effects of san simeon earthquake on structures · pdf fileeffects of san simeon earthquake on...

Effects of San Simeon Effects of San Simeon Earthquake on StructuresEarthquake on Structures

Rakesh K. Goel, PhD, PEProfessor, CE & ENVE

Cal Poly, San Luis Obispo, CAEmail: [email protected]

Presented atNevada Earthquake Safety Council Meeting

May 5, 2004

May 5, 2004 Nevada Earthquake Safety Council Meeting Goel - 2

AcknowledgementAcknowledgement• 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)


OutlineOutline• Seismology• Ground Motion• Performance of Structures

Paso RoblesAtascaderoOceanoSan Luis Obispo

• Performance of Wineries• Retrofit of URM Buildings


The Ground ShakesThe Ground Shakes

• A moderate earthquake of Magnitude 6.5 strikes the Central Coast of California on December 22, 2003 at 11:15:56 AM local time

2 confirmed dead40 injured in Paso Robles/Templeton area.1 building collapsed and more than 40 severely damaged in Paso Robles AreaAtascadero City Hall damaged and closed for operations.Estimated loss in excess of $200 millions


Seismological AspectsSeismological Aspects


Shaking Intensity: Highest Shaking Intensity: Highest Intensity VIIIntensity VII

Information: USGS


Faults: Central CoastFaults: Central Coast• Seismic hazard to

central coast of California

HosGri FaultCambria FaultOceanic FaultSan Simeon FaultRinconada FaultSan Andreas Fault

Information: USGS


Prior Earthquake in Vicinity of Prior Earthquake in Vicinity of San SimeonSan 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.


Recorded MotionsRecorded Motions


Recorded AccelerationsRecorded AccelerationsHoriz Apk (g)Station Name Station

No./ID Network Dist.

(km) Ground Struct.Cambria – Hwy 1 Bridge 37737 CGS 13 .179 - - San Antonio Dam 36258 CGS 22 .12 .22 Templeton – 1-story Hospital 36695 CGS 38 .483 1.28 Parkfield – Vineyard Canyon 36441 CGS 49 .09 - - Los Osos – Point Buchon 36427 CGS 52 .09 - - San Luis Obispo - Rec Ctr 01083 USGS 62 .165 - -

Information: CISNEpicenter

http://www.slocoupons.com/maps_1.htm


Motions in TempletonMotions in Templeton


Directivity EffectsDirectivity Effects• Larger motion in

Templeton than in Cambria

PGA = 0.48g in Templeton and 0.18g in Cambria

• Directivity effects led to larger motions in Templeton

Fault rupture started at the epicenter and progressed South-East towards TempletonLarger accelerations occur in the direction of fault rupture due to Doppler-Type effects


Comparison with Design CodeComparison with Design Code


Structural PerformanceStructural Performance


Structural PerformanceStructural Performance• Significant structural

damage in Historic Downtown district of Paso Robles

• Significant nonstructural damage in Templeton and Atascadero

• Minor to moderate nonstructural/geotechnical damage in Oceano

• Minor nonstructural damage in San Luis Obispo


Damage in Paso RoblesDamage in Paso Robles


Damage in Paso RoblesDamage in Paso Robles• Major damage in

three blocks of historic downtown district of Paso Robles

Bounded by 12th and 13th streets in east-west direction, and Spring and Railroad Streets in the north-south direction


Concentration of Damage in Concentration of Damage in Paso RoblesPaso Robles

• A large number of historic Un-Reinforced Masonry (URM) buildings in the three block area

• URM buildings are susceptible to earthquake damage

Many such buildings are more than 100 years oldNot designed for seismic loadsLack detailing to transfer seismic forces from structure to the foundation

• State and local codes require retrofit but the deadline was 2008 to 2018

There is a recent push by the local city governments to advance the retrofit deadline


Acorn BuildingAcorn Building• 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


