Avoiding disproportionate collapse

1
Avoiding Disproportionate Collapse in High-Rise
Buildings
April 2008
Uwe Starossek
ASCE SEI 2008 Structures Congress, Vancouver,
Canada April 24-26, 2008 Uwe Starossek Avoiding
disproportionate collapse in high-rise buildings
Hamburg University of Technology
1/19
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World Trade CenterSeptember 11, 2001

Studies should be conducted to determine
whether there are feasible design and
construction features that would permit such
buildings to arrest or limit a collapse, once it
began. (FEMA Report 403, May 2002)
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Suggested design approach
? on the one hand, the design methods as
described in the current codes are
applied ? on the other hand, an additional
assessment with regard to collapse resistance
is made ? not necessarily based on
reliability theory but rather on
judgment and a decision-making process ?
analyses are generally carried out
deterministically
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Design criteria (additional assessment regarding
p.c.)
?
?
?
?
5
Design objectives

• assumable extent of accidental circumstances
• assumable extent of initial local failure
• acceptable extent of collapse progression
• acceptable extent of damage to remaining
  structure
• applicable load combinations and safety factors

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Additional design criteria
?
?
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Design strategies

• high safety against local failure (prevent local
  failure)
• specific local resistance of key elements
• non-structural protective measures
• design for load case local failure (presume
  local failure)
• alternate paths
• isolation by segmentation
• prescriptive design rules (indirect design)

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Confederation Bridge, Canada

• alternate paths cannot be provided
• isolation by segmentation

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Confederation Bridge, Canada
insertion of hinges
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Confederation Bridge, Canada

• segment borders must be able to sustain either
  large forces
• or large displacements

• reduction of continuity can lead to increase of
  robustness

insertion of hinges
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More examples

• isolation by segmentation

Pentagon Building
Paris Airport Terminal
weak
strong
weak
weak
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More examples

• isolation by segmentation

structural system
Murrah Federal Building
Collapse stopped at rebar discontinuity in
transfer girder!
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Comparison of design methods
segmentation
alternate paths
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Collapse-resistant design of high-rise building
(1)
Specific local resistance of primary system
leading to an arrangement of independent
primary and secondary load
transfer systems
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Collapse-resistant design of high-rise building
(1)
secondary load transfer system
alternatively, limiting collapse of secondary
system through horizontal segmentation
primary system with high specific local resistance
transfer of loads of failing floors to floors
below thus providing alternate paths
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Collapse-resistant design of high-rise building
(2)
Vertical segmentation with
energy-dissipating shock-absorbing zones
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Collapse-resistant design of high-rise building
(2)
segment border


shock-absorbing segment border
shock-absorbing device telescoping steel
tubes with compressible filling
vertical segmentation by shock-absorbing zones
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Conclusions

• The adequacy of a particular design method
  depends on the
• structural system and the design objectives.
• For large and slender high-rise buildings, the
  alternate-path
• approach can be used if a set of limited
  accidental actions is
• agreed upon.
• Larger accidental circumstances are tolerable
  when the design of
• the primary system is based on the
  specific-local-resistance
• approach.
• In that case, an arrangement of independent
  primary and
• secondary load transfer systems is arrived at.
• Alternatively, a collapse can be arrested by
  vertical segmentation
• with energy being dissipated in shock-absorbing
  zones.

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Thank you!
ASCE SEI 2008 Structures Congress, Vancouver,
Canada April 24-26, 2008 Uwe Starossek Avoiding
disproportionate collapse in high-rise buildings
Hamburg University of Technology
19/19