Non Structural Hazards
Non-structural Hazards
Northridge Earthquake
Loma Prieta Earthquake
• Ground shaking disturbs anything not attached
Non-structural damage
• Falling ceilings,
objects
• Pipes, chimneys, etc
Non-structural Hazards
• Internal lighting
fixtures and utility
equipment should be
fasted to structural
elements
• Bookcases, closet
and heavy furniture
should be fastened to
the wall studs
Non-structural Hazards
• Brick chimneys should be reinforced and braced
• Cape Mendocino, 1992
Awareness of ones surroundings is
key:
• Avoid heavy mirrors, pictures or books
above or near beds
• Have window covering if bed is near a
window
• Avoid any heavy furniture, book cases or
glassware capable of blocking escape
routes
• Securely bolt or attach book cases to wall
at frame
Mitigation:
to reduce the amount of risk
Long-term Risk Mitigation
• Retrofitting
• Building codes
• Legislation
– Earthquake hazard reduction programs
– California Seismic Safety commission
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Insurance
Earthquake warning systems
Education
Earthquake recovery
Retrofitting:
to strengthen existing structures
and add flexibility to stiff building materials.
Design failures
House off foundation
Connections
Soft story
HOG
Cripple wall failure
Freeway connections
Unreinforced masonry
Structural failure due to
resonance
Irregularly shaped
buildings
Retrofitting
• To prevent non-structural damage in
frequent minor ground shaking
• To prevent structural damage and
minimize non-structural damage in
occasional moderate ground shaking
• To avoid collapse or serious damage in
rare major ground shaking
Soft Story
Strengthen connections. Add shear
walls, and use of cross-beams in
soft-story
Shear Walls
• Help dissipate energy
• Prevents
concentration of
energy at vertical and
horizontal connections
Unreinforced sheer wall
Shear Walls
Shear walls absorb
seismic energy
Cripple walls
Retrofitting Cripple Walls
• Retrofit cripple walls
to help dissipate
• Cross-bracing or
shear walls are
added
• Plywood panels are
securely added over
the studs
House off the foundation
Bolting House to Foundation
• Add bolts of various
types to strengthen
the connection.
Resonance: change period of
building
Dampers: may be added or
included in original design
• Force from the
dampers is out of
phase with the
structure
• Changes the period
of a structure to
avoid resonance
• Inhibit movement
Viscous Dampers (energy is absorbed by silicone-based fluid
passing between piston cylinder arrangement)
Testing dampers in the
laboratory
Viscous Dampers
Western portion of the Bay Bridge
Shaking causes
piston to stiffen.
Energy is
transferred from
connection to
connection.
Tuned Mass
Damper
• 730 ton mass
• Tallest building in the
world
• Taipei 101
• Hundreds of miles
away from the China
earthquake’s
epicenter
Friction Pendulum Bearings
• Structure moves
along the bearing to
accommodate
seismic shaking
Benicia-Martinez Bridge
• Completed in 2007
• 13 feet in diameter
• 53 inches of
displacement
• 5 million pound load
capacity
• 5 second period
Base Isolators: isolates
structure from ground shaking
• Before and during
an earthquake
Structural Designs
• Super high-rise Condominium
• 241 units
• 28 floors
Base isolation test
• University of San
Diego
• Shake tables
• Right structure on
base isolators
San Francisco City Hall
• Loma Prieta
earthquake
• Dome twisted off steel
frame
• $293 million retrofit
• 530 base isolators
– Supporting columns
jacked up and cut
– Isolator positioned
– Column replaced
USC Hospital: 1994 building codes
The Base-Isolated USC
Hospital Building
• 149 isolators that support the steel
structure
• 68 isolators that support the perimeter
frames
• 81 isolators that support internal columns
• standards of 1988, 1994 building codes
USC Hospital Building
• Damage associated with the Northridge
earthquake was minimal
• Displacement near the epicenter would
exceed the designed displacement of 26
centimeters
• Design improvements are needed for the
type of base-isolation system
Roadways: pre1970; less seismic
consideration
Testing strength of connections in laboratory
Freeway column collapse
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¾ inch rebar
stronger material- increases flexibility
