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    Default Question about WTC collapse.

    I read the NIST report and also Vincent Dunn's on what the factors were in the collapse of the World Trade Center.
    From what I gathered, the crash alone wouldn't have brought down the towers. It was fire.
    My question is this: do I understand correctly that the World Trade Center was built to the 1968 NYC building codes, even though those codes had not even been approved yet? And the reason that those codes were used was to save time, money and weight, because the lighter you go, the taller you can build? AND in some cases, fire resistive times were reduced from 3 hours to 2 hours?
    Answer, please.
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    Art, I do not believe the Trade Center needed to, or did conform to NYC building codes, 1938 or 1968. The Port Authority being a multi state agency has a standing variance as do Federal buildings within the city.
    Don't quote me on it, this is my understanding, (possibly my misunderstanding)

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    E229Lt,
    I actually read the same thing - that the Port didn't have to build it to standards. I'll try to find the documentation.

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    Artie/tk:
    You are both correct. Dunn's report stated: The WTC started construction in the 1970s. And the WTC towers built by the Port Authority of New York did not have to comply with the minimum requirements of the new 1968 performance building code.
    But the architect's report for NIST-Dr. S. Shyam Sunder-stated:The 1968 New York City Building Code was comparable to other codes of the era (1964 New York State, 1967 Chicago, and 1965 BOCA/BBC national model code). Documents suggest that the WTC towers generally were designed and maintained consistent with the requirements of the 1968 New York City Building Code. Areas of concern included fireproofing of WTC floor system, height of tenant separation walls, and egress requirements for the assembly use space for the Windows of the World in WTC 1 and Top of the World observation deck in WTC 2.
    I think this is where I got confused.
    Both Dunn's and the NIST Response to the World Trade Center Disasterare both very fascinating documents for anyone interested in looking at a detailed synopsis of the WTC disaster.
    Something that I found compelling was the inclusion of the HVAC system as a contributing factor, the construction of both the elevator shafts and means of egress to minimum standards and the fact that hi-rises did not require a factoring of an aircraft impact in its design.
    Wow.
    CR
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    and the fact that hi-rises did not require a factoring of an aircraft impact in its design.
    I believe that the WTC designers did factor in aircraft impact. What I have seen, if I remember right, is that they never figured out the damage that would be done by the fire caused by the jet fuel. I watched a show where I believe one of the architects said they didn't have the computer modelling capabilities to do such scenarios.

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    Originally posted by firepics


    I believe that the WTC designers did factor in aircraft impact. What I have seen, if I remember right, is that they never figured out the damage that would be done by the fire caused by the jet fuel. I watched a show where I believe one of the architects said they didn't have the computer modelling capabilities to do such scenarios.
    I recall watching a show about it a couple years ago (Discovery Ch?). They did say an aircraft impact WAS figured in, but the calculations were based on a smaller plane (707 I think) and not one with a full fuel load. The resulting fire was also figured, but again, not a full fuel load and they expected the fireproofing on the columns to remain intact.
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    This goes back to the fundamental abscence of consideration of fire as a load to be resisted in the classic structural engineering curriculum. Any training that a structural engineer got in the effects of fire on buildings was through their personal interest in the subject or due to a negative first hand experience during their career.

    In my opinion, the engineering community could "get away" with this with older technology that required massive structures to build high rise buildings. The heavier members could absorb a lot of heat for an extended period of time so that fire suppression efforts could be successful before the structural capacity of the building was reduced to the point where a complete collapse would occur.

    With the advent of computer analysis and the development of new technologies for structural framing, it became possible to build lighter structures that were just as strong as the older, heavier buildings when it came to resisting gravity and wind loads. They could even be designed to with stand earth quakes. However, these new buildings did not have the same capacity to absorb the heat generated by modern fire loads. The design philosophy rested on the supposition that properly designed sprinkler systems would provide adequate protection and limit fire growth so that the building frame would not see a catastrophic fire exposure. For that reason, the scenario that unfolded in the WTC was not a design criteria. Computer analysis also allowed builing frames to be successfully designed that were not redundant so that when an extra ordinary fire event occurs, the damage to the supporting framing is greater and the chance of general vs. localized collapse is increased. Before 911, these buildings and new technologies had not experienced damage to such a large scale that total failure resulted (although the frame of the One Meridian Plaza Building was so severely damaged that the building could not be repaired and had to be taken down).

    Engineering has a history of incidents where we think we have all the answers and our arrogance has bitten us on the behind later because we overlooked a possibility or failed to consider all the angles of a potential problem. I would guess the Titanic is the most famous example of this. Heck, there's a whole series about this sort of thing on the History Channel.
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    Sorry, I guess I sort of hijacked the thread. As to CR's original question, I agree that from what I have read, the Port Authority did not have to abide by the New York City code. I don't know what specific code, if any, the building was built to. It may be that the building incorporated features from several codes as the designer and the Port Authority saw fit to use them based on the budget and anticipated usage of the building.

    One problem of the use of 1968 era building codes was that they could not anticipate the fire load of a modern occupancy. No one in 1968 could anticipate the proliferation of plastics in furnishings. The idea of a personnal computer at every workstation was unthinkable. The rate and amount of heat released by these modern furnishings and office equipment was inconceeivable. It's dificult to design something for the future if you don't know what the future holds.

    I believe that there is a concensus in the investigations that the jet fuel burned off rather quickly. However, the jet fuel ignited the office furnishing, computers, etc. It was the high heat and rapid release of energy generated by this burning material that ultimately degraded the structural framing to the point where the buildings collapsed. Gee, that got long winded too, but I think it's at least more in line with Art's original post....
    Last edited by CJMinick390; 04-19-2005 at 11:03 AM.
    Chris Minick, P.E., Firefighter II
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