Core Column Data
There were two types of core columns used in WTC 1 and 2, box columns and rolled wide flange shapes which will be referred to here as I-beams. The yield strengths of the core box columns were 36 ksi or 42 ksi. The I-beams were one of four grades, but the yield strengths were primarily 36 ksi or 42 ksi. About 1% of the core columns were 45 ksi or 50 ksi steel. The columns in lower floors were almost exclusively large box columns up to 12 in. by 52 in. (0.30 m by 1.32 m). NIST indicates that the plates of the box columns were up to 7 in. (178 mm) thick. There seems to be a problem with this thickness since columns 12 in. in width could not accommodate sides of 7 in. in thickness. The following figure shows NIST's understanding of the layout of the core columns and the floors of transition from box columns to I-beams.
The architectural drawings differ from the NIST data in the floors at which the column transitions are made. The following figure gives the transition floors from this source.
There are a few floors for which the data have not yet been determined. As was noted in the discussion on [WTC 1,2 Structural Data Sources data sources] , discrepancies in data will be resolved by accepting the architectural drawings as authoritative unless it can be shown otherwise.