IS 12843 limits how far an erected column may deviate from vertical — both per storey and cumulatively over the full height. Out-of-plumb columns carry their axial load eccentrically, generating P-Δ second-order moments the design did not include; the per-storey and overall-height limits cap that effect. Plumb is checked by survey/plumb-line/instrument during and after erection.
Key Requirements
•Out-of-plumb limited per storey AND cumulatively over the total height (the smaller governs)
•Excess lean → P-Δ eccentricity and second-order moments outside the IS 800 design
•Check verticality progressively during erection (correct early — hard to fix once loaded/locked)
•Survey/instrument verification of plumb at completion against IS 12843
•Out-of-tolerance lean requires assessment/correction, not acceptance
Practical Notes
✓Plumb errors compound up the height — control them storey-by-storey during erection; correcting a leaning frame after it is loaded is far harder and costlier.
✓An out-of-plumb column is an eccentricity problem: the structure may look fine but carry moments the design never checked.
Common Mistakes
⚠Checking only overall plumb, not per-storey (cumulative drift hidden).
⚠Accepting out-of-plumb lean without a P-Δ/eccentricity assessment.
⚠Correcting plumb too late (after loading/locking the frame).