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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
CEE 4606 - Capstone IIStructural Engineering
Lecture 3 Seismology, Earthquakes, and Roof Design
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Earthquake Loads“Earthquakes systematically bring out the
mistakes made in design and construction - even the most minute
mistakes; it is this aspect of earthquake engineering that makes it an educational
value far beyond its immediate objectives.”
-Newmark and Rosenbluth
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Ductile vs. Non-ductile Concrete Construction
• Note the obvious differences of capability of concrete columns to take load after earthquake damage.
• The spirally reinforced column (ductile reinforcing) has an obvious capacity to carry much more load than the tied corner column (non-ductile reinforcing).
San Fernando, 1971
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Ductile vs. Non-ductile Concrete Construction
• This photo was taken while looking at the exterior of a damaged classroom building
• The column suffered a shear failure.
• Note that the column did not fail at the top (where anticipated) due to combined shear and bending
Peru, 1974
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Photo of Column from the Inside• Note that at the top of the
column ductile reinforcing was used (ties very close together).
• The failure occurred where the spacing of ties was expanded.
• Ductile reinforcing of concrete is a necessity.
• Follow the IBC and ACI codes for seismic detailing requirements
Peru, 1974
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Earthquake Design• Of course the degree of
importance of an earthquake loading in any given location is related to the seismicity of the region:– Likelihood of occurrence– Probable intensity of the earthquake
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
How is seismicity determined?• Historical records
– China 3000 years– Middle East 2000 years– Latin America ???
• In the 1960’s the US developed the World Wide Standardized Network
• 120 stations in 60 different countries
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Seismographs• Instrument that
records the earth’s motion
• North-South • East-West• Vertical• Pen-Plotter• Digital
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
What causes earthquakes?
The lithosphere is broken into rigid plates that move.
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Arabian Plate
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Seismic Waves• When the earth shakes it releases
seismic waves• Body waves pass through the “body”
of the planet (fastest waves and can be refracted and reflected)
• Surface waves stay near the surface• There are many different types of
waves
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Types of Seismic WavesP Wave
S Wave
Love Wave
Rayleigh Wave
Body
Surface
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Body Waves
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Primary Waves• P-waves (body waves)• Are the fastest; consequently, they
reach the recording station first.• Move in a push-pull fashion, alternating
pulses of compression and tension• Can travel in any medium• Arrival at your site may be accompanied
with thunder-like noises and rattling windows (similar to a sonic boom)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Like a slinky
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Secondary Waves• S waves (body waves)• The second wave to reach the recording
station• Transverse waves that propagate by
shearing or shaking particles in their path at right angles to the path of advance
• Travel only through solids• The wave motion that is most damaging to
structures
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Snapping a piece of rope
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Love Waves• Surface waves• Motion is essentially an S wave that
has no vertical displacement• Moves the ground from side to side
90 degrees to the direction of propagation
• Can be very damaging to structures
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Love Waves
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Rayleigh Waves• Most common surface wave• Similar to water wave except they have
a backwards rotation• Cause horizontal and vertical
movement• Slower than Love waves• Pass through ground and water• Long periods and travel a long way
(once they get started)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Being on a ship
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Waves
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Waves
P waves travel approximately 1.7 times faster than S waves
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Locating the Source• The epicenter can be located using the
lengths of time the various seismic waves take to reach a seismograph
• P waves travel approximately 1.7 times faster than S waves; therefore, the larger the difference in arrival time, the farther away from the epicenter you are
• This gives you distance• What about direction?
