A school gym frame in six working days: the sequence

Monday, 6:40 a.m., and the yard is cold enough that the tape measure wants to stay coiled. The gym package sits on three bunks by the shop door: twelve columns, six rafter pairs, purlins, and the loose angle for the door jambs. The crane is booked for six working days and the school wants the roof closed before the first hard frost. What follows is the note I kept on the back of the erection plan, written while the picks were happening, not cleaned up after.

What got checked before the first pick

The shake-out starts at the bunks, not at the foundations. Each column came off the truck and went onto timber, then got taped from the bottom of the base plate to the top of the cap plate, read against the dimension line on the shop drawing. Twelve columns, all W12x65, all called at 24 ft 3 in. Ten read within 1/8 in. Two read a quarter inch long. That sits inside the mill tolerance the AISC Code of Standard Practice allows on a rolled shape, and outside what I want when the anchor bolts are already poured, so those two went to the west end, where the base plates had the most shim room.

Base plates were burned on the shop table, kerf running about 1/16 in on 3/4 in plate, and every plate got a caliper at four corners: reading 0.742 to 0.756 in against the callout, which matches the mill certificates for the two heats on the job. The certificates also gave the yield, 50 ksi on both heats, which is what the drawings assume.

Which end of the building gets the first pick?

That one is answered on the drawing, not in the field. The braced bays fell on the two interior bays at the west side of the gym, so the iron went up west to east, which put the crane on the parking pad for four of the six days and on the gravel apron for the rest.

The crane was a 60 ton rough terrain, set on mats, working at a 38 ft radius for the column picks and 52 ft for the far rafter halves. First pick was the two grid B columns, 815 lb each with the base plate on. Then the grid C pair, then the horizontal bracing between them, so a stable two bay frame was standing before anything else left the ground. The anchorage rule on this job is the one in OSHA's steel erection standard: four anchor bolts per column unless the drawings justify two, and nobody leaves the ground on a bay that cannot take the load.

Six days, in the order the picks went

Monday: shake-out, anchor bolt as-builts with a tape and a string line, four columns set. The worst bolt group read 3/8 in out, which the slotted holes in the base plate absorbed without a field modification.

Tuesday: the remaining eight columns, the X bracing in both braced bays, plumb on all twelve. Plumb was read with a level and a plumb line against the 1:500 column tolerance in the AISC Code of Standard Practice, which on a 24 ft column works out to about 9/16 in. Worst column read 3/8 in.

Wednesday: rafters. Six pairs, bolted at the ridge with 7/8 in A325 bolts, turn of nut per the RCSC specification, a third turn past snug on the short bolts and a half turn on anything over four diameters long. Last rafter landed at 1:15 p.m.

Thursday: 0.4 in of rain by 9 a.m. The crane sat. The crew did not.

Friday: purlins, edge angle, safety cable, first deck bundles set on the frame.

The following Monday: decking closed out and the frame handed to the roofer.

When did the frame stop needing the crane?

Wednesday, 1:15 p.m., when the last ridge connection came tight. Before that the frame depended on the choker and two tag lines. After the purlins went on Friday and the deck was screwed down Monday, the braced bays and the diaphragm carried it.

The check that ran behind the crane was bolt-up. Acceptance was the rotation, match marked on the nut and the bolt end, and a torque wrench read afterward at 470 lb ft as a check that nothing had been left finger tight. Every bolt in the braced bays was read and one in four everywhere else. Two bolts in the northeast braced bay came out and were replaced: the nuts had been run down on washers that had already spun, so the turn was not readable.

The crane released at noon Friday. It had been booked through Monday.

The weather day that cost nothing

Thursday's rain cost zero days on the frame. The deck bundles were already on the ground, the bolt-up was behind, and the touch-up on the two field welds at the door jamb could happen under a tarp. What it did cost was a crane day, since the rental ran calendar days rather than working days.

What made the day cheap was the order the work was planned in. Column picks and rafter picks need the crane. Bolt-up, layout, touch-up and bundle staging do not. Anything that could come off the crane came off it in the schedule before the job started, which is a decision made at a desk, not in the rain.

What this note does not cover

This is a set of readings taken on one job by one crew. It is not a special inspection report and does not stand in for one.

It does not cover the welding. The two field welds at the door jamb were made to a procedure qualified under AWS D1.1, and this note records no result beyond a visual that was not flagged.

It does not cover the foundation or the anchor bolt layout past the one string line reading. Those bolts were set by others.

It does not cover the deck diaphragm design, the fire protection, or the paint system beyond a dry film check on the touch-up.

It does not cover what the engineer of record accepted. Two columns landed a quarter inch long and were shimmed at the west end. That is a field decision belonging to somebody with a stamp, and this note records the reading, not the approval.

If you are running the next one

Write the pick sequence on the back of the erection plan before the crane shows up, and write the instrument reading next to each member as it lands. The readings are what let you go back at a supplier, or defend a half day to a GC.

If you are the GC writing the schedule, book the crane for the days it is actually needed, not the days the building is standing. On this job one of the six days was rain, and none of it touched the frame, because the work that did not need the crane was already sitting behind it.