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  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

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

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

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

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

World Trade Center 7 – South Tower Collapse  Collapse of South Tower did not impact World Trade Center 7

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)

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

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)

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

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

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

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

World Trade Center 7 – The fire and collapse Fire apparent on 6, 10, 11Car fire and dark smokeCollapse

World Trade Center 7 – Collapse Sequence WTC 7 with smoke and fire (note 2 mechanical penthouses on roof)

World Trade Center 7 – Collapse Sequence  Mechanical Penthouse on East disappears  Evidence of interior failure

World Trade Center 7 – Collapse Sequence  Mechanical penthouse on West disappears  Evidence of Propagating Interior Failure

World Trade Center 7 – Collapse Sequence  A kink develops  Evidence of frame failure propagating to facade

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

World Trade Center 7- The collapse

World Trade Center 7 – Foundation Plan

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

World Trade Center 7 – Truss Location

World Trade Center 7 – Diaphragm 5 th Floor 14”reinforced slab and steel tees embedded 7 th Floor 8” reinforced slab

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

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

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

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

World Trade Center 7 – Location of Kink in Elevation South ElevationNorth Elevation

World Trade Center 7 – Kink (revisited)

World Trade Center 7 – Isolating the Failure Area Floor intact; Failure occurs below Floor 12

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 5 th through 7 th floor)  Failure in columns of gravity frame  Failure continued from lower floors to 47 th floor

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

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