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<p>Watermark: Fire Safety Academy logo icon, 70 px, 45 % opacity</p> <p><b>New page</b></p><div>== Summary ==<br /> Collapse initiation in WTC 7. Left: on Floor 13 the heated east floor beams expand and push the girder between Columns 79 and 44 off its support. Right: falling floors leave Column 79 unbraced over nine storeys and it buckles. Based on National Institute of Standards and Technology (2008), pp. 6, 22 and 53–54.<br /> <br /> Original illustration for [[Progressive collapse]], level 4 Expert.<br /> <br /> * Source basis: National Institute of Standards and Technology (2008), p. 6 (Figure 1–5, typical floor with column numbering: redraw, do not copy), p. 22 (girder between Columns 79 and 44 pushed west on Floor 13, cascade to Floor 5, eastward buckling), p. 53 (about 15 m spans, thermal elongation, simple shear connections), p. 54 (one-sided framing, no shear studs on the girder, Column 79 without lateral support for nine floors)<br /> * Alt text: Plan of a WTC 7 floor corner where expanding beams push a girder off Column 79, and an elevation of Column 79 buckling after the floors fell.<br /> <br /> == Licensing ==<br /> New drawing by Fire Safety Academy. © Fire Safety Academy.</div>

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