*Bridges: Structures and Materials, Ancient and Modern DOI: http://dx.doi.org/10.5772/intechopen.90718*

*3.1.2.1 Steel truss bridges*

*Infrastructure Management and Construction*

this bridge's type.

in **Figure 6**.

**Figure 5.**

**Figure 6.**

**98**

*Forth bridge, Edinburgh, Scotland [5].*

*Golden Gate suspended bridge, San Francisco, U.S.A. [6].*

*3.1.2.2 Suspension bridges*

Since the increase of traffic flow and weight of vehicles started, the wooden bridges were already insufficient to support these vehicle loads and the structures began to use steel materials. With the structural steel available on construction market, these bridges had a significant improvement, including the increase of spans length covered and supporting higher loads. Steel trusses bridges replaced wooden trusses and began to build bigger structures. **Figure 5** shows an example of

The introduction of suspended bridges was an important innovation, due the very large spans length that they can cover. These structures have very large geometries with visual impact on the users, using them as a symbol for the city. Examples of such structures are the Brooklyn Bridge, located in New York and the Golden Gate Bridge, located in California. The overview of the Golden Gate Bridge is shown

The geometry of the suspended bridges consists of two central support towers, the main cables supported between the towers, the secondary cables supported on the main cables, the main deck and supporting girders. As a structure, all cables work as tension elements and support the main deck where the traffic flows.

Due the tension cables, suspended bridges can take advantage of the ability to obtain very large spans without intermediate supports. They are widely used to cross very large rivers where conventional bridges are unable. However, one of the disadvantages of this type of structures is the aerodynamic stability, product of the slenderness relationship between main slab, span clearage and the action of thrust forces produced by the wind loads.
