needed. Choosing the right anchor type matters at least as much as calculating the load itself.
The four anchors ranked for dynamic behaviour
- Concrete screw — gradual failure with maximum energy absorption. The most recommended solution.
- Chemical anchor — gradual failure with some energy absorption. Particularly recommended in weak or cracked concrete.
- Heavy-duty (dynamic) anchor — high pull-out load, but sudden failure. A reasonable option, mainly under seismic and vibration loading.
- Wedge anchor — holds less under dynamic load and fails abruptly. Not recommended for blast loading.
A closing word — an approval is not a guarantee of performance
The fact that an anchor is approved for dynamic loading under a European standard means only that the anchor was tested for loads of that kind. It says nothing about how well it actually performs under them. Most designers ask only for the approval, and then design on static loads alone.
There is no logic in that. It is like checking that a candidate went to university without checking whether they passed the exams.
Common questions
Is every anchor “approved for seismic” also suitable for explosions?
Not necessarily. A seismic approval tests cyclic behaviour, which is substantially different from a one-off shock such as an explosion. Look at the specific test results for shock and dynamic loading rather than assuming an approval for one transfers to the other.
Why does a wedge anchor fail more suddenly than a concrete screw?
The wedge anchor relies on a point expansion mechanism — once it reaches the failure threshold, its resistance drops away sharply. The concrete screw fails gradually through continuous slip along the thread, which allows it to absorb energy as it goes.
Which anchor is best suited to blast-protection systems?
On the behaviour measured in the laboratory, the concrete screw offers the combination of energy absorption and gradual failure that best suits blast protection. The chemical anchor is another good option, particularly where the concrete is of low quality. In every case, consult a structural engineer specialising in dynamic loading before settling on the final solution.
When should a chemical anchor be preferred over a concrete screw?
When the base concrete is weak or cracked, or when the job calls for a deep embedment and an unusually high load. The chemical anchor forms a continuous bond along the whole borehole and performs well even in less-than-ideal concrete, whereas a concrete screw depends on the quality of the concrete around its thread.
Can a generic safety factor replace choosing the right anchor?
Not advisable. A blanket factor — three times the load for dynamic actions, say — ignores the substantial differences between anchor types: some of them actually gain capacity under dynamic loading while others lose it dramatically. Sound design rests on real test data for the specific anchor chosen, not on a sweeping assumption.