Effects of San Simeon Earthquake on Structures

Effects of San Simeon
Earthquake on Structures
Presented at
Nevada Earthquake Safety Council Meeting
May 5, 2004
Rakesh K. Goel, PhD, PE
Professor, CE & ENVE
Cal Poly, San Luis Obispo, CA
Email: [email protected]
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Acknowledgement
Sam Vigil, Cal Poly, SLO
Garret Hall, Cal Poly, SLO
Khalid Mosalam, UC Berkeley
Josh Marrow, SGH
Lew Rosenberg, SLO County Geologist
United State Geological Survey (USGS)
California Integrated Seismic Network
(CISN)
• The Tribune (San Luis Obispo, CA)
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Outline
• Seismology
• Ground Motion
• Performance of Structures
ÎPaso Robles
ÎAtascadero
ÎOceano
ÎSan Luis Obispo
• Performance of Wineries
• Retrofit of URM Buildings
May 5, 2004
Nevada Earthquake Safety Council Meeting
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The Ground Shakes
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A moderate earthquake of Magnitude 6.5 strikes the
Central Coast of California on December 22, 2003 at
11:15:56 AM local time
Î2 confirmed dead
Î40 injured in Paso Robles/Templeton area.
Î1 building collapsed and more than 40 severely
damaged in Paso Robles Area
ÎAtascadero City Hall damaged and closed for
operations.
ÎEstimated loss in excess of $200 millions
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Seismological Aspects
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Shaking Intensity: Highest
Intensity VII
Information: USGS
May 5, 2004
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Faults: Central Coast
• Seismic hazard to
central coast of
California
ÎHosGri Fault
ÎCambria Fault
ÎOceanic Fault
ÎSan Simeon Fault
ÎRinconada Fault
ÎSan Andreas Fault
Information: USGS
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Prior Earthquake in Vicinity of
San Simeon
• M5 to M6 (?) earthquake in 1853
• M5.7 earthquake in 1906
• ML6.2 earthquake in 1952
• Current earthquake of Mw = 6.5 in 2003
• Appears to be a pattern of significant event
about every 50 year.
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Recorded Motions
May 5, 2004
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Recorded Accelerations
Station Name
Cambria – Hwy 1 Bridge
San Antonio Dam
Templeton – 1-story Hospital
Parkfield – Vineyard Canyon
Los Osos – Point Buchon
San Luis Obispo - Rec Ctr
Station Network
No./ID
37737
36258
36695
36441
36427
01083
Dist.
(km)
CGS
CGS
CGS
CGS
CGS
USGS
Information:
13
22
38
49
52
62
CISN
Horiz Apk (g)
Ground Struct.
.179
-.12
.22
.483
1.28
.09
-.09
-.165
--
Epicenter
http://www.slocoupons.com/maps_1.htm
May 5, 2004
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Motions in Templeton
May 5, 2004
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Directivity Effects
Larger motion in
Templeton than in
Cambria
Î PGA = 0.48g in Templeton and
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0.18g in Cambria
Directivity effects led to
larger motions in
Templeton
Î Fault rupture started at the
epicenter and progressed
South-East towards Templeton
Î Larger accelerations occur in
the direction of fault rupture
due to Doppler-Type effects
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Comparison with Design Code
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Structural Performance
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Structural Performance
Significant structural
damage in Historic
Downtown district of
Paso Robles
Significant nonstructural
damage in Templeton
and Atascadero
Minor to moderate
nonstructural/geotechni
cal damage in Oceano
Minor nonstructural
damage in San Luis
Obispo
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Damage in Paso Robles
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Damage in Paso Robles
• Major damage in
three blocks of
historic downtown
district of Paso
Robles
ÎBounded by 12th and
13th streets in eastwest direction, and
Spring and Railroad
Streets in the northsouth direction
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Concentration of Damage in
Paso Robles
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A large number of historic Un-Reinforced Masonry
(URM) buildings in the three block area
URM buildings are susceptible to earthquake
damage
Î Many such buildings are more than 100 years old
Î Not designed for seismic loads
Î Lack detailing to transfer seismic forces from structure to the
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foundation
State and local codes require retrofit but the deadline
was 2008 to 2018
Î There is a recent push by the local city governments to
advance the retrofit deadline
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Acorn Building
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Two-story URM building
built in 1892
The building collapsed
during the San Simeon
earthquake killing two
people
Building had to be
demolished and
replacement is planned
Photo: Paso Robles Chamber of
Commerce
May 5, 2004
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Collapse of Acorn Building
Photo: Rakesh Goel
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Acorn Building
Roof not tied properly to
the walls
East-west motion
imposed large
deformations on the
outer wall in second
story leading to its
collapse
The roof slides to the
side, bends over the
first floor wall, and
crushes cars and two
victims
May 5, 2004
Sketch: The Tribune (1/24/03), SLO, CA
