Erection tolerances
Column plumb check against the permitted deviation per storey
- where
- permitted deviation (mm)
- storey height (mm)
- divisor in the limit h/k (600 in the NSSS)
- minimum permitted deviation (mm)
- measured deviation as % of permitted
- measured offset of top relative to base (mm)
Explain this equation
Checks whether a column is plumb enough in one storey. Use it when surveying the frame before final bolting and before floors are cast.
h is the storey height and k the divisor in the limit h/k, 600 under the NSSS. Δ_min is the smallest permitted deviation, 5 mm. Δ_p is the permitted deviation, whichever is larger. δ_m is the measured offset of the top of the column from its base, and U shows it as a percentage of the limit.
The limit grows with height because a small lean adds up over a tall column. The minimum stops the limit becoming unrealistically tight on short columns. Utilisation compares the measured lean, ignoring direction, with the limit.
Sense check: a 3 m storey allows 5 mm; a 4.2 m storey allows 7 mm. A reading of 4 mm in a 4 m storey uses 60% of the allowance.
Watch out: check the overall deviation from the base as well, and survey in calm weather out of strong sun, which bends columns.
Checks a measured column out-of-plumb against the specification limit for one storey, h/600 or 5 mm under the NSSS.
Enter your values to see the result.
Good to know
NSSS-based checklists give column plumb as ±h/600 or 5 mm per storey, with a maximum of ±25 mm base to eaves for single-storey columns and ±50 mm overall for multi-storey frames up to 10 storeys (taller frames by agreement with the engineer). SCI quotes 5 mm for a 3 m column. If the project works to BS EN 1090-2 Annex B instead, set k and the minimum to the class in the execution specification. Measure in calm weather and note the temperature and sun: one-sided heating bends columns.
Common mistake
Checking each storey but not the accumulated deviation from the base, or plumbing a column before the beams and bracing that fix it are connected.
Limits
One storey or one single-storey column. Overall limits and plan position at the base are separate checks.
Sources
- BCSA National Structural Steelwork Specification for Building Construction, 7th edition, 1st revision (2023) – Section 9 accuracy of erected steelwork; Section 7 cambers; 8.6.2 reference temperature 20 °C
- AJB Setting Out: QA checklist, structural steelwork (citing the NSSS: column plumb ±h/600 or 5 mm per storey, max ±25 mm single storey and ±50 mm overall up to 10 storeys; beam level ±10 mm; level at each end of a beam ±5 mm; top of base plate ±5 mm)
- SCI P178 Design for construction, ch. 8 Tolerances (non-verticality of a 3 m column: 5 mm offset under the NSSS)
- BS EN 1090-2:2018+A1:2024 Execution of steel structures and aluminium structures – Technical requirements for steel structures (8.2.2 bolt protrusion; 8.5 preloaded bolts: Fp,C = 0.7 fub As; torque method Mr,2 = km d Fp,C, first step about 0.75 Mr,i, second step 1.10 Mr,i; combined method Mr,1 = 0.13 d Fp,C simplification; k-classes K0, K1, K2; Annex B tolerances)
- BCSA: A guide to the erection of multi-storey buildings (Publication 42/06), and BCSA erection guidance on method statements and stability
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.