Thermal expansion of composite girders

This NIST report (NCSTAR 1-9) is giving me a serious headache, as I reread it for the umpteenth time.

Quote:

Table 8–2 Progression of observed failures. Temperature (°C) Time (s) Beam Girder Event 1.44 103 89 First shear stud failure 1.54 154 131 Both seat bolts of girder to Column 79 had failed 1.62 194 164 Both top clip bolts of girder to Column 79 had failed 1.83 300 252 All but three shear studs had failed 2.04 406 339 Both seat bolts of girder to Column 44 had failed 2.10 436 364 Northmost floor beam began to buckle laterally 2.18 476 398 Both top plate bolts of girder to Column 44 had failed 2.90 600 500 All floor beams began to buckle This analysis demonstrated possible failure mechanisms that were used to develop the leading collapse hypothesis further.

Firstly, they fail to apply heat to the composite slab:

Quote:

No thermal expansion or material degradation was considered for the slab, as the slab was not heated in this analysis.

Which is very strange, as Cardington test showed that

Quote:

In all these cases, composite steel deck floors had demonstrated robustness and resistance to fire far greater than was indicated by standard fire tests on single beams or slabs.

This obviously calls into question the table above, and their assesment of the shear studs.

Secondly, while I mention shear studs, they exclude them from girder 79-44, implying it gave no resistance to beam expansion, which is obviously false, and it would also have an impact on the thermal expansion of this girder also.

Lastly, they fail to account for the loss of strength of the axial forces for the beam as it is heated, instead applying the full strength of the beam against the girder and the shear studs.

As an aside, it was interesting to note that the first failure would have occurred simply by pouring a cup of coffee on it.

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