INTRODUCTION [Arthur Scheuerman in his book "Fire in the Skyscraper" postulated] the mysterious "kink" in the north face of Building 7 was the result of collapsing core columns pulling the north face inward: http://www.crono911.net/docs/ScheuermanWTC7a.pdf Most researchers seem to concur, at least tacitly. I have reviewed much of the Building 7 content on this forum, and have found a few references of concurrence, but no discussion to the contrary. Some will ask, "What does it matter?" It matters a great deal. Understanding the motions of what we can see, reveals what is happening with what we can't see. More so, an accurate understanding of the Building 7 perimeter frame motions beg other pivotal questions, all of which are topics for separate threads. This thread focuses on motions of the perimeter frame through the first four floors of collapse. Understanding these motions will require a reassessment of many theories and assumptions about what was occurring out of view, inside the building, the lower north and west faces, the east and south faces, and and in what sequence. In my studies of WTC collapses, I have found no accurate assessment of these motions; the motions which created the north face crimp. This study is an attempt to correct the record. There was no inward motion of the north face of Building 7; it was not pulled inward. EDITORIAL NOTE This study is about the perimeter frame of Building 7. All references to "onset" refer to the perimeter frame, not "the building". I use the term "perimeter frame", rather than "moment frame", as it more quickly communicates the structural element under discussion for the casual, non-engineering oriented reader. PANEL 1 - REFERENCE LINES I used the well known West Side Highway video of collapse, as it offers the best view of the north face, and it was taken with a stationary camera. Panel 1 establishes base lines from which to measure/observe subsequent motion: The 2 vertical lines establish position of the north vertical corners prior to any motion of the perimeter frame. Those lines are superimposed on each subsequent frame in order to easily see how the structure has moved. Location of each vertical line is determined by features on the two buildings in the foreground, which are stationary. I took great pains to ensure placement of the lines in subsequent frames is accurate. The vertical lines are exactly vertical in order to have a dependable line of reference. Of note, the NW corner of the structure is tilting slightly to the east. The far right edge of the white foreground building shows the same tilt, which means this pre-onset tilt is due to the camera not being exactly plumb. Horizontal reference is established with the indented roof line of the white foreground building, which easily shows downward motion. PANEL 2 - ONSET The first movement is the east corner moving to the east, as well as an apparent dip in the roof line. The west corner has not moved, and there is no downward motion. Note the entire visible east side has moved to the east. The east corner is virtually parallel to it's starting line. This is not a "localized deformation", as some researchers have asserted. The pivot point of this motion is far below what is visible. The entire east corner appears to be moving east. But how could it? The west corner hasn't moved. The building is not shifting to the east; only the east corner has moved. This one frame of onset has enough information to prove the north face was not being "pulled inward", but frames from further along in collapse will make it more clear. For this frame, let's examine the dip, or curve in the roof line and lines of the floors. If a straight line becomes curved, it's straight line measurement from end to end will be shortened. That is axiomatic, and should require no visual examples. It is fact therefore, that the straight line measurement between the corners of the roof line has shortened, not lengthened, as it appears at onset. It doesn't matter what direction the curve is making; the straight line measurement between the corners is shortened. It is impossible that the east corner is moving east, despite the appearance of it doing so. Casual observers would likely conclude the roof line curve is a downward dip. It isn't. A simple view of the roof line at near eye level reveals there is no downward roof line curve which approximates the curve noted in Panel 2: This frame was taken at approximately four floors of descent. The roof line curve therefore, is on a horizontal plane. It is the street level camera angle that makes it appear to be on a vertical plane, or a dip. The curve is definitely "inward", relative to positions of the roof line corners. That does not mean inward relative to the original plane of the north face. This appears to be where NIST made their mistake. Additionally, note the bottom of the curve is not centered on the north face; it is located in the east half, close to where the crimp later develops. The importance of this fact will be shown further along in this analysis. PANEL 3 - ONSET OF DESCENT The structure has dropped approximately 1/2 of a floor. It appears that the east corner has moved further east, but the west corner has made a noticeable tilt to the east as well, which seems to account for the further expansion of the east corner. The roof line curve has deepened, and lines of the floors display more curvature than in Panel 2. PANEL 4 - TWO FLOORS OF DESCENT Panel 4 shows more east corner movement to the east. The west corner has tilted slightly more east, but the east corner movement to the east is more than the increased west tilt. The roof curve has deepened further, and again, that means the straight line measurement between the north roof corners has shortened more. PANEL 5 - FOUR FLOORS OF DESCENT At four floors of descent, the east corner has again moved slightly east, and the west corner has tilted slightly more to the east. The two movements appear to offset one another, and only slight movement to the east is discernible for the remaining descent of the east corner. Most notable in Panel 5 is the first sign of the crimp; the roof line is now "V" shaped, rather than curved. PANEL 6 - FLOOR LINE COMPARISON This is an important piece of the puzzle. I've divided the north face into two "halves", with the crimp line as center. In the west half, the floor lines have not changed angle after four floors of descent, except for a slight angle attributed to the structure tilting east as it fell. Notice the east half indeed has changed angle considerably. If the north face were being pulled inward, both halves would have changed angles, as both halves would have to be pulled inward at onset. Note the entire visible east half has turned to face more to the camera. PANEL 7 - NORTH FACE MEASUREMENT COMPARISON I measured the two "halves" at pre-onset and after four floors of descent, then transposed the pre-onset lines on the latter. Virtually all of the apparent expansion to the east of the east corner is attributed to the east half alone. The west half has not altered it's orientation to the camera. CONCLUSIONS The north face is folding vertically. The motion is little different from a closing door: The east half of the north face is turning on an arc toward the camera, which accounts for the east corner expanding toward the east. If the north face were being pulled inward, the east corner (or both corners) would visibly be pulled inward with it. The following rough overhead diagram shows what is occurring at onset: Note that even though the straight line distance of corner to corner has shortened, the corner appears to have moved to the east from the viewing angle. Since the angle of the east vertical corner did not change, in other words, it remained relatively parallel to it's starting position, the motion can be said to pivot at a point far below what is visible. The entire east half of the perimeter frame is falling over to the north. This begs a few pivotal questions. Why did the entire structure then, not fall north with it (the west half fell to the south)? Why was there no deformation of the SW corner? Answers to those questions will reveal this one mistake by NIST led to other serious mistakes, but those are answers for another thread. Thank you for reading.