Public Infrastructure

1
Public Infrastructure
Bridges
2
Bridges

• What bridges do
• How do you design a bridge?
• Types of bridges

3
What Bridges Do

• Cross over a natural obstacle
• River/creek
• Canyon/valley
• Cross over a man-made facility
• Road
• Railroad
• Canal

4
How Do You Design Bridges?

• For most of history Trial error
• Beginning in 1800s Structural engineering
• Today Use computers to model bridges
  performance
• Bridge engineers need to understand physics,
  materials, construction methods, math

5
How Do You Design a Bridge?

• Safety
• Carry intended loads
• Economy
• Construction cost
• Maintenance cost
• Esthetics
• How it looks
• How it fits in to surrounding neighborhood

6
Bridge Forces

• How are forces resisted?
• Transfer
• Dissipation

7
3 Basic Types of Bridges

• Beam bridge
• Up to 200 feet
• Arch bridge
• Up to 800 feet
• Suspension bridge
• Up to 7,000 feet

8
Beam Bridges

• The first bridges
• Logs across a stream
• Simple
• Cheap
• Need strong materials

9
Beam Bridge
10
Transfer of Force
11
Arch Bridges

• Ancient design
• Can last a long time
• Expensive hard to build

12
Arch Bridge
13
Dissipate Force
14
Suspension Bridges

• Can bridge long distances
• Wide, high, clearances

15
Suspension Bridge
16
Transfer of Force
17
Cable-Stayed Bridges
18
Truss Bridges

• Use wood or steel to make triangles
• Early railroad bridges

19
Cantilever Bridges
20
Box Girder Bridges
21
Box Girder Sections

• Concrete
• Steel composite with concrete
• Polymer composites

22
Culverts

• Smallest
• Usually carry water under roads

23
Movable Bridges
24
Covered Bridges
25
Date of Construction of US Bridges
26
Chicago Skyway

• Opened 1958
• 7.8 miles
• Current 250 million renovation

27
Chicago Movable Bridges

• Types
• Vertical lift
• Swing
• Bascule
• Different types
• Many designs developed in Chicago
• 52 movable bridges in Chicago today
• Some immobilized