Featured Research

from universities, journals, and other organizations

NIST Tests Provide Fire Resistance Data On World Trade Center Floor Systems

Date:
August 30, 2004
Source:
National Institute Of Standards And Technology
Summary:
The Commerce Department’s National Institute of Standards and Technology (NIST) has reported that results from a series of four fire resistance tests conducted this month on composite concrete-steel trussed floor systems typical of those used in the World Trade Center (WTC) towers showed that the test structures were able to withstand standard fire conditions for between one and two hours.

(Graphic courtesy of National Institute Of Standards And Technology)

August 27, 2004 -- The Commerce Department’s National Institute of Standards and Technology (NIST) today reported that results from a series of four fire resistance tests conducted this month on composite concrete-steel trussed floor systems typical of those used in the World Trade Center (WTC) towers showed that the test structures were able to withstand standard fire conditions for between one and two hours. The tests are part of NIST’s building and fire safety investigation of the WTC disaster on Sept. 11, 2001.

The 1968 New York City building code – the code that the towers were intended but not required to meet when they were built – required a two-hour fire rating for the floor system.

Shyam Sunder, lead investigator of the NIST WTC investigation, explained that the four laboratory tests provide only a means for evaluating the relative fire resistance rating of the floor systems under standard fire conditions and according to accepted test procedures. Sunder cautioned, “These tests alone cannot be used to determine the actual performance of the floor systems in the collapse of the WTC towers. However, they are already providing valuable insight into the role that the floors may have played in causing the inward bowing of the perimeter columns minutes before both buildings collapsed.”

“The fire conditions in the towers on 9-11 were far more extreme than those to which floor systems in standard U.S. fire rating tests are subjected,” Sunder said to a group that gathered to watch yesterday’s final test at Underwriters Laboratories (UL) in Northbrook, Ill. “Our investigation’s final assessment of how the floor system performed in the WTC fires also must consider factors such as the combustible fuel load of the hijacked jets, the extent and number of floors involved, the rate of the fire spread across and between floors, ventilation conditions, and the impact of the aircraft-damaged towers’ ability to resist the fire,” Sunder said.

All four WTC floor system fire tests used the standard procedure known as ASTM E119 for rating the fire resistance of a building structural unit such as a floor system, column or beam under prescribed conditions. The tests were conducted as part of a NIST contract at two separate UL fire test laboratories to take advantage of the different capabilities available at these facilities.

The first two tests, conducted earlier this month at the UL facility in Toronto, Canada, looked at the fire performance of 11-meter (35-foot) floor systems coated with a near-uniform 19-millimeter-thick (0.75-inch) layer of fireproofing material. This is representative of the span size and as-applied average fireproofing thickness of the floor systems in the WTC towers.

One floor system in the Canadian tests was restrained (prevented from expanding due to thermal conditions) while the other was not. Understanding the impact of restraining or not restraining the WTC floor systems during ASTM E119 testing is important. Floor systems tested under ASTM E119 traditionally have been restrained; however, the novel design of the floor systems in the WTC towers did not qualify as either fully restrained or fully unrestrained.

Past experience with the ASTM E119 test method would lead investigators to expect that the unrestrained floor system would not perform as well as the restrained assembly, and therefore, it would receive a lower fire rating. The Canadian tests actually yielded the opposite result: the restrained WTC floor system was fire rated at 1.5 hours while the unrestrained floor system was rated at two hours. NIST investigators will consider this difference when evaluating the performance of the actual WTC floor systems.

For the two experiments at UL in Illinois, 5-meter (17-foot) truss spans – the standard size used in U.S. fire resistance tests – were built. Both were restrained. The test on Aug. 19, 2004, was conducted on a floor system with a fireproofing thickness of 19 millimeters (0.75 inch), the same as the 11-meter assemblies tested in Canada. Yesterday’s final fire test used a 5-meter truss with a fireproofing thickness of 13 millimeters (0.5 inch). This was the thickness of the truss fireproofing originally specified when the WTC towers were built. Therefore, if an ASTM E119 fire resistance test had been conducted on the WTC floor system prior to construction, these would have been the test conditions. NIST has no evidence or record indicating that such a test was ever done.

