“Lateral walk off” was the phrase used by the National Institute of Standards and Technology (NIST) to describe the mechanism by which thermal expansion in the 13th floor framing of World Trade Center 7 (WTC 7) allegedly caused the loss of vertical support for a critical girder and its tributary floor area. According to NIST, excessive horizontal displacement at one end of the girder triggered a chain reaction of events that ended in the complete collapse of the building as reported in NCSTAR 1A1, 1-92 and 1-9A3.
This anomalous failure mode was announced by NIST’s lead investigator, Dr. Shyam Sunder, at a press conference on August 21, 2008. The NCSTAR reports on WTC 7 were issued as draft reports for public comment that day, and the public was given four weeks to respond. This was hardly an adequate amount of time for review considering the significance to the architectural-engineering profession and the fact that NIST’s analysis “tested the limits of computational capabilities,” according to NCSTAR 1-9 Section 1.2.2.
Although the finite-element method of structural analysis was well established prior to 2001, the “new modeling capability” of the fire-structure interface was not what structural engineers and analysts considered a well-established method at the time. Apparently, the Twin Towers analysis was the first trial using this method to translate fire-dynamics data into structural-analysis data4.
As I discovered through years of painstaking review of hundreds of documents after the final NCSTAR reports were released — indeed, four weeks was not enough — crucial structural information was omitted from NCSTAR 1-9 without explanation, and NIST’s collapse-initiation sequence for WTC 7 was based on speculation.
“It’s too late to correct it,” said the Red Queen: “when you’ve once said a thing, that fixes it, and you must take the consequences.” — Lewis Carroll, Through the Looking Glass
While NIST must indeed take the consequences of what it has said, technical errors and omissions in government-issued engineering reports need to be addressed in a professional and scientific manner, and it is never too late to do so. In particular, the ethical practice of structural engineering requires a clear understanding of failure modes in order to prevent them.
This article describes a series of FOIA (Freedom of Information Act, 5 U.S.C. § 552) requests that I filed from 2009 to 2014 seeking information related to the alleged walk-off failures in WTC 7. Excerpts from these FOIA requests and appeals to NIST are indented in the following paragraphs. Links to the FOIA requests, appeals, and responses are provided throughout. All relevant documents regarding the design and construction of WTC 7 can be obtained by request from NIST, so that anyone with the requisite expertise can verify my observations.
NIST’s responses, or lack thereof, to my technical questions should be enlightening to anyone studying the WTC tragedy.
I submitted FOIA Log #09-49 in February 2009 with the intent to study the collapse-initiation hypothesis reported by NIST. FOIA Log #09-49 stated:
The following specific shop fabrication and erection drawings are requested:
- structural steel erection layout plan of floor 13
- the steel deck erection layout plan of floor 13
- details of the 13th floor girder (W33x130) spanning between columns 79 and 44
- details of column 79 at floor 13
- details of column 44 at floor 13
- details of W24x55 beams that were attached to the east side of the girder
- details of the W12x26 beam that was attached to the west side of the girder
- general notes and specifications applicable to the construction of floor 13
The following specific structural design drawings are requested:
- the structural framing plan of floor 13
- structural framing details referenced on the framing plan of floor 13
- general notes and specifications applicable to the construction of floor 13
- technical specifications related to the shear studs
Most of the drawings requested were obtained in October 2010. These facilitated a review of 13th floor framing and a partial review of the applicable connections. Conspicuously missing were fabrication details of the 13th floor girder (W33x130) spanning between columns 44 and 79.
I submitted FOIA Log #10-037 in January 2010. This request sought NIST’s calculations that substantiated the lateral walk-off failures. The intent was never to obtain ANSYS input data for extensive processing by computer. FOIA Log #10-037 stated:
“Walk off” is the term NIST used to describe the failure mode where a girder moved axially or laterally off its bearing seat losing all vertical support. The walk-off failure was assumed to be complete when lateral displacement of the girder end moved past the point at which the girder web was aligned vertically with the edge of the bearing seat. The following statements by NIST authors are found in NCSTAR 1-9.