Nevada Earthquake Safety Council Meeting
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Marlow Interior Building
• Two-story URM
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building located on
corner of 12th and
Park Street
Large open windows
on street sides of
the building
Solid walls with few
openings on other
two sides
May 5, 2004
Photo: Rakesh Goel
Nevada Earthquake Safety Council Meeting
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Marlow Interior Building
Significant asymmetry
in building plan
Î Torsional (or twisting)
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motions in addition to
swaying motions during
the earthquake
Significant cracks in
walls facing the street
sides
Î Large demands on these
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walls due to torsion (or
twisting)
Building had to be
demolished and a
replacement is planned
May 5, 2004
Photo: Sam Vigil
Nevada Earthquake Safety Council Meeting
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Bistro Laurent Building
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One-story URM building
Retrofitted by tying roof
diaphragm to the walls
Only minor to moderate
structural damage
Î No cracks in the masonry
walls
Î Few bricks from the
decorative parapet
separated
May 5, 2004
Photo: Rakesh Goel
Nevada Earthquake Safety Council Meeting
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Bistro Laurent Building:
Retrofit Details
Photo: Rakesh Goel
May 5, 2004
Photo: Rakesh Goel
Nevada Earthquake Safety Council Meeting
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Ali’s Persian Rug Building
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Three-story URM
building built in 1918
Building partially
retrofitted
Damage to masonry
façade and parapets
Î No ties between façade
and the main wall
Î Bricks peeled due to outof-plane motion and
stresses imposed on the
joints due to drift
May 5, 2004
Photo: Khalid Mosalam
Nevada Earthquake Safety Council Meeting
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Ali’s Persian Rug Building:
Repair (1/18/04)
Photo: Rakesh Goel
Photo: Rakesh Goel
Photo: Rakesh Goel
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Rustic Ranch Furniture
Gallery
• One-story URM
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building sandwiched
between two other
buildings
No structural
damage apparent
except for broken
window glass
Photo: Rakesh Goel
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Rustic Ranch Furniture
Gallery
Photo: Rakesh Goel
Photo: Rakesh Goel
May 5, 2004
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Paso Robles Inn
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Observation tower did
not suffer damage
Î Brick façade supported
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on space frame
One of the unreinforced
masonry building
housing quest quarters
was damaged
Î Significant cracks in walls
Î Building planned to be
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demolished
Moderate nonstructural
damage
Photo: Rakesh Goel
Î Broken window glass
May 5, 2004
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Paso Robles Inn: Precaution
Photo: Rakesh Goel
On 12/23/03
May 5, 2004
Photo: Rakesh Goel
On 1/18/04: Boarded-Up
Nevada Earthquake Safety Council Meeting
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Carnegie Library
Photo: Rakesh Goel
Photo: Rakesh Goel
Photo: Rakesh Goel
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Damage in Atascadero
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Atascadero City Hall
• Reinforced concrete
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space frame
Brick façade
Built in 1918 by
town founder E. G.
Lewis
Partially retrofitted
May 5, 2004
Photo: Rakesh Goel
Nevada Earthquake Safety Council Meeting
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Atascadero City Hall
Photo: Lew Rosenberg
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Atascadero City Hall
• Brick façade peeled
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off the rotunda
Moderate cracking
in interior partition
walls
City Hall has been
closed
Photo: Rakesh Goel
May 5, 2004
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Atascadero City Hall
• Retrofit prevented parapet collapse
Photo: Rakesh Goel
May 5, 2004
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Atascadero City Hall
• Typical nonstructural damage
Photo: Rakesh Goel
Photo: Rakesh Goel
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Typical Damage to Contents
Photo: Rakesh Goel
Photo: Sam Vigil
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Damage in Oceano
May 5, 2004
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Damage in Oceano
• About 50 miles from the epicenter
• Pavement damage at Oceano airport
• Sink holes and damage to tanks at
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Waste Water Treatment plant
Damage to houses close to the beach
ÎShifting off the foundation
• More than 30 water main break
• Street pavement damage
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Damage in Oceano
• Damage typical of lateral spreading/
loose sandy soils
Photo: Lew Rosenberg
Pavement Damage
May 5, 2004
Photo: Lew Rosenberg
House Damage
Nevada Earthquake Safety Council Meeting
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San Luis Obispo
May 5, 2004
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San Luis Obispo (SLO)
• More than 125 unreinforced-masonry
