Chimney Dismantling - OI Manufacturing, Alloa
- Structure: 75 m reinforced concrete chimney (tapering shell)
- Engineering output: Weight schedule at 1 m increments for lift planning
- Minimum lifting safety factor: FoS ≥ 2.0 (crane capacity ≥ 200% of worst-case lifted weight, incl. rigging & dynamic allowance)
- Deliverables: Weight tables, lift envelopes, sequencing notes, exclusion-zone guidance, hold-points & QA checklist
- No maintenance/inspection history
- Impact: Unknown wall thickness variation, reinforcement density and local defects required conservative assumptions and onsite verification.
- Height, taper & variable thickness
- Impact: Accurate weight distribution per metre was critical to crane selection, rigging configuration and cut lengths.
- Safety-critical lifting in a live industrial setting
- Impact: Crane siting, ground bearing, wind-speed limits, exclusion zones and communication protocols had to be clearly defined and enforced.
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1) Survey, assumptions & verification
- Compiled available drawings/records; undertook dimensional checks and visual inspection notes.
- Established conservative material assumptions (e.g., concrete density, reinforcement allowance, any liner/insert allowances where applicable).
- Embedded hold-points to reconcile actual measured piece-weights (via load indicator) against calculated values and update the plan if required.
2) Weight calculations & lift envelopes
- Produced a 1 m increment weight schedule accounting for taper and thickness variation, plus rigging and dynamic load allowances.
- Set lift envelopes and radius charts compatible with the selected crane duty, including wind limits per manufacturer’s charts and FoS ≥ 2.0.
3) Dismantling strategy & sequencing
- Recommended a top-down phased dismantling: cut ring segments to controlled lengths to maintain shell stability; avoid excessive eccentricity.
- Defined cut geometry and temporary bracing/prop allowances where local weaknesses might occur (e.g., near openings or construction joints).
- Provided exclusion zone principles and tag-line control notes to manage swing and rotation.
4) Site safety & QA controls
- Aligned with BS 7121 (planning of lifting operations) and BS 5975 (temporary works).
- Required lift plan sign-offs, daily briefings, radio protocol, and a permit-to-lift process with stop rules if conditions (e.g., wind) exceeded limits.
- Included ground bearing checks for crane mat design inputs and clear red/amber/green criteria for proceeding.
- Predictable lifting operations enabled by a validated 1 m weight schedule and FoS-based crane selection.
- Risk reduced through conservative assumptions, measured-weight reconciliation and clearly defined hold-points.
- Efficient programme with cut lengths tailored to crane radius/duty and site logistics, improving productivity while maintaining safety.
Structural calculations · Lift study & duty envelope · Dismantling methodology advice · Temporary works/method constraints · Risk assessment & QA/hold-points · Exclusion-zone guidance
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