Anchor testing glossary
The terms and symbols used in Staht's guides to testing anchors and fixings on site, under BS 8539 and NASC TG4:25. Each guide also defines a term the first time it uses it. See all our guides.
Terms and symbols
- Characteristic action, N_Ek
The load the design applies to one anchor, without safety factors; the "unfactored load"
- Allowable resistance, N_R,all
The load an anchor may carry in a base material, found from site tests
- Recommended resistance, N_rec
The manufacturer's recommended load for an anchor in a given base material
- Characteristic resistance, N_Rk
The resistance 95% of anchors are expected to exceed, worked out from tests to failure
- Ultimate resistance, N_Ru
The failure load in a test; N_Ru,m is the mean of a series
- Test load, N_test
The load a preliminary test anchor must hold: NEk × νtest ÷ (α_dist × Ω)
- Proof load, N_p
The load an installed anchor is proof tested to: NEk × νP,test
- Proof factor, ν_P,test
1.5 where at least 2.5% (under 5%) of anchors are tested, 1.25 where at least 5% are
- Test factor, ν_test
The multiplier on N_Ek in a preliminary test, by anchor, base material and loading
- ν_ave and ν_low
Divisors applied to the average and lowest failure loads after a preliminary test failure
- Condition factor, Ω
A factor of 1.0 or less for conditions the test doesn't reproduce, such as wet or cracked concrete
- Reduction factor, α_dist
0.4 + adist ÷ (5 × hef), for hef up to 150 mm and adist between 1.5 × hef and min(3 × hef; 450 mm): removes any benefit from bridge supports set close to the anchor
- Support spacing, a_dist
The spacing of a test bridge's supports: to the axis of point supports, or the clear width between continuous ones
- Reaction spacing, L
The distance from the anchor's centre line to the closest bridge support
- Effective embedment depth, h_ef
The depth to the lowest point at which the anchor grips the base material
- Nominal embedment depth, h_nom
The anchor's installed depth; for nylon anchors h_ef is taken as half of it
- First movement, N_1st
The load at which an anchor starts to move, usually taken at 0.1 mm; N_1st,m is the mean
- Load relaxation
The drop in reading when loading stops, as stresses spread into the base material
- Preliminary test
A test on 5 anchors, installed only for the test, to find whether an anchor suits a base material
- Proof test
A test on a sample of installed anchors to check they were installed correctly
- Test to failure
A test that loads an anchor until it fails, to measure its resistance
- Discrete area
Part of a job with a different anchor, base material, weather exposure or installation team
- Specifier
The person who designs the connection and selects and specifies the anchor
- Tie duty
The working load a scaffold tie must carry, from a TG20 or TG30 compliance sheet or a design
- Characteristic edge distance and spacing, c_cr and s_cr
The edge distance and spacing at which an anchor reaches its full resistance
- Minimum edge distance and spacing, c_min and s_min
The smallest edge distance and spacing allowed for an anchor
- ETA
European Technical Assessment: an anchor's assessed performance and conditions of use
- EAD
European Assessment Document: the method an ETA is assessed to
- EOTA TR 053
EOTA's Technical Report on job-site tests of metal injection anchors in masonry
- Creep
Slow movement under a sustained load; why nylon anchors take higher test factors
- Concrete cone failure
Failure in which a cone of concrete breaks out with the anchor
- Bond failure
Failure of the bond between resin and the base material or the anchor rod
- Pry-out
A shear-test failure in which the anchor is levered out without breaking
- Full-scale deflection (FSD)
A gauge's full range; accuracy is often stated as a percentage of it
- Partial factors, γ_M and γ_F
Factors on material resistance and on actions used in design to Eurocode methods
- Coefficient of variation, v
The standard deviation of failure loads divided by their mean