Prefab house assembly: how to minimize crane setup changes?
Prefab houses are cheap to make in the factory but expensive on site if assembled in the wrong order. Choose a component, place it on the facade following the load-path rule, and see how many setup changes you need compared with the machine.
What the model calculates, and what it doesn't
The house is a grid module × floor seen from the elevation, five component families: foundation, column, floor slab (beam–slab), wall panel (solid / window / door) and roof panel. Each component can only be placed once what it rests on is in place: ground-floor column on the foundation, upper-floor column joined to the column below and a floor slab must be adjacent to the grid line for workers to stand on, slabs rest on both ends, walls stand between two columns on the slab, and the roof rests on the top-floor columns. Placing a piece wrongly means the crane must take it down, costing tLoi minutes.
Fixture changes are the key figure: every time the crane switches to another component family, the lifting fixture, slings and rigger must be changed — tDoiGa minutes of crane idle time. The baseline assembler follows the rules and the family order: foundation → floor → columns (finishing one floor before the next) → walls for the whole house → roof; its number of fixture changes is the benchmark. Truck trips = total load units ÷ capacity per truck, rounded up.
Stage 4 uses a real load chart of the Liebherr LTM 1060-3.1 (60 t) mobile crane — public excerpt published by Nordic Crane : counterweight 12.8 t, full slewing, taking the maximum lifting capacity across all boom lengths at each radius and reading at the next larger radius (the safe way to read a load chart). Radius is measured in plan from the crane center to the center of the component. Component weights are game assumptions (precast foundation 4.8 t, floor slab 4.2 t…, plus 0.3 t for hook and cable) — a real project must take them from fabrication drawings; outriggers, crane pad, wind and lifting height are not accounted for.
Not calculated: temporary bracing and safety when erecting columns, wind load before slabs are in place, joints and erection tolerances, weather, crane radius, loading sequence on the truck. Minutes and load units are model assumptions to compare the two assembly methods, not construction productivity norms.
Frequently asked questions
Why can't the upper-floor column be erected even when the column below is already in place?
The model requires the floor slab next to that column line to be in place first — workers need a floor surface to stand on, hook the cable and fix the column. This is the practical reason many crews work floor by floor, slab then column, rather than erecting the whole frame and laying floors afterward.
Are the in-game minutes used for scheduling?
No. The minutes per component and per fixture change are assumptions so the two assembly methods can be compared. Actual schedules depend on the crane, crew, joints and site conditions — CGD handles that in the construction method statement.
Have real project parameters? Send them to CGD and get feedback on the design scope
This simulation stops at the principle. For a specific project, CGD builds the model on real operating data and floor plan drawings.
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