Collapse of Acorn BuildingCollapse of Acorn Building

Photo: Rakesh Goel


Acorn BuildingAcorn 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

Sketch: The Tribune (1/24/03), SLO, CA


Marlow Interior BuildingMarlow Interior Building

• Two-story URM 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

Photo: Rakesh Goel


Marlow Interior BuildingMarlow Interior Building• Significant asymmetry

in building planTorsional (or twisting) motions in addition to swaying motions during the earthquake

• Significant cracks in walls facing the street sides

Large demands on these walls due to torsion (or twisting)

• Building had to be demolished and a replacement is planned

Photo: Sam Vigil


Bistro Laurent BuildingBistro Laurent Building

• One-story URM building• Retrofitted by tying roof

diaphragm to the walls• Only minor to moderate

structural damageNo cracks in the masonry wallsFew bricks from the decorative parapet separated Photo: Rakesh Goel


Bistro Laurent Building: Bistro Laurent Building: Retrofit DetailsRetrofit Details

Photo: Rakesh GoelPhoto: Rakesh Goel


Ali’s Persian Rug BuildingAli’s Persian Rug Building• Three-story URM

building built in 1918• Building partially

retrofitted• Damage to masonry

façade and parapetsNo ties between façade and the main wallBricks peeled due to out-of-plane motion and stresses imposed on the joints due to drift

Photo: Khalid Mosalam


Ali’s Persian Rug Building: Ali’s Persian Rug Building: Repair (1/18/04)Repair (1/18/04)

Photo: Rakesh Goel

Photo: Rakesh Goel

Photo: Rakesh Goel


Rustic Ranch Furniture Rustic Ranch Furniture GalleryGallery

• One-story URM building sandwiched between two other buildings

• No structural damage apparent except for broken window glass

Photo: Rakesh Goel


Rustic Ranch Furniture Rustic Ranch Furniture GalleryGallery

Photo: Rakesh Goel

Photo: Rakesh Goel


Paso Robles InnPaso Robles Inn• Observation tower did

not suffer damageBrick façade supported on space frame

• One of the unreinforced masonry building housing quest quarters was damaged

Significant cracks in wallsBuilding planned to be demolished

• Moderate nonstructural damage

Broken window glass

Photo: Rakesh Goel


Paso Robles Inn: PrecautionPaso Robles Inn: Precaution

Photo: Rakesh GoelPhoto: Rakesh Goel

On 12/23/03 On 1/18/04: Boarded-Up


Carnegie LibraryCarnegie Library

Photo: Rakesh Goel

Photo: Rakesh Goel Photo: Rakesh Goel


Damage in AtascaderoDamage in Atascadero


Atascadero City HallAtascadero City Hall

• Reinforced concrete space frame

• Brick façade• Built in 1918 by

town founder E. G. Lewis

• Partially retrofittedPhoto: Rakesh Goel



Photo: Lew Rosenberg



• Brick façade peeled off the rotunda

• Moderate cracking in interior partition walls

• City Hall has been closed

Photo: Rakesh Goel


Atascadero City HallAtascadero City Hall• Retrofit prevented parapet collapse

Photo: Rakesh Goel


Atascadero City HallAtascadero City Hall• Typical nonstructural damage

Photo: Rakesh Goel

Photo: Rakesh Goel


Typical Damage to ContentsTypical Damage to Contents

Photo: Rakesh Goel

Photo: Sam Vigil


Damage in OceanoDamage in Oceano


Damage in OceanoDamage in Oceano

• About 50 miles from the epicenter• Pavement damage at Oceano airport• Sink holes and damage to tanks at

Waste Water Treatment plant• Damage to houses close to the beach

Shifting off the foundation• More than 30 water main break• Street pavement damage


Damage in OceanoDamage in Oceano• Damage typical of lateral spreading/

loose sandy soils

Photo: Lew RosenbergPhoto: Lew Rosenberg

Pavement Damage House Damage


San Luis ObispoSan Luis Obispo


San Luis Obispo (SLO)San Luis Obispo (SLO)• More than 125 unreinforced-masonry

buildings in downtown area• About 25 have been seismically upgraded• No significant structural damage reported

