WTC Core Construction
Below: portion of south tower core visible briefly during collapse.
Core Column Inspectionhttp://wtc.nist.gov/pubs/NISTNCSTAR1-1C.pdf p. 39-40 (p. 93-94 in PDF file)
Inspection of the core columns was performed in two phases. In one phase, staff from the consulting firm of Cordry, Carpenter, Dietz and Zack inspected core columns from the elevator shafts. In the other
phase, PANYNJ Quality Assurance Division staff inspected selected core corner columns from office
area floors. They also inspected lateral core bracing at two locations from an elevator lobby on the
Core columns inspected from elevator shafts—The consultant randomly selected a total of 25 elevator
shafts for inspection. Table B1 in the survey report contains a list of the elevator shafts that were visually
inspected. Lateral bracing members, columns, and floor framing between the 2nd and 7th floors were
inspected from eight other express elevator shafts.
Elevator core framing was inspected primarily with fireproofing materials in place. Only in elevator shaft
number 52 between the 44th and 55th floors was the fireproofing removed at the column splices.
According to the report, no defects were found in the existing fireproofing material. In most of the shafts,
several small regions and a few large areas of fireproofing were found to be missing from core framing
members, which, according to the report, was probably due to the high-speed elevators moving up and
down the shafts. In particular, an 8 in. wide by 1 ft 6 in. long area of fireproofing was found to be missing
on the top flange of the beam between shaft numbers 30 and 31 on floor 22. Also, 100 percent of the
fireproofing was found to be missing from the south face of column 908 between floors 27 and 29 in shaft number 1. All exposed steel members were found to be in good condition with only isolated locations of light surface corrosion on the steel. Some minor shrinkage cracks were reported in the troweled-on fireproofing materials on the columns.
Gypsum wallboards surrounding the elevator shafts were also found to be in good condition, although
isolated holes were detected at various locations as outlined in Table B2 of the survey report. At shaft
number 4, a piece of wallboard was found to be loose in the southeast corner of the shaft; facility
personnel repaired this piece.
Close-up inspection of column splices and eccentric-braced column connections with fireproofing
removed at the locations designated in Tables B3 and B4 showed that all bolts, welds, and structural steel in good condition. No defects in the welds were found after EQAD personnel performed ultrasonic
tests on the butt welds at the column splices and magnetic particle tests on the fillet welds at the
eccentrically-braced column connections.
Column splices and eccentrically-braced column connections in the express elevator shafts were not
tested due to restricted access.
Quality Assurance personnel inspected the lateral bracing of the core columns at two locations (one
between columns 606 and 607 and one between columns 907 and 908) on the 4th floor. Light surface
corrosion was found on the bracing, splice plates, and bolts. The welds were tested using the magnetic
particle method and were found to be in good condition, and no cracks were observed.
Core columns inspected from office area floors—Quality Assurance personnel inspected core corner
columns at eight splice locations (see Table B6 in the survey report for locations). Seven of the splices
were welded, and the welds were tested using the ultrasonic and magnetic particle methods. The eighth location was a bolted splice connection. No defects were found in any of the welded splices. Steel columns exhibited light surface corrosion, as did the bolted splice on the bolts and splice plates.
Recommendations – No priority recommendations for repair were made in the report. It was recommended that the fireproofing that was missing from the elevator shaft framing members be replaces, including those regions where the fireproofing was removed for up-close inspection during the condition survey. This report also recommended that the holes in the gypsum wallboards surrounding the elevators, which are listed in Table B2 of the survey report, be repaired.