Progressive Collapse

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Comparing progressive collapse due to fire in
differing structural systems.
Mark Dobossy Graduate Student Dept. of Civil and
Environmental Engineering Princeton University
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Presentation Outline

• Progressive Collapse and Homeland Security.
• Case Study The Bankers Trust Building.
• Overview of the research.
• Initial Results.
• Where do these results lead us?

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What is Progressive Collapse?

• Progressive collapse occurs when a key member, or
  members of a structure fail.
• The isolated failure of this key member or
  section then initiates a sequence of events,
  causing failure of the entire structure.
• Current U.S. building codes contain few
  provisions as to designing with progressive
  collapse in mind.

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H.S. and Progressive Collapse

• In many situations, an attack on a structure
  initiates catastrophic progressive collapse.
• Both the World Trade Center, and the Murrah
  Federal Building failed in a progressive manner.
• In the wake of the many IRA bombings in England,
  the English Building Code was changed to include
  progressive collapse provisions. (Ronan Point)
• Currently Embassys and some Government Buildings
  are the only U.S. structures to have strict
  progressive collapse and blast provisions.

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Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

Map of Bankers Trust location.
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Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

A photo of the BT Building
7
Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

A photo of the BT Building
8
Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

A photo of the BT Building
9
Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

Bankers Trust floor plan. Bays highlighted.
10
Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

Bankers Trust floor plan. Bays highlighted.
11
Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

Bankers Trust floor plan. Columns highlighted.
12
Bankers Trust Specs

• Location 130 Liberty St.
• Owned by Deutsche Bank.
• Built in 1974.
• 40 stories tall.
• Moment frame system.
• Each bay 26 wide.
• 7 bays x 7 bays.
• Central group of columns off-center.

Bankers Trust floor plan. Columns highlighted.
13
Bankers Trust September 11th

• Bankers Trust was in debris field of collapsing
  tower 2.
• Sustained substantial damage from falling debris.
• Load bearing column removed from 18th down to 8th
  floor.
• No fires, and no progressive collapse.

Aerial shot of BT, Sept 17, 2001.
14
Bankers Trust September 11th

• Bankers Trust was in debris field of collapsing
  tower 2.
• Sustained substantial damage from falling debris.
• Load bearing column removed from 18th down to 8th
  floor.
• No fires, and no progressive collapse.

Second floor lobby.
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Bankers Trust September 11th

• Bankers Trust was in debris field of collapsing
  tower 2.
• Sustained substantial damage from falling debris.
• Load bearing column removed from 18th down to 8th
  floor.
• No fires, and no progressive collapse.

Damage to load bearing column.
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Bankers Trust September 11th

• Bankers Trust was in debris field of collapsing
  tower 2.
• Sustained substantial damage from falling debris.
• Load bearing column removed from 18th down to 8th
  floor.
• No fires, and no progressive collapse.

Shot of surviving BT building.
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Bankers Trust

• The survival of the Bankers Trust building left
  several questions
• What areas of the buildings design helped to
  prevent progressive collapse?
• Would the structure have performed significantly
  different if it were a different structural
  system?
• How would the building have performed if fires
  had occurred (as in WTC 7)?
• What can we take from this design to decrease
  risk of progressive collapse in other structures?

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Research Summary

• Redesign the structure using three different
  structural systems.
• Moment frame.
• Moment frame with braced core.
• Simple frame with braced core.

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Research Summary

• Redesign the structure using three different
  structural systems.
• Moment frame.
• Moment frame with braced core.
• Simple frame with braced core.

Moment frame model.
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Research Summary

• Redesign the structure using three different
  structural systems.
• Moment frame.
• Moment frame with braced core.
• Simple frame with braced core.

Moment frame w/ braced core model.
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Research Summary

• Redesign the structure using three different
  structural systems.
• Moment frame.
• Moment frame with braced core.
• Simple frame with braced core.

Simple frame w/ braced core model.
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Research Summary

• Different codes are also being tested for each
  structural system.

Wind Code NYC Code Calif. Code
MF X X X
MF-BC X X
SF-BC X X
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Program Overview Input

• Step 1 Requests and receives data on structural
  geometry.
• Step 2 Randomized explosion generated and
  applied to structure.

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Program Randomized Explosion

• Randomized explosion is generated using three
  random variables.
• Resulting fires and heat field are then imposed
  on the structure.

X3
X2
X1
Explosion generation.
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Program Overview Fire Model

• Step 3 Sends signal to fire progression module
  to progress the current state of the fire.
• Step 4 Checks time step. If not at time step
  for structural check, progresses fire again.

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Program Overview Structure

• Step 5 Checks members for failure. If a member
  has failed, initiate progressive collapse module.
• Step 6 Check for structural survival. If
  structure has failed, output data. If not, check
  fire.

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Results Obtained

• Simple Frame fails long before others (60 min)
• MF-BC fails next (160 min)
• Moment Frame survives longest (200 min)

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Impact of Results

• This research will aid in the development of easy
  to use design provisions for progressive
  collapse.
• It will also help to identify current structures
  at high risk, and will aid in developing
  effective retrofits.
• Finally, it will help in the placement of sensors
  throughout a structure, by identifying key weak
  areas throughout the system.

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Conclusions

• The prevention or delay of progressive collapse
  in large buildings is an important area to
  strengthen in our current infrastructure.
• Initial results indicate the need for more
  redundancy in how structures are designed.
• There is still much to be learned from this
  research, which may change the way buildings are
  designed.