Pick and Carry vs. the Static Chart
A 150-ton crawler with 90 ft of boom (roughly 310,000 lb operating weight) must pick a 16,000 lb generator from a truck at 30 ft radius and walk it 140 ft to a pad; rigging is 600 lb. The static chart shows 28,000 lb at 30 ft. The travel chart - boom in line with the tracks, level firm ground - shows 18,000 lb at 30 ft for pick-and-carry. The route crosses a 6 in. concrete slab with a 2 in. step at a construction joint, then 60 ft of compacted gravel. The operator plans to pick, swing 90 degrees so the load rides over the side, and carry it 8 ft off the ground so the spotter can see underneath.
1. Which chart governs, and is 16,600 lb acceptable on this route?
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The travel chart governs - 28,000 lb is irrelevant once the crane moves with the load.
- Gross load = 16,000 + 600 = 16,600 lb against 18,000 lb. That is 92% of chart with a 1,400 lb margin - and the route is not 'level firm ground.'
- Two chart notes are already being violated by the plan:
- Boom in line with the tracks: swinging the load 90 degrees to carry it over the side is outside the travel chart's basis and puts the load's moment across the crawler's weak axis.
- Level firm ground: a 2 in. step at a slab joint is an impact. Dropping a track over a step can momentarily multiply the load on the boom and on the ground, and 92% leaves no room for it.
Better plan: reposition the truck so the carry radius is shorter (a few feet of radius buys thousands of pounds on a travel chart); keep the boom in line with the travel direction; carry the load as low as practical - roughly 2-3 ft of ground clearance, not 8 ft, since height adds overturning moment and blocks the operator's view; never travel and swing simultaneously; ramp or plate the joint so there is no step. If the margin cannot be improved, break the move down or use a larger crane.
2. Check the ground under the route and state what has to be done before the walk.
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Ground bearing during travel:
- 310,000 + 16,600 = 326,600 lb over 144 sq ft of track = ~2,270 psf (~16 psi) average - and travel is not even: weight shifts fore and aft as the crane rocks, and the step at the joint concentrates load on a short length of track.
- A 6 in. unreinforced slab is unlikely to take that without cracking, and a cracked slab edge can punch up under a shoe. Get the slab checked, or mat/plate the crossing.
Route survey before the walk:
- Walk the entire 140 ft on foot - look for soft spots, patch repairs, trench backfill, vaults, basement walls, culverts, and any underground void. Surface appearance proves nothing.
- Verify compaction or bearing capacity along the gravel section, not just at the setup point.
- Remove or ramp the 2 in. step; verify the cross-slope and grade everywhere on the route against the manual's travel limits.
- Confirm no overhead obstructions or power lines along the path.
- Clear the route of personnel; assign a spotter ahead of the crane with a clear stop signal; keep everyone out of the track path and out from under the load.
3. Who directs the move, and what communication has to be in place?
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- A designated signal person/spotter walks ahead of the load-side track, in the operator's line of sight, and directs the travel. If the operator loses sight of that person, the crane stops - travel is not continued on assumption.
- The signal person is not also rigging or handling the load; their only job is directing the move and watching the route and clearances.
- Agreed, standard hand signals plus a radio; a horn signal to stop; everyone briefed before the move on the route, the stop point, and where they may not stand.
- No one under the load, on the load, or between the load and a fixed object to 'steady' it. Taglines only, from outside the swing/fall zone.
- The operator stops and resets if anything changes - ground condition, wind, visibility, or the load starting to swing.
- Brief emergency plan: where the load is set down if the move has to be aborted, and who makes that call.