Decking in a Northeast wind: the pattern the crew checks twice

The bundle sits on the beams with two banding straps still on it and a tag that says 1,200 lbs. The forecast for the afternoon says gusts to 35 mph out of the northwest, which on this frame means the wind comes across the short dimension of the sheets. Before anybody cuts a strap, the foreman walks the bay with a tape and a can of layout paint, and marks where the first row of fasteners goes. That walk is the whole article. Everything after it is just following the marks.

What gets written on the back of the drawing before the pick

Three lines, in pencil, on the back of the erector's set: bundle count and weight, the sheet length as it came off the truck, and the wind call for the day. Then the two numbers that drive the fastening: the side-lap spacing and the end-lap spacing, taken off the deck manufacturer's placement drawings, not off memory. On this job the sheets are 3 in. deep, 36 in. wide, 20 ga., spanning 8 ft. between beams, which puts us in the middle of the span table for a 1.5 in. flute bearing. The placement drawing calls for a 36/4/36 pattern: a row of fasteners at the side lap, four fasteners per sheet per intermediate support, a row at the end lap. That is the pattern we check twice. It is also the pattern somebody will try to shorten at 4 p.m. when the wind picks up and the crew wants to go home.

Do you stage bundles on the frame or on the ground?

On the ground, if the site allows it, and away from the lift path. A 1,200 lb bundle has a lot of surface area and very little weight, which is the worst combination there is for wind. The staging plan for this job put bundles on dunnage outside the building line, banded, with the long axis into the prevailing wind so a gust has less to grab. Bundles that have to be landed on the frame get landed one at a time, banded, and fastened down or tied off before the next pick comes up. A bundle sitting free on a bay of deck, unbanded, at 2 p.m. with a front coming through is the way deck ends up in the parking lot.

Which line on the drawing decides the side lap?

The side lap is decided by the sheet profile, not by the crew. Nest the sheets so the male leg of one sits in the female leg of the next and the panels are fully engaged along the full length, then check that engagement with a tape at three points: each end and the middle. If a sheet is not fully nested, the fasteners at that lap go in crooked, the lap opens, and the diaphragm value the engineer counted on is not there. The AISC Code of Standard Practice treats deck as a structural element with tolerances like anything else, and it does not have a clause that forgives a lap that was never closed. We check nesting before we check anything else, because a bad lap makes every number after it meaningless.

How much torque on a deck fastener, and who checks it?

The fasteners here are #12 self-drilling screws with a bonded washer, driven with a clutch-nosed screw gun set so the screw seats and the clutch releases rather than the screw stripping out the thin sheet. The check is not a torque wrench for most of the field work, it is a visual and a hand check: the washer is compressed and seated, the screw is not stripped, the sheet is pulled down tight to the support. On the QA row, ten fasteners picked at random per bay, we use a torque wrench on the ones we can reach and read them at 25 to 30 in.-lb, which is inside the range the deck manufacturer publishes for 20 ga. to 16 ga. material. One screw that spins free in a stripped hole is counted as a miss, not as a screw. Misses get a new fastener beside it, not a bigger one in the same hole.

When does the crew call it for the day?

The honest answer is that the call is made before anybody is on the deck, not during. The rule on this job was: if sustained wind is forecast above 25 mph, or gusts above 35, deck setting stops. Under that, bundles stay banded and on the ground, and the crew goes to something that does not involve a 20 ft. by 3 ft. sail. Above it, sheets already placed get fastened to the pattern, not to a shorter pattern because the crew is in a hurry. A half-fastened bay at the end of the day is the actual hazard, more than the wind itself. The OSHA steel erection standard has its own requirements for securing deck and for what happens when a load is suspended, and the practical version of it is: never leave a bay in a condition that only holds because the wind has not changed yet.

What this note does not cover

It does not cover the diaphragm design. The number of fasteners the engineer needs for lateral load comes off the drawings and the deck manufacturer's span and fastener tables, which follow the Steel Deck Institute's design standards, and a pattern that looks right in the field can still be short for the diaphragm if somebody misread the sheet. It does not cover the fall protection plan, the leading edge, or the holes in the deck, which have their own requirements under OSHA and their own inspection. It does not cover welding of deck, shear studs, or anything that involves a stud gun and a wrench, all of which have separate procedures and separate documentation. It does not certify that the pattern on this job is correct for any other job: 20 ga. at 8 ft. is not 18 ga. at 10 ft., and the placement drawing is the only thing that says which is which. And it does not cover what the bundle weighed when it left the yard versus what the tag said, which is a receiving question and not a field question.

What a GC or an owner can ask for

Ask for the placement drawings, and ask whether the bundle staging plan is on the site logistics drawing before the first pick. Ask the foreman what the wind call is for the day and who makes it, and get the answer before the deck starts, not after. Then, at the end of a windy day, walk the deck or have somebody walk it and look at the laps. If the laps are closed, the washers are seated, and there is not a bundle sitting unbanded on a bay overnight, the note on the back of the drawing did its job. If there is one bundle loose on the frame, that is the conversation, and it takes two minutes to have it.