Why does my bridge fold?

Some joints can still move. Add diagonal beams until every joint sits inside a triangle.

It uses the same method engineers use for pin-jointed trusses: each beam carries only a push or a pull along its length.

Can I get a cheaper design?

Usually. Swap steel for wood on beams that stay green during the crossing, and remove beams the truck never loads.

Design a truss bridge with wood and steel beams on a tight budget, then send a truck across to see which beams hold and which one snaps.

Span Builder

0% · Getting ready

Tap grid points to add joints. The two anchors on the banks are fixed. Pick Wood or Steel, then tap two joints to join them with a beam.
Lay a road along the top line from bank to bank, then support it with triangles below. Triangles are rigid, squares fold.
Stay inside the budget. Wood is cheap and weak, steel is strong and costs more than twice as much.
Press Send the truck. Beams turn red as the load rises, and a beam that goes past its limit snaps. Clear all three gaps.

Controls: mouse, touch or keyboard. Made by CalcoTools.

Build triangles. A bridge made of triangles can carry a load, a bridge made of rectangles collapses.
Use steel only where the truck shows red, such as the beams near the middle of the road. Wood is fine near the banks.
Longer beams cost more, so a taller truss is stronger but not always cheaper.
Your lowest cost for each level is saved, so come back and beat it.

Why does my bridge fold?: Some joints can still move. Add diagonal beams until every joint sits inside a triangle.
Is the physics real?: It uses the same method engineers use for pin-jointed trusses: each beam carries only a push or a pull along its length.
Can I get a cheaper design?: Usually. Swap steel for wood on beams that stay green during the crossing, and remove beams the truck never loads.