Pull testing anchors in brickwork and blockwork

Anchors in masonry usually need testing because the maker's data, or the ETA's conditions, often do not cover the bricks or blocks on the job. Tests to find an allowable resistance are rarely needed in concrete, where BS 8539:2012+A1:2021 recommends anchors with a European Technical Assessment (ETA). In practice, they are mostly needed in masonry.

No tests are needed when the anchor has an ETA for the category of masonry, and the units on the job are at least as strong and at least as large as the ETA states. If they are weaker or smaller, tests are needed. See when you need to site test.

Put test anchors in the solid body of a brick or block, clear of mortar joints and well in from the edges of the wall, as BS 8539 Clause 5.3.3.3.2 recommends.

Sometimes the working anchors cannot help landing in joints: render may hide the coursing, or a bracket's hole pattern may not line up with it. In that case, Figure 7 of the same clause sets out what to do.

On a rendered or plastered wall where you cannot see the joints, or cannot keep anchors inside the bricks, the specifier may set Ω = 0.75 and have you test in solid brick. Ω divides the test load, so this raises the load to cover working anchors that end up in joints.

On brickwork, stand the bridge feet on the bricks around the one that holds the anchor. That way the joints round the anchor's brick are tested too, so soft or old mortar, or a brick loosened by heavy drilling, shows up in the result.

In blockwork, keep the closest support at least 1.5 × hef from the anchor, where hef is the effective embedment depth. A smaller bridge can still be used with αdist, as long as its support spacing adist is more than 1.5 × h_ef; otherwise use a wider one. See choosing a bridge.

On perforated or hollow bricks, angle the feet so that neither sits along a row of holes.

Proof tests don't use αdist. Use the neighbouring units where you can; with large units, the closest support can come in to 0.5 × hef.

Anchors go into dense concrete blocks with hef = 80 mm, for short-term loading. The specifier gives NEk = 1.5 kN and Ω = 1.0. ν_test for a non-nylon anchor in masonry under short-term loading is 3.

• Staht t25 standard bridge: L = 63.5 mm, from a support spacing adist of 127 mm, the clear distance between the feet along the bridge (Staht datasheet). L is less than 1.5 × 80 = 120 mm, so αdist applies, and adist (127 mm) is more than 1.5 × hef (120 mm), so equation B.12 holds. αdist = 0.4 + 127 ÷ (5 × 80) = 0.718. Ntest = 1.5 × 3 ÷ 0.718 = 6.27 kN.
• Staht Bridge 375-25: L = 187.5 mm, more than 120 mm, so αdist = 1.0. Ntest = 1.5 × 3 ÷ 1.0 = 4.50 kN.

The wider bridge gives a lower test load, and less load on the blockwork. Our test-load calculator works this out for any support spacing, and warns when a bridge is too narrow for the method.

An anchor with an ETA for a category of masonry, used in units weaker or smaller than the ETA states, can be tested in two ways, under BS 8539 Annex B.2.2.

• 5 to 15 tests to failure (Annex B.2.2.1), with the result worked out by statistics. See preliminary tests.
• 15 or more tests to failure, to the relevant European Assessment Document (EAD) and its EOTA Technical Report. For metal injection anchors in masonry (EAD 330076 with EOTA TR 053), N1 is the mean of the lowest 5 results, and the characteristic resistance is αdist × 0.7 × β × N_1, no higher than the ETA's value for the same category of masonry.

The EAD route needs more tests, so it takes longer. The two routes give different answers; BS 8539 accepts either.

No reduction for support spacing is needed where EOTA TR 053 expects the failure to stay local: anchors deeper than 150 mm in multi-leaf walls of small solid bricks, anchors in mortar joints, and anchors in hollow or perforated bricks. The supports must still be more than 1.5 × h_ef apart and leave room for the failure to form. See choosing a bridge.

A test anchor only tells you about the working anchors if it goes in the same way, so have a competent installer follow the manufacturer's instructions to the letter, hole cleaning included. Drill with bits inside the ISO 5468 medium tolerance range; new bits carrying the PGM inspection mark qualify. Leave bonded anchors for at least their recommended curing time before testing them.

Before you test, look at the brick and the joints around it. Cracks across the brick or round its joints mean drilling or setting has damaged it.

Shear tests are rarely needed, because shear resistance is usually limited by the strength of the anchor or of the structure. They may be needed when fixing into low-strength masonry. See shear testing.