Trusses & infill.
One roof. Two cranes. Which plan pays?
Your job: complete the same roof with eight planar trusses or four assembled boxes. Compare planar trusses with pre-assembled boxes, choose the main crane size, and run the plan to see the effect on time and modeled cost.
Blue: erection / infill included in a box · Gold: field infill · Hatched: tandem assist
Sample assumptions & cost breakdown
This is a scheduling puzzle with invented rates, not a crane selection or lift study. Both crane sizes are assumed capable of their assigned picks. The larger crane’s speed advantage is a game assumption, not a rule about crane size.
| Work unit | Smaller main | Larger main |
|---|---|---|
| One planar truss (8 total) | 1.5 days | 1 day |
| One assembled box, tandem pick (4 total) | 2 days | 1 day |
| One field-infill bay | 1 day on the small crane, for either method | |
| Field-infill scope | Planars: 7 bays · boxes: 3 gaps between boxes | |
Both methods complete the same roof: eight truss lines and seven bays between them. With planars, every bay needs field infill, including the gaps between successive pairs. Infill starts only after both adjacent trusses are erected. Each box includes two trusses and the infill between them. The four boxes complete bays 1, 3, 5 and 7 as they are erected; field infill is required only in bays 2, 4 and 6 between boxes. Tandem picks have priority, so both cranes erect all four boxes before the small crane fills those three gaps. Ground assembly is assumed complete before day 1.
The small assist/infill crane costs $1,500 per day. Both cranes remain hired through completion. Boxes add $2,500 per box for ground assembly, including its internal infill. Displayed cost covers those crane days and the box assembly allowance only; mobilization, other labor, fabrication, engineering, and site costs are excluded.
Your runs
| Method / main crane | Days | Cost | Result |
|---|
What this puzzle makes visible
Fewer picks do not automatically mean a better plan. Larger assemblies can tie up a second crane, change infill timing, and move effort to ground assembly.
A few terms, explained
A planar truss is a single flat frame. A box joins trusses into a three-dimensional assembly on the ground. Infill is the steel spanning each roof bay. For planars it is erected between every adjacent pair of trusses. For boxes, internal infill is preassembled and only the gaps between boxes remain for field erection. A tandem pick uses both cranes on one load.
Explore the idea in Field Notes
About these crane-planning puzzles
Field Notes explores how steel erection plans connect physical work, time, and resources. These small games turn a few of those decisions into something you can try: move a crane, share the work, or change the erection method and watch what happens.
No crane-planning experience is required. The numbers are invented to make the tradeoffs easy to see. A winning game plan is not a field-ready erection plan.
Real crane planning also requires equipment-specific load charts and configurations, rigging and load-sharing checks, ground conditions, clearances, temporary stability, access, weather, and qualified review. Those checks are outside these games.
Read Field Notes ↗