A suspension bridge is made up of a deck, which hangs on strong, horizontal cables, which are on vertical suspenders. The main forces in a suspension bridge are the tension in the cables and compression in the pillars. Tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. Compression is the opposite; it is the result of the subjection of a material to compression, which results in reduction of volume as compared to an uncompressed but otherwise identical state. Because most of the force on pillars is vertically downwards and they are stabilized by the horizontal cables, the pillars can be made very thin. In a suspended bridge, cables suspended via towers hold up the road deck. The weight is transferred by the cables to the towers, which is then transferred to the ground.
Having a very small weight compared to the deck and cars being supported, the horizontal cables will form a parabola. You can see the shape from the constant increase of slope of the cable with distance of the deck. This increase in slope at each connection with the deck provides a support force. Combined with the simple constraints on the deck, this makes the suspension bridge much simpler to design and analyze than a other bridges, where the decks are in compression.
Suspension bridges have multiple advantages over other bridge types including;
Longer main spans are achievable than with any other type of bridge
Less material may be required than other bridge types, even at spans they can achieve, leading to a reduced construction cost
Except for installation of the initial temporary cables, little or no access from below is required during construction, for example allowing a waterway to remain open while the bridge is built above
May be better to withstand earthquake movements than heavier and more rigid bridge
However they have a few disadvantages as well;
Stiffness or aerodynamic profiling may be required to prevent the bridge deck vibrating under high winds
The relatively low deck stiffness compared to other (non-suspension) types of bridges makes it more difficult to carry heavy traffic where high concentrated live loads occur
Some access below may be required during construction, to lift the initial cables or to lift deck units. This access can often be avoided in cable construction
Having a very small weight compared to the deck and cars being supported, the horizontal cables will form a parabola. You can see the shape from the constant increase of slope of the cable with distance of the deck. This increase in slope at each connection with the deck provides a support force. Combined with the simple constraints on the deck, this makes the suspension bridge much simpler to design and analyze than a other bridges, where the decks are in compression.
Suspension bridges have multiple advantages over other bridge types including;
Longer main spans are achievable than with any other type of bridge
Less material may be required than other bridge types, even at spans they can achieve, leading to a reduced construction cost
Except for installation of the initial temporary cables, little or no access from below is required during construction, for example allowing a waterway to remain open while the bridge is built above
May be better to withstand earthquake movements than heavier and more rigid bridge
However they have a few disadvantages as well;
Stiffness or aerodynamic profiling may be required to prevent the bridge deck vibrating under high winds
The relatively low deck stiffness compared to other (non-suspension) types of bridges makes it more difficult to carry heavy traffic where high concentrated live loads occur
Some access below may be required during construction, to lift the initial cables or to lift deck units. This access can often be avoided in cable construction
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