Steel over a corridor that stayed open: how the picks were sequenced

The rigging sheet is on the tailgate, the outrigger floats are down on their mats, and the first beam of the morning is already off the ground when the word comes to hold. The pick is not the hard part. The building underneath it is. Note E-031 covers an addition to an occupied school, two new wings tying into a corridor that stayed open from the first column to the last piece of decking. Nine picks crossed the roof line over eleven days, each in a window written down before the crane left the yard.

What got written down before the crane was ordered

The first document on this job was not a shop drawing, it was a pick plan, and it existed before the crane was reserved. It carried the crane's location, its boom length, the radius at each pick, the weight of each pick with rigging added, and the percentage of chart that combination used. Means and methods belong to the erector, which is what the AISC Code of Standard Practice says plainly, and the crane work itself falls under OSHA 1926 Subpart CC. Three beams carried the heaviest picks: W24x84 at 40 ft 6 in, which is 3,402 lb of steel. The spreader bar added 480 lb, the slings and shackles another 118 lb, so the plan carried 4,000 lb for a pick. That number, not the member weight, is the one that goes against the chart.

What does the chart say this crane can pick at that radius?

A 90 ton truck crane on this job, 110 ft of main boom, outriggers fully extended on 4 ft x 4 ft timber mats. The radius was measured, not estimated: a tape from the center of rotation to the hoist line with the load just clear of the mats, which read 58 ft on the heavy picks. The chart in the cab at 110 ft of boom, 58 ft of radius and full 360 degree swing reads 9,600 lb. Against a 4,000 lb pick that is 42 percent of chart. Worth saying out loud: the same chart carries separate lines for outriggers fully extended, mid-extended and retracted, and on this machine the mid-extend line sits roughly 30 percent under the fully extended one.

How wide does the flag line run?

The line on the ground did two jobs. First it kept people out from under a swinging load, run 12 ft outside the swing radius, which put it past the corridor doors on the north side and short of the parked cars on the south. Cones every 10 ft, tape strung between them, no gap a person could walk through without ducking. Second, the line marked where the boom was allowed to go: the swing was restricted to a sector so the boom could not pass over the corridor outside a window, and the operator proved the stop before the first pick with the boom empty. A flagger stood at each end whenever a load was in the air, two people, no exceptions, because the ends are where somebody walks in from.

The windows, read off the building's own schedule

Traffic set the plan, so it started with the building's day: 6:45 in the morning to about 4:15, the corridor carrying students between periods and a lunch crowd that filled it. That left two clean windows: 6:00 to 7:15, and 4:15 until the light went. Between them sat a single 40 minute closure, posted twelve days ahead, emptied by the building's own staff with a marshal at each end. The count came to four picks in the morning window, four in the evening, one beam through the posted closure. On a school gym job the same season the whole roof went on in six days, because the gym emptied at a set hour. That is the difference between a building that stops and one that does not.

What got checked before each lift over the roof line

The checklist was read out loud on the tailgate before every pick, starting with the drawing, not the crane. Pick plan sheet, radius, boom length, load. Then the geometry over the building, which is where this job was different: hook height at the pick was 74 ft, the ridge line sat at 41 ft 6 in, the parapet cap at 44 ft. With a 40 ft beam hanging level, the low point of the rigging cleared the parapet by 8 ft 4 in at the top of the arc. That number came off paper first, with a tape and a chalk line on the wall, then got confirmed on the first pick. Also on the list: the slings and shackles read against their tags; two tag lines on every 40 ft member, because one line gives you a spinning beam; plywood over the roof membrane wherever a sling could touch.

What did the wind do?

Wind is the one item on that list nobody controls, so the pick plan carried a number: no picks above 20 mph sustained, and the call was on the gust rather than the average. On the fourth morning the handheld read 14 mph at the cab with gusts to 19, and the beam went up. Two days later it read 22 on a gust while the member was still on the trailer, and the pick came off the schedule. It went up the next morning at 6:20, into the window it had been planned for. Calling a pick costs an hour. A beam that catches the parapet cap costs a season.

What this note does not cover

This is a record of how the picks were sequenced on one addition, not a lift plan, and it does not replace one. It does not cover the crane's inspection records under OSHA 1926.1412, or the qualification of the operator and the signal person, which sit in 1926.1427 and 1926.1428. It does not cover the bearing capacity of the ground below the mats: that number came from somebody else's soils report. It does not cover fall protection for the connectors, the final bolt-up, the decking, the fire watch during torch work, or the corridor's own egress plan. It does not say the corridor was safe for the people in it during a window. That was the building's call, with notice posted and its own staff walking the ends. And it covers one crane on one site.

What a GC or an owner can ask for

Ask the erector for the pick plan and the chart page matching each crane setup, and ask to see the radius marked on the ground before the first pick goes up. Then ask the building for its traffic at 15 minute resolution across a week, because the difference between "the corridor closes at 4" and "the corridor is empty by 4:20" is either a window or no window at all. Write the windows into the schedule as constraints, not courtesies, and put the marshals and the posted notice in the budget. The measuring in this note took about twenty minutes a day. The eleven days went to waiting on the building instead of fighting it.