Transcript Bridges - ndteched

Structures
What things do I need to
find out in order to predict
if what I design will stand
up to the use I intend to
put it through?
Structures Key Terms:

Force:
A push or pull exerted by one
object on another.

Compression:
The effect of a force which tends to
shorten an object in the direction of
the force.
Structures Key Terms:

Compression
cont.:
A compressive force
compresses or
shortens the object
it is acting on.
Structures Key Terms:

Compression
cont.:
The stand is in
compression
Structures Key Terms:

Tension:
A situation, in which force is applied
to an object that stretches, expands
or lengthens the object.
Structures Key Terms:

Tension cont.:
A tensile force
expands or
lengthens the
object it is acting
on.
Structures Key Terms:

Tension cont.:
The rope is in tension.
Structures Key Terms:

Deflection:
A measure of deformation of a
structure due to applied loads.

Stress:
All objects can be deformed with the
application of an external force. The
external force is called stress.
Structures Key Terms:

Strain:
It is the degree of deformation. The
elongation of a material under stress
divided by the material’s length prior
to stress.
Structures Key Terms:

Equilibrium:
A state of balance due to the equal action
of opposing forces in a structure.

Friction:
A force that opposes the motion or
intended motion of a body in contact with
another body.
Newton’s 1st Law of Motion

Every object in a state of uniform motion
tends to remain in that state of motion unless
an external force is applied to it.
Newton’s 1st Law of Motion
Newton’s 1st Law of Motion
Newton’s 2nd Law of Motion

Acceleration is produced when a force
acts on a mass. The greater the mass (of
the object being accelerated) the greater
the amount of force needed (to accelerate
the object).
Newton’s 2nd Law of Motion
Newton’s 3rd Law of Motion

For every action there is an equal and
opposite reaction.
Newton’s 3rd Law of Motion
Bridges
There are basically 4 different
types of bridges:
Arch Bridge
Suspension Bridge
Beam/Truss Bridge
Cable-stayed Bridge
Bridge Types:
Arch Bridge
Arch bridges are not stable during
construction until the two sides meet.
Therefore, scaffolding, or "centering,”
must be assembled below, or cables
must be anchored to hold it up. The
latter allows the traffic below to
continue until the bridge is complete.
Bridge Types:
Arch Bridge
Bridge Types:
Suspension Bridge
Suspension Bridges use steel cables
to support weight. Steel wire is very
strong and can support large tensile
forces. A single 0.1” thick wire can
support more than half a ton without
breaking!
Bridge Types:
Suspension Bridge
Bridge Types:
Suspension Bridge
Bridge Types:
Beam/Truss Bridge
Beam Bridges consist of a horizontal
beam supported at each end by piers.
The weight of the bridge and traffic on
it pushes straight down on the piers,
so the beam itself must be strong.
Beam bridges are categorized by the
design, location and composition of
the trusses used.
Bridge Types:
Beam/Truss Bridge
These are a few common types
(notice the location of the roadway
colored gray in each):
Bridge Types:
Beam/Truss Bridge
Howe Kingpost Truss
Pratt or Through Truss
Bridge Types:
Beam/Truss Bridge
Deck Truss
Warren Truss
Bridge Types:
Beam/Truss Bridge
Bridge Types:
Beam/Truss Bridge
Bridge Types:
Cable-Stayed Bridge
Cable-stayed bridges differ from
suspensions bridges in the way that
the cables are connected to the
towers.
In cable-stayed bridges, the cables
are attached to the towers, which
bear the load alone.
Bridge Types:
Cable-Stayed Bridge
The cables of a suspension bridges ride
freely across the towers, transmitting
the load to the anchorages at either
end.
Cable-stayed bridges are distinguished
by the number of spans, number of
towers, girder type, number of cables
and the arrangement of their cables.
Bridge Types:
Cable-Stayed Bridge
Typical towers include:
Bridge Types:
Cable-Stayed Bridge
Typical cable arrangements include:
Mono
Fan
Bridge Types:
Cable-Stayed Bridge
Bridge Types:
Cable-Stayed Bridge
Bridges:


An engineer would choose the correct
bridge based on how far it must span from
one support to the next.
Each bridge deals differently with tension
and compression.
 If part of the bridge cannot stand the
compression it will buckle.
 If part of the bridge cannot stand the
tension it will snap.
Bridges:



Engineers consider shapes under heavy
loads when building large structures.
Triangles are the only shapes that cannot be
deformed without changing the length of one
of its sides
Arches are strong because the force
resulting from a heavy load placed at the top
spreads down the sides to the foundation.
Bridges Key Terms:

Abutment:
Is a part of a structure that
bears the weight of an arch, it
supports the end of a bridge or
anchors the cables of a
suspension bridge.
Bridge Key Terms:

Abutment Cont.:
Bridges Key Terms:

Key Stone:
The central
wedge-shaped
stone of an arch
that locks its
parts together.
Bridges Key Term:

Buckling:
Failure caused by bending, giving
way, or crumpling due to excessive
force.