University of Alaska Building 7 Report

2002). In May 2002, FEMA published the World Trade Center Building Performance Study (FEMA, 2002). The purpose of the study was “to examine the damage caused by the events, collect data, develop an understanding of the response of each affected building, identify causes of observed behavior, and suggest studies that should be performed.” The FEMA Report was inconclusive as to the cause of WTC 7’s collapse, but it proposed a number of scenarios for further investigation. Based on the fact that the east penthouse fell approximately 7 seconds before the rest of the building fell, the FEMA Report suggested that the collapse initiated on the east side of the building on the interior, most likely at the transfer trusses between floors 5 and 7. FEMA also suggested that there were not enough combustibles on these floors to sufficiently weaken the structural members. Thus, FEMA hypothesized that diesel fuel stored in the lower levels of the building was somehow pumped and discharged through severed pipes and this somehow fed fires for several hours. The report noted that its best hypothesis had “only a low probability of occurrence” and that further investigation was needed. NIST would later rule out the diesel fuel hypothesis. 1.4.2 National Institute of Standards and Technology, November 2008 NIST began a more in-depth investigation into the collapse of WTC 1, WTC 2, and WTC 7 in August 2002. This effort was conducted under the mandate of the National Construction Safety Team Act (NCSTA), which was signed into law on October 1, 2002. NIST put its WTC 7 investigation on hold in 2005 to focus on completing its report on the collapse of WTC 1 and WTC 2 that year. Eventually, in November 2008, NIST released its final report on WTC 7 (NIST, 2008, NCSTAR 1A). Below is a moderately detailed description of NIST’s collapse initiation hypothesis, which will be examined in the following chapters. 1.4.2.1 Floors with Fires The NIST report provides photographic evidence of fires occurring on Floors 7 to 9, 11 to 13, 19, 22, 29, and 30 (NIST, 2008, NCSTAR 1A). The report states that fires on the four upper floors (19, 22, 29, and 30) were of relatively short duration and inconsequential in terms of causing the collapse. The NIST report claims that the fire on the 12th floor in the northeast corner of the building was primarily responsible for initiating the collapse by causing heat-induced failures of the 13th floor structure.

University of Alaska Building 7 Report

Articles inside

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