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

December 2, 2003

H. S. Lew 

Richard Bukowski 

Nick Carino 

Dat Duthinh
Contractors Contractors

Rolf Jensen & Associate, Inc.S. K. Ghosh Associates, Inc.Rosenwasser/Grossman Consultin

Engineers P.C.
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 str• Document the design and construction of fire 

egress systems

• Compare then current building regulatory and 

requirements

• Document maintenance and modifications to 

protection, and egress systems

• Document the fuel system for emergency po
Building Code Used Building Code Used 

WTC 1 and WTC 2:• Not required to comply with any building cod

York Authority was established as an interstunder a clause of the U.S. Constitution)

• May 1963: PONYA instructed designers to c

NYCBC (1938 edition)

• Designers were to follow “acceptable 

practices” where code provisions were 

• September 1965: PONYA instructed design

with second and third drafts of new NYC Buthe final design of WTC 1 and WTC 2

• NYC adopted a new code in December 196
Building Code Used Building Code Used 

WTC 7:• Developed and owned by Silverstein Dev

Corporation

• Built as a PONYA Tenant Alteration Proje• NYC Building Code 1968 edition
Building Codes Reviewed Building Codes Reviewed

(Structural System) (Structural System)

• NYC Building Code - 1968 edition• NY State Building Code - 1964 edition• Chicago Building Code - 1967 edition• BOCA Basic Building Code - 1965 edition

(National Model Building Code)

• NYC Building Code - 2001 edition 
National Standards Adopted by National Standards Adopted by 

Building Codes Building Codes 

For structural design• NYCBC (1968)

1963 AISC Spec., 1963 ACI 318 Code

• NY State BC (1964)

Appropriate national standards

• Chicago BC (1967)

1963 AISC Spec., 1963 ACI 318 Code

• BOCA Basic Building Code (1965)

1963 AISC Spec., 1963 ACI 318 Code

• NYC Building Code (2001) 

1989 AISC Spec., 1989 ACI 318 Code 
Structural Requirements Reviewe

Structural Requirements Reviewe

• Dead loads• Live loads• Live load reduction• Lateral loads (wind and earthquak• Progressive collapse resistance
Dead Loads Dead Loads

• Weights of materials and constructions• Building codes provide unit weights (densitie

design 

• Most codes have similar unit weights for 

e.g., steel = 490 pcf; concrete = 150 pcf
Live Loads Live Loads

• Loads produced by use and occupancy• Codes specify basic live load values for design• Code provisions are based on experience and • Expressed as equivalent uniform loads

• e.g., office = 50 psf; lobby = 100 psf• All five codes have the same values

• Concentrated loads treated separately
Live Load Reduction Live Load Reduction

• Codes allow reduction of basic live load, bec

unlikely that all floors are fully loaded simulta

• Accumulation of loads on columns and walls

• Character of live loads• Tributary area on a single floor• Number of supported floors• Ratio of dead load to live load

• Accumulation of loads on girders and beams

• Contributory area• Magnitude of live loads• Ratio of dead load to live load
Live Load Reduction Methods Live Load Reduction Methods

• Percentage method

• 100% (roof), 85%(top floor), 80% (next floo• 50% (limit)

• Dead load to live load ratio method for live lo

(ASNI A58 1955 to1981)

• 0.08% per square foot of area supported by • Nor more than 60% or R%

where, R = 100 x [(D+L) / (4.33 L)]

D = Dead load L = Live load
Reduced Live Load for Beams, Girders 

Reduced Live Load for Beams, Girders 

(Dead Load to Live Load Ratio Method

(Dead Load to Live Load Ratio Method

Contributory Area

(sq ft) NYC Building Code* Chicago Code N

100 or less 100 100 

100 - 150 100 95 150 - 200 80 - 85 95 200 - 300 80 - 85 90 300 - 450 60 - 75 85 450 - 600 50 - 70 85 

600 - and more 40 - 65 

Also 

depends on 

the D/L ratio

85 

All numbers in % * For columns, limited to 80% ** Limited to 40% (

 Separate requirements for computing the contributory areas for beams a
Reduced Live Loads for Columns 

Reduced Live Loads for Columns 

(Percentage Method) (Percentage Method)

