World Trade Center 7
Building Performance Assessment
Overview WTC 7 – General Characteristics Framing Connections September 11th, 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 (7th Floor and below)
Perimeter bracing and moment frame
Core bracing below 7th floor
Perimeter bracing and moment frame
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
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 6th Floor on North Face
World Trade Center 7 – The fire
Fire visible on 11th floor of East Face
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)
World Trade Center 7 – The fire
6th Floor on fire; 10th and 11th Floors with damage
World Trade Center 7 – The fire and collapse
Fire apparent on 6, 10, 11 Car fire and dark smoke Collapse
World Trade Center 7 – Collapse Sequence
WTC 7 with smoke and fire (note 2 mechanical penthouses on roof) 1 2 3 4 5
World Trade Center 7 – Collapse Sequence
Mechanical Penthouse on East disappears
Evidence of interior failure
1 2 3 4 5
World Trade Center 7 – Collapse Sequence
Mechanical penthouse on West disappears
Evidence of Propagating Interior Failure
1 2 3 4 5
World Trade Center 7 – Collapse Sequence
A kink develops Evidence of frame
failure propagating to facade
1 2 3 4 5
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
World Trade Center 7-The collapse
World Trade Center 7 – Foundation Plan
World Trade Center 7 – Floor 5-7 Framing Plan
Truss 1
Truss 2Truss 3
World Trade Center 7 – Truss Location
World Trade Center 7 – Diaphragm5th Floor 14”reinforced slab and steel tees embedded7th Floor 8” reinforced slab
World Trade Center 7 – 5th to 7th Floor Truss Details
World Trade Center 7 – Truss 1
7th floor
6th floor
5th floor
World Trade Center 7 – Truss 2
7th floor
6th floor
5th floor
World Trade Center 7 – Truss 3
7th floor
6th floor
5th floor
Cantilever transfer
World Trade Center 7 – Location of Kink in Elevation
South Elevation North Elevation
World Trade Center 7 – Kink (revisited)
World Trade Center 7 – Isolating the Failure Area
Floor 12-47 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 5th through 7th floor)
Failure in columns of gravity frame Failure continued from lower floors to 47th
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