In short
Load the anchor along its axis, through parts rated for the test load. Projecting studs take a threaded coupler with at least 1.5 × the bolt diameter engaged, or a Staht threaded washer in the tool adaptor jaw, which engages up to 1.0 × the bolt diameter. Eyes take a clevis. Proof testing a headed anchor means removing its bolt.
This guide explains how site tests are planned and carried out under BS 8539:2012+A1:2021. It does not replace the standard, the anchor manufacturer's data, or the instructions of the specifier or engineer responsible for the job, who decides the test plan, the loads and the factors. A test records what happened on the day; it does not approve a fixing for use.
Key figures
| Thread engagement on a coupler | At least 1.5 × the bolt diameter |
|---|---|
| Staht threaded washers, 25 kN pack | M6 to M16 |
| Staht threaded washers in the t60 kit | M6 to M20 |
| Staht slotted washers, for headed bolts | M6 to M16 |
| Staht clevis | Captive pin, 60 kN maximum |
| Staht drop rod for 375 and 575 bridges | 500 mm, with M16 thrust nut rated to 60 kN |
How should a pull tester connect to an anchor?
A pull tester should connect to the anchor itself, so the load runs along the anchor's axis with nothing else in the load path that could bend, slip or carry part of the load. For scaffold ties, NASC TG4:25 says the load goes directly on the anchor, not through the tie tube or the fixing.
Before testing, think about the weakest part of the load path, not just the tester. The bridge, adaptor, clevis, rod and nut must each be rated above the highest test load, with a margin to spare; for a preliminary test, our test-load calculator works out that load. A hollow ram may only take a rod that is thin for the force it can apply, so use high-strength rod there, with a nut of matching grade, and look over every rod for damage before each test. Finally, make sure the tester has more stroke than the anchor is likely to move.
What are the ways to connect a tester to an anchor?
A tester connects through a pulling frame, a threaded coupler, a bolt testing adaptor or a clevis, depending on what the anchor presents at the surface. The table matches each to the anchor, says what it can show, and names the Staht part that does the job.
Which connection, and which Staht part, for which anchor?
| What the anchor presents | Connection | What it can show | Staht part |
|---|---|---|---|
| A nut or bolt that can be clamped down | Pulling frame: a plate with a bush sized to the anchor, clamped at the recommended torque | First movement and the clamping force | – |
| A projecting threaded stud, M6 to M16 | Threaded coupler, or a threaded washer in a tool adaptor jaw | The load; first movement if a torqued nut sits under the connection | Tool adaptor jaw and threaded washer pack, 25 kN |
| A projecting threaded stud, M6 to M20 | Threaded washer in a tool adaptor jaw | As above | Threaded washer pack in the t60 kit |
| A small bolt head | Bolt testing adaptor (top hat), or a clevis with a U bracket | The load | Slotted washer pack with the tool adaptor jaw, M6 to M16 |
| A ring or an eye | Clevis | The load | Clevis assembly, captive pin, up to 60 kN |
| Larger threads | Threaded adaptor, fitted to the M16 drop rod to convert it to the larger thread (Staht datasheet TDS 143) | The load | M22, M24, M27 and M30 threaded adaptors; 7/8", 1" and 1 1/8" adaptors are also listed |
| Reinforcing bar, R6 to R25 | Rebar adaptor on a heavy-duty tester | The load | Rebar adaptors R6 to R25 |
| An anchor under a 375 or 575 bridge | 500 mm drop rod and M16 thrust nut, to the clevis or tool adaptor jaw | The load | 375/575 drop rod and thrust nut |
What should I check when using a threaded coupler?
Check the thread first: engage at least 1.5 × the bolt diameter of thread in a threaded coupler, the recommended minimum, which on an M12 stud is 18 mm. Staht's threaded washers are as thick as their thread size, 6 mm for M6 up to 20 mm for M20 (Staht datasheets TDS 110 to 115), so they engage at most 1.0 × the bolt diameter; the 1.5 × figure is the recommendation for threaded couplers. If the stud is too short for that with the nut on, taking the nut off is only an option for anchors that need no installation torque (see below); for an anchor set by torque, use a pulling frame clamped at the installation torque, or ask the specifier.
Whether the nut and fixture stay on depends on how the anchor is set.
- Anchors set by torque: leave the fixture on and the nut tightened to the manufacturer's installation torque, and pull from above the nut. When the load reaches the clamping force, the washer under the nut goes slack. Record that load as first movement; it is also the clamping force.
- Anchors that need no installation torque (for example some undercut, displacement-controlled and bonded anchors): only these may be tested with the nut and fixture off.
Can I proof test an anchor with a bolt head?
To proof test a headed anchor you have to take its bolt out and fit a test bolt, which may not seat the same way. If proof tests are planned, specify the stud version of the same anchor where the maker offers one.
Where can I find these parts?
Staht's connection parts are listed with each tester and in the adapters range:
- Tool adaptor jaw, threaded washer pack, 25 kN and slotted washer pack;
- clevis assembly, for eyes and eyebolts;
- threaded adaptors, for larger and imperial threads;
- rebar adaptors and heavy-duty testers;
- 375/575 drop rod and thrust nut, for the wider bridges.
The t60 kit includes an anchor jaw, a clevis, threaded washers from M6 to M20 and slotted washers from M6 to M16.
How far should a ring bolt be screwed in before a test?
At least six full turns (NASC TG4:25 §8.2), with no forcing; fewer may not develop the anchor's full strength. Once it is fully home, back it off to line up with the tie tube. Wound hard into the end of the thread, it can shear the socket's shell. See scaffold anchor types.
How do I keep the load straight?
Pull square to the surface, or along the anchor's own line if it was set at an angle. Adjustable bridge legs let you do this on an uneven wall or soffit. See choosing a bridge.
More questions
At least 1.5 times the bolt diameter of thread should engage in a test coupler. For an M12 stud, that is at least 18 mm of thread.
No. Apply the load to the anchor itself. Testing through a tie tube or fixture adds parts that can bend or slip, and NASC TG4:25 says the load goes directly on the anchor.
Use a pulling frame clamped at the recommended torque, or a threaded coupler above a nut tightened to the installation torque. The washer comes loose when the load reaches the clamping force.
The Staht clevis assembly, with a captive pin, connects the drop rod of a t25 or t60 to an eyebolt, up to 60 kN. For eyebolt tests to BS 7883, see eyebolt and fall arrest anchor testing.
The specifier or engineer who asked for the test sets what is tested and whether movement is measured. The tester chooses a connection that meets those needs and records it in the report, which states facts and does not approve the fixing. See what goes in a site test report.
Sources
- BS 8539:2012+A1:2021 Code of practice for the selection and installation of post-installed anchors in concrete and masonry, BSI
- NASC TG4:25 Anchorage systems for scaffolding, Sections 8.2 and 11.1, NASC
- Staht clevis assembly product data, Staht
- Staht threaded washer pack product data, Staht
Adaptors for every anchor
Threaded washers, slotted washers, clevises and threaded adaptors for the Staht t25 and t60.