BRIDGESBRIDGES

• History of Bridge Development

• How Bridges Work

• Basic Concepts

• Types of Bridges

• Concepts Associated with Bridge Engineering

• Truss Analysis

• Tips for Building Bridges

• Bridge Construction

Work Plan Work Plan

700 A.D. Asia700 A.D. Asia

100 B.C. Romans100 B.C. Romans

Natural BridgesNatural Bridges

Clapper BridgeTree trunkStone

The ArchNatural Cement

Roman Arch Bridge

History of Bridge DevelopmentHistory of Bridge Development

Great Stone Bridge in China

Low BridgeShallow Arch

1300 A.D. Renaissance1300 A.D. Renaissance

Strength of MaterialsMathematical TheoriesDevelopment of Metal

First Cast-Iron BridgeCoalbrookdale, England

1800 A.D.1800 A.D.

Britannia Tubular Bridge

1850 A.D.1850 A.D.

Wrought Iron

Truss BridgesMechanics of Design

Suspension BridgesUse of Steel for the suspending cables

1900 A.D.1900 A.D.

1920 A.D.1920 A.D.

Prestressed ConcreteSteel

2000 A.D.2000 A.D.

History of Bridge DevelopmentHistory of Bridge Development

How Bridges Work?How Bridges Work?

• Waves travel at hundreds of kilometer with the flow of traffic on a bridge.

• Bridges are designed to handle this type of movement, as well as natural effects, such as wind and earthquakes.

• Bridges have a life of their own. Understanding the static forces are a hugecomponent to making them successful.

Compression Tension

Basic Basic Vocabulary Vocabulary

Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.

Compression - a force which acts to compress or shorten the thing it is acting on.

Tension - a force which acts to expand or lengthen the thing it is acting on.

Force - any action that tends to maintain or alter the position of a structure

Basic Concepts Basic Concepts

Beam - a rigid, usually horizontal, structural element

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

Beam

Pier

Load - weight distribution throughout a structure

Truss - a rigid frame composed of short, straight pieces joined to form a series of triangles or other stable shapes

Stable - (adj.) ability to resist collapse and deformation; stability (n.) characteristic of a structure that is able to carry a realistic load without collapsing or deforming significantly

Basic Concepts Basic Concepts

To dissipate forces is to spread them out over a greater area, so that no one spot has to bear the brunt of the concentrated force.

To transfer forces is to move the forces from an area of weakness to an area of strength, an area designed to handle the forces.

Buckling is what happens when the force of compression overcomes an object's ability to handle compression. A mode of failure characterized generally by an unstable lateral deflection due to compressive action on the structural element involved.

Snapping is what happens when tension overcomes an object's ability to handle tension.

Basic Concepts Basic Concepts

Types of BridgesTypes of BridgesBasic Types:

•Beam Bridge•Arch Bridge•Suspension Bridge

Types of Bridges: Types of Bridges: Beam BridgeBeam Bridge

• The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

Forces

When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

Types of Bridges: Types of Bridges: Beam BridgeBeam Bridge

Forces

Every bar in this cantilever bridge experiences either a pushing or pulling force. The bars rarely bend. This is why cantilever bridges can span farther than beam bridges

Types of Bridges: Types of Bridges: Truss BridgeTruss Bridge

• 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.

Types of Bridges: Types of Bridges: Arch BridgesArch 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.

Types of Bridges: Types of Bridges: Arch BridgesArch 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.

Types of Bridges: Types of Bridges: Suspension BridgesSuspension 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.

Types of Bridges: Types of Bridges: Suspension BridgesSuspension 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.

• Cable-stayed bridges are becoming the most popular bridges for medium-length spans (between 500 and 3,000 feet).

Types of Bridges: Types of Bridges: Cable-Stayed BridgesCable-Stayed Bridges

How do the following affect your structure?

ForcesLoadsMaterialsShapes

Things You Should Consider Things You Should Consider in Your Bridge Designin Your Bridge Design

Pythagorean Theorem

Basic math and science conceptsBasic math and science concepts

Bridge EngineeringBridge Engineering

a

c

b c2=b2+a2

Density 163 ± 10 kg/m³

low density   4.7 MPamedium density 12.1 MPahigh density 19.5 MPa

low density   7.6 MPamedium density 19.9 MPahigh density 32.2 MPaElastic Modulus - Compression   460 ±   71 MPaElastic Modulus - Tension 1280 ± 450 MPa

Compressive Strength¤

Tensile Strength¤

Bridge EngineeringBridge Engineering

Balsa Wood Information

Truss AnalysisTruss Analysis

Bridge EngineeringBridge Engineering

Structural Stability Formula

K = 2J - R

Where:K = The unknown to be solvedJ = Number of JointsM = Number of MembersR = 3 (number of sides of a triangle)

K Results Analysis: If M = K Stable Design If M < K Unstable Design If M > K Indeterminate Design

Truss AnalysisTruss Analysis

Bridge EngineeringBridge Engineering

Structural Stability Formula (Example)

JointsJ=9

MembersM=15

K = 2 (9) – 3 = 15

15 = M = K then The design is stable

Tips for building a bridgeTips for building a bridge

1. Commitment - Dedication and attention to details. Be sure you understand the event rules before designing your prototype.

1) Draw your preliminary design

2) ALL joints should have absolutely flush surfaces before applying glue.

Glue is not a "gap filler", it dooms the structure!

3) Structures are symmetric.

4) Most competitions require these structures to be weighed. Up to 20% of the structure's mass may be from over gluing.

• Stresses flow like water. • Where members come together there are stress

concentrations that can destroy your structure. • Here is a connection detail of one of the spaghetti

bridges.

The Importance of ConnectionsThe Importance of Connections

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We wish you luck!We wish you luck!