Editing Suspension bridge (section)

===Structural analysis=== <!-- Please see the article discussion if you think the terms parabola and catenary should be swapped. -->
[[File:Comparison catenary parabola.svg|thumb|upright=1.25|Comparison of a catenary (black dotted curve) and a parabola (red solid curve) with the same span and sag. 
The main [[force (physics)|force]]s in a suspension bridge of any type are [[tension (mechanics)|tension]] in the cables and [[compression (physical)|compression]] in the pillars. Since almost all the force on the pillars is vertically downwards, and the bridge is also stabilized by the main cables, the [[column|pillars]] can be made quite slender, as on the [[Severn Bridge]], on the Wales-England border.

In a suspended deck bridge, cables suspended via towers hold up the road deck. The weight is transferred by the cables to the towers, which in turn transfer the weight to the ground.

{{hidden top|title=More details}}
The catenary represents the profile of a simple suspension bridge or the cable of a suspended-deck suspension bridge on which its deck and hangers have negligible mass compared to its cable. The parabola represents the profile of the cable of a suspended-deck suspension bridge on which its cable and hangers have negligible mass compared to its deck. The profile of the cable of a real suspension bridge with the same span and sag lies between the two curves.
{{hidden bottom}}
]]

The main cables of a suspension bridge will form a [[catenary]] when hanging under their own weight only.  When supporting the deck, the cables will instead form a [[parabola]], assuming the weight of the cables is small compared to the weight of the deck. One can see the shape from the constant increase of the gradient of the cable with linear (deck) distance, this increase in gradient at each connection with the deck providing a net upward support force. Combined with the relatively simple constraints placed upon the actual deck, that makes the suspension bridge much simpler to design and analyze than a [[cable-stayed bridge]] in which the deck is in compression.