University of Alaska Building 7 Report

In the NIST investigation, ANSYS was used to model local failures and LS-DYNA was used to model large-scale collapse. When column buckling appeared to be imminent in ANSYS, the analyses were continued in the LS-DYNA 47-story model (NIST, 2008, NCSTAR 1-9, Vol. 2). The damage was applied in LS-DYNA as a sudden removal of damaged or failed elements as calculated in the ANSYS analysis. Buckled beams were modeled by removing flange and web elements, such that the beam would lose its axial and flexural strength, but the weight of the beam would remain in the calculation (see Figure 2.3). The connection damage data from ANSYS was transferred to the LS-DYNA global model using a damage index. Horizontal support and vertical support were specified separately (see Figure 2.4 and Figure 2.5).

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