A control element (COMBIN37), a unidirectional linear spring element with the capability of turning on and off during an analysis, was used to model walk-off [p. 480.]
The travel distance for walk off was 6.25 in. along the axis of the beam and 5.5 in. lateral to the beam [p. 482.]
A control element was used to model beam walk-off in the axial direction. Beam walk off in the lateral direction was monitored during the analysis [p. 482.]
Lateral girder walk-off at columns 79 and 81 was the failure mode allegedly responsible for the start of collapse. I respectfully request a copy of the structural calculations or ANSYS analysis results that substantiate the walk-off failures at columns 79 and 81.
NIST responded in January 2010 with an abbreviated version of the 16-story ANSYS model input data, but connection models and analysis results were withheld on public safety grounds. In July 2009, the NIST director had determined that releasing certain data “might jeopardize public safety”5, and in April 2011 the U.S. District Court agreed with NIST that release “would provide instruction to individuals wanting to learn how to simulate building collapses and how to most effectively destroy large buildings”6.
Although these decisions could have been interpreted as a deterrent, the forbidden ANSYS models were not required to study the framing and connections. My review of the drawings continued with neither interest nor intent to simulate building collapses or to learn how to destroy buildings.
I submitted FOIA Log #11-209 in August 2011 and requested the following:
- Irwin G. Cantor P.C., Structural Engineers (1985). Structural Design Drawings, 7 World Trade Center
- Irwin G. Cantor P.C., Structural Engineers (1985). Structural Calculations, 7 World Trade Center
Files released through FOIA #11-209 included 34 sheets of drawings for the building plus seven sheets of drawings for the Plaza Bridge that connected Building 7 to the WTC Plaza across Vesey Street. No calculations were released.
I submitted FOIA Log #12-009 in October 2011 and requested the following:
- Frankel Steel Limited (1985). Erection Drawings, 7 World Trade Center
- Frankel Steel Limited (1985a). Fabrication Shop Drawings, 7 World Trade Center
2,587 files released through FOIA #12-009 included steel erection plans, column schedules, bracing elevations and details. 22 sheets in PDF format included erection drawings for floors one through 17, and 42 sheets in TIF format included erection drawings for the entire building. The remaining 2,523 sheets in TIF format illustrated various fabrication details throughout the structure. These fabrication drawings included many details not shown on the structural design drawings by Cantor, and they enabled a detailed review of the entire structural system. Again, conspicuously missing — for reasons unknown — were fabrication details of the floor girders spanning between columns 44 and 79. This information gap included floors 8 through 43.
Several researchers and I conducted a detailed review of the structural and fabrication drawings with a focus on the framing and connections surrounding the collapse-initiation area in the northeast quadrant. Then, in March 2012, I submitted a request to the NIST FOIA Office for information bearing on the following list of 10 questions and the decisions NIST made in relation to them. Due to the technical nature of the questions, this request was not processed through the FOIA Office, and it was not assigned a FOIA log number. Instead, the request was forwarded to the NIST Engineering Lab for a response. Specific questions are emphasized for clarity.
The Engineering Lab at NIST responded in June 2012 by publishing two additional FAQs (Frequently Asked Questions) and an updated errata file on its website. Except for questions 2, 3 and 8, these questions remain mostly unanswered.
- NCSTAR 1-9 states that the girder spanning between columns 44 and 79 at floor 13 lacked shear studs to provide composite action with the concrete floor slab,7 and this agrees with a partial framing plan included in the report.8 An article appeared in the Canadian Structural Engineering Conference Proceedings — 1986 describing the fabrication and construction of the steel structure.9 Figure 5 of this article clearly shows 30 shear studs equally spaced along the girder at typical floors including floor 13. How did NIST confirm that shear studs were in fact omitted from the girder at floor 13?
