John Gillengerten, S.E.fault was a M5.1 in 2000, located 10 miles NW of Napa, near Yountville. South...
Transcript of John Gillengerten, S.E.fault was a M5.1 in 2000, located 10 miles NW of Napa, near Yountville. South...
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Performance of Buildings and Nonstructural Components
in the South Napa Earthquake
John Gillengerten, S.E.
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FEMA P-1024
• FEMA/ATC special project to gather information on the performance of buildings and nonstructural components in the South Napa earthquake
• Project Team:
– Michael Mahoney, FEMA Project Officer
– Maryann Phipps and John Gillengerten, Technical co-Directors
– Ayse Hortacsu, ATC Project Manager
– Many other contributors in specific areas of expertise
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South Napa Earthquake
• M6.0, depth 11.7km on the West Napa fault
• Surface rupture length 14km, located along the west side of Napa Valley
• The last earthquake on this fault was a M5.1 in 2000, located 10 miles NW of Napa, near Yountville
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South Napa Earthquake
• Time of event, 3:20am on August 24, resulted in minimal casualties
• Only one death reported related to the South Napa earthquake– A 65-year-old woman struck by a
television who refused hospital aid and died of an intracranial hemorrhage two weeks later.
• Once again, we were very lucky -12 hours earlier, the streets were full of people attending a downtown street festival
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FEMA P-1024
• Effort based on ATC-38 program:
– Ground motion instrument site selected
– Every building within a 1,000 ft. radius is investigated
• Compare building performance against a known ground motion value
• Study centered on USGS seismometer N016 – peak acceleration = 0.65g
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FEMA P-1024 Scope
• Performance of Buildings
– Newer buildings (Post-1998)
– Non-URM, Pre-1998
– Retrofitted and un-retrofitted URM
– Outside the instrument study area: Healthcare, residential, manufactured housing, schools, healthcare, wineries
• Performance on Nonstructural Components
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Performance Surveys
• 68 buildings surveyed within 1,000 ft of Station N016– Interior and exterior surveys
for 50 of the buildings
– exterior only surveys for 18 buildings
– 77% of buildings constructed in 1950 or earlier
– Median age of buildings is 84 years
– URM buildings make up 40% of the buildings
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Newer Buildings
• Buildings constructed to recent codes generally performed well structurally
• Some newer buildings suffered significant nonstructural damage
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Pre-1998 Buildings
• The vast majority of older, non-URM structures also performed well structurally
• Known vulnerabilities, such as poor wall to roof connections, did result in significant damage and loss of use
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Unreinforced Masonry Buildings
• A 1986 California law requires localities to establish a seismic retrofit program for URM buildings.
• Napa URM retrofit ordinance– Passed in 2006, mandatory retrofit within 3 years– Objective: “to reduce the risk of death or injury”– Of the 26 URM buildings within 1,000 foot of Station N016, 19
had been retrofitted
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Retrofitted Unreinforced Masonry Buildings
• 13 buildings suffered no structural damage or the damage was deemed insignificant
• 3 buildings suffered minor damage, 1 building moderate damage, 2 were heavily damaged
• Some exterior masonry loosened or fell from three of the damaged buildings
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Un-retrofitted URM
• 3 posted UNSAFE and inaccessible for inspection
• 1 heavily damaged
• 1 moderately damaged
• 2 suffered insignificant damage
• Some buildings had significant loss of masonry
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Healthcare Facilities
• 5 hospitals and 13 skilled nursing facilities located between 4 and 10 miles from the epicenter
• Wide range of structural types, some buildings over 50 years old
• No facility suffered serious damage
• Nonstructural damage did interfere with the delivery of some healthcare services
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Residential Construction
• 61 of 116 buildings in Napa posted UNSAFE were residential buildings
• Damage concentrated heavily on two key deficiencies: masonry chimneys and unbraced cripple walls
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Manufactured Homes
• Since September 1994, a lateral tiedown system is required for new manufactured homes in California
• Majority of the homes in Napa were installed prior to bracing requirements
• Braced and unbraced homes failure rate about the same
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Nonstructural Components
• Fire sprinkler failures
– Interaction between heads and piping or other components
– In most cases, the water could not be turned off
– Serious flooding and water damage in some buildings
– Pipe and anchor failures
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Nonstructural Components
• Light curtain wall systems – Some modern structures
suffering substantial cracking and loss of veneer
– In at least one case, the curtain wall system appears to have been designed without a mechanism to accommodate interstory drift without damage
– The performance of adhered veneer was directly related to the performance of the substrate and the strength and condition of the adhesive material
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“Free” end dislodged, grid dropped
Failed splice“Fixed” end pulled out of wall
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Wine Industry
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Schools
• 31 public school sites in Napa County
• One or two-story buildings of wood frame or reinforced masonry construction
• Little or no structural damage to any of the schools, but…
– Repairs estimated at $8 million
– Loss of contents $9 million
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Napa County High SchoolHospital offices
Contents
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Contents
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“Furniture”
Stone Bridge School
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South Napa EQ Observations
• Seismically retrofitted older buildings (URM’s):
– Test of URM seismic retrofit strategies
– Performed well, with a few notable exceptions.
• Un-retrofitted URM buildings did not perform as well
• Partial wall collapse in one building resulted in five other buildings being red-tagged
• Newer construction performed well structurally
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South Napa EQ Observations
• Masonry chimneys continue to be a serious problem and threat in residential construction
• Unbraced cripple wall foundations did not perform well
• Buildings with cripple walls retrofitted for flood performed well
• Lateral bracing systems for manufactured housing need further review and development
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South Napa EQ Observations
• Nonstructural damage is typically the largest contributor to financial losses (>80%).
– We are now very good at life safety.
– We are still not very good at damage reduction
• Damage to nonstructural components can cause injury or death.
• Fire sprinkler piping damage and resultant water damage greater than expected.