A fire rating of two hours was determined from the August 19 test with the “as-installed” (19 millimeters) fireproofing thickness. This matches the 1968 New York City building code rating for floor systems in Construction Class IB buildings (the designation assigned to the WTC towers when they were built). A fire rating of one hour was determined from yesterday’s test with the “as-specified” (13 millimeters) fireproofing thickness based on the ASTM E119 standard in place during the 1960s.

One question raised by the data from the four tests is whether or not a fire rating based on the ASTM E119 performance of a 5-meter floor system is “scalable” to a larger floor system – such as the WTC towers assemblies that were 11-meter (35-feet) and 18-meter (60-feet) lengths. This was identified when one of the larger-scale tests in Canada had a lower fire resistance rating than the smaller-scale test in Illinois.

The findings from the ASTM E119 WTC floor system tests discussed yesterday may be revised and additional findings may be included in the NIST investigation team’s final report, scheduled for release as a draft document in December 2004. NIST is not making any recommendations at this time. All recommendations will be made in the final report.

More information on the NIST WTC investigation is available at http://wtc.nist.gov.

As a non-regulatory agency of the U.S. Department of Commerce’s Technology Administration, NIST develops and promotes measurement, standards and technology to enhance productivity, facilitate trade and improve the quality of life.


Story Source:

The above story is based on materials provided by National Institute Of Standards And Technology. Note: Materials may be edited for content and length.


Cite This Page:

National Institute Of Standards And Technology. "NIST Tests Provide Fire Resistance Data On World Trade Center Floor Systems." ScienceDaily. ScienceDaily, 30 August 2004. <www.sciencedaily.com/releases/2004/08/040829130757.htm>.
National Institute Of Standards And Technology. (2004, August 30). NIST Tests Provide Fire Resistance Data On World Trade Center Floor Systems. ScienceDaily. Retrieved April 21, 2014 from www.sciencedaily.com/releases/2004/08/040829130757.htm
National Institute Of Standards And Technology. "NIST Tests Provide Fire Resistance Data On World Trade Center Floor Systems." ScienceDaily. www.sciencedaily.com/releases/2004/08/040829130757.htm (accessed April 21, 2014).

Share This



More Matter & Energy News

Monday, April 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Why Did Nike Fire Most Of Its Nike FuelBand Team?

Why Did Nike Fire Most Of Its Nike FuelBand Team?

Newsy (Apr. 19, 2014) Nike fired most of its Digital Sport hardware team, the group behind Nike's FuelBand device. Could Apple or an overcrowded market be behind layoffs? Video provided by Newsy
Powered by NewsLook.com
Small Reactors Could Be Future of Nuclear Energy

Small Reactors Could Be Future of Nuclear Energy

AP (Apr. 17, 2014) After the Fukushima nuclear disaster, the industry fell under intense scrutiny. Now, small underground nuclear power plants are being considered as the possible future of the nuclear energy. (April 17) Video provided by AP
Powered by NewsLook.com
Horseless Carriage Introduced at NY Auto Show

Horseless Carriage Introduced at NY Auto Show

AP (Apr. 17, 2014) An electric car that proponents hope will replace horse-drawn carriages in New York City has also been revealed at the auto show. (Apr. 17) Video provided by AP
Powered by NewsLook.com
Honda's New ASIMO Robot, More Human-Like Than Ever

Honda's New ASIMO Robot, More Human-Like Than Ever

AFP (Apr. 17, 2014) It walks and runs, even up and down stairs. It can open a bottle and serve a drink, and politely tries to shake hands with a stranger. Meet the latest ASIMO, Honda's humanoid robot. Duration: 00:54 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins