Shear testing anchors on site

Anchors are generally shear tested on site only when an allowable resistance in shear is needed and the manufacturer has no recommended shear load for the base material. This is rare, because an anchor's shear resistance is usually limited by the strength of the anchor itself or of the structure. They may be needed when fixing into low-strength masonry. These tests come under Clause 9.2 of BS 8539:2012+A1:2021.

You will usually find a maker's shear figures for concrete; for other base materials they are often missing.

No. Proof tests are not generally needed in shear, because the quality of installation affects an anchor's tensile performance. NASC TG4:25 notes that once tension tests have shown the anchors were installed correctly, it is safe to assume they will perform in shear as the manufacturer's data says. See proof testing explained.

A shear test follows the same test regimes as a tension test, such as preliminary tests or tests to failure, with one difference: displacement often decides the result, so the load is usually applied in steps and the displacement measured at each one.

1. Fix the rig. Fix the reaction frame that supports the tester to the base material with 2, 4 or 6 bolts. Concrete screws can be suitable.
2. Fit the shear bracket. The test anchor sits in a bushed shear bracket, which turns the tester's pull into a load along the surface.
3. Set up a dial gauge. Mount it on a separate stand so the test cannot disturb it, placed to record the anchor's movement.
4. Load in steps. At each step, let the load and displacement settle, then record both.
5. Record the result. Note the highest load, the displacement and the failure mode, such as pry-out.

The Staht shear test rig is a modular accessory that works with a t25 or t60 load cell. Its chassis is fixed by 4 anchors, spaced to suit typical UK and European brick centres. The sliding head has a PTFE gasket to reduce friction, a keyhole to watch the base material and a datum boss for measuring displacement. Bushes from 6 to 20 mm suit anchors from M6 to M20.

The rig comes as a kit with a 25 kN t25 load cell, with a t60 load cell, or without a load cell for owners of either tester. See the shear testers.

Only as a preliminary test, and only if the manufacturer agrees, so ask them first. A proof load cannot show the safety margin near an edge, and a test to failure risks breaking the edge off. The question should rarely come up: anchors are meant to be specified within the maker's edge distances, so it arises only when some were set too close. For a test across an edge, the rig bears against the edge itself, clear of the anchor.

Where an anchor carries tension and shear together, checking each against its recommended load is not enough. NASC TG4:25 shows one check for scaffold anchors:

Napp ÷ Nrec + Vapp ÷ Vrec ≤ 1.2

where Napp and Vapp are the working tension and shear loads, and Nrec and Vrec the recommended tension and shear loads. Ask the anchor manufacturer for the check that applies to its anchor.

Example: Napp = 2.0 kN with Nrec = 3.5 kN gives 0.571. Vapp = 1.5 kN with Vrec = 3.0 kN gives 0.500. The total is 1.071, which is within 1.2.

Shear from more than one source, such as sideways wind load and vertical load, is combined into one resultant shear load first. Most anchors have very little resistance to bending, so loads across the anchor should reach it as pure shear.

No. Its test load is set for tension alone. When the anchor also carries shear, the responsible engineer may raise the test load so there is margin for both. See preliminary tests and our test-load calculator.