See FAQ 2710. NIST never confirmed the shear studs were omitted. Since the alleged collapse-initiation sequence depended entirely on the lack of shear studs, NIST should have confirmed the absence of shear studs, as prescribed in NFPA 92111. The author of the 1986 article, John J. Salvarinas, was the project manager for Frankel Steel Limited (one of the two steel fabricators) during the construction of WTC 7, so it is just as likely for the article to be correct as for the structural plans (with obvious inconsistencies as described in question 2 below) to be correct.
- Frankel Steel drawings E8/9 through E20 and E24 through E44/45 all note: "FOR ADDITIONAL STUDS SEE CUST. DWG. S8 REV. I." Cantor sheet S-8 released by the NIST FOIA office includes revision H but not revision I. Sheet S-8-10 revision I shows 30 shear studs on the girder. Sheet S-8-19 revision I shows an additional bottom flange plate on the girder and no shear studs on the W24 beams east of the girder. Sheet S-8-20 revision I shows 30 shear studs on the girder and an unidentified number of studs on the W24 beams. Was sheet S-8 revision I included in the construction documents for this building? What additional floor loading was present on floors 10, 19 and 20, and were these variations in loading and section properties included in the analytical models?
See FAQ 27. There are discrepancies in the structural drawings. It appears there were “revision I” sheets for specific floors (numbered S-8-xx) rather than one “S8 revision I” sheet for multiple floors. Although the additional floor loading was unknown, this does not preclude incorporating more robust section properties and shear studs clearly shown on the plans for specific floors.
- NCSTAR 1-9 Section 8.8 describes the partial-floor LS-DYNA model used to develop failure modes of floor framing and connections. The seated-beam connection shown in Figures 8-21 and 8-2312 was compared to Frankel Steel drawing 1091. This drawing illustrates the one-inch thick bearing plate was 12 inches long. Does the partial-floor model account for the full length of the bearing plate? Why does the 16-story ANSYS model account for only an 11-inch long13 bearing plate?
See June 2012 updates to the errata file (McAllister 2009)14. Frankel Steel drawings 1091 and 9114 show the bearing length to be 6.25 inches — not 5.5 inches — parallel to the girder. The errata file is inconsistent with the shop fabrication drawings.
- The seated-beam connection shown in Figures 8-21 and 8-23 was also compared to Frankel Steel drawing 9114. This drawing illustrates ¾-inch thick partial-height web stiffeners welded to the girder web and bottom flange. Fillet welds connecting the stiffeners were more than adequate to transfer the vertical shear from the girder web to the stiffeners. Why were these stiffeners omitted from the partial-floor model?
NIST did not respond to question 4.
- Thermal expansion caused erection bolts to shear off at each end of the girder. The elongated girder then contacted the column 79 flange in the partial-floor model15. The girder was then restrained from excessive lateral displacement by the column side plates. Figure 8-2716 appears to show the girder rotated but restrained between the column side plates. The girder was also restrained from excessive lateral displacement at column 44 by the column flanges as shown in Frankel Steel drawing 9102. How did lateral walk-off or rocking occur considering these restraints at both ends?
NIST did not respond to question 5.
- Table 8-217 lists observed failures in the partial-floor model, but lateral walk-off of the girder from its seat is not listed as an observed failure. How was walk-off verified as a possible failure mode if it was not observed in the partial-floor model?
See FAQ 28. NIST’s response included the following statement: “Results confirmed that possible failure modes included: lateral-torsional buckling of the wide flange shapes, bolt shear failure, stud shear failure, and the potential for the girder to walk off its seat at either column.” However, the predicted response of the system — according to Table 8-2 — did not include girder walk off.
- Table 8-2 shows that the northern floor beam (W21x44) buckled laterally before other beams buckled in the partial-floor model. Frankel Steel drawing E12/13 shows three W12x19 beams that laterally braced the W21 to the perimeter frame, but Figures 8-22 and 8-2719 indicate that the partial-floor model did not include these framing members. Why were these beams omitted when they obviously affect the buckling characteristics of the northern floor beam?
NIST did not respond to question 7.
