Suspension bridge

• Old suspension bridges were usually built using rope/vegetable fibre
• The ropes could withstand tension forces while they were new but they would quickly deteriorate
• Suspension bridges are usually constructed for very long spans
• An example is the Chirundu bridge across Zambezi river between Zimbabwe and Zambia
• Steel cables are suspended from high towers and the road/railway is supported below the cables
• The vertical supports reduce the span of the bridge and reduce bending

A suspension bridge

• The cables are in tension
• The greater the load the greater the tension
• The pillars/towers (abutments) are in compression
• Long spanned bridges are now possible due to the strength of modern steel cables
• Cables are also continuous and do not need joins
• They are made up of hundreds of wire so the failure of one wire strand will not result in the whole structure failing
• Cables in a suspension bridge are in the form of an inverted arch
• This best accommodates the forces that are acting on the cables and bridge
• While in an arch bridge the arch is in compression
• The inverted arch in the suspension bridge is entirely in tension
• The curved cables carry these tensions

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