Load security on a working platform with a materials hoist
A 6 m high intermediate scaffold carries a working platform 1.2 m wide. Two workers are laying blocks and a third is loading a materials hoist bracket mounted at the end standard. Blocks are stacked three pallets high beside the hoist, and a mixer sits on the platform mid-span. The design load is stated as 2.0 kPa uniformly distributed, with no point-load allowance noted. The platform boards are 225 mm nominal, laid with visible gaps at two joints and one board showing a split at a knot. The hoist rope runs over the guard-rail top rail without a sheave. Workers report the platform 'bouncing' near the hoist.
1. Assess the loading and the platform condition against the design, and state what must change.
Read the worked answer
Treat the stated 2.0 kPa as a uniformly distributed allowance only - it does not authorise concentrated loads.
Loading check:
- Three pallets of blocks beside the hoist is a heavy concentrated load over a small footprint at the end of the scaffold, exactly where the hoist bracket also applies load. That is a point load and an eccentric load, neither covered by a UDL figure. The designer must confirm or the stack must be reduced and relocated to spread load over the standards.
- The mixer mid-span is another point load; it also vibrates. Confirm it is within design or remove it to ground and pump/barrow materials.
- The hoist bracket needs its own design check and a proper fixing; a bracket at an end standard with a rope over the guard-rail is not acceptable.
Platform condition:
- Gaps at joints and a split board mean the platform is not fit for purpose - boards must be laid close-butted, supported at the specified spacing, and free of defects. Replace the split board and close the gaps.
- The 'bouncing' is a symptom of inadequate support, loose boards, or overloading near the hoist; investigate before further use.
Changes: reduce and reposition block stacks, remove the mixer from the platform or get design approval, fit a proper sheave/guide for the hoist rope so it does not bear on the guard-rail, replace defective boards, and re-inspect and tag before work resumes.
2. What does the bouncing tell you, and how would you investigate and control it before allowing work to continue?
Read the worked answer
Bouncing under load is a warning, not a nuisance. It suggests one or more of: boards not properly supported or butted (movement at joints), transoms too far apart for the board span, loose couplers allowing movement, a standard settling under the concentrated hoist load, or the platform being overloaded locally.
Investigation:
- Clear the platform and the ground below; barricade and tag.
- Competent person checks transom spacing against the board span and design, board condition and bearing, coupler torque, standard plumb and base/settlement, and the hoist bracket fixings.
- Compare actual loads (blocks, mixer, workers) with the design; if point loads are not covered, get the designer to confirm or change the method.
- Check the foundation at the hoist end for settlement or soft spots.
Controls before restart:
- Correct the cause - add supports/transoms, replace boards, re-torque or replace couplers, re-level and re-seat bases, redesign the hoist bracket.
- Impose a loading regime: marked stacking limits, designated material areas over standards, no mixer on the platform unless designed, housekeeping to keep the platform clear.
- Brief the crew on the limits and why the bouncing mattered.
- Re-inspect, record and re-tag; monitor for recurrence over the next shifts. If it recurs, stop and escalate to the designer.