- NCSTAR 1-9 has numerous references to walk off due to thermal expansion. One reference20 says the lateral walk off at columns 79 and 81 “…was monitored during the analysis.” How does the analytical model shown in Figure 11-1521 measure and monitor lateral walk off during the analysis?
See FAQ 28. NIST’s 16-story analysis included the use of special connection models and special-purpose scripts written in ANSYS Parametric Design Language to monitor relative displacements between column 79 and the W33x130 girder. These features of the analysis were not disclosed due to public safety concerns as revealed in FOIA #10-037, so their validity could not be verified.
- The ANSYS analytical model for the seated-beam connection at column 79 shown in Figure 11-1522 does not account for the presence of web stiffeners shown in Frankel Steel drawing 9114. A lateral displacement of 5 ½ inches23 would not cause a loss of vertical support with the stiffeners in place. The assumption that the girder flange would yield in flexure when the girder web moves past the edge of the bearing seat is incorrect. Why were these stiffeners omitted from the 16-story ANSYS model when they obviously affect the bending characteristics of the girder bottom flange?
NIST did not respond to question 9.
- Please describe or illustrate quantitatively the displaced shape (translation and rotation) and temperature of the girder cross section at each end and at intermediate points along the span where beams were attached on the east side for the ANSYS Case B 4.0-hour analysis. What were the axial forces (magnitude and direction) and temperatures in the five beams framing into the girder on the east side at this stage of the analysis?
NIST did not respond to question 10.
Conspicuously absent from the FAQs and the errata file is any mention of the stiffeners that were welded to the web and bottom flange of the critical girder at the bearing connection to column 79. As stated in NCSTAR 1-924, the loss of vertical support for this girder and its entire tributary floor area was assumed by NIST engineers based on the pretense of a bottom-flange flexural failure. The inclusion of the stiffener plates would have prevented this type of failure. Figures 1 and 2 below, which I had prepared in 201225, accurately depict the seated-beam connection at column 79 as detailed on the fabrication shop drawings. Note the stiffener plates on each side of the girder web. The figure above, taken from Hulsey et al. 202026 Figure 3.8 with permission, illustrates an ABAQUS model of the critical girder displaced more than six inches laterally with a stress distribution insufficient to cause a flange failure. Column 79 and its side plates are not shown for clarity.
There have been several other inquiries to NIST regarding the omission of the stiffeners, and these inquiries prompted two responses from non-technical NIST personnel attempting to justify the omission. (The NIST Engineering Lab was finally forced to issue a justification for the omission of the stiffeners in response to a request for correction to NCSTAR 1A and NCSTAR 1-9 that was submitted in 2020.) The inquiries and responses that pre-date the 2020 WTC 7 request for correction are discussed in the following FOIA DOC-NIST-2014-001436, which I submitted in July 2014.
On March 19, 2012 I requested all available public information under the control of NIST regarding ten questions related to the 7 World Trade Center (WTC 7) collapse initiation outlined in Chapters 8 and 11 of NIST NCSTAR 1-927. You forwarded my request to the Engineering Lab for a response, and the request was not assigned a FOIA log number. Most of my questions were never answered.
I recently learned that others with similar questions have received responses from NIST to two or more of the questions that were not answered in June 2012 when the WTC Investigation Team updated the errata file and FAQs for WTC 7. Does this mean new information was found or developed by NIST in the last two years?
The recent responses originated from Michael Newman in the Public and Business Affairs Office28 and from Jim Schufreider in the Congressional and Legislative Affairs Office29. These two responses are neither correct nor germane to the question of flange stiffness and strength—questions 4 and 9 in my letter dated 3/19/12, and they are invalid from the standpoint of a scientific inquiry into the collapse mechanism.
The bearing stiffeners shown on Frankel Steel drawing 9114 prevent flange local bending as well as web local yielding, web local crippling, and web sidesway buckling. The lateral walk-off and removal of critical framing members from the ANSYS model was assumed based on the pretense of a girder flange local bending failure;30 the stiffeners were therefore required to be included in the analysis.
