Federal Building and Fire Safety Invest

of the World Trade Center Disast

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

ANALYSIS OF BUILDING AN

CODES AND PRACTICE

June 23, 2004

H. S. Lew 

Richard Bukowski 

Nick Carino 
WTC Investigation Objective #3 WTC Investigation Objective #3

Determine procedures and pracused in the design, constructionoperation, and maintenance of W1, 2, and 7.
Project #1 Areas of Focus Project #1 Areas of Focus

Criteria and Procedures for:• Design and construction• New and innovative design features• New and innovative technologies and materials• Passive and active fire safety systems • Emergency access and egress systems• Structural modifications, inspection, and mainte
Scope

• Document the design and construction of struc• Document the design and construction of fire p

egress systems

• Compare then current building regulatory and 

requirements

• Document maintenance and modifications to s

protection, and egress systems

• Document the fuel system for emergency powe
Document Design and Constructio

Document Design and Constructio

Structural Systems Structural Systems

• Provisions used to design and construct the build• Tests performed to support the design• Criteria that governed the design of the structura• Methods used to proportion structural members• Innovative systems, technologies, and acceptanc

used by PANYNJ

• Details of variances granted by PANYNJ• Special fabrication and inspection requirements a

yard

• Inspection protocol during construction
Status of Project Status of Project

• Contractor submitted near final drafts on:

- Design and construction of structural s- Design and construction of fire protect

systems

- Then current building regulatory and c

requirements

- Maintenance and modifications to stru

protection and egress systems

- Fuel system for emergency power in W
WTC 1 and 2 WTC 1 and 2 

Architects:

Minoru Yamasaki & AssociatesEmery Roth & Sons (Architect of Record)

Structural Engineers:

Skilling, Helle, Christiansen & JacksonSkilling, Helle, Christiansen & Robertson (19(Engineer of Record)
Building Codes Used in Design Building Codes Used in Design 

WTC 1 and 2 WTC 1 and 2

WTC 1 and 2

Initial design:Port Authority instructed architect & engineeuse the1938 edition of New York City BuildinFinal design:Port Authority instructed architect & enginee1965 to revise design in accordance with the third draft of new code (adopted in Decembe
Building Codes Used in Design Building Codes Used in Design 

WTC 1 and 2 WTC 1 and 2

1938 edition vs. 1968 edition

- Elimination of fire tower as a required mea- Reduction in the number of required stairs- Reduction in fire rating of shaft walls from - Use of uniform partition load based on wei

per unit length.

- Introduced Class 1B construction for busin

and unlimited building height.
Review of Drawings by New York C

Review of Drawings by New York C

Department of Buildings Department of Buildings

1975 Letter from Architect of Record to Por

- NYC/DOB reviewed WTC 1 & 2 drawings - Made 6 comments concerning the plans 

1938 code.

- Architect submitted responses to the com

Authority in March 1968.
Code Conformance Agreement bet

Code Conformance Agreement be

Port Authority and NYC Building D

Port Authority and NYC Building D

1993 MOU between Port Authority and NYC Bui

- Reaffirmation of longstanding stated policy of 

conform to New York City Building Code. 

- Each project reviewed and examined for code 

Port Authority.

- Plans prepared and sealed by NY State licens

professional.

- Port Authority design professional approving t

not have assisted in the preparation of the pla

- Variances from code, acceptable to Port Autho

submitted to New York City Building Departmeconcurrence.
Code Conformance Agreement bet

Code Conformance Agreement be

Port Authority and NYC Building D

Port Authority and NYC Building D

1995 Supplement to 1993 MOU

- In lieu of any review by Port Authority, tenan

NY State licensed design professionals to preview tenant’s plan and to certify that plans 

Building Code.

