Contrary to popular belief September 11, 2001 was not the first time a steel framed building collapsed due to fire. Though the examples below are not high rise buildings, they make the point that fire alone can collapse a steel structure.
The McCormick Center in Chicago and the Sight and Sound Theater in Pennsylvania are examples of steel structures collapsing. The theater was fire protected using drywall and spray on material. A high rise in Philly didn't collapse after a long fire but firefighters evacuated the building when a pancake structural collapse was considered likely. Other steel-framed buildings partially collapsed due fires one after only 20 minutes.
The steel framed McCormick Center was at the time the World's largest exhibition center. It like the WTC used long steel trusses to create a large open space without columns. Those trusses were unprotected but of course much of the WTC lost it's fire protection due to the impacts.
"As an example of the damaging effect of fire on steel, in 1967, the original heavy steel-constructed McCormick Place exhibition hall in Chicago collapsed only 30 minutes after the start of a small electrical fire."
http://www.wconline.com/CDA/Archive/
24ae78779d768010VgnVCM100000f932a8c0____
[Note this article has several comments from engineers who back the
WTC collapse theory.]
"The unprotected steel roof trusses failed early on in the fire"
http://www.chipublib.org/004chicago/disasters/mccormick_fire.html
The McCormick Place fire "is significant because it illustrates the fact that steel-frame buildings can collapse as a result of exposure to fire. This is true for all types of construction materials, not only steel." wrote Robert Berhinig, associate manager of UL's Fire Protection Division and a registered professional engineer. He also discusses UL's steel fire certification much more knowledgably than Kevin Ryan. He is an example of one more highly qualified engineer who supports the collapse theory.
http://www.iaei.org/subscriber/magazine/02_d/berhinig.htm
From the FEMA report of the theater fire, my comments in [ ]
www.interfire.org/res_file/pdf/Tr-097.pdf
On the morning of January 28, 1997, in the Lancaster County, Pennsylvania township of Strasburg, a fire caused the collapse of the state-of-the-art, seven year old Sight and Sound Theater and resulted in structural damage to most of the connecting buildings.
The theater was a total loss, valued at over $15 million.
pg 6/74
The theater was built of steel rigid frame construction to allow for the large open space of the auditorium, unobstructed by columns... The interior finish in the auditorium was drywall.
The stage storage area, prop assembly building, and prop maintenance building were protected with a sprayed-on fire resistant coating on all structural steel. The plans called for the coating to meet a two-hour fire resistance assembly rating. The sprayed-on coating, which was susceptible to damage from the movement of theater equipment, was protected by attaching plywood coverings on the columns to a height of eight feet.
The walls of the storage area beneath the stage were layered drywall to provide a two-hour fire protection rating for the mezzanine offices [the WTC used drywall as fire protection in the central core] , and sprayed-on fire-resistant coatings on the structural
steel columns and ceiling bar joists supporting the stage floor.
pg 15/74
The two theater employees told the State Police Fire Investigator that when they first discovered the fire they noticed that the sprayed-on fire proofing had been knocked off the underside of the stage floor bar joists and support steel. The fire proofing was hanging on the wire mesh used to hold the coating to the overhead. The investigation revealed that the construction company's removal of the stage floor covering down to the corrugated decking involved striking the floor hard enough to knock off the sprayed-on protection, exposing the structural steel and bar-joists in the storage area. [The theater's spray-on fireproofing was newer and more modern than at the WTC, The theater was only seven years old. If striking the floor during renovations was enough to dislodge it imagine the impact of a 767]
pg 16/74
Temperatures of 1000° F can cause buckling and temperatures of 1500° F can cause steel to lose strength and collapse. When the heat and hot gases reached the stage ceiling they extended horizontally into the auditorium, causing the roof to fail all the way to the lobby fire wall. The fire also extended horizontally from the stage to the elevated hallway, causing the structural steel to fail and buckle in the prop assembly and prop maintenance buildings
pg 17/74
Once the heat of the fire caused the structural steel to fail in the storage area (aided by the damage to the sprayed-on fire protection during renovation), interior firefighting became too hazardous to continue. The truck crews ventilating the roof noted metal
discoloration and buckling steel.
pg. 21/74
The two hour fire resistance-rated assembly in the storage area beneath the stage was damaged during the stage floor renovation, leaving the structural members unprotected from the ensuing fire.
pg. 26/74
Buildings constructed of steel should, in effect, be considered unprotected and capable of collapse from fire in as few as ten minutes. Fire resistant coatings sprayed onto structural steel are susceptible to damage from construction work.
The impact of fire and heat on structural steel members warrant extreme caution by firefighters.
pg. 36/74
Unless the steel members are cooled with high-volume hose streams, the fire's heat can rapidly cause steel to lose its strength and contribute to building collapse.
pg. 37/74
Other Fires
In February 1991, a fire broke out in One Meridian Plaza - a 38 story office building in Philadelphia. The building was built during the same period as the WTC and had spray-on fire protection on its steel frame. Despite not suffering impact damage, authorities were worried it might collapse.
"All interior firefighting efforts were halted after almost 11 hours of uninterrupted fire in the building. Consultation with a structural engineer and structural damage observed by units operating in the building led to the belief that there was a
possibility of a pancake structural collapse of the fire damaged
floors."
http://www.usfa.fema.gov/downloads/txt/publications/tr-049.txt
About 2 years later, the NYFD was concerned that a steel framed building that partially collapsed during after a gas explosion might collapse entirely due to the resulting fire.
http://www.usfa.fema.gov/downloads/pdf/publications/TR-068.pdf
Part of a floor of an unprotected steel frame building collapsed in Brackenridge, Pennsylvania on, December 20, 1991, Killing 4 volunteer firemen
http://www.usfa.fema.gov/downloads/pdf/publications/TR-061.pdf
Part of the roof of a steel framed school in Virginia collapsed about 20 minutes after fire broke out
http://www.usfa.fema.gov/downloads/pdf/publications/tr-135.pdf
