University of Alaska Building 7 Report

expansion earlier and then also collapsed at this time. There was no fire on the 10th floor, which means that heating could not have caused the west girder under the 11th floor to have lost its connection to Column 79. In this case, NIST claimed that the same girder under Floor 13 pushed Column 79 to the east enough to break the knife connection to Column 79 two stories below on the girder under the 11th floor. It is then alleged that this series of failures left Column 79 laterally unsupported from the south and west for 9 stories, causing it to buckle. 1.4.2.5 Collapse Propagation According to NIST, the buckling of Column 79 caused by the loss of lateral support over 9 stories triggered a progressive collapse of the entire building, starting with the subsequent buckling of nearby Columns 80 and 81, the subsequent collapse of the east penthouse above Columns 79, 80 and 81, and then a westward progression of core column failures that redistributed loads to the shell of exterior columns. 1.4.3 Arup and Nordenson, April 2010 Experts working in connection with engineering firms Ove Arup & Partners (Arup) and Guy Nordenson and Associates (Nordenson) were retained by the plaintiffs in “Aegis Insurance Services, Inc. v. 7 World Trade Center Company, L.P.” to perform structural analysis in support of the claim that the collapse of WTC 7 resulted from deficient design, thus making the defendants liable for the destruction of the electrical substation over which WTC 7 was built. The Arup and Nordenson reports, as they are referred to hereafter, were filed with the court in April 2010. The Arup report concluded that girder A2001 (the same girder that NIST reported was pushed off its seat by thermally expanding beams to the east of the girder) was actually pulled off its seat by the sagging of beams to the east of the girder. The largest displacement of the beams east of girder A2001 was analyzed by UAF to be 3.2 inches in the gravitational direction in SAP2000. This girder walk-off, according to the Nordenson report, then caused the same cascade of floor failures and buckling of Column 79 reported by NIST. However, contrary to NIST’s findings, Nordenson found that the alleged failure of other girder connections framing into Column 79 on lower floors, which was necessary along with the aforementioned cascade of floor failures in order for Column 79 to buckle, could not have been caused by thermal

University of Alaska Building 7 Report

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REFERENCES

Figure 4.20 Velocity comparison between Chandler measurement (green plotted line) and UAF simulation (red plotted line). Bold green trend line illustrates free fall

Figure 4.17 (a) Comparison of simulated collapse to perspective 1; (b) comparison of simulated collapse to perspective 2

2.7 Summary and Conclusion

3.2.2 Girder A2001 Web Stiffeners Prevent Flange Failure and Girder Walk-off

Table 2.3 Comparison of UAF and NIST Modeling

4.6 Results of Core Column/Exterior Column Failure Analysis

2.6.2 ABAQUS Analysis

3.2.3 Lateral Support Beams Prevent Beam Buckling

2.6.1 SAP2000 Thermal Deformation Analysis

Figure 2.36 Modeling process for a beam to girder shear connector, “STC.”

Table 2.1 Column loading for the Floor 12 and 13 assembly

Figure 2.21 SAP2000 model of entire WTC 7 without roof

Figure 2.24 Column number layout of Floor 13 (NIST, 2008, NCSTAR 1A

Figure 2.26 Small section of typical floor slab of WTC 7 with finer meshing

Figure 2.29 Plan View: Model of floor slabs in strong direction (parallel to flutes

Figure 2.46 Seated moment connection of exterior girders to exterior columns ABAQUS model

2.2 Solid Works Modeling

2.1.3 Background Studies

1.5.3 Approach 3: Simulating the Collapse of WTC 7

Figure 2.5 Area of floor where connection failure was modeled by NIST

1.5.2 Approach 2: Evaluation of NIST’s Collapse Initiation Hypothesis

Figure 2.6 Progressive collapse separated into two parts

Figure 2.3 Approach used to model buckled beams in LS-DYNA model (NIST, 2008, NCSTAR 1-9, Vol. 2

1.4.3 Arup and Nordenson, April 2010

Figure E.3 Finite Element Model of WTC7 in SAP2000, as viewed from the south

Figure 1.6 WTC 7 was in free fall for approximately 2.25 seconds over a distance of approximately 8 stories or 32.0 meters (NIST, 2008, NCSTAR 1A

EXECUTIVE SUMMARY

2.2 Hypothetical Failure Mechanisms for West Penthouse and North Face Roofline

Figure 1.4 WTC 7 tenants on September 11, 2001 (FEMA, 2002

Figure 1.9 WTC 7 steel frame building geometry prior to its collapse (FEMA, 2002

Figure 1.5 The collapse of WTC 7 at 5:20 PM (source unknown

1.4.2 National Institute of Standards and Technology, November 2008