- Design professionals reviewing and certifyin

tenants should not be the same design profeproviding certification that the project was coin accordance with the plans and specificatio
Structural Requirements Structural Requirements 

• Dead loads• Live loads• Live load reduction• Lateral loads
WTC 1 and 2 WTC 1 and 2
WTC 1 and 2 WTC 1 and 2 – Live Load Reducti

Live Load Reducti

Drawing used with permission of PANYNJ.
WTC 1 and 2 WTC 1 and 2 – Live Load Reducti

Live Load Reducti

Drawing used with permission of PANYNJ.
Design Wind Pressures Design Wind Pressures 

1968 NYC Building Code 1968 NYC Building Code

Design Wind Pressure on Ve

Height Zone (psf of projected solid 

(ft above curb level) Structural Frame G

0 – 50

a 15 

0 – 100 20 

101 – 300 25 301 – 600 30 

601 – 1000 35 

Over 1000 40 
Design Wind Pressures Design Wind Pressures

1968 NYC Building Code 1968 NYC Building Code

• Alternate method

– “Suitably conducted model tests”– Fastest-mile wind velocity of 80 mph 

ground

– Simulate and include all factors invo

consideration of wind pressure

• Pressure and suction effects• Shape factors• Gust, etc.
Design Wind Load for WTC 1 & 2 Design Wind Load for WTC 1 & 2

S

=

S

±

S′

M

=

M

±

M ′

(

)

(

)

2

2

1 S

z

V

D

H

C

z

=

ρ

o

S

(

)

2

1

(

)

2

2

M

z

V DH

C

z

=

ρ

o

M

- Story Shear

- Story Moment
Sample Column Design for WTC 1 Sample Column Design for WTC 1 

Used with permission of PANYNJ.
Design Wind Load for WTC 1 & 2 Design Wind Load for WTC 1 & 2

S

=

S

±

S′

M

=

M

±

M ′

(

)

(

)

2

2

1 S

z

V

D

H

C

z

=

ρ

o

S

(

)

2

1

(

)

2

2

M

z

V DH

C

z

=

ρ

o

M

- Story Shear

- Story Moment
Design Wind Load for WTC 1 & 2 Design Wind Load for WTC 1 & 2

• Aerodynamic coefficients for shear (

C

S) a

(

C

M) are determined from wind tunnel-bas

coefficients.

• Wind tunnel tests conducted at Colorado 

University and National Physical Laborato

• Actual values of 

C

S and

C

M used to obtai

moment values are not available.

• NIST is working with LERA (under a cont

to determine baseline performance for or
WTC 7 

Architect of Record:

Emery Roth & Sons

Structural Engineer of Record:

The Office of Irwin G. Cantor
Building Codes Used in Design Building Codes Used in Design 

WTC 7

Design:Developed by Seven World Trade Company aDevelopment Corp as a “Tenant Alteration ProBased on 1968 New York City Building Code aLocal Laws.
Design Loads for WTC 7 Design Loads for WTC 7

Used with permission of PANYNJ.
Standards Used for Structural Sys

Standards Used for Structural Sys

WTC 1 & 2 

Steel – 1963 AISC SpecificationsConcrete – 1963 ACI BuildingCodePrequalifying load tests

WTC 7

Steel – 1978 AISC SpecificationsConcrete – 1977 ACI Building Code
Tests Performed to Support the De

Tests Performed to Support the De

Exterior Wall Panel Tests

• University of Western Ontario• Load-deflection characteristics• “Most effective construction”

for wall panels

• 15 different tests were run

replicating the 20th, 47th, and

74th floor exterior walls

Drawing used w
Tests Performed to Support the De

Tests Performed to Support the De

Wind Tunnel Tests

• Meteorological Program• Wind Tunnel Program• Structure Damping Program• Physiological Program

0°
Tests Performed to Support the De

Tests Performed to Support the De

WTC 1 and 2 WTC 1 and 2

Viscoelastic Damping Unit Tests

• Conducted in accordance with specification

mechanical properties of damping units

• Two sets of tests

- Massachusetts Institute of Technology- Minnesota Mining and Manufacturing Com
Tests Performed to Support the De

Tests Performed to Support the De

WTC 1 and 2 WTC 1 and 2

Floor Truss Tests

• Full-scale flexural tests • Interior panel connection tests

(Between floor truss and bridging truss)

• Bearing capacity tests • Shear knuckle tests
Tests Performed to Support the De

Tests Performed to Support the De

WTC 1 and 2 WTC 1 and 2

Shear Knuckle Tests

Drawing used w
Innovative Systems, Technologies 

Innovative Systems, Technologies 

WTC 1 & 2 WTC 1 & 2

• Framed – tube framing system for lateral load resi

steel building.

