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TLC aired a program tonight which addressed the probable causes of the World Trade Center collapse.
From the onset of the show, narration suggested the *unique* structural design of the World Trade Center led to the eventual failure of the building after the planes hit.
The buildings had orginally been planned to house over 12 million square feet of office space. However, due to limitations in elevator design, ground elevators serving all floors nessecary to create the required sqaure footage, proved too costly.
Minoru Yamasaki, the WTC cheif archetect, was sent back to the drawing board to develop a facility that could house the nessecary sqaure footage while accomodating elevator traffic economically. Minoru Yamasaki devised a plan to section off each tower into 4 equilivent veritical units, with each section housing elevators serving its respective section. This elevator configuration allowed 110 stories to be built in two twin towers to fullfill the square footage specifications.
The orginal group responsible for underwriting the operation made it clear the towers were to be built as soon as possible. Although I didnt get all the details, something about the 1960's space race, and America wanting to make its mark to the Soviets, prompted the expediated design of the towers, which soon went into construction in the late 60's.
A second significant structural engineering dilemia was severe regional wind storms. Apparently New York gets some pretty fierce wind storms which had to be accounted for in High rise design.
The option was chosen to construct twin towers having a "tube" design, which could both minimze construction materials and resist massive external wind forces. Essientially, a tube design consists of a strong load supporting external frame, coupled with a load supporting center frame, punctuated by by open space inbetween.
Looks something like this:
---------------------
lxxxxxxxxxxxxxxxxxxxxxl
lxxxxxxxxxxxxxxxxxxxxxl
lxxxxxxxxl=====lxxxxxxl
lxxxxxxxxl=====lxxxxxxl
lxxxxxxxxl=====lxxxxxxl
lxxxxxxxxxxxxxxxxxxxxxl
lxxxxxxxxxxxxxxxxxxxxxl
---------------------
A tube design is disimilar to traditional "frame" designs, which are characterized by steel cubes constructed adjacent to the other, providing the building superstructure.
The tube design not only allowed the open space office tenets 'loved', but reduced the amount of total steel required to construct the twin towers by half!! The contractors loved it.
Inherent in all tube designs are 'trusses'. Apparently, these trusses are prefabricated flooring supports which create the floorbase between the external load bearing frame, and the internal load bearing frame. Trussus are attached like bridges connecting the external outer frame, to the inner frame, to create a floor support.
=xxxxxxxxxxxxxxxxxxxxxxxxl
=xxxxxxxxxxxxxxxxxxxxxxxxl
=xxxxxxxxxxxxxxxxxxxxxxxxl < external frame
= ------------------------l
= ----------------------- l
=xxxxxxxxxxx^xxxxxxxxxxxxl
=xxxxxxxxx truss xxxxxxxxxxl
From this design, MIT scientists identified two major problems which caused the WTC structural failure.
When the planes hit, massive amounts of burning kerosine created temperatures exceeding 1200 degrees inside the impacted floors. Although steel does not break when exposed to high tempatures, high temperatures can soften and 'warp' existing steel beams.
Investigators found that steel truss's, and major load supporting beams in the center of the WTC, were covered with little fireretardent. Either the fireretardent was blown off in the intial explosion created by jet liner impact, or the steel beams and trusses contained in the WTC wernt covered with sufficent fire retardent prior to WTC construction. Either way, the truss's and major load supporting center beams in the affected WTC floors, lacked sufficent fire retardent to prevent steel expansion and softening when exposed to high temperatures.
Since the trusses were composed of relativily thin steal beams fastened together, they were the first load bearing structures to overheat, warp, then fail.
Because the World Trade Center was created so "efficently", only a minimum amount of construction materials were used to satisfy load bearing requirements. The Tube design of the building meant that truss's had to perform the dual function of not only creating flooring supports, but also hold *in* the external frame as downward force pushed the external frame out.
As the trusses overheated, expanded, and broke off from the external frame, the downward force normally redistributed by the now warped internal frame and nonexistent trussess, caused a massive redistribution in load to the external frame, which essientially buckelled out at the fail points.
Once the external load bearing frame buckeled at the fail points, the momentum of falling upper building sections overwhelmed intact lower external and internal load bearing frames, which resulted in systemic structural failure.
The program included an extensive interview with the cheif Structural engineer for the WTC. He was remorsefully, but expressed that had an alternative structural design been chosen, the project may have not been undertaken due to increased duration and costs associated with other structural designs available at the time.
It was a really interesting show. Morbid, but important.
