Erection tolerances
Beam level check: each end against specified level and end to end
- where
- deviation at ends A and B (mm)
- measured levels at ends A and B (m)
- specified level (m)
- difference between the ends (mm)
Explain this equation
Checks surveyed beam levels at both ends against the specified level and against each other. Use it during the frame survey before decking and slabs go on.
L_s is the specified top of steel level. L_A and L_B are the measured levels at each end. δ_A and δ_B are how far each end is from the specified level, and δ_AB is how much one end is higher than the other.
Each deviation is a simple difference of levels, multiplied by 1000 to turn metres into millimetres. The end-to-end difference shows if the beam is sloping even when both ends are within the overall limit.
Sense check: ends 7 mm and 3 mm high are both inside ±10 mm, and the 4 mm difference is inside ±5 mm.
Watch out: take levels at the connections, not at midspan, where camber and deflection change the reading.
Compares surveyed top-of-steel levels at both ends of a beam with the specified level and with each other.
Enter your values to see the result.
Good to know
NSSS-based checklists give beam level relative to the specified level as ±10 mm at the supporting column, and the level at each end of the same beam as ±5 mm relative to each other. Adjacent beams within 5 m are also checked against each other. Survey at the connection, not at midspan, because deflection and camber are excluded from these tolerances.
Common mistake
Surveying at midspan, where camber and self-weight deflection make the beam look out of level.
Limits
Levels in metres to a common datum. Does not include camber or deflection; see the camber check.
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)
- BCSA National Structural Steelwork Specification, 5th edition (cl. 3.4.5 HD bolt holes 6 mm over bolt diameter; 8.1.6 steel packs; 9.2 foundation and HD bolt check before erection; 9.6 erected components)
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.