I repeat my question and my request.
The ANSYS model for the seated-beam connection at column 79 shown in Figure 11-15 did not account for the presence of bearing stiffeners shown in Frankel Steel drawing 9114. A lateral displacement of 5 ½ inches32 or 6 ¼ inches33 would not cause a loss of vertical support with the stiffeners in place. NIST assumed that the girder flange would yield in flexure when the girder web moved past the edge of the bearing seat. Why were these stiffeners omitted from the 16-story ANSYS model when they obviously affect the bending stiffness and strength of the girder bottom flange?
I understand that you are not required to create a record that does not exist; I am requesting all available information in NIST's possession related to this question and the decisions that NIST has made in relation to it including written correspondence, meeting minutes, calculations, etc. If you decide to forward this to the Engineering Lab again, then I respectfully request a technical response signed by a licensed engineer qualified to address the question in a professional and scientific manner.
This inquiry is made for a scholarly purpose; it is not for any commercial use. Thank you for your consideration.
The NIST FOIA Officer responded to this request in September 2014 with a denial: “NIST has no documents that are responsive to your request.” I subsequently filed an appeal in October 2014 that included the following exhibits:
- Exhibit A: FOIA request DOC-NIST-2014-001436 dated 7/21/14
- Exhibit B: Final response letter from the FOIA Officer dated 9/22/14
- Exhibit C: Statement of the reason why the withheld records should be made available
- Exhibit D: Statement of the reason why denial of the records was in error
- Exhibit E: FOIA request letter dated 3/19/12
- Exhibit F: NIST response to Exhibit E dated 6/27/12 (updated FAQs and Errata file)
Statement (Exhibit C)
Why should the withheld records be made available? The simple answer is because — as a practicing structural engineer for over 28 years — I need to know what NIST engineers were thinking when they declared that ordinary office fires caused the complete collapse of the former 7 World Trade Center (WTC 7) on September 11, 2001. The NIST Engineering Lab has not been responsive to technical inquiries, so I have resorted to FOIA requests for information. My questions and conclusions about NCSTAR 1-9 have been drawn from my experience studying this report, related reports and construction documents for seven years since 2007.
My study is research-oriented and not speculative. I have no interest in simulating building collapses or devising ways to destroy buildings. It is important to emphasize this because the pervasive fear of terrorism following the September 11 attacks enables NIST to withhold structural-analysis data pursuant to 15 U.S.C. § 7306(d).
A detailed answer to the leading question above requires some background information about the specific technical question stated in Exhibit A:
Why were these stiffeners omitted from the 16-story ANSYS model when they obviously affect the bending stiffness and strength of the girder bottom flange?
This question arose early in 2012 while studying shop fabrication drawings of the building; it is related to a specific mode of failure at a specific location that triggered the initiation of collapse according to NCSTAR 1-9. As stated in Exhibit A and in NCSTAR 1-934, the subsequent loss of vertical support for a critical girder and its entire tributary floor area was assumed by NIST engineers based on the pretense of a bottom-flange flexural failure. The inclusion of stiffener plates, however, would have prevented this type of failure. Although the omission of stiffener plates from the analysis has been acknowledged — not justified — by NIST officials, the NIST engineers have refused to comment on this observation with any technical explanation whatsoever.
After obtaining original construction drawings of the building (from NIST through FOIA requests) and studying them for several months, I compiled a list of technical questions related to the collapse-initiation sequence discussed in Chapters 8 and 11 of NCSTAR 1-9. A FOIA request submitted to NIST in March 2012 (Exhibit E) sought information about the decisions NIST made in relation to the list of technical questions. This request was not assigned a FOIA log number, and it was not processed through the NIST FOIA office. Instead it was forwarded to the NIST Engineering Lab for a response. An incomplete response (Exhibit F) was received on 6/27/2012 in the form of addendums to the errata file35 and “Answers to Frequently Asked Questions” (questions 34 and 35).36 As you can clearly see for yourself, there was nothing about stiffeners in the response. When I brought this objection to the attention of the NIST Engineering Lab, the NIST FOIA Officer and the NIST Director, no one had the professional courtesy to respond. The lack of communication did nothing to bolster my confidence in the NIST study of WTC 7.
