We’ve seen steel takeoffs go sideways for a simple reason: the estimator counted what looked like a beam instead of checking what the drawing actually called for.
Take a W24x55 beam. On an AISC Erection Drawing, three members can look almost identical on the plan. But their piece marks may be B12, B13, and B14, with different lengths and quantities. Treating them as one repeated member can throw off the entire takeoff.
That is why we prefer reading steel by the piece mark first.
The mark tells you what you're looking at
A piece mark connects the member shown on the erection drawing to its corresponding shop or fabrication information. AISC describes erection drawings as the field-installation drawings used to identify and locate individual shipping pieces.
So instead of asking, “How many beams look like this?” ask, “How many times does this piece mark occur?”
Then check the Member Schedules for the size, length, and other information needed for the quantity.
A small counting error gets expensive
Say your plan contains 18 members that appear identical. If two are actually different piece marks and you count all 18 using the same size or length, your Steel Tonnage Takeoff is already off.
That is the part of steel estimating that is easy to underestimate. The drawings may look repetitive. The steel package often isn't.
Read the mark. Verify the schedule. Then count.
It takes a little more discipline upfront, but it is far cheaper than discovering the mistake after the bid is submitted.
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