Scope — Erection Tolerances vs Fabrication Tolerances
IS 12843 specifies the permissible deviations of a steel structure as ERECTED — column plumb/verticality, levels, alignment and member position — distinct from material rolling tolerances (IS 1852/IS 12779) and shop fabrication tolerances. Erection tolerances are the defined accept/reject band that keeps the as-built geometry close enough to the IS 800 design assumptions (no unintended eccentricity/second-order effects).
Key Requirements
•Applies to the erected structure geometry — not rolling (IS 1852/IS 12779) or shop fabrication tolerances
•Permissible deviations defined for plumb, level, alignment and position of members/structure
•Erected geometry must stay within tolerance so IS 800 design assumptions (no extra eccentricity) hold
•Specify the applicable tolerance class in the contract/specification (it is the accept/reject basis)
•Survey-verify the erected structure against IS 12843 before sign-off
Practical Notes
✓Erection tolerances are not pedantry — out-of-plumb columns and mis-aligned members introduce eccentricity and second-order moments the IS 800 design did not allow for.
✓Distinguish the three tolerance regimes: rolling (IS 1852/IS 12779), shop fabrication, and erection (this code) — disputes arise when they are conflated.
Common Mistakes
⚠Conflating erection tolerances with rolling/fabrication tolerances.
⚠No specified tolerance class in the contract (no objective accept/reject basis).