We see different examples of the materials used to make bridges, including stone, cast iron, brick and steel. Using plastic is a good idea; it is light, easy to build from, doesn't need cranes, and can be glued together. To give it strength, plastic can be reinforced with glass. This makes it strong and flexible enough to support its weight two times over.
The clip could be used to stimulate investigations into “Which shape provides the strongest structure for a bridge?” or alternatively setting children challenges into creating the strongest possible bridge structure using one sheet of paper and two books and seeing if it could hold a set amount of weight, 10 cubes for example. Changing the shape of the paper between the books, from flat to curved or folded in half, will alter the strength of it, and children could start suggesting reasons why.