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