About this project
Three tunnels with the same span and three different roofs, joined by a thin bar so they print as one piece. Print it and look at the three ceilings.
The tunnels
FLAT is a plain bridge across the full span. RIB is the same roof with internal ribs: each rib is a pier, and the ribbed-span readout shows how short the longest remaining bridge has become. PITCH replaces the bridge with a gable, so the roof is two overhangs and no bridge at all; the readout gives the overhang angle from vertical, and the validator refuses a pitch below 45 degrees.
Sizing
Span, cavity height, roof thickness and tunnel length size the three tunnels together. Wall and floor thickness, rib thickness and the gap between tunnels are fixed numbers you can change in the Variables panel.
What to look for
The underside of FLAT is the honest result for a bridge of that span on your printer. The underside of RIB shows what halving (or thirding) the span buys. PITCH should be clean at 45 degrees on almost any machine, which is the point: a design move removed the bridge instead of tuning for it.