Once work is organized into work packages, we need a way to size each package. In steel erection, tonnage is usually the first quantity we reach for. It gives us a convenient way to spread the labor budget and track progress. The problem is that we do not make tonnage in the field. We make picks.
That describes the raising operation. Bolting, welding, decking and detail work need their own quantities and production assumptions within the same work package.
Two work packages can contain the same tonnage and require very different amounts of effort. The same tonnage may hide differences in:
- The number of picks
- The number and type of connections
- Crane movements
- Rigging and setup requirements
- The level of repetition
One package may contain a smaller number of heavy, repetitive picks. Another may contain more pieces, connections and crane movements. The tonnage is the same, but the time required to complete the work may be very different.
Piece count cannot replace tonnage on its own. Not every piece is a pick, and not every pick behaves the same. Some pieces are erected individually, while others may be assembled or grouped before they are lifted. Some picks are repetitive, while others require substantially more rigging, coordination or setup. Defining a planned pick requires judgment and a consistent set of rules.
Once that unit is defined, we can begin looking at throughput:
- Tonnage tells us how much weight was installed.
- Picks tell us how many installation events produced it.
- Cycle time tells us how quickly the operation moved through them.