Thank you for having the courage to present ROOSD at the Vancouver hearings. Jim Fetzer is well away of it as a result of my hundreds of posts about it on a DEEP POLITCS thread titled "Where did the Towers Go?" It was the longest thread with a lot of acrimony and sent to their "bear pit" but it still can be read and contains a good discussion and debate.
Interesting presentation. I don't think the slides properly represent the key features of ROOSD. Your slides seem to focus solely on the behavior of the *walls* which, by the way is a poor term for the facade columns assemblies which were load bearing and supported more than 50% of the axial loads.
There is no evidence of the facade falling further than 440 feet from either tower and that was the panels from the West facade of tower 1 which landed over at the WFC and the Winter Garden.
ROOSD is the collapse mechanism as you suggest but the mechanism of initiation is not part of ROOSD. The ROOSD began as a result of core failure at the plane strike zones which then led to the collapse from BUCKLING of the last surviving columns which were then unable to support the mass above the strike zone region and the section above collapsed down. In so doing it allowed the 16 or 30 stories of building above the buckling zone to deliver the threshold kick off mass to begin the ROOSD which was not a progression of floor slabs being separated and then dropping from the columns one after the other, but an avalanche of debris which destroyed each slab... fracturing, crushing ripping the trusses and concrete from the truss seats which supported it. The ROOSD, in destroying the floor slabs left the facade and many of the core columns behind as it raced downward within what was the cage-like structure of the facade.
The caging and ROOSD destruction and dropping left the facade laterally unsupported as the floor system had provided the required lateral stability to the facade. The floors also transmitted lateral wind loads to the stiff core as part of the strategy to provide stiffness to the tower. The growing collapsing floor mass was also exerting an outward force at the inside of the facade *cage* ...at its descending bottom and this plus Euler instability of the increasing slenderness ratio (1/12 in the intact tower to over 1/400 in some instances) led the facade to bulge and separating its panels at the connections of one panel to another and then the toppling away from the facade of large assemblies of panels. The larger the number of panels remaining attached to each other the further they fell from the tower (height location obviously determined how far they landed as well). There were many single panels which broke away and smaller number of panel assemblies which remained as a unit and these fell close to the tower.
ROOSD also stripped the core of much if its bracing. The core was a 3D lattice like structure (steel frame) and required bracing to stand erect. Steel wide flange beams were the bracing used to maintain the core's integrity. No bracing .. the core cannot stand. The core columns, like the facade was assembled from 36' long steel sections (not staggered however as the facade *membrane*), and was built of both fabricated box sections and cold rolled WF shapes. All columns reduced in cross sectional areas and were of decreasing strength the higher in the tower they were. The collapsing ROOSD debris/mass broke much of the bracing at the weak beam stub connections leaving the columns without lateral support and only held *in column* by the weaker splice plates at their end-to-end connections. These columns were growing increasingly *slender* and their slenderness ratio was increasing (from its original braced 1/12 to as much as 1/480+ without bracing) as the bracing was progressively stripped away by the ROOSD moving down the structure.
No columns were crushed by ROOSD, but all eventually buckled or toppled from Euler described forces after the ROOSD had concluded. Some were broken free during ROOSD and added to the ROOSD mass. These surviving columns are seen in the collapse videos and one, cc501 of tower 1 stood 78 stories much of it with no lateral support at all. Many core columns survived the ROOSD standing about 50 stories before they succumbed to EULER buckling (excessive slenderness ratio).
Most of the ejections seen emerging from the windows as the ROOSD raced down the tower caged by the facade were ahead of the front of ROOSD destruction. This material is most likely the contents of the floors being pushed outward (it had no other place to go) as the floor slab above this floor came down in about .1 seconds. Each floor contained 18,000 cubic yards of air which had to be displaced and the rapid displacement or 18,000 cu yard of air on the floor to the outside through the windows (smashing them of course) created huge over pressure and very destructive winds of up to 400 mph in a .1 second pulse. The window ejections are likely NOT the concrete from the slabs.
The driving ROOSD mass was the floor concrete and other heavy objects such as the hat truss steel, mech floor steel, antenna parts or heavy mechanical equipment... this made up the growing and gathering avalanche material. ROOSD was NOT PANCAKES... it was a rolling mixing vertical avalanche of self grinding materials. It was not a pile of dust, nor only massive sections of slabs. Each ROOSD impact with the floor it descended upon caused more crushing and fracturing of the ROOSD mass itself. Each 4" slab was fractured in small fraction of .1 seconds between floor impacts.
The threshold ROOSD mass has not been precisely determined. But the typical twin tower floor was designed to support 58 psf live load (reduced by request of PANY from the NYC Code requirement of 100 psf). The mass which came down on the top intact slab was north of 30,000 tons in tower 1 and more than double in tower 2.
The NIST diagram you cited is incorrect. The OOS slabs were of uniform spec... the spans of areas of the slabs varied and so the loads on the truss seat supports would vary depending on the slab load presented to the truss seat... and so the short spans had less load on the truss seats which, being the same design as the long span truss supports therefore had a larger safety factor... the slabs were the same spec for the entire pour/area. The corner sections were supported on truss seats on 2 adjacent sides and a transfer truss bearing on the corners of the core and one column location at the facade. See the attached slide which indicates approximate loading at each truss seat. The cited NIST analysis/diagram is rubbish.
It is important to note that the core side of the floor system supported the trusses on a *belt girder* which encircled the core and the belt girder was supported on beam stub outlookers and these same outlookers are also the means for attaching the inside the core bracing. The bolted connections of the outlookers was what failed in many cases. Beam stub outlookers are one the most common method used to make a rigid moment connection. A bearing seat connection allows rotation and movement.
Tom's analysis arrived at the ROOSD mechanism using an examination of how the facade (and the surviving core) behaved... plus it includes the observations of the descending crush front inside the facade cage. ROOSD is derived from observation but it has been described in engineering literature. Tom did not invent ROOSD but he has given it an acronym.'
It is stunning that neither NIST nor the professional engineering community has mentioned the ROOSD explanation.
The falling /peeling /pushing away of the facade was a ROOSD artifact. The columns of the towers both facade and core could neither prevent or contribute to the ROOSD process... but they were both victims of ROOSD in the end. ROOSD did not crush or buckle any columns... it was the destruction mechanism of the floor system and the towers cannot stand without their floors.
ROOSD is self sustaining once the threshold conditions present and requires no connection joint weakening of the truss seats or of the columns connections one to another.
Thank you for presenting this important work at the conference. If you would like to use any of my slides you can contact me.
by dadeets » Wed Jun 13, 2012 3:01 am 
Vancouver ROOSD (1 of 10).pdf
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