Hamza wonders why so many structures, like bridges, cranes, buildings and the Eiffel Tower are made of interlocking triangles. When triangles are used in bridge structures, they are called trusses which are a series of translated or rotated congruent triangles, making the structure extremely strong. In a truss bridge, the joints on the bottom are in tension, or pulling apart, while the joints on top are in compression, or pushing together. A spaghetti truss bridge also proves to be a surprisingly strong structure.