Progressive Collapse

							Comparing progressive collapse due
to fire in differing structural systems.


                                             Mark Dobossy
                                          Graduate Student
              Dept. of Civil and Environmental Engineering
                                        Princeton University
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?
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.
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 Embassy’s and some Government
  Buildings are the only U.S. structures to have strict
  progressive collapse and blast provisions.
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.
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
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
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
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.
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.
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.
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.
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.
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        Second floor lobby.
  progressive collapse.
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.
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.
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?
Research Summary
• Redesign the structure
  using three different
  structural systems.
  – Moment frame.
  – Moment frame with
    braced core.
  – Simple frame with
    braced core.
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.
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.
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.
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
Program Overview: Input




• Step 1: Requests and receives data on
  structural geometry.
• Step 2: Randomized explosion generated
  and applied to structure.
Program: Randomized Explosion
                          • Randomized explosion
                            is generated using
                            three random
                            variables.
        X2          X3    • Resulting fires and
                            heat field are then
                            imposed on the
  X1
                            structure.



  Explosion generation.
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.
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.
Results Obtained
• Simple Frame fails long before others (~60 min)
• MF-BC fails next (~160 min)
• Moment Frame survives longest (~200 min)
                      Simple Frame - Braced Core                                      Moment Frame - Braced Core                                           Moment Frame

            12                                                             12                                                             14


                                                                                                                                          12
            10                                                             10

                                                                                                                                          10
             8                                                              8
                                                               Frequency




                                                                                                                              Frequency
Frequency




                                                                                                                                           8
             6                                                              6
                                                                                                                                           6

             4                                                              4
                                                                                                                                           4


             2                                                              2
                                                                                                                                           2


                                                                            0                                                              0
             0
                 40     50      60         70      80   More                    130      140    150         160   170   180                    180   190      200         210   220   230
                                     Bin                                                              Bin                                                           Bin
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.
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.