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F2009abn
sixteen
seismic design
Seismic Design 1Lecture 17
Applied Architectural StructuresARCH 631
lecture
© Reuters 2004
APPLIED ARCHITECTURAL STRUCTURES:
STRUCTURAL ANALYSIS AND SYSTEMS
ARCH 631
DR. ANNE NICHOLS
FALL 2015
Seismic Design 2
Lecture 16
Architectural Structures III
ARCH 631
F2007abn
Earthquake Design
• dynamic vs. static loading
– amplification of static affect
– time duration
– acceleration & velocity
F2009abn
Earthquake Design
• hazard types
– surface fault ruptures
– ground failures
– tsunamis (sea waves)
Seismic Design 3Lecture 17
Architectural Structures IIIARCH 631
http://nisee.berkeley.edu/godden
Seismic Design 4
Lecture 16
Architectural Structures III
ARCH 631
F2007abn
Earthquake Design
• hazard types: ground shaking
2
F2007abnSeismic Design 5Lecture 16
Architectural Structures IIIARCH 631
Earthquake Design
• fundamental considerations
– building configuration
• symmetry with respect to mass
– stiffness or vibration control
• symmetry with respect to lateral resistance mechanisms
• member sizes, rigidity, braces, dampers
– anchorage of parts and components
• seismic joints
– “tie the building together”
Seismic Design 6
Lecture 16
Architectural Structures III
ARCH 631
F2007abn
Earthquake Design
• building response
Seismic Design 7
Lecture 16
Architectural Structures III
ARCH 631
F2007abn
Earthquake Design
• building response
– seismic joints
– L, T, H
shapes bad
Seismic Design 8Lecture 16
Architectural Structures IIIARCH 631
F2008abn
Earthquake Design
• building response
– center of mass
• ex.:
– center of rigidity
• ex. (R = 1/ δ):
– torsion (eccentricity)
NS
NS
WxW
xΣ
Σ=
y
yE R
xRr
Σ
Σ=
3
Seismic Design 8
Lecture 16
Architectural Structures III
ARCH 631
F2007abn
• lateral ground movement
• drift
Low-Rise Response
Seismic Design 9Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Frequency and Period
• natural period of vibration
– avoid resonance
– hard to predict seismic period
– affected by soil
– short period• high stiffness
– long period• low stiffness
“To ring the bell, the sexton must pull on the downswing of the bell in time
with the natural frequency of the bell.”
F2007abnSeismic Design 10
Lecture 16
Architectural Structures III
ARCH 631
Earthquake Design
• codes
– purpose is to provide a simple uniform
method of determining potential
earthquake forces in any location with
enough accuracy to ensure a safe and
economical building design
– National Earthquake Hazards
Reduction Program (NEHRP)
– evaluate structural response (spectrum) to
earthquake (motion vs. time)
Seismic Design 11Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Earthquake Design Loads
• derived from W & amplification factors
• at base of structure:
– Z, zone
– I, importance (1.0 – 1.5)
– C, stiffness related to period of vibration
– RW, response modifications
for building type (1.25 – 8)
• distribution per floor
– simple vs. tall -
WRZICWV =
Wh
hWxx
∑
4
F2012abn
Earthquake Design Loads (ASCE-7)
• at base of structure:
– W, usually dead load but can include some live load
– Cs, seismic design coefficient
– SDS, short period design spectral response acceleration
– SD1, one second design spectral response acceleration
– R, response modification factor
– I, importance factor
– T, building period
– S1, mapped one-second spectral acceleration Seismic Design 13Lecture 16
Applied Architectural StructuresARCH 631
WCVS
=
)I/R(
SC DS
S=
)I/R(T
SD1
but not greater than
F2012abn
Earthquake Design Loads (ASCE-7)
Seismic Design 14Lecture 16
Applied Architectural StructuresARCH 631
F2009abn
Earthquake-Resistant Structures
• absorb energy input from ground motion
• pins can’t, rigid frames can– energy goes into forming
plastic hinges (ductility)
– continuous
– steel, timber or reinforced concrete
• redundancy helpful
• use rigid diaphragms
• horizontal members fail before verticalsSeismic Design 13Lecture 17
Architectural Structures IIIARCH 631
http://nisee.berkeley.edu/godden
Seismic Design 13Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Earthquake Design
• soft first stories
– problematic
– ground level story weaker than those above
• usually higher
• reduced strength in vertical elements
• significantly increased mass above
5
Seismic Design 14Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Earthquake Design
• want horizontal elements to fail before vertical elements do
Seismic Design 15Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Earthquake Design
• passive base isolation
– low stiffness layer
between foundation
and structure
Seismic Design 16Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Earthquake Design
• tuned mass damping systems
Seismic Design 17Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Earthquake Design
• dampers
• elastomer bearings
– neoprene or rubber
• sliding systems
• friction pendulum systems
6
F2011abn
Sendai Mediatheque, Japan, 2011
Seismic Design 19Lecture 16
Architectural Structures IIIARCH 631
© Wizneko 2011
F2013abn
Damage Levels – FEMA
Seismic Design 22Lecture 16
Applied Architectural StructuresARCH 631
• Operational
– minimal or no damage to structure
– extremely low risk to life safety
• Immediate Occupancy
– minimal to no damage to structure, minor damage to non-structural,
– very low risk to life safety
F2013abn
Damage Levels – FEMA (cont.)
Seismic Design 23Lecture 16
Applied Architectural StructuresARCH 631
• Life Safety
– may have extensive damage to structure, some repair may be economically impractical
– low risk to life safety
• Collapse Prevention
– not suffered complete or partial collapse, may have severe internal damage to structure, likely complete economic loss
– damage that poses risk to life safety
Seismic Design 18Lecture 16
Architectural Structures IIIARCH 631
F2007abn
Architectural Considerations
Video – Buildings at Risk
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