Comparing progressive collapse due to fire in differing structural systems.

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

2. 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?

3. 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.

4. 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.

5. 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.

6. 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.

15. 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.

16. 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.

17. 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?

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

19. 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.

20. 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.

21. 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.

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

23. Program Overview: Input • Step 1: Requests and receives data on structural geometry. • Step 2: Randomized explosion generated and applied to structure.

24. 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.

25. 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.

26. 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.

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

28. 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.

29. 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.