• Steel floor truss – concrete composite system to p

stability and diaphragm action.

• Uniform exterior column geometry by employing 1

of steel.

• Application of viscoelastic dampers to control build• Wind tunnel testing to establish design wind value

building.

• Use of 3-story prefabricated exterior steel-column 

construction process.
Document Modifications to Structu

Document Modifications to Structu

• PANYNJ Guidelines for Inspection, Repair and 

Structural Systems of WTC 1, 2, and 7- Tenant Construction Review Manuals

• 1971, 1979, 1984 (revised 1990), 1997• Technical criteria to be used by tenants 

facilities

Scope of work, design criteria, and plDesign by registered architect or prof

• Structural Requirements• Inspection Program
Document Modifications to Structu

Document Modifications to Structu

- Architectural and Structural Design Guidelines 

• Requirements for tenant alterations in W• Structural design guide

Minimum floor loads, core hole sizes, 

• Structural specifications• Standard details
Document Modifications to Structu

Document Modifications to Structu

• PANYNJ Programs for Inspection, Repair and M

Structural Systems of WTC 1, 2, and 7- Facility Condition Survey (1990, 1991, 1997, 2

• Condition of buildings• Recommendations for repairs and upgra

- Structural Integrity Inspection Program (1991,

1996, 1997, 1998, 1999, 2000)• Detect, record and correct distresses and 

could lead to structural problems
Structural Integrity Inspection

• Inspection/monitoring of 16 items, inc

- Space usage- Accessible columns- Bracing below elevation 294 ft- Hat trusses- Floor framing over mechanical a- Floor framing over tenant areas- Natural frequency measurement- Natural frequency of floors- Damping units

Document Modifications to Structu

Document Modifications to Structu
• Space usage – identify possible overloading

- Distribute granite slabs on floor106 over a la

• Accessible columns – check condition of column

shafts.

- Missing fireproofing on columns (1996, 1998

• Bracing below elevation 294 ft. 

- No priority recommendation (1991, 1995).

• Hat trusses – check overall condition.

- No priority recommendation (1992, 1995).

• Floor framing over mechanical areas – check con

(1992, 1996, 1999).

- Repair fireproofing.

Structural Integrity Inspection Structural Integrity Inspection

WTC 1 and 2 WTC 1 and 2
• Floor framing over tenant spaces – check overall 

framing system (1992, 1995, 1997, 1999).- Missing fireproofing on columns (1996, 1998

• Natural frequency measurements – WTC 1 only 

- Measure and computed values are similar (1- No analysis made since 1998.

• Natural frequency of floors – WTC 1 & 2 (1996).

- No appreciable difference between analysis 

values.

• Viscoelastic damping units – WTC 1 & 2.

- Damping units were in good condition.

• Post 1993 explosion – pre and post repair inspec

- Six inspections were made by LERA, U.S. A

WJE, Proto Mfg, and Lucius Pitkin.

