This may not be the best word. I would assert that the towers and to a lesser extent 7wtc were rather unorthodox designs from a structural POV. They look sort of convetional as far as "glass box" skyscapers go. 7wtc does have a typical no structural curtain wall skin... the thing we see coming down... the twins had very unorthodox and I believe never before done...a structural load 120" or so wide and 3 stories tall factory pre assembled panel system for the facade. It was all bolted together... no welds.
Unorthodox is also a bad way to describe the way the twins were designed and really doesn't apply to WTC7. The structural wall of the twins was shown to be very good at redistributing loads after the high speed impacts they were subjected to.
SanderO wrote:The floor system for all three was basically a long span column free donut surrounding a more conventional column grid.
This is by no means unorthodox. In fact it's normal even today.
SanderO wrote:Another odd ball or unorthodox and never before seen was that 7 WTC was build using the air rights to an existing main power sub station. The massive transformers and equipment meant that the column grid of the tower above could not have all the columns axially bearing directly on the foundations. Instead several of the 40 story column loads were carried by massive site erected 3 story high truss floors 5-7 and most of the north facade above floor 7 was carried on the end of massive cantilever trusses... 9' deep.
Your describing an engineering solution to a field condition. Could you explain how this was "odd ball" or actually contributed to the demise of the building?
There have been several studies done, none to my knowledge have faulted the transfer truss system.
SanderO wrote:One take away which is hard to dispute.... is that the FORM of collapse was very much a product of the structural *scheme* or design. We can discuss this.
I wouldn't dispute this because it's true. It's also irrelevant when discussing the failure of a building that exceeded the expected (reasonable) design requirements.
SanderO wrote:One concept for structures is redundancy in the sense that loads can "easily" be redirected to other paths (columns). This of course requires that there be strong beams which can serve as the *pathway" for the loads.... and or that portions of slabs can function (not collapse) when they lose support on one side...and become cantilevered slabs.
Now we're getting into meat. How were the twins and WTC7 deficient in these requirements? Naturally this raises the question of what should be considered as a required redundancy.
SanderO wrote:Design is often a delicate balance.... lighter structure (dead loads) means smaller columns below. The presumed live loads would be the same on each floor so reducing the dead load will make the building lighter and less expensive to build.
I'm not sure where you are going here.
Yes, there is a balance between design and economics. If you're claiming economics are making (or made in the case of WTC) buildings unsafe then this is something you will need to substantiate.