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Use Multiple Seismographs
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Example Problem
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Example Problem continued
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
We use that procedure for all earthquakes
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Magnitudes of Earthquakes• The magnitude is an estimate of the
relative size (amplitude) of an earthquake measured from a seismogram
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Richter Scale• 1935, Charles Richter of CIT defined the
magnitude of an earthquakeMagnitude - the logarithm to the base ten of the maximum seismic wave amplitude (in thousandths of a millimeter) recorded on a standard seismograph at a distance of 100 kilometers from the earthquake center
• For every tenfold increase in amplitude on the seismogram, the Richter Number increases by 1.0
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Magnitudes• Earthquakes of
magnitude < 5.0 are not expected to cause structural damage
• Earthquakes > 5.0 are potentially very damaging
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Procedure for Measuring Magnitude
• S - P = 24 sec• Max height = 23
mm• Connect points
with a straight line
• Read intersection• Magnitude = 5.0
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Earthquake Intensity• Intensity is the severity of the
ground motion at any point• The measuring scale is the
Modified Mercalli (MM)• Scale of I to XII• I - Nothing to XII - Total Destruction
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Relating Richter to Mercalli
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
El Salvador• 7.6 magnitude quake• January 2001• Centered off the Salvadoran coast
about 65 miles southwest of San Miguel
• There were pockets of destruction, with destroyed towns next to areas that were completely unscathed
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Tremors were felt at our site
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Earthquakes Over 5.0 Richter in Honduras, 1900 - 1980
Structural damage would be expected in structures designed in accordance with US codes
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Earthquake Design
Section 1613 –DefinitionsSection 1614 –General
– Exceptions– Additions and/or alterations– Change of use
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Earthquake Design• Considerations are similar to wind
– site characteristics– occupancy– structural configuration and system– height and weight– zoning (wind speed vs. ground
acceleration)• Section 1615 – Site Ground Motion
Figures 1615 (1) through (10)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Figure 1615(1) – East Coast• Contours• Acceleration in
% of gravity• Linear
interpolation• Specific time of
response (.2 sec)
• Assumption of 5% damping
• Site Class
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Section 1616 – EQ Load Criteria Selection
• Seismic Design Criteria– Lateral resisting systems– Continuous path
• Seismic Use Group and Importance Factors (I, II, or III)– Table 1604.5 – Same as for wind design
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Section 1616.3 – Seismic Design Category
• Design Categories A – F (used to be Zones 1 – 4) impacts:– Structural system– Height and plan limitations– Components design– Types of analysis
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
• Section 1617 – EQ Loads – Minimum Design Lateral Force and Related Effects– 1617.4 Equivalent Lateral Force Procedure
• Equation 16-34 • Base Shear, V = CsW
– 1617.5 “Simplified” Procedure• Equation 16-49 • Base Shear, V = 1.2SDSW/R
Types of Analysis
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
• Based on calculating the base shear, V, of the structure and distributing the load vertically to the different story heights
Static Procedures
m2
m1
F2
F1
V
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
1618 - Dynamic Analysis Procedures
• Modal Response Spectrum Analysis• Linear Time-History Analyses• Nonlinear Time-History Analyses• Alternative Advanced Analyses• Generally, the simple analyses
provide more conservative designs
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Other Sections• 1619 – Soil Structure Interaction
Effects• 1620 – Design, Detailing
Requirements and Structural Component Load Effects
• 1621 – Architectural, Mechanical, and Electrical Component Requirements
• 1622 – Nonbuilding Structures
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Some Information Sources
• www.usgs.gov• www.nhc.noaa.gov• www.eeri.org• Compendix - Database of
engineering journals (thru VU library)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Chapter 15 Roof Assemblies and Rooftop Structures
• 1501 – General• 1502 – Definitions• 1503 – Weather
Protection• 1504 –
Performance Requirements
• 1505 – Fire Classification
• 1506 – Materials• 1507 – Requirements
for Roof Coverings (largest section)
• 1508 – Roof Insulation• 1509 – Rooftop
Structures• 1510 - Reroofing
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Roof Design
• Constraints– Material availability– No lifting equipment– Typical construction practice
• Structural Layout• Critical Loads
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Truss Questions• Are the trusses supported by the
columns on the porch?– Trusses should be supported by columns
• Do the walls extend to the roof or to the base of the truss?– Trusses will be exposed on the interior
of the structure• Truss information?
– Constructed from 2 - 5”x2”x1/16” channels welded together
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Truss Construction
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Trusses
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Connection Detail
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Homework
• Continue research on wind and seismicity of Honduras– Determine a design wind speed– Determine the ground acceleration
• Determine the loads for your roof design
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Next Lecture
• Load paths• Construction considerations• Design guides• Review of Progress Report #1
Requirements
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