Structures
Real World Engineering
Ms. Sicola
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Live loads refer to loads that do, or can,
change over time. Objects that move
around in or on a structure, like people,
furniture, and cars, are all examples of
live load.
In addition to live loads, what is known as
environmental loads are loads that are
created naturally by the environment and
include wind, snow, seismic, and lateral
soil pressures.
Dead loads: The weight of the structure
itself is called the dead load. Anything
permanently attached to the structure is part
of its dead load -- including the columns,
beams, nuts, and bolts. These are loads that
typically do not change over time.
http://www.pbs.org/wgbh/buildingbig/lab/loads.ht
ml
Live loads vs dead loads
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Static loads are usually gravity-type loads. These would include the weight of the
structure itself or any other load that is stationary.
Dead loads are static forces that are relatively constant for an extended time.
An elevator is an example where static loading occurs. When ten people stand in an
elevator waiting for the doors to close, they are exerting a load on it that is static
because the people and the elevator are not moving relative to each other. The stresses
within the elevator have time to reach equilibrium under such conditions.
Static Loads
The lower columns of the skyscraper are
squeezed by the heavy weight above
them. This squeezing force in called
compression.
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Compression is a force that squeezes a
material together. When a material is in
compression, it tends to become shorter.
http://www.pbs.org/wgbh/buildingbig/lab
/forces.html
The weight of the roadway and all the cars traveling
on the bridge pull on the vertical cables in this
suspension bridge. The cable are in tension.
Tension is a force that stretches a material apart.
When a material is in tension, it tends to become
longer.
Compression vs. Tension
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Buckling occurs when an object bends and
gives way under pressure or strain.
Example above shows a pressure from both
the top and sides causing buckling of this
column.
https://www.youtube.com/watch?v=NBcToktU
2oI
http://www.pbs.org/wgbh/buildingbig/lab/forc
es.html
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Deflection is the degree to which a structural
element is displaced under a load. It may refer to
an angle or a distance.
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Example shown below a bam subject to a point
load at its mid-span where it will experience
deflection.
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The neutral axis is an imaginary plane
that runs through the center of a
structural member and along which no
stress occurs.
Pressure is the continuous physical force exerted
on or against an object by something in contact
with it. Pressure can cause buckling in an object.
Buckling, Deflection, and Neutral Axis
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Column or pillar in architecture and structural
engineering is a structural element that
transmits, through compression, the weight of
the structure above to other structural elements
below.
In other words, a column is a compression
member.
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Girders are a type of beam. There are two kinds
of beams namely 'Primary beam' and ‘Secondary
beam'. Girders comes under the category of
primary beam, its main job is to directly transfer
loads coming over it to columns upon which it
rests.
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A Beam is a structural member which spans
horizontally between supports and carries loads
which act at right angles to the length of the
beam. Furthermore, the width and depth of the
beam are "small" compared with the span.
Beams are considered secondary beams or, its
main job is to first transfer loads on it to Girders
or Primary beams which in turn transfer the
loads to columns supporting it.
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Columns, Beams, Girders
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Cross Bracing
Cross Bracing is a system utilized to reinforce
building structures in which diagonal supports
intersect.
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Dampening reduces the amplitude of an
oscillation on an object or structure
◦ Examples include dampening on shock
absorbers of the car suspension when it
moves up and down,
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Tacoma Narrows Bridge collapse
◦ https://www.youtube.com/watch?v=xox9B
VSu7Ok
Taipei 101 Tower would sway back and forth up to
60cm (2 feet) each way within five seconds
The Taipei 101 engineers included a 730-ton
counter giant pendulum to act as a
counter weight.
Shock absorbers or dampers
are added to the structure to
dissipate the seismic shock
Dampening
The Tacoma Narrows Bridge collapse is an
example of the torsion created from the
violent winds/ oscillations that caused it to
ultimately fail
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Torsion is a twisting force upon an object
or structure
The column above from the Parthenon shows
how the column segments have slid past each
other
Shear is a force that causes parts of a material to
slide past one another in opposite directions
Twisting and Shearing
WIND
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When wind blows on a structure, it is
called wind load. Wind loads push
horizontally on a structure.
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Cross-Bracing: Cross-bracing is an
excellent way to stiffen a structure
experiencing wind load. When the wind
blows, the diagonal brace squeezes
together and prevents the structure from
flopping over.
EARTHQUAKES
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When the ground beneath a structure
jerks back and forth during an
earthquake, the structure is
experiencing an earthquake, or seismic
load. Earthquake loads push and pull
horizontally on a structure. They can
also move vertically up and down
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https://www.youtube.com/watch?v=fqzTB
dFa884
“P” waves (up and down) vs. “S” waves (side
to side)
Wind Force
Vs.
Earthquake Force
OSCILLATION
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Oscillation is a motion that
repeats itself in a regular cycle,
such as a pendulum.
Winds, Oscillations, Earthquakes
EARTHQUAKES
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When the ground beneath a structure
jerks back and forth during an
earthquake, the structure is
experiencing an earthquake, or seismic
load. Earthquake loads push and pull
horizontally on a structure. They can
also move vertically up and down
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https://www.youtube.com/watch?v=fqzTB
dFa884
“P” waves (up and down) vs. “S” waves (side
to side)
A P wave, or compressional wave, is a seismic
body wave that shakes the ground back and
forth in the same direction and the opposite
direction as the direction the wave is moving.
An S wave, or shear wave, is a seismic body
wave that shakes the ground back and forth
perpendicular to the direction the wave is
moving.
Winds, Oscillations, Earthquakes
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PSF or Pounds per Square Foot is a system
of measurement used in engineering and
architecture to understand the live load and dead
load weight imposed on a structure
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Pound-force per square foot (psf) is a unit of
pressure where a force of one pound-force (lbf )
is applied to an area of one square foot (ft²).
1 psf = 1 lbf / ft²
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PSF or Pounds per Square inch is a system of
measurement used in engineering and
architecture to understand the live load and dead
load weight imposed on a structure
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Pound-force per square inch (psi) is a unit of
pressure where a force of one pound-force (lbf )
is applied to an area of one square inch (in²).
1 psf = 1 lbf / in²
PSI is most commonly used in
architecture and engineering
PSF vs PSI