From the onset of the show, narration suggested the *unique* structural design of the World Trade Center led to the eventual failure of the building after the planes hit.
The buildings had orginally been planned to house over 12 million square feet of office space. However, due to limitations in elevator design, ground elevators serving all floors nessecary to create the required sqaure footage, proved too costly.
Minoru Yamasaki, the WTC cheif archetect, was sent back to the drawing board to develop a facility that could house the nessecary sqaure footage while accomodating elevator traffic economically. Minoru Yamasaki devised a plan to section off each tower into 4 equilivent veritical units, with each section housing elevators serving its respective section. This elevator configuration allowed 110 stories to be built in two twin towers to fullfill the square footage specifications.
The orginal group responsible for underwriting the operation made it clear the towers were to be built as soon as possible. Although I didnt get all the details, something about the 1960's space race, and America wanting to make its mark to the Soviets, prompted the expediated design of the towers, which soon went into construction in the late 60's.
A second significant structural engineering dilemia was severe regional wind storms. Apparently New York gets some pretty fierce wind storms which had to be accounted for in High rise design.
The option was chosen to construct twin towers having a "tube" design, which could both minimze construction materials and resist massive external wind forces. Essientially, a tube design consists of a strong load supporting external frame, coupled with a load supporting center frame, punctuated by by open space inbetween.
Looks something like this:
---------------------
lxxxxxxxxxxxxxxxxxxxxxl
lxxxxxxxxxxxxxxxxxxxxxl
lxxxxxxxxl=====lxxxxxxl
lxxxxxxxxl=====lxxxxxxl
lxxxxxxxxl=====lxxxxxxl
lxxxxxxxxxxxxxxxxxxxxxl
lxxxxxxxxxxxxxxxxxxxxxl
---------------------
A tube design is disimilar to traditional "frame" designs, which are characterized by steel cubes constructed adjacent to the other, providing the building superstructure.
The tube design not only allowed the open space office tenets 'loved', but reduced the amount of total steel required to construct the twin towers by half!! The contractors loved it.
Inherent in all tube designs are 'trusses'. Apparently, these trusses are prefabricated flooring supports which create the floorbase between the external load bearing frame, and the internal load bearing frame. Trussus are attached like bridges connecting the external outer frame, to the inner frame, to create a floor support.
=xxxxxxxxxxxxxxxxxxxxxxxxl
=xxxxxxxxxxxxxxxxxxxxxxxxl
=xxxxxxxxxxxxxxxxxxxxxxxxl < external frame
= ------------------------l
= ----------------------- l
=xxxxxxxxxxx^xxxxxxxxxxxxl
=xxxxxxxxx truss xxxxxxxxxxl
From this design, MIT scientists identified two major problems which caused the WTC structural failure.
When the planes hit, massive amounts of burning kerosine created temperatures exceeding 1200 degrees inside the impacted floors. Although steel does not break when exposed to high tempatures, high temperatures can soften and 'warp' existing steel beams.
Investigators found that steel truss's, and major load supporting beams in the center of the WTC, were covered with little fireretardent. Either the fireretardent was blown off in the intial explosion created by jet liner impact, or the steel beams and trusses contained in the WTC wernt covered with sufficent fire retardent prior to WTC construction. Either way, the truss's and major load supporting center beams in the affected WTC floors, lacked sufficent fire retardent to prevent steel expansion and softening when exposed to high temperatures.
Since the trusses were composed of relativily thin steal beams fastened together, they were the first load bearing structures to overheat, warp, then fail.
Because the World Trade Center was created so "efficently", only a minimum amount of construction materials were used to satisfy load bearing requirements. The Tube design of the building meant that truss's had to perform the dual function of not only creating flooring supports, but also hold *in* the external frame as downward force pushed the external frame out.
As the trusses overheated, expanded, and broke off from the external frame, the downward force normally redistributed by the now warped internal frame and nonexistent trussess, caused a massive redistribution in load to the external frame, which essientially buckelled out at the fail points.
Once the external load bearing frame buckeled at the fail points, the momentum of falling upper building sections overwhelmed intact lower external and internal load bearing frames, which resulted in systemic structural failure.
The program included an extensive interview with the cheif Structural engineer for the WTC. He was remorsefully, but expressed that had an alternative structural design been chosen, the project may have not been undertaken due to increased duration and costs associated with other structural designs available at the time.
It was a really interesting show. Morbid, but important.
Last edited:
thats all i can recall for now
