Feed the erection crane.
A pre-assembly yard. A transporter. A separate erection operation.
Your job: feed the erection crane using the fewest occupied yard bays. Six box trusses must be built and painted on cribbing, then transported to another site. You control how many boxes can be in the yard at once. Start with one, run the plan, then try two and compare the finish time.
How the yard works · need a hint?
A forklift unloads the loose steel into an available bay. The yard crane supports ground assembly on cribbing. A separate crew paints the box and allows it to cure in that same bay.
The SPMT, a self-propelled modular transporter, drives beneath a ready box and raises its deck to pick it up from the cribbing. It travels to the erection site, stays until the erection crane removes the box, then returns empty. No yard-crane lift is needed to put the box on the SPMT.
Every box stays in its bay until SPMT pickup is complete. The transport lane stays clear. Your inventory limit controls when the next load of loose steel is released.
Try this: Compare two inventory limits. Does filling another bay improve the finish time, or just create a longer queue?
What are we testing?
Does starting more boxes help the erection crane finish sooner? Compare your runs below. If a higher yard limit gives the same finish time, that extra inventory has not improved throughput. The challenge is to find the lowest limit that still meets the schedule.
Your runs
Run a plan to compare finish time and average yard inventory.
Modeled durations and assumptions
Each box needs 1 hour of forklift unloading and 2 hours of yard-crane ground assembly. The forklift, yard crane, paint crew and erection crane are separate resources. Each handles one box at a time. Painting happens on cribbing, so no move to another bay is modeled.
Challenge 01: paint/cure 4 hours; SPMT pickup 1 hour; loaded travel 2 hours; erection 2 hours; empty return 2 hours. Challenge 02: paint/cure 6 hours; pickup, loaded travel, erection and empty return each take 1 hour.
Oldest ready work goes first. The yard starts empty; erection waiting includes startup. Inventory counts boxes in yard bays, including their loose-steel loads, but excludes transported and erected boxes. Average inventory is measured at each hourly step until completion. The target is completion of all six boxes, not return of the final empty SPMT.
Fictional durations and geometry for a flow puzzle. This does not check crane capacity, rigging, ground bearing, cribbing design, paint requirements, transport clearance or assembly stability.