Thread: Structural engineering council casts doubt on NIST’s WTC 7 Report

The Council on Tall Buildings and Urban Habitat (CTBUH) has published comments on the NIST WTC 7 Report. The CTBUH questions critical points of the NIST WTC 7 collapse theory and also highlights problems with the writing NIST report itself.
The CTBUH criticisms focus on two technical issues The conjectured failure of shear studs and bolts on the supposedly critical Column 79:
Several conclusions drawn in the NIST report on the contribution of structural
components in failure initiation are unexpected and have raised concerns
within the Council. These conclusions involve the role of both shear studs and
local global buckling of the floor beams in failure initiation. The Council
believes that the local connection performance was a significant part of the
global failure and would like to have seen a more explicit analysis of the
connection failure. (See also comment on Chapters 11-13.)
The NIST analysis (p. 353), shows that shear studs and the bolts holding the
primary Column 79 failed before the temperature of the steel reached 200˚C.
This implies a fundamental weakness that would be picked up by a
conventional PBD analysis. These temperatures are very low compared to a
fire protection test that assumes that steel loses strength at 550˚C.
The failure of shear studs is surprising, and has been modeled in a very
simplistic way, which may overestimate the failure of this element. Prior
studies and real fire cases have not previously identified shear stud failure as
a significant possibility Page 5
…
It is difficult to understand why the top bolts of the girder would fail at
connection to Column 79 Page 5

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