Accelerations were about 17%g in SLO compared to perhaps more than 50%g in Paso RoblesPerformance 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


San Luis ObispoSan Luis Obispo

Historic Ah Louis Store survived with minor damage

Mission San Luis Obispo deTolosa came out with onlya minor crack

Photo: Rakesh Goel

Photo: Rakesh Goel


Damage to Templeton Area Damage to Templeton Area WineriesWineries


Damage to WineriesDamage to Wineries

• Wineries along Hwy 46 west of Templeton sustained heavy nonstructural damage

damaged glasses and bottles of wine in tasting facilitiesbroken bottles in the valuable wine librariesruptured stainless steel wine tankscollapse of wine barrels stacked in pyramids and on portable steel racks rupture of wine barrels and loss of a substantial amount of wine



Photo:Josh Marrow

Photo:Josh Marrow

Photo:Josh Marrow


Summary of FindingsSummary of Findings• Unreinforced masonry (URM) buildings are

highly susceptible to seismic loadingPotential for collapseSignificant hazard from falling bricks from façade

• Even basic seismic retrofit – tying floor/roof diaphragm to walls – minimized the collapse potential for URM building

San Simeon earthquake tested several retrofitted buildings in Paso RoblesMost retrofitted buildings survived without major damage


Summary of FindingsSummary of Findings• Buildings on street corners performed poorly

Asymmetric in building plan due to large open windows on street sidesTorsional 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 mid-block

End buildings gets kicked out by neighboring buildingNeed special attention during retrofit


Summary of FindingsSummary of Findings

• Current system of stacking wine barrels is not safe during earthquakes

Wine barrels topple and ruptureMay lead to significant dollar loss during earthquake


Retrofit of URM BuildingsRetrofit of URM Buildings


Retrofit Objectives: FEMARetrofit Objectives: FEMA--356356• Building Performance Levels

Collapse preventionLife safetyImmediate occupancyOperational

• Earthquake Hazard Level: Probability of exceedance in 50 years (Return Period in years)

50% (72): Frequent20% (225): Occasional10% ( 475): Rare2% (2,475): Extremely rare


Retrofit ObjectivesRetrofit Objectives• Select a combination of acceptable level of

building performance and earthquake hazardBasic Safety Objectives: Life safety during 10% and collapse prevention during 2% eventEnhanced Objectives: Basic safety + Better performance during lower level eventLimited objectives: Basic safety – Poorer performance during lower level event

• Higher cost for enhanced performance and lower cost for limited performance


URM Seismic Retrofit URM Seismic Retrofit MethodsMethods

• Epoxy InjectionFill cracks with epoxy to restore composite action in cracked walls

• Anchoring & TyingTie the floor/roof to the wallAnchor unsupported masonry walls


URM Retrofit MethodsURM Retrofit Methods• Bracing of URM walls to increase stability

Steel sections, reinforced masonry, concrete buttress, or FRP strips

• Overlays to increase flexural strength of URM walls

High-strength cement mortar ½ inch to 1 inch thick, reinforced with thin steel wire meshFiber (Glass or Carbon) Reinforced Polymers (FRP) layers


URM Retrofit MethodsURM Retrofit Methods• Reinforcement to increase in-plane and out-

of-place flexural strengthInternal: Steel bars inserted in holes drilled in plane of the URM wallsExternal: Attach reinforcement (steel plates or angles) to the surface of the URM wallPost-Tensioning: Insert steel wires and post-tension to create compression in the wall


URM Retrofit MethodsURM Retrofit Methods• Base isolation and energy dissipation

devicesUsed for retrofit of historical buildingsExpensive


Cost of URM Seismic RetrofitCost of URM Seismic Retrofit• Higher the rehabilitation objectives, higher the

costAim for basic safety objectivesLimited objectives may be acceptable if cost is prohibitive

• Cost can range from $10 to $100 per square foot

Cost can be minimized if seismic retrofit work combined with other upgradesTypical cost in SLO has been about $20 per square foot

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