Bridge Facts: Arch Bridges

Typical Span 200’ – 800’ distance between supports

Physical Principles

These bridges take advantage of the natural strength of the arch form. The weight is carried outward along the curve of the arch to the supports at each end. These supports push in on the bridge keep it from bending or spreading out.

Pros and Cons

It is hard to build an arch bridge because it is not stable until the entire arch is complete. Aesthetically pleasing. Do not experience bending, and can be built from materials that resist compression, but not bending.

Footbridge in Boston, do you know where?

Foot bridge over the Charles River, near Harvard Bridge for the Green Line, at the Museum of Science

Longfellow Bridge over the Charles River

Bridge Facts: Beam Bridges

Typical Span Up to 250’ distance between supports

Physical Principles

A beam bridge consists of a horizontal beam supported at each end by vertical posts. The weight of the beam pushes straight down on the posts. To make longer bridges, posts are used at intervals along the length of the bridge. Each bridge section between posts will experience bending due to its own weight and the weight of the load on it. To resist bending, trusses or girders (solid walls) are used to make the beam stiffer.

Pros and Cons

Simplest and most inexpensive type of bridge. Many posts are needed to support long spans.

Harvard Bridge, across Charles River, on Mass Ave, near MIT (facing NorthEast)

Railroad bridge, across Charles River, near BU Bridge Harvard Bridge, MassAve, near MIT (facing SouthWest)

Tobin Bridge, Boston (short span) Tobin Bridge, Boston (long span)

Bridge Facts: Suspension Bridges

Typical Span 2,000’ – 7,000’ distance between supports

Physical Principles The roadway is suspended from huge main cables that extend from one end of the bridge to the other. The main cables are draped over the tops of two high towers, and are secured at each end in massive anchor blocks. A set of thinner, vertical suspension cables go from the main cable to the roadway.

Pros and Cons Light, strong, and flexible. Light bridges must strong enough to resist being blown by high winds. Most expensive bridges to build.

http://willhicks.files.wordpress.com/2008/07/brooklyn-bridge1.jpg Brooklyn Bridge, New York City

Pell Bridge, Newport Rhode Island

http://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/GoldenGateBridge.jpg/800px-GoldenGateBridge.jpgGolde Golden Gate Bridge, San Francisco

Bridge Facts: Cable-Stay Bridges

Typical Span 500’ – 2,800’ distance between supports

Physical Principles The roadway is supported solely by the towers, there is no need for anchor blocks as are used in suspension bridges. Diagonal cables stretch from the tower right to the roadway. Cables may be located in the center of the roadway, or on either side. There may be one tower or two.

Pros and Cons Cable stay bridges use less cable than suspension bridges, and are cheaper and faster to build. Cannot be used to span the mile-plus spans that Suspension bridges can.

Zakim Bridge, Boston

Zakim Bridge, Boston (side view)

Millau Viaduct, Millau France, 2004

Interesting Bridges – Try to figure out the types: Arch, Beam,

Suspension, Cable Stay or some combination of a few styles?

Entrance ramp to Zakim Bridge

Notice the Duck Boat!

What type of Bridge is the entrance ramp?

Museum of Science, Boston The building itself is a bridge

Drawbridge near Tobin Bridge

The BU Bridge

Name 3 types of bridges that you can find in this bridge

Confederation bridge, Prince Edward Island, Canada, 8 miles, 1997

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The Sagamore Bridge, Sagamore Mass. (Cape Cod)