Bridges Presentation

clanmurderΠολεοδομικά Έργα

15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

64 εμφανίσεις



Bridge Engineering:

Lessons from

Rome to Tacoma

Clear Lake MS Engineering
03
-
27
-
2006

700 A.D. Asia

1,304 years
ago

100 B.C. Romans

2,104 years ago

Clapper Bridge


Tree trunk


Stone


Arch design

evenly distributes

stresses


Natural concrete


made from mud


and straw

Roman Arch Bridge

History of Bridge Development

Great Stone Bridge in China


Low bridge


Shallow arch


Allows boats

and water to pass

through

History of Bridge Development

Truss Bridges


Mechanics of
Design


Wood

Suspension Bridges


Use of steel in
suspending cables

1900

1920


Prestressed
Concrete


Steel

2000

Compression

Tension

Basic Concepts

Span

-

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

Compression





Tension

-

Force

-

Concrete has good compressive strength,
but extremely weak tensile strength.
What
about steel cables?

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 on a structure

The type of bridge used depends on the obstacle. The main
feature that controls the bridge type is the size of the obstacle.

Types of Bridges

Basic Types
:


Truss Bridge


Beam Bridge


Arch Bridge


Suspension Bridge


Floating Bridge

Truss

Beam

Arch

Suspension

Floating

Truss Bridge

Typical Span Lengths

40m
-

500m

World's Longest

Pont de Quebec


Total Length

863m

Center Span

549m

A Matsuo Example

2
nd

Mameyaki Bridge

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.

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.

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

Beam Bridge

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.

Types of 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

Arch 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.

Types of 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

Suspension Bridges


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.

Types of Bridges

Floating Bridge

Floating
Bridges

Retractable!

But high maintenance!

How do the following affect your structure?


Ground below bridge


Loads


Materials


Shapes



Bridge
Engineering

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

Summary

Bridge Engineering

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.


Case Study:
Tacoma Narrows
Failure

The first Tacoma Narrows suspension bridge collapsed due to wind
-
induced
vibrations on Nov. 7, 1940. The bridge over engineered it to withstand hurricane
winds, but the wind that day was only 40 mph… what happened!?