Seismic fragility analysis of building structures subjected to Vrancea earthquakes' Innovative appro

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Seismic fragility analysis of building structures
subjected to Vrancea earthquakes. Innovative
approaches for seismic performance upgrade

• Dan LUNGU, UTCB
• Radu VACAREANU, UTCB
• Alexandru ALDEA, UTCB
• Cristian ARION, UTCB
• Mihail IANCOVICI, UTCB

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CONTENT

• Seismic fragility analysis
• representative building types
• capacity curves
• fragility analysis background, damage states
  development, case study
• seismic risk mapping
• Innovative approaches for seismic performance
  upgrade (under development)

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Workflow

• Fragility analysis
• estimation of earthquake damage to buildings
  given knowledge of the model building type and an
  estimate of the level of ground shaking
• extent and severity of damage to structural
  components of a building - described by one of
  five damage states None, Slight, Moderate,
  Extensive and Complete
• Propose unitary and relative simple procedures,
  engineering usable, in order to assess the
  seismic fragility of buildings
• Seismic risk mapping
• Decision technically, economically and socially
  acceptable

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Representative building types
BUILDING CAPACITY (push-over) curve - used (with
inelastic demand spectra) to
determine peak building response FRAGILITY
CURVES describe the probability of reaching or
exceeding different states of damage given
peak building response
DAMAGE FUNCTIONS
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Capacity curves parameters (A,D)
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Fragility functions background

• Building fragility curves for Slight, Moderate,
  Extensive and Complete damage states
• Each curve is characterized by
• median value of the demand parameter (i.e.
  spectral displacement, etc) that corresponds to
  the threshold of the damage state
• variability associated with that damage state
• The conditional probability of being in, or
  exceeding, a particular damage state,
• ds, given the spectral displacement, Sd, is
  defined by the functionHAZUS,1997
• Sd,ds - median value of spectral displacement at
  which the building reaches the threshold of the
  damage state, ds,
• ?ds - the standard deviation of the natural
  logarithm of spectral displacement for damage
  state ds, and
• ? - the standard normal cumulative distribution
  function

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Fragility analysis damage state medians

• Median values of structural component fragility
  based on
• building drift ratios that describe the
  threshold of damage states
• Damage-state drift ratios are converted to
  spectral displacement HAZUS, 1997
• is the median value of spectral displacement of
  structural components for damage state, ds,
• dR,Sds- drift ratio at the threshold of
  structural damage state, ds,
• a2 - fraction of the building (roof) height
  at the location of push-over mode
  displacement
• h - building height

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Fragility analysis damage state variability

• Total variability of each structural damage
  state, bSds - modeled as a combination of three
  contributions to structural damage variability,
  bC, bD and bM(Sds), HAZUS, 1997
• bSds - total variability for structural
  damage state, ds,
• bC - variability of the capacity curve,
• bD - variability of the demand spectrum,
• bM(Sds) - uncertainty in the estimate of the
  median value of the threshold of
  structural damage state, ds
• Uncertainty in the damage-state threshold of the
  structural
• system - assumed to be ßM(Sds) 0.4, for all
  structural damage
• states and building types HAZUS, 1997

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Case study

• RC frame, Bucharest
• GF10S
• Building height - 30,8 m
• Design code - low P13-70
• Fundamental period of vibration - 1,34s

Dy6 cm Du89 cm Ay0.14g Au0.20g
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M-C Simulation
Fragility curves parameters, 1990-2002
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Seismic risk mapping

• Central Bucharest 123 buildings built prior to
  1945 and identified as having seismic risk of
  class 1 in case of a strong earthquake, Mw?7.5

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Innovative approaches for seismic performance
upgrade (under development)

• Decision
• Technically sound
• Economically feasible
• Socially acceptable

Effectiveness for certain structural types and
ground motions characteristics
CURRENT
INNOVATIVE
Passive Semi-active Active Hybrid, response
control
Shear wall Column jacketing Steel braces External
steel frame etc.
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Example Linear FVD (Vrancea 1977 EQ, NS comp.,
INCERC station, Bucharest)
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CONCLUSIONS

• The probabilistic approach is the only one that
  incorporates uncertainties and enables
  quantification of the safety level.
• Interstory drift at threshold of damage states
  can be analytically evaluated for different
  structural typologies.
• Monte-Carlo simulation is a very powerful tool
  that can validate and complete the database on
  seismic behavior and fragility of buildings.
• The state of the practice in seismic design and
  seismic
• performance evaluation has to incorporate the
  basic concepts of seismic vulnerability and risk.