Structural Integrity Inspection Structural Integrity Inspection
• Modification and Repairs to Structural F

of WTC 1 and 2

- Repairs Related to Explosion of February 16

• Bowed Column 324 above Level B2• Missing and bowed diagonals between Colum

Column 327 (Level B1)

• Cracked column splice at Column 324• Bent spandrels and damaged floor beam conn

Document Modifications to Struct

Document Modifications to Struct
Document Modifications to Structu

Document Modifications to Structu

Drawing used with permission of PANYNJ.
Modification and Repairs to the Structur

System of WTC 7

• Floor slabs removed on the east side of 

accommodate trading floors for Salomo

• Columns were reinforced with plates.• Penthouse addition on east side of build• Replacement of previously removed floo

Document Modifications to Struct

Document Modifications to Struct
Interim Findings Interim Findings

WTC 1 and 2 WTC 1 and 2

• Changes made to building design and 

due to change in code provisions:- Eliminated fire tower as a required means 

- Reduction in the number of required stairw- Reduced size of doors to stairs from 44 in. - Reduced fire rating of shaft walls from 3 h - Changed partition loads from 20 psf to one 

weight of partition per unit length.

- WTC 1 and 2 classified as Class 1B const

business occupancy and unlimited building 
Interim Findings Interim Findings

WTC 1 and 2 WTC 1 and 2

- New York City Department of Buildings re

design drawings in 1968.

- Code conformance agreement (MOU) es

between Port Authority and New York Citof Buildings in 1993, amended 1995.

- Port Authority developed structural inspe

examine systematically the integrity of str
Interim Findings Interim Findings

WTC 1 and 2 WTC 1 and 2

Design loads:

Dead load: Greater than or equal to design 

in NYC Building Code.

Live load: Greater than or equal to design 

in NYC Building Code.

Live Load Reduction:

Equal to or more stringent than Code requirements.

Wind load: Information on design values is 

(Wind tunnel tests were conducState University and National PLaboratory, U.K.)
Interim Findings Interim Findings

WTC 7

Design loads:

Dead load: Greater than or equal to design 

in NYC Building Code.

Live load: Design values base on anticipatLive Load Reduction: 

No information available. 

Wind load: Information on design values is 

(Wind tunnel tests were conducof Western Ontario.)
Fire Resistance Ratings (1968 NYC Build

Fire Resistance Ratings (1968 NYC Build

WTC 1 and 2 WTC 1 and 2

• Construction Class 1B (3 hour protected

• 3 hours on columns• 2 hours on floors• 2 hours on exit access corridors 

• 1 hr permitted but 2 hr used to perm

dead ends

• 2 hours for shaft enclosures• 1 hour for tenant separation (demising
Means of Egress Means of Egress

WTC 1 and 2 WTC 1 and 2

• Occupant load (per floor) 390

- 39000 sq ft net @ 100 sq ft per perso

• Units of exit width required, 6 

- 390 @ 60 persons per 22 in. unit on s

• Min clear width of stairs 44 in.• Door widths 36 in. (min) to 48 in. (max)
Elevators (99 in each tower) Elevators (99 in each tower) 

WTC 1 and 2 WTC 1 and 2

• By Code not utilized for fire service acce

occupant egress during an emergency.

- Elevators were used for occupant eg

after 1 was hit and before 2 was hit.

• Three elevator “zones” with sky lobbies 

44th and 78th floors).

- 8 express concourse to 44.- 10 express concourse to 78.- 24 locals per zone in groups of 6.- 7 freight elevators (1 serving all floor- All retrofit with Firefighters Emergenc

ASME A17.1).
Fire Suppression Fire Suppression

WTC 1 and 2 WTC 1 and 2

• Standpipes

- Located within 145 feet of any point- Outlets located within stairways- Tanks on mechanical floors and cross 

standpipes

- Standpipe communication system

• Sprinklers only required below grade 
Fire Alarm System Fire Alarm System

WTC 1 and 2 WTC 1 and 2

• Installed in corridors above minimum cod

requirements

• Smoke detectors

- 4 per floor at air return grilles to preve

recirculation of smoke.

