Anchor test load calculator

A preliminary test load is NEk × νtest ÷ (αdist × Ω); a proof load is NEk × 1.5 or 1.25, depending on the sample. The calculator does the first; the second is simple enough to do by hand. Both follow BS 8539:2012+A1:2021, Annex B.

Preliminary test (Annex B.2.3.1):

1. Take the characteristic action N_Ek from the specifier.
2. Find the test load factor ν_test from the base material, the loading and the anchor: 5 or 3.5 for a nylon anchor; otherwise 3 or 2 in concrete and 4 or 3 in masonry, for long-term or short-term loading.
3. Work out the reduction factor αdist from the bridge's support spacing adist and the effective embedment depth hef. If adist is at least 3 × hef, αdist = 1.0. Otherwise, for hef up to 150 mm and adist more than 1.5 × hef, αdist = 0.4 + adist ÷ (5 × hef). Deeper than 150 mm there is no formula: the calculator gives 1.0 only where adist is at least 3 × hef, and otherwise shows the result is outside this method, for the engineer to decide. If adist is 1.5 × hef or less, use a wider bridge. In concrete, a preliminary test also needs the closest support more than 1.0 × hef from the anchor (adist ÷ 2 for a bridge centred on it); if it is not, use a wider bridge. Staht's figures, 127 mm for the t25 and t60 standard bridges and 375 mm and 575 mm for the wider bridges, are the clear distance between the feet along the bridge (Staht datasheets), the basis the industry's published bridge table uses. That errs on the safe side: the feet of a four-leg bridge actually sit further from the anchor, so the clear spacing gives a slightly higher test load, never a lower one.
4. Take the condition factor Ω from the specifier, as a single value for the case: one of the listed conditions, or, where more than one applies, the value the specifier gives.
5. Ntest = NEk × νtest ÷ (αdist × Ω). Test 5 anchors, installed only for the test, to this load.

Proof test (Annex B.3):

1. Take N_Ek from the specifier.
2. Choose the proof factor with the engineer responsible: 1.5 where at least 2.5% (but less than 5%) of the anchors are tested, or 1.25 where at least 5% are.
3. Np = NEk × ν_P,test.
4. Check Np is no more than 1.5 × Nrec, the manufacturer's recommended resistance in that base material, allowing for any spacing or edge distance reductions.
5. Work out the sample: the percentage of all anchors, rounded up, and at least 3 in each discrete area.

The calculator shows each factor it used, then the test load:

• Test load factor ν_test, from the base material, loading and anchor you chose.
• Condition factor Ω, from the condition you chose, or the specifier's value for Other.
• Support spacing for no reduction, the smaller of 3 × h_ef and 450 mm.
• Reduction factor α_dist, worked out exactly from equation B.12, so a result can differ by 0.01 kN from one worked by hand with α_dist rounded.
• Test load N_test, NEk × νtest ÷ (α_dist × Ω): load 5 anchors, installed only for the test, to it.

It gives no test load, and shows a warning instead, in three cases:

• In concrete, the nearest support is too close: L (adist ÷ 2) is 1.0 × hef or less. Use a bridge with wider support spacing.
• The support spacing is outside this method: in masonry, adist is 1.5 × hef or less. Use a wider bridge, or ask the engineer how to test.
• The embedment and support spacing are outside this method: hef is over 150 mm and adist is under 3 × h_ef. Equation B.12 does not apply there, and the engineer decides.

For proof loads, use the steps above; the calculator covers preliminary tests only.

A bonded anchor in stonework carries a long-term load. The specifier gives NEk = 0.75 kN and hef = 45 mm. The anchor will see temperatures above the manufacturer's normal service range, and the test is at normal temperature, so the specifier gives a single Ω of 0.8 for this case, having taken the long-term loading into account. νtest for a non-nylon anchor in masonry under long-term loading is 4. The test uses the Staht t25 standard bridge, with a support spacing adist = 127 mm, the clear distance between the feet along the bridge (Staht datasheet). These are the figures the calculator opens with.

• 3 × hef = 135 mm, more than 127 mm, so αdist applies. 127 mm is more than 1.5 × h_ef (67.5 mm), so equation B.12 holds.
• α_dist = 0.4 + 127 ÷ (5 × 45) = 0.4 + 0.564 = 0.964.
• N_test = 0.75 × 4 ÷ (0.964 × 0.8) = 3.0 ÷ 0.771 = 3.89 kN.

With a Staht Bridge 375-25, αdist = 1.0 and Ntest = 3.0 ÷ 0.8 = 3.75 kN.

300 anchors are installed in one area of concrete. The specifier gives NEk = 4.2 kN, and the manufacturer's recommended resistance Nrec = 4.5 kN.

• 2.5% sample: N_p = 4.2 × 1.5 = 6.3 kN. The limit is 1.5 × 4.5 = 6.75 kN, so 6.3 kN is allowed. 2.5% of 300 is 7.5, so test 8 anchors.
• 5% sample: N_p = 4.2 × 1.25 = 5.25 kN. 5% of 300 is 15, so test 15 anchors.

The engineer responsible for the specification chooses between them.

Scaffold ties tested under NASC TG4:25 use simpler multiples of the tie duty: 2 × for preliminary tests (3 × for nylon anchors) and 1.25 × for proof tests. See scaffold tie test loads.