On 6/29/2006 2:42:40 PM, Dan Minette ([EMAIL PROTECTED]) wrote: > > OTOH, the shock that is transmitted though the structure by the > > pounding from above would significantly overpressure the shear > > strength of the bolts that tied the horizontal structure to the > > vertical structure. > > Does anyone know if there was welding performed in addition to > > bolting? Or would that inhibit the neccessary flexing required of > > such > > a tall structure? > > Let me ask a counter-question on this. Take a cross-beam welded and > bolted > to a vertical beam. How far could the cross beam move straight > down, > at the > point of attachment, before it shears apart from the vertical beam? > My > guess is that the 1 foot I referred to vastly overestimates the > distance > that the vertical beam would be offset at the point of attachment > before > breaking. Wouldn't a 1" movement at the point of attachment be > enough to > break the weld and shear the bolt? >
1/10th would break the weld handily and 1/4 to 1/2 for the bolt. (Bolt holes are not tightly fitted and there is often some variation in bolt hole pattens. You often see bolt holes being redrilled or torch cut to make the fit right.) The reason I asked is because welding adds strength WRT shearing forces but stiffens the joins. A stiffer join means that force is transmitted through the structure more efficiently, so weakening vibrations could have sundered the lower parts of the structure before the actual wave of collapse reached a particular level. This would be an effect that could explain why the entire structure gave way almost all at once. Maybe resonance? I remember an event in KC years ago where people dancing caused a bridge over a reception hall in a hotel caused the bridge to collapse and kill a few people. The cause was resonance. Everyone stomping their feet in time. Of course there are any number of forces at work during a chaotic event like the collapse of the WTC. Any and all of them could be operative. I'm interested in understanding the subject a bit better through an exploration of what occurred at different levels of the engineering of the structure. Having worked construction in similar buildings over the years and being aware of the nuts and bolts (NPI) of their construction, I find this all very interesting. xponent Frequency Maru rob _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
