Zerdly

Bridge Works

Span a canyon with a truss: joints, members and a budget. Then roll the load across and see which members stretch, which squeeze and which are close to breaking.

Design a truss bridge within budget, then roll a load across and watch every member's force.

FreeOn this device

Joint and member lists (keyboard building)
  • Left bank (0, 0)
  • Right bank (4, 0)

    A game model: a pin-jointed truss solved for small movements, with fictional strengths. It ignores buckling, fatigue and the bridge's own weight, and says nothing about real bridge safety. The road needs a joint at least every 2 units; the load is tested every quarter unit.

    First crossing: span 4. Cost 0 of 148. 0 joints, 0 members.

    Controls

    • Build: tap a grid point to add a joint; tap two joints in turn to connect them with the material chosen under New members.
    • Material switches a member between light and heavy; Remove deletes a joint or member. Undo steps back.
    • Test rolls the load across. Play, Pause, Step and the position slider replay it; Back to editing returns to the unloaded bridge.
    • The joint and member lists under the canyon do everything by keyboard: add a joint by its coordinates, then use Connect to.

    The rules

    • Each member only stretches or squeezes along its length, and joints are pins — so shapes made of triangles hold, and squares fold.
    • The road (y = 0) must run from bank to bank with a joint at least every 2 units. The load is tested every quarter unit along it.
    • A test fails if the design is over budget, a member's force passes its strength (light 120, heavy 240), the road sags past the canyon's limit, or the structure can move freely.
    • A member costs its length times 10 (light) or 18 (heavy), rounded up.

    Scoring, saving and limits

    A canyon is complete when its bridge passes. The budget is 25% above a reference design, so there is room to experiment.

    Your design for each canyon and the canyons you have completed are kept on this device.

    A game model with fictional strengths. It ignores buckling, fatigue and the bridge's own weight and says nothing about real bridge safety. Movement is drawn exaggerated so it can be seen.

    Questions

    Why does it say Unstable structure?
    Some part can move without stretching any member — usually a square without a diagonal, or a joint held by only one member.
    Which members need to be heavy?
    Test with light members and look for red ones; make just those heavy to save money.
    Do I have to use the extra anchors?
    No. Ledges and rocks are extra supports you may connect to; every canyon can be crossed without them.