1. Bridge Engineering: Lessons from Rome to Tacoma
Modified by Matthew Silbernagel
Clear Lake MS Engineering

2. Great Stone Bridge in China
History of Bridge Development
100 B.C. Romans
2,104 years ago
700 A.D. Asia
1,304 years ago
Clapper Bridge
Roman Arch Bridge
Tree trunk
Stone
Arch design
evenly distributes
stresses
Natural concrete
made from mud
and straw
Clapper Bridges employed all over the world, most notably in England. Originally, tree logs used, but they tended to rot. Stones were better, but difficult to maneuver. The Romans developed highways that connected the empire. Bridges helped them do this.
Great Stone Bridge in China
Low bridge
Shallow arch
Allows boats
and water to pass
through

3. History of Bridge Development
1900
1920
Truss Bridges
Mechanics of Design
Wood
2000
Suspension Bridges
Use of steel in suspending cables
Prestressed Concrete
Steel

4. Basic Concepts
Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.
Force -
Compression
Tension
Compression –
Tension -
Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?

5. Basic Concepts Beam - a rigid, usually horizontal, structural element
Pier
Pier - a vertical supporting structure, such as a pillar
Cantilever - a projecting structure supported only at one end, like a shelf bracket or a diving board
Load - weight on a structure

6. Types of Bridges Basic Types: Truss Bridge Beam Bridge Arch Bridge
Suspension Bridge
Floating Bridge
Floating
Truss
Beam
Arch
Suspension
The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.

7. Truss Bridge Typical Span Lengths 40m - 500m World's Longest
Pont de Quebec
Total Length
863m
Center Span
549m
A Matsuo Example
2nd Mameyaki Bridge
Typical 40m to 500m
All beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.

8. Types of Bridges Beam Bridge
Consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

9. Types of Bridges Beam Bridge Forces
When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

10. Types of Bridges Arch Bridges
The arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.

11. Types of Bridges Arch Bridges Forces
The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

12. Types of Bridges Suspension Bridges
This kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.

13. Types of Bridges Suspension Bridges 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, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.

14. Types of Bridges Floating Bridge
Pontoon bridges are supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads.
While pontoon bridges are usually temporary structures, some are used for long periods of time.
Permanent floating bridges are useful for traversing features lacking strong bedrock for traditional piers.
Such bridges can require a section that is elevated, or can be raised or removed, to allow ships to pass.

15. Floating Bridges
Retractable!
But high maintenance!

16. Ground below bridge Loads Materials Shapes Bridge Engineering
How do the following affect your structure?
Ground below bridge
Loads
Materials
Shapes

17. Bridge Engineering Summary
To design a bridge like you need to take into account all the forces acting on it:
The friction of the earth on every part
The strength of the ground pushing up the supports
The resistance of the ground to the pull of the cables
The dead weight and all vehicle loads
Then there is the drag and lift produced by wind and water
The turbulence as fluids pass the towers
Need to use appropriate materials and structural shapes in the cheapest way, yet maintaining a certain degree of safety.
To account for natural disasters, engineers design bridges with a factor of safety: usually around 3 or 4.

18. Case Study: Tacoma Narrows Failure
The first Tacoma Narrows suspension bridge collapsed due to wind-induced vibrations on Nov. 7, The bridge over engineered it to withstand hurricane winds, but the wind that day was only 40 mph… what happened!?