Evidence for bolted connections for all core column H beams in the WTC1 collapse initiation region:
From NIST NCSTAR 1-1Chttp://wtc.nist.gov/pubs/NISTNCSTAR1-1C.pdf
From pg 48 of a WTC1 inspection
Core corner columns inspected from office area floors—Core corner columns were inspected at all four corners of the 92nd to 93rd floors and at three corners at the 77th to 78th floors. All seven locations were inspected by removing the five or more layers of gypsum wallboard around the splice locations, which were 3 ft 0 in. above the finished floor level.
On the 92nd to 93rd floors, all four splices were bolted connections. No defects were found at any of the bolted splices. Welded splices were found at all three locations on the 77th to 78th floors, and were tested using the dye penetrant method. Results from the tests showed that there were no surface cracks in the welds. Steel plates, bolts, and welds that were visible were found to have only light surface corrosion.
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 Chapter 3 Draft for Public Comment 40 NIST NCSTAR 1-1C, WTC Investigation
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.
The pg 48 quote verifies that all four corner columns on floor 92 were bolted, not welded.
We can also look at the NIST steel inventory for bolted splice plates. From NIST NCSTAR 1-3B:
C-65 (s-8) (904A: 86–89) and C-60. Notice the remains of bolted splice plates at the ends of the H beams. (left click to see the full image)
g) C-155 (904A: 83–86), notice the splice plate and bolts at the far end.
h) HH (605A: 98–101), This splice plate is from the 98th floor of WTC1. It is held to each beam by only 4 bolts in each plate.
c) C-30 (1008B: 104–106)
C-80 (WTC1 603A, 92-95), notice the bolt holes.
Left click to see the full image. The same column below:
From the NIST steel inventory and excerpts from an inspection report we know that the following CC connections are bolted splices:
The 4 core corner columns 501, 508, 1001 on the 92nd floor and
1008 on the 92, 104 and 106 floors
904 on the 83, 86 and 89 floors
605 on the 98th floor
603 on the 92 and 95th floors
and we see no evidence of welded H beam connections above the 86th floor. It is reasonable to assume that all H beam connections in the collapse initiation area of WTC1 were bolted splice connections.
From the available literature we discovered that there is a horizontal plane on the 98th floor right through the core where all core columns naturally break in two if the connecting bolts are removed. Every 114+ story core column is already "cut" at the 98th floor. All one need do is remove the top bolt connectors and push the top part over a little, taking advantage of existing "cuts" by manipulating (removable) bolt connections.