Grades 3–5 · Systems
How does a suspension bridge pass a load to the ground?
A suspension bridge has a road deck that appears to hang in the air. It is held by vertical cables called hangers. These join the deck to the large curved main cables above it.
A vehicle pushes down on the deck. The hangers pull upward on the deck and pass the load into the main cables. Cables are good at carrying a pull, called tension. A slack piece of rope cannot stand up like a post, but a stretched rope can support a hanging weight.
The main cables pass over towers. Their pull loads the towers, which carry a squeezing force called compression down to their foundations. Those foundations spread forces into the supporting ground.
The portrait view follows one tower and the nearby anchorage. The enlarged cable line shows the pulling connection supporting the deck.
The ends of the main cables are held by large anchorages. These resist the cables’ pulling force, so the whole system includes both the tower foundations and the cable anchors. The drawing shows a conventional anchored bridge. Its deck, cables, towers and ground work together; the long span is possible because the load has a continuous route through connected parts.
About this explanation
Starting knowledge: Recognize a bridge deck and distinguish a pulling connection from a supporting post.
Sources
- PBS / WGBH — Building Big: Suspension Bridge Forces
- PBS / WGBH — NOVA: Suspension Bridges
- NGSS / National Science Teaching Association — Structure and Function: Grade-Band Progression