100%

85%80%75%70%65%60%55%50%

80%80%80%75%70%65%60%55%50%

Roof 

1st floor below

2nd floor below

3rd floor below

4th floor below

5th floor below6th floor below7th floor below

8th and subsequent

floor below

NYC Building Code

(Alternative Method)

Chicago Code

NY State

Building Co
Wind Pressure Distributions of Wind Pressure Distributions of 

Different Building Codes Different Building Codes

Ground Level

100 ft300 ft600 ft

1000 ft1200 ft

20

25

30

35

40

NYC Building 

Code 

1968 and 2001

12

28

32

35

37

NY State 

Code 1964

20

42.5

Chicago 

Code 

1967
Earthquake Load Earthquake Load

• NYC Building Code (1968) - No provisions• NY State Building Code (1964) - No provisions• Chicago Building Code (1967) - No provisions• BOCA Basic Building Code (1965)

• Based on 1961 UBC (Base shear V = ZK

• NYC Building Code (2001)

• Based on1988 UBC (Base shear V = ZIK
Load Combination Load Combination

• Account for most unfavorable combination • Account for likelihood of simultaneous occ

different loads

• Load factor < 1.0• Increased allowable stresses
Load Combination Load Combination

• NYC Building Code (1968)

0.75 (D + L + W)

• NY State Building Code (1964)

Increase allowable stress by 33% if

σwind › 0

Ignore stress due to wind if

σwind < 0.33 

σ D

• Chicago Building Code (1967)

Increase allowable stress by 33% for D + L+ 

• BOCA Basic Building Code (1965)

Same as Chicago Building Code

• NYC Building Code (2001)

0.75 (D + L+ W or E)

D = dead load, L = live load, W = wind load, E = earth
Provision for Progressive Collapse 

Provision for Progressive Collapse 

• 1968 NYC Building code 

• No provision

• 1981 NYC Building Code

(Rules of the City of New York, 1973)

• Alternative load path method• Specific local resistance method
Interim Findings Interim Findings

1. PONYA adopted 1968 NYC Building Code 

WTC 1 and WTC 2, and WTC 7

2. Designers were allowed to use “acceptable 

practices” with approval of PONYA where cwere obsolete (1963 directive)

3. Minimum basic live loads are the same for f4. All five codes have live load reduction provi

For beams and girders: 1967 Chicago Code is 

conservative than othe

For columns and walls: Permitted reduction is 

five codes.
Interim Findings Interim Findings

5. All five codes have similar wind pressure dis

• For tall buildings (e.g., over 1000 ft), the large

obtained from BOCA (1965).

6. The 1968 NYC Building Code does not have 

provisions. The 2001 NYC Building Code asseismic zone factor of 0.15 (0.075 ≤ Z ≤ 0.40

7. All five codes recognize low probability of th

occurrence of design gravity and wind loads

• Load factor of 0.75• Increase allowable stress by 33%

8. NYC by Rule introduced progressive collaps

requirement in August 1973.
Fire Protection and Egress S

Fire Protection and Egress S
Building Codes Reviewed Building Codes Reviewed

(Fire Protection and Egress Systems) (Fire Protection and Egress Systems)

• NYC Building Code - 1968 edition• NY State Building Code - 1964 edition• Chicago Building Code - 1967 edition• BOCA Basic Building Code - 1965 edition

(National Model Building Code)

• NYC Building Code - 2001 edition • NFPA 101 - 1966 edition
National Fire Safety Standards Ad

National Fire Safety Standards A

1968 NYC Building Codes 1968 NYC Building Codes

• Sprinkler systems

• RS 17-2:NFPA 13 (1966) 

• Fire alarm systems

• RS 17-5:NFPA 72 (1967)

• Smoke management

• RS 13-1:NFPA 90A (1967)

• Egress systems 

• Covered in the Building Code
Review of Code Provisions Review of Code Provisions

• Construction Classes – Unsprinklered

• Class 1A and 1B: NYC 68, NYS 64, BOCA 65 (Un• Class 1A and 1B: NYC 01 (Height limited to 75 ft. • Class 1A only: Chicago 67 (Unlimited height)

• Fire Resistance Rating (all codes, except NYC 01)

• Class 1A 

Columns: 4 hours (supporting more than one floBeams : 3 hours (floor construction)