Others have submitted similar inquiries to NIST regarding the omission of the stiffeners within the last two years. These inquiries are discussed in Exhibit D, while the remainder of this exhibit focuses on a discussion of erroneous and misleading responses issued by NIST to two other inquiries. These statements by NIST officials were noted in Exhibit A, so the NIST FOIA Officer has no excuse for being unaware of them. They are quoted here again for your convenience.
Newman, M. (2013), “The web stiffeners shown at the end of the girder in Frankel drawing #9114 prevent web crippling. The structural analyses of WTC 7 did not show any web crippling failures. Therefore, the web crippling plates did not need to be included in the models/analyses.” (October 25).
Schufreider, J. (2014), “NIST detailed structural analysis of the girder in question indicated that web buckling did not occur under the combined effects of gravity loads and fire. Because there was no web buckling of Girder A2001, NIST did not consider the web stiffeners as a factor in the final NIST analyses.” (July 11).
As stated in Exhibit A, these two pseudo-technical responses are neither correct nor germane to the question of flange stiffness and strength, and they are invalid from the standpoint of a scientific inquiry into the collapse-initiation mechanism. Here is an analogy to illustrate my point.
Shear walls in a concrete frame building prevent excessive movement and damage in an earthquake. An analysis without these shear walls did not indicate excessive movement and damage or instability when the building was subjected to combined gravity and seismic loading. The walls, therefore, did not need to be included in the analysis.
This analogy and the preceding responses by NIST officials are incorrect from an analytical perspective. The shear walls provide stiffness and strength as they redistribute static and dynamic forces in the building system. Stiffeners in the connection of girder A2001 to column 79 provided stiffness and strength to redistribute static forces on the bearing plate, and they prevented a local bending failure of the bottom flange as the girder moved laterally as discussed in NCSTAR 1-9. Increased stiffness provides increased resistance to load and deformation. One cannot simply ignore stiff structural elements and hope to obtain a correct analysis. Ignoring the effects of stiffeners in a critical connection is wrong.
Web crippling, web buckling and flange bending are three different responses to concentrated forces at the end of a girder. The Public Affairs Officer and the Director of the Congressional and Legislative Affairs Office at NIST are obviously not qualified to address this question, and they have issued erroneous and misleading claims to members of the public. I urge you to seek professional opinion from qualified engineers who are not affiliated with NIST or the Department of Commerce.
Were the NIST engineers who conducted the study of WTC 7 aware of these responses? Do they agree with these responses? The Engineering Lab never acknowledged or responded to my questions regarding the stiffeners in 2012 (Exhibit E). Any record of communication between parties regarding this issue should be made available to the public to clarify any misconceptions. All public inquiries related to this question and corresponding NIST responses should also be made available.
Statement (Exhibit D)
Why was denial of records in error? The simple answer is because the NIST FOIA Officer stated incorrectly in Exhibit B that “NIST has no documents responsive to your request.” My request was for all available information in NIST's possession related to this question and the decisions that NIST has made in relation to it. This question refers to the question in Exhibit A:
Why were these stiffeners omitted from the 16-story ANSYS model when they obviously affect the bending stiffness and strength of the girder bottom flange?
I am aware of multiple inquiries and responses to inquiries in NIST's possession — including my own — that relate to the question of omission of stiffeners from the analysis of a specific critical connection.
- FOIA request (inquiry) from Ronald H. Brookman to NIST dated 3/19/12 (Exhibit E).
- E-mail response from Ronald H. Brookman to the NIST WTC Investigation team, Director Patrick Gallagher and FOIA Officer Catherine Fletcher dated 7/1/12. This included the question “What about the 3/4-inch stiffeners (questions 4 and 9)?” that was not addressed in NIST's response to Exhibit E on 6/27/12.
