1. Bridges

2. There are three major types of bridges:
beam bridge
arch bridge
suspension bridge

3. The biggest difference between the three bridge types is the distances they can cross in a single span (distance between two bridge supports).
span distances
beam bridge
up to 200 feet
arch bridge
up to feet
suspension bridge
up to 7,000 feet

4. STRESS… Tension Compression TORSION Shear
is a push or pull (a force) that acts on a structure.
There are 4 kinds of stress…
Tension
Compression
TORSION
Shear

5. consists of a horizontal beam
The beam bridge
consists of a horizontal beam
supported at each end by piers.
The weight on the beam pushes straight down on the beam and the piers (compression force). This makes the beam bend (tension force). The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 200 feet.

6. is a beam bridge reinforced with triangular supports called trusses.
The truss bridge
is a beam bridge reinforced with triangular supports called trusses.
Truss Bridge Forces
The compression and tension forces on this bridge are spread across the bars of the trusses. This reduces the stress on the beam and piers, and enables truss bridges to span farther than plain beam bridges.

7. Arch Bridge Forces
Compression is the only force acting on arch bridges.
The compression force is directed down along the curve of the arch to the supports at each end.
The supports, called abutments or buttresses, push back on the arch and prevent the ends of the arch from spreading apart. This prevents the arch from collapsing.

8. Arch bridges can be made from many different materials…
stone

9. cast iron or steel

10. concrete

11. brick

12. Suspension Bridge Forces
In all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway (compression), but because the roadway is suspended, the cables transfer the load (weight) into compression in the two towers. The two towers support most of the bridge's weight.

13. Low-tech High-tech Lynn Canyon Park suspension bridge, Vancouver
The Akashi-Kaikyo Bridge in Japan is currently the longest bridge in the world, being some four kilometers in total length with a centre span of 1990 meters.
Lynn Canyon Park suspension bridge, Vancouver

14. Cable-Stayed Bridges
The cable-stayed bridge, like the suspension bridge, supports the roadway with massive steel cables, but in a different way. The cables run directly from the roadway up to a tower, forming a unique "A" shape.

15. Cable-stayed bridges, like the Sunshine Skyway in Florida, require less cable and can be built much faster than suspension bridges. Cable-stayed bridges are becoming the most popular bridges for medium-length spans (between 500 and 3,000 feet).
The Leonard P. Zakim Bunker Hill Bridge, part of The Big Dig Project in Boston, is the widest cable-stayed bridge in the world (183 feet wide).
Sunshine Skyway Bridge St. Petersburg, Florida and Bradenton, Florida

16. Cantilever Bridges Cantilever bridges link
Quebec Bridge
A cantilever bridge is a bridge built using cantilevers: structures that project horizontally into space, supported on only one end.
The distribution of forces in a cantilever bridge is shown in this demonstration using chairs, poles, counterweights, and humans.   
Cantilever bridges link
Firth of Forth Bridge, Scotland

17. Which type of stress is acting on the Tacoma Narrows Bridge, shown below?
Torsion, from high winds, tore this bridge apart in 45 minutes on November 7, Click on the link below to see a video of the bridge just before it collapsed.
The Tacoma Narrows Bridge Disaster, November 1940

18. Now that you’ve become an expert on bridges, take the Bridge Challenge
Now that you’ve become an expert on bridges, take the Bridge Challenge. Just click on the link below.
Bridge Challenge

19. Great Bridge Websites
DLT Bridges
Building Big: Bridges
Making the Modern World: Bridge Design
Richman Galleries