Fire Endurance Testing * of Fire Endurance Testing * of 

WTC Tower Typical Floor Construct

WTC Tower Typical Floor Construct

John Gross, Bill Grosshandler, Monica Starnes

• Test results will provide fire endurance 

ratings to evaluate three primary factors

– test scale– fireproofing thickness– thermal restraint

* ASTM E119 - Standard Test Methods for Fire Tests of 

Building Construction and Materials
Fire Endurance Testing of Fire Endurance Testing of 

WTC Tower Typical Floor Construct

WTC Tower Typical Floor Construct

• Three tests will be performed...

– 17 ft (5.2 m) span assembly, 

thermally restrained

– 35 ft (10.7 m) span assembly, 

thermally restrained

– 35 ft (10.7 m) span assembly, 

thermally unrestrained
Fire Endurance Tests Fire Endurance Tests

• Test 1: 17 ft (5.2 m) span assembly, thermally 

restrained 

– Represents current US practice for establishing a 

fire endurance rating of a building construction. 

– Typical of the floor assembly test furnaces used by 

the US testing laboratories that routinely conduct tASTM E119 test.
Fire Endurance Tests Fire Endurance Tests

• Test 2: 35 ft (10.7 m) span assembly, thermally 

restrained 

– Twice the scale of the first test. Represents a fullscale assembly of a 35 ft floor panel. – Allows direct comparison to Test 1 of the effect of 

test scale on fire endurance rating. 

– Includes individual rod and double angle structural 

members. Steel temperatures will be recorded for comparison of fireproofing thickness and the limitincriteria. 
Fire Endurance Tests Fire Endurance Tests

• Test 3: 35 ft (10.7 m) span assembly, thermally 

unrestrained 

– Allows direct comparison to Test 2 of the effect of 

thermal restraint on fire endurance rating.

– Tests 2 and 3 will bound behavior of a floor system 

that is indeterminately restrained.
ASTM E119

Standard Test Methods for Fire Tests of Bui

Construction and Materials

• ASTM E119 prescribes a standard exposing fire 

controlled extent and severity

• Performance is defined as the period of resistanc

to standard exposure before the first critical point behavior (conditions of acceptance or end point conditions) is observed.

• Conditions of acceptance include (for floor system

– Sustained applied load during classification period– Maximum temperature on unexposed side of the 

specimen

– Maximum and average temperatures of the steel 

joists
Elevations of Test Configuration Elevations of Test Configuration

END VIEW

(Note: Bridging trusses are not shown for clarity)

Main trusses

Reinforced concrete 

slab with metal 

decking

Steel bars Steel double 

angles

SIDE VIEW

(Note: Bridging trusses are not shown for clarity)
Plan View of Test Configuration Plan View of Test Configuration

Main truss Main truss

Bridging 

truss

Steel 

bars
Instrumentation Instrumentation

• Temperature Measurements (exceed ASTM E11

requirements)

– Measurement of the temperature of the steel along 

length of the members

– Measurement of the temperature of the unexposed 

surface (top) of the concrete slab

– Measurement of the temperature of the bottom of th

concrete slab (steel deck)

• Deflection (not required by ASTM E119)

– Deflection measurements will be made at 9 location

on the unexposed side of the specimen as well as amid-span on the bottom chord of both main trusses
Instrumentation (Cont’d) Instrumentation (Cont’d)

• Gas Temperatures (not required by ASTM E119)

– Gas temperatures will be continuously recorded at 

three locations using plate thermometer and aspiratthermocouples

• Heat Flux (not required by ASTM E119)

– Radiative heat flux will be measured at lower surfac

metal deck and to the bottom flange of the main trusses using wide-angle radiometers
Thermocouples on Main Trusses Thermocouples on Main Trusses
Thermocouples on Unexposed Surfa

Thermocouples on Unexposed Surfa

of Concrete Slab of Concrete Slab
ASTM E119 Conditions of Acceptan

ASTM E119 Conditions of Acceptan

(or end point criteria)* (or end point criteria)*

• Transmission of heat through the specimen shall 

have been such as to raise the average temperaton its unexposed surface more than 250 oF (139 above its initial temperature.

• The temperature of the steel shall not have excee

1300 oF (704 oC) at any location

• The average temperature of the steel recorded by 

four thermocouples at any section shall not have exceeded 1100 oF (593 oC)

* Tests will be conducted until specimen fails to sustain the ap

load (without damaging the furnace)
Schedule for Testing Schedule for Testing

• Start – “Kick-off” meeting with Contractor 

held August 18, 2003

• Testing – approximately 9 months• Results – shortly thereafter
May 2003 Progress Report: Fire Prote

May 2003 Progress Report: Fire Prote

(Page 74) (Page 74)

• In October 1969, ... , the Port Authority stated, in a le

to the fireproofing contractor, that

– “All Tower beams, spandrels, and bar joists requiring s

on fireproofing are to have a 1⁄2

′′ [1/2 in] covering of Ca

– The above requirements must be adhered to in order t

maintain the Class 1-A Fire Rating of the New York CitBuilding Code.”[1]

[1] Letter dated October 30, 1969 from Robert J. Linn (Manag

Project Planning, The World Trade Center) to Mr. Louis Di(Mario & DiBono Plastering Co., Inc.).
May 2003 Progress Report: Fire Prote

May 2003 Progress Report: Fire Prote

(Page 80) (Page 80)

• In 1999, the Port Authority established “guidelines 

regarding fireproofing repairs, replacement, and upgrades” for the towers. The guidelines for tenant spaces may be summarized as follows:

– For full floors undergoing new construction or renovatio

the bar joists should be fireproofed with 1-1/2 in of spramineral fiber fireproofing. Refireproofing requires remoof existing material and controlled inspection.

– For “tenant spaces less than a full floor undergoing new 

construction or renovation,” the floor trusses “need only meet the original construction standard. Fireproofing sbe inspected and patched as required to the greater of in or to match existing” if it has already been upgraded 1-1/2 in. 
Truss Specified Mechanical Properties

Top ChordA242Typically 2.5” x 1.5” x 0Bottom ChordA36 Typically 3” x 2” x 0.37”WebA36 (60’ truss) (1.09” rA242 (35’ truss) (0.98” 

ASTM Specificat

A36: Yield Point = 36ksA242-70 type 2: Yield P

About 50 truss variants (60’, 35’, bridging trusses, 20+ variants p
As-Built Properties Built Properties

• Truss components typically meet contemporaneo

specification. A36 components far exceed minimums.

• No obvious differences 

(chemistry/microstructure/mechanical) between steel specified as A36 and that specified as A242

• Truss steel would meet (chemistry and yield 

strength) present-day A572 (Type 2 or Type 4) Grade 50 steel
Selection of Key Test Parameters Selection of Key Test Parameters

• Fireproofing Thickness• Steel Specification

Should the planned tests address the fire endurance 

rating of ...

• what was originally specified for the design?

– 0.5 in of fireproofing per letter to DiBono– minimum steel strength (36 ksi; 50 ksi)

• as-built conditions at time of collapse?

– 0.75 in of fireproofing per measurements– Supplied steel strength (over 55 ksi)
If test is for ... If test is for ...

Specified Conditions• Will provide design information not available in th

early 1960s

• Will establish minimum performance expectation 

specified system

As-built Conditions

• Will provide as-built information for investigative 

purposes

• Will establish data on performance of as-built sys

at time of collapse
Other Considerations... Other Considerations...

• Steel primer paint

Should the planned tests have primed or unprimed steel?

– WTC steel was primed – Testing Laboratories generally require that steel 

not be primed or require the use of specific primers