- No manual initiating devices.
Miscellaneous Requirements Miscellaneous Requirements

WTC 1 and 2 WTC 1 and 2

• Emergency power not required.• Stair pressurization not required.• Smoke purge system not required.• Some requirements for exit signs and lig

of egress.
Fire Resistance Ratings Fire Resistance Ratings

WTC 7

• Construction Class 

- 1C (2 hour sprinklered) per Fire Safety Plan 

building in 1990 (permitted under LL16 1984

- 1B (3 hour protected) per PA supported by c

and drawings

1 

Tenant separation (demising) wallsShaft enclosures

2

2

Floors

2 1-

Columns

3

2

Type 1B Typ
Means of Egress Means of Egress

WTC 7

• Two 58 in. stairs provided 6 units of exit 

persons per floor.

- Area of 44,000 sq ft net @ 100 for gro

yield 440 per floor.

• Total building daytime population estima

partially handicapped, no wheelchairs) w(1990 Fire Safety Plan).
Elevators Elevators

WTC 7

• By Code not utilized for fire service acce

occupant egress during an emergency.

• 38 elevators total (all equipped with FES

- 28 passenger and 2 freight serving al- 2 passenger serving floors 28-45.- 2 passenger serving floors 44-47.- 3 passenger serving floors 45-46.- 1 passenger serving floors 2-3 (audito
Fire Suppression Fire Suppression

WTC 7

• Complete sprinkler system (LL16-1984).• Standpipes

- Located within 145 feet of any point.- Outlets located within stairways.- Tanks on intermediate floors.- Standpipe communication system.
Fire Alarm System Fire Alarm System

WTC 7

• Class E alarm and voice communication • Fire command station in lobby• Floor warden stations• Smoke Detectors

- Elevator lobbies- Sprinkler waterflow- HVAC protection

• Manual initiating devices

- Report to fire department
Miscellaneous Requirements Miscellaneous Requirements

WTC 7

• Emergency Power

- Alarm & Communication system- Fire pumps- 3 elevators- Emergency lighting- Smoke control and stair pressurizatio

• Controlled inspection of Spray Applied F

firestopping
Modifications Modifications

WTC 1 and 2 WTC 1 and 2

• LL5-1973 and LL16-1984 had major impacts on WTC 

incorporated into initial WTC 7 design

- Compartmentation 

• 7500 sq ft with 1-hr• 10,000 sq ft with 2-hr• 15,000 sq ft with 2-hr and smoke detectors• Not required if sprinklered

- Class E alarm and voice communication system- Fire command station in garage (later moved to l- Emergency power for exit signs and egress lighti- Sprinkler system- Smoke control/purge- Controlled inspection of Spray Applied Fireproofi

- Carpet in exit access corridors- Stair re-entry every four floors
Modifications Modifications

WTC 7

• Review of 120 tenant alteration reports r

the only modification to fire and life safetthe relocation of sprinkler heads and detaccommodate partition locations.
MOU’s Between PA and FDNY Covering 

Between PA and FDNY Covering 

Facilities in NYC Facilities in NYC

• PA policy to implement FDNY recommendations after i

facilities and for prior review of fire safety systems introfacilities adopted April 15, 1993 and formally executed 

- Inspections generally coordinated with PA but can - Report of findings and recommendations from Bure

to PA will be implemented and formally responded.

- Plans for new systems or modifications to existing 

submitted for review and approval.

- Intent to comply with local codes and regulations.- PA reserves the right to petition for variances in un

• Formally amended February 2, 1995 to provide for plan

certification by licensed engineer or architect not involvthe plans and retained by PA in lieu of FDNY review an

- Follows the MOU between PA and DOB dated Nov

amended in June 1995 with regard to building regu
Interim Findings Interim Findings

• While not subject to the building and fire regulatio

City, the PA generally followed these at the desigthey evolved over the life of the buildings through local laws:

- LL5-1973- LL16-1984

• The fire and life safety systems in WTC 1, 2, and 

consistent with the requirements of national codeaccepted practices. 

• PA developed tenant manuals and alteration pro

conducted regular condition surveys.

• PA addressed some problems over an extended 

- Adequacy of and upgrades to fireproofing.- Tenant separation walls.- Sprinkler retrofits.- Inspection by independent third parties.