How do you build a bridge without glue?

Short answer: use the weight of the bridge and the load to hold the pieces together, with interlocking joints and a form that pushes members tighter under load. Some contests require this so that the bridge can be taken apart and reused.

How it works

In a glue-free bridge, sticks are held by friction, notches, weaving or wedging. Because nothing is bonded, joints can't carry a pull, so the design must keep the sticks in compression or pinned in place. Arch-like forms are common, since the load squeezes the pieces together.

Design ideas

1. Use compression forms. Arches and woven or stacked designs push sticks against each other.
2. Interlock sticks by crossing them in layers, or by notches where the rules allow.
3. Handle the outward push. Arches push at the feet, so the bridge must resist spreading on its own if the supports don't hold it. See arch or truss.
4. Keep the pieces uniform, so you can replace one without rebuilding.

Practice

• Build small test sections and load them by hand.
• Time the assembly. Some contests have a time limit. See building on site.
• Check whether a joint material, such as string or tape, is allowed.

Read the rules carefully, since categories differ on what counts as a joint. See reading your rulebook and popsicle stick tips.