• Class 1B

Columns: 3 hours (supporting more than one floBeams : 2 hours (floor construction)
NYC Building Code Provisions NYC Building Code Provisions

(Fire Resistance in hours) (Fire Resistance in hours)

Floors

3

2 

Columns

4

3

1938 1968 
Review of Code Provisions Review of Code Provisions

• Codes do not provide criteria for selecting C

Class (1A vs. 1B)

• Selection of Construction Class is at discret

Owner/Architect
Review of Code Provisions Review of Code Provisions

• NYC Local Law 5 (1973) for New and 

Buildings (Full compliance by 1988)

• Applicable to new office buildings and ret

existing office buildings over 100 ft in heig

• Compartmentation required for unsprinkle

greater than 7500 ft

2

• Complete sprinkler protection could be pr

compartmentation

• Automatic stair door unlocking or unlocke• Approved evacuation plan and drills
Review of Code Provisions Review of Code Provisions

• NYC Local Law 5 (1973) for New and 

Buildings (Full compliance by 1988)

• Fire safety director and fire wardens• Fire command station in lobby• Voice communication system• Elevator recall• Zone smoke control and stair pressurizat• Stair pressurization not required if fully sp
Review of Code Provisions Review of Code Provisions

• NYC Local Law 16 (1984)

• Required sprinklers for buildings taller th

new business, new and existing hotels

• Emergency lighting in exits and corridors• Remoteness of exits (30 ft or 1/3 travel d• Full compliance by 1987
Code Provisions and Contempora

Code Provisions and Contempora

for Fire Protection and Egress Sy

for Fire Protection and Egress Sy

• Sprinklers mainly in industrial and storage sp

• Rare even in high-rise buildings (except underg

• Fire alarm systems

• Manual initiation for occupant notification• Control of fans and dampers to prevent smoke • Coded audible to indicate location of fire

• Smoke management not yet developed

• Required by insurance to mitigate property loss• “smoke proof towers” and top vented stairs

• Egress system design based on 22 in. units o

• Occupant loads and capacities consistent• Scissor stairs common in NYC, remoteness ad
Fuel System for Emergency Powe

Fuel System for Emergency Powe

• Four systems

• Basic system, 1987 (5th floor)

• Ambassador modification, 1994 (9th floor)

• American Express modification, 1994 (8th floor)

• Mayor’s Emergency Office, 1999 (7th floor)

• Main tanks under loading dock (12,000 gal) and 

• Day tanks (275 gal) at generators (floors 5, 7, 8, • Pumps and piping
Fuel System for Emergency Powe

Fuel System for Emergency Powe

• Protection

• Main tanks buried

•

1st floor tank room 4-hr, sprinklers (high h

• Pump room sprinklered•

5th and 7th floor generator room not sprink

•

8th and 9th floor generator room was sprin

• Fuel pipe-in-pipe draining to catch basin w
Fuel System for Emergency Pow

Fuel System for Emergency Pow

CORE 

Loading Dock and 1st Floor 

Storage tanks Da

Core 

G
Fuel System for Emergency Powe

Fuel System for Emergency Powe

9th Floor

Day tank Core

Generator

CORE

7th floor

Generators Day tank

Core 

Day tank

Generator
Interim Findings Interim Findings

1. Construction Class for high-rise buildings: 

1968 NYC, 1964 NYS and 1965 BOCA 1967 Chicago – Class 1A only

2. Fire resistance ratings for Class 1A and 1B 

these codes

3. For unsprinklered high-rise buildings, 1967 

required more stringent fire resistance ratin

4. 1968 NYC Code reduced fire resistance rat

edition, 2001 edition reduced further from 1
Interim Findings Interim Findings

5. 1968 NYC Code contains provisions on topic

in other codes

e.g., limits on smoke developed by mate

6. NYC Local Law 5 (1973)

• Compartmentation not needed in fully spr• Compartmentation of unsprinklered areas 

7. NYC Local Law 16 (1984)

• Required sprinklers for buildings taller tha
Status of Project Status of Project

• Document the design and construction of str

systems - 60% complete

• Document the design and construction of fire 

egress systems - 60% complete

• Compare then current building regulatory an

requirements - 70% complete

• Document the maintenance and modification

and fire protection and egress systems - 50% 

• Document the fuel system for emergency po

80% complete
Thank You Thank You

Questions? Questions?