Vertical rebar is wrapped with rebar
Set into footing and superstructure
1994 Earthquake
Roads and Highways
• Thicker rebar
• More rebar
• Vertical portion
wrapped
• Connections secured
using various
methods
Bridges and Roads
• Sheaths surrounding
highway piers to
prevent concrete from
crumbling off the
rebar during seismic
shaking
Sheaths added
to columns
Strengthening connections
Post 1970
• Pre-1970
Hinge Joint
Restrainers
Strengthening Moment Frames
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Two girders
Vertical couples
Stiffen frame
Absorb seismic
energy
Cross bracing
Built into the original design
Added to strengthen older structures
Unreinforced Masonry URM
Unreinforced Masonry URM
Add steel and wood
bracing
Steel beams and bolts add
flexibility to the bricks
Retrofitting strengthens weak
structures
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Shear walls: dissipate energy
Cross bracing: strengthens connections
Dampers: change period of building
Base isolators: reduces shaking of bldg
Steel: adds flexibility to stiff material
Strengthen connections: structure will
accommodate more movement
• Addition of rebar to concrete: adds strength and
flexibility
• Sheaths around columns: prevents concrete
from crumbling
Bay Bridge East Span Retrofit
vs. Replacement
Seismic
Performance
Lifeline
Connection
Life Expectancy
Moderate to
major damage
Would not be
safe
50 years
Minor to
moderate
Would provide
safe route
150 years
Design/cost
1.1 billion
1.5 billion
Bay Bridge East Span Retrofit
vs. Replacement
Life Cycle
Rail
Financing
Bicycle/
Pedestrian
Redecked in 2
years
Significant
modification
Legislature
None
Concrete/steel
minimal main.
Can
accommodate
Has financing
package
15.5 foot wide
path
Bay Bridge East Span Retrofit
vs. Replacement
Bay Bridge East Span Retrofit
Current Status
• California Department of Transportation
(Caltrans): unseal proposals June 3rd
• Some portions currently under construction
• Bridge building firms from around the world
backed down due to time table and budget
• 729 million and 47 month time-table
• Foundry devoted to project:50,000 tons of
steel,
• Crane would have to be brought around the
cape of South America
Bay Bridge East Span Retrofit
vs. Replacement
Bay Bridge East Span Retrofit
vs. Replacement
San Francisco Oakland Bay
Bridge
• Replace versus retrofit due to cost
• Initially the cost to replace was 1.5 billion
versus 1.1 billion to retrofit
• Current cost 6.5 billion, to be completed 2013
New Eastern Span: Oakland Bay
Bridge
Golden Gate Bridge
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Completed in 1937
Suspension bridge
388 million to retrofit
42 million vehicles
per year
• Retrofit is separated
into three
construction phases
The Golden Gate Bridge
• Phase 1 was
completed in
December 2001
• New supports were
added to the north
viaduct
The Golden Gate Bridge
• The second phase
of retrofitting
involves the south
viaduct, anchorage,
Fort Point Arch, and
south Pylons.
• Complete
Additional cross-beams
The Golden Gate Bridge
• Third phase
• Not yet funded
• Retrofit the North
anchorage, the main
span and towers
Building Design
• The Transamerica
building is constructed
for earthquake
resistance
• A broad well braced
base and narrow top
• Strong-motion
instruments recorded
12 cm more motion at
the top during 1989
Transamerica Building
Hayward City
Hall
• Friction pendulum
seismic isolation
• Hydraulic viscous
dampers
• Isolation structural
frame
Seismic design incorporated into structure design
Earthquake Resistant
Structures
Dublin Emergency Services- built
with support in design, should be
operational after an earthquake
San Mateo County Offices- steel
frame on pile foundation, pre-cast
concrete with aluminum walls
Earthquake Resistant
Structures
Saratoga Public Librarysingle story wood frame,
seismic elements exposed
City of San Franciscocurved shear wall,
basement walls resisting
hydrostatic pressures
Alaska Pipeline
Pipeline on
rollers across
the Denali Fault
trace.
Seismic design incorporates:
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Shear walls
Cross bracing
Strengthening of connections
Dampers
Base isolators
Ductile building materials
Weight evenly distributed throughout all
floors in multiple story buildings