At a Glance:
Students design and build a truss bridge from toothpicks (economical) and destructively test it (fun) to determine its load-bearing capacity.
Concepts: Students gain the perspective of civil and structural engineers as they investigate the most effective way of using materials.
Details: On a 15-cm by 35-cm piece of poster board or thin cardboard, students sketch an imaginary river over which their bridge will span. The sketch indicates the width of the riverbanks and the location of the bridge abutments. Then, they design and draw a truss bridge that will span the imaginary river and anchor into the riverbed at the desired locations.
Two copies of the bridge drawing are taped to foam board and used as construction patterns. The drawings are covered with waxed paper to protect them from glue. Toothpicks are arranged on the drawings along the top, bottom, left-facing diagonal trusses, and vertical abutment members and securely glued to each other. After the glue has dried for 35 minutes, the bridge sides are carefully removed from the waxed paper and turned over. Then, the remaining diagonal trusses are glued in place and the bridge sides are allowed to dry for an hour.
When the glue is dry, the completed sides are lifted from the waxed paper. The bridge pattern is removed from the foam board and replaced with the sketch of the river. The bridge sides are positioned upright on the sketch so that they span the river. They are anchored by piercing the foam board with the ends of the toothpicks that form the bridge abutments. Then, the sides are connected with toothpicks glued to form the roadbed and upper and lower support members.
After allowing the glue to dry overnight, the bridge's weight-bearing capacity is tested using the Pitsco Toothpick Bridge Tester.
At a Glance:
Students design and build a truss bridge from toothpicks (economical) and destructively test it (fun) to determine its load-bearing capacity.
