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World Trade Center 7

World Trade Center 7. Building Performance Assessment. Overview. WTC 7 – General Characteristics Framing Connections September 11 th , 2001 events Damage to WTC 7 Sequence of Collapse Analysis and Conclusion What is next. World Trade Center 7 - General.

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World Trade Center 7

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  1. World Trade Center 7 Building Performance Assessment

  2. Overview • WTC 7 – General Characteristics • Framing • Connections • September 11th, 2001 events • Damage to WTC 7 • Sequence of Collapse • Analysis and Conclusion • What is next

  3. World Trade Center 7 - General • Constructed 1985 (last stage of World Trade Center complex) • 47 stories • Architect: Emory Roth & Sons • Structural: Irwin G. Cantor • Structural (Con Ed Substation): Leslie E. Robertson Associates

  4. World Trade Center 7 – General (cont’d) • Located north of WTC 1 and 2 across Vesey Street • Uses: - Con Edison - Shipping Ramp - Offices

  5. World Trade Center 7 - Framing • Materials: Steel, concrete, granite • Interior bracing and moment frames (7th Floor and below) • Perimeter bracing and moment frame Core bracing below 7th floor Perimeter bracing and moment frame

  6. World Trade Center 7 – Framing (cont’d) • Trusses up to 7th floor; between 22nd and 24th floor • Diaphragm at 5th and 7th floor (T-sections in slab) • Framing typical 8th to 47th floor

  7. World Trade Center 7 - Connections • Mainly seated connections at exterior columns and single shear plate at the interior beams • Gravity frame: bolt 7/8” ASTM A325 • Wind frame: bolt 1” ASTM A490 • Types of connections: - moment - column splice - bracing - cladding

  8. World Trade Center 7 – South Tower Collapse • Collapse of South Tower did not impact World Trade Center 7

  9. World Trade Center 7 – Events of September 11, 2001 (cont’d) • (10:28 am) North Tower collapses, WTC 7 is damaged and begins to burn Looking South (WTC 7 in foreground)

  10. West mechanical penthouse East mechanical penthouse Collapse of WTC 1 Looking South at the North Face (note mechanical penthouses)

  11. World Trade Center 7 - Evidence of Damage from WTC 1 collapse Looking East at the Southwest Corner, floors 8-18 (according to fireperson’s verbal report)

  12. World Trade Center 7 – The fire Fire appears on 6th Floor on North Face

  13. World Trade Center 7 – The fire Fire visible on 11th floor of East Face

  14. World Trade Center 7 – The fire Fire visible on 5th,6th, 10th and 11th Floor of North Face (as counted from top from original video knowing WTC 7 is 47 stories)

  15. World Trade Center 7 – The fire 6th Floor on fire; 10th and 11th Floors with damage

  16. World Trade Center 7 – The fire and collapse Fire apparent on 6, 10, 11 Car fire and dark smoke Collapse

  17. World Trade Center 7 – Collapse Sequence WTC 7 with smoke and fire (note 2 mechanical penthouses on roof) 1 2 3 4 5

  18. World Trade Center 7 – Collapse Sequence • Mechanical Penthouse on East disappears • Evidence of interior failure 12 3 4 5

  19. World Trade Center 7 – Collapse Sequence • Mechanical penthouse on West disappears • Evidence of Propagating Interior Failure 1 2 3 4 5

  20. World Trade Center 7 – Collapse Sequence • A kink develops • Evidence of frame failure propagating to facade 1 2 3 4 5

  21. World Trade Center 7 – Collapse Sequence • Floors 11 and below fail • Failure propagates “bottom-up” to 47th floor as structure sinks into the foundation • World Trade Center 7 collapses after sustaining impact damage and burning for 7 hours 1 2 3 4 5

  22. World Trade Center 7-The collapse

  23. World Trade Center 7 – Foundation Plan

  24. World Trade Center 7 – Floor 5-7 Framing Plan Truss 1 Truss 3 Truss 2

  25. World Trade Center 7 – Truss Location

  26. World Trade Center 7 – Diaphragm5th Floor 14”reinforced slab and steel tees embedded7th Floor 8” reinforced slab

  27. World Trade Center 7 – 5th to 7th Floor Truss Details

  28. World Trade Center 7 – Truss 1 7th floor 6th floor 5th floor

  29. World Trade Center 7 – Truss 2 7th floor 6th floor 5th floor

  30. World Trade Center 7 – Truss 3 Cantilever transfer 7th floor 6th floor 5th floor

  31. World Trade Center 7 – Location of Kink in Elevation South Elevation North Elevation

  32. World Trade Center 7 – Kink (revisited)

  33. World Trade Center 7 – Isolating the Failure Area Floor 12-47 intact; Failure occurs below Floor 12

  34. World Trade Center 7 – Failure Analysis • Failure occurred below floor 11 • Failure occurred in the interior, initially, (disappearance of mechanical penthouses) and from East to West • Failure propagated due to diaphragm floors (trusses and transfer girders on the 5th through 7th floor) • Failure in columns of gravity frame • Failure continued from lower floors to 47th floor

  35. World Trade Center 7 – Partial vs. Total Collapse • “The tying together of the steel units means that if one part of the building is distorted by fire, torsional or eccentric loads beyond the designed capacity may be placed in the balance of the building, starting the progressive collapse of the building, often far beyond the area involved in fire. As a matter of fact, the better the building is tied together to resist wind load, the more likely it probably is to suffer progressive collapse due to fire distortion.” Francis L. Brannigan, Building Construction For The Fire Service, NFPA, Quincy, Massachusetts, 1982

  36. Next:Doing the analysis With help from Willa Ng, Chris Hewitt, Audrey Massa

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