buildings in downtown area
• About 25 have been seismically upgraded
• No significant structural damage reported
ÎAccelerations were about 17%g in SLO compared
to perhaps more than 50%g in Paso Robles
ÎPerformance of unreinforced-masonry buildings in
SLO would not be significantly different than in
Paso Robles if the shaking in SLO had been
stronger
• City Council and Chamber of Commerce
discussing advancing the retrofit deadline
May 5, 2004
Nevada Earthquake Safety Council Meeting
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San Luis Obispo
Photo: Rakesh Goel
Historic Ah Louis Store
survived with minor damage
May 5, 2004
Photo: Rakesh Goel
Mission San Luis Obispo de
Tolosa came out with only
a minor crack
Nevada Earthquake Safety Council Meeting
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Damage to Templeton Area
Wineries
May 5, 2004
Nevada Earthquake Safety Council Meeting
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Damage to Wineries
• Wineries along Hwy 46 west of Templeton
sustained heavy nonstructural damage
Îdamaged glasses and bottles of wine in tasting
facilities
Îbroken bottles in the valuable wine libraries
Îruptured stainless steel wine tanks
Îcollapse of wine barrels stacked in pyramids and
on portable steel racks
Îrupture of wine barrels and loss of a substantial
amount of wine
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Damage to Wineries
Photo:Josh Marrow
Photo:Josh Marrow
May 5, 2004
Photo:Josh Marrow
Nevada Earthquake Safety Council Meeting
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Damage to Wineries
Photo:Josh Marrow
Photo:Josh Marrow
Photo:Josh Marrow
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Summary of Findings
• Unreinforced masonry (URM) buildings are
highly susceptible to seismic loading
ÎPotential for collapse
ÎSignificant hazard from falling bricks from façade
• Even basic seismic retrofit – tying floor/roof
diaphragm to walls – minimized the collapse
potential for URM building
ÎSan Simeon earthquake tested several retrofitted
buildings in Paso Robles
ÎMost retrofitted buildings survived without major
damage
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Summary of Findings
• Buildings on street corners performed poorly
ÎAsymmetric in building plan due to large open
windows on street sides
ÎTorsional motions impose larger demands on
lateral load resisting elements during earthquake
• Buildings at the end of the block performed
poorly compared to similar buildings in midblock
ÎEnd buildings gets kicked out by neighboring
building
ÎNeed special attention during retrofit
May 5, 2004
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Summary of Findings
• Current system of stacking wine barrels
is not safe during earthquakes
ÎWine barrels topple and rupture
ÎMay lead to significant dollar loss during
earthquake
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Retrofit of URM Buildings
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Retrofit Objectives: FEMA-356
• Building Performance Levels
ÎCollapse prevention
ÎLife safety
ÎImmediate occupancy
ÎOperational
• Earthquake Hazard Level: Probability of
exceedance in 50 years (Return Period in years)
Î50% (72): Frequent
Î20% (225): Occasional
Î10% ( 475): Rare
Î2% (2,475): Extremely rare
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Retrofit Objectives
• Select a combination of acceptable level of
building performance and earthquake hazard
ÎBasic Safety Objectives: Life safety during 10%
and collapse prevention during 2% event
ÎEnhanced Objectives: Basic safety + Better
performance during lower level event
ÎLimited objectives: Basic safety – Poorer
performance during lower level event
• Higher cost for enhanced performance and
lower cost for limited performance
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URM Seismic Retrofit
Methods
• Epoxy Injection
ÎFill cracks with epoxy to restore composite
action in cracked walls
• Anchoring & Tying
ÎTie the floor/roof to the wall
ÎAnchor unsupported masonry walls
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URM Retrofit Methods
• Bracing of URM walls to increase stability
ÎSteel sections, reinforced masonry, concrete
buttress, or FRP strips
• Overlays to increase flexural strength of URM
walls
ÎHigh-strength cement mortar ½ inch to 1 inch
thick, reinforced with thin steel wire mesh
ÎFiber (Glass or Carbon) Reinforced Polymers
(FRP) layers
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URM Retrofit Methods
• Reinforcement to increase in-plane and outof-place flexural strength
ÎInternal: Steel bars inserted in holes drilled in
plane of the URM walls
ÎExternal: Attach reinforcement (steel plates or
angles) to the surface of the URM wall
ÎPost-Tensioning: Insert steel wires and posttension to create compression in the wall
May 5, 2004
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URM Retrofit Methods
• Base isolation and energy dissipation
devices
ÎUsed for retrofit of historical buildings
ÎExpensive
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Cost of URM Seismic Retrofit
• Higher the rehabilitation objectives, higher the
cost
ÎAim for basic safety objectives
ÎLimited objectives may be acceptable if cost is
prohibitive
• Cost can range from $10 to $100 per square
foot
ÎCost can be minimized if seismic retrofit work
combined with other upgrades
ÎTypical cost in SLO has been about $20 per
square foot
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