- E-mail inquiry from David Cole to Michael Newman at NIST dated 7/26/13. In this inquiry Mr. Cole asked: “Given that Frankel drawing #9114 shows ¾" web/flange stiffeners installed on the girder at the 13th floor column 79 connection, why weren't the stiffeners reported in NCSTAR 1-9 and shown in the figures listed above?”
- Michael Newman's e-mail response to David Cole (see Exhibits A and C) dated 10/25/13.
- Response letter from Jim Schufreider at NIST to Ms. Madeline Peare in the office of U.S. Senator Barbara Boxer dated 7/11/14. This letter from Mr. Schufreider refers to a letter from Eric Jose Vizcaino dated 5/20/14 and another letter from Mark Graham (no date given).
The Office of the General Counsel (OGC) at the U.S. Department of Commerce denied the Appeal on June 25, 2015 — approximately 180 working days after it was filed — upholding the FOIA Officer’s determination that “NIST has no documents that are responsive to your request.”
NIST employs numerous scientists, engineers, technicians, and support and administrative personnel, yet — according to the OGC and the NIST FOIA Office — no one at NIST had any record of correspondence regarding the omitted stiffeners. Furthermore, the acting Assistant General Counsel was satisfied that a thorough search for records was done by the NIST FOIA Office after one technical member of the Engineering Lab searched their files. Anyone reading the subject Appeal knows this is not an adequate search. Exhibit D of the Appeal lists multiple records responsive to request DOC-NIST-2014-001436. I’m sure there are others.
In conclusion: Crucial structural information was omitted from NCSTAR 1-9 without explanation, and NIST’s collapse-initiation sequence reported for WTC 7 was based on speculation. See Hulsey et al. 2020 Chapter 3.0 for the University of Alaska Fairbanks (UAF) evaluation of NIST’s collapse-initiation hypothesis. The UAF study clearly shows that inclusion of the web stiffeners prevents lateral walk off.
In response to the 2020 WTC 7 request for correction, the NIST Engineering Lab finally offered a justification for the omission of the web stiffeners — a variation on the erroneous and misleading responses issued by non-technical NIST personnel. This new justification will be addressed in a subsequent article dissecting NIST’s response to the WTC 7 request for correction.
NIST has work to do to correct the NCSTAR reports. The question is how and when it will be compelled to do so.
1 S. Shyam Sunder et al., NIST NCSTAR 1A, Final Report on the Collapse of World Trade Center Building 7, Washington: U.S. Government Printing Office, November 2008.
2 Therese P. McAllister et al., NIST NCSTAR 1-9, Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7, Washington: U.S. Government Printing Office, November 2008.
3 Robert MacNeill et al., NIST NCSTAR 1-9A, Global Structural Analysis of the Response of World Trade Center Building 7 to Fires and Debris Impact Damage, Washington: U.S. Government Printing Office, November 2008.
4 S. Shyam Sunder et al., NIST NCSTAR 1, Final Report on the Collapse of the World Trade Center Towers, Washington: U.S. Government Printing Office, September 2005, Section E.2, p. xxxvii.
5 Gallagher, Patrick (2009), "Findings Regarding Public Safety Information", NIST, July 9.
6 Kollar-Kotelly, Colleen (2011), "Memorandum Opinion, Michael Quick v. U.S. Dept. of Commerce, NIST", Civil Action 09-02064 (CKK), U.S. District Court for the District of Columbia, April 7.
7 McAllister et al., p. 342.
8 McAllister et al., p. 343. This is taken from Cantor sheet S-8 revision H dated 8/5/85.
9 John J. Salvarinas, ''Seven World Trade Center, New York, Fabrication and Construction Aspects,'' Canadian Structural Engineering Conference Proceedings—1986, (Canadian Steel Construction Council, Willowdale, Ontario, 1986), pp. 11-1 - 11-44.
10 https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-7-investigation. See items 27 and 28 which were originally numbered 34 and 35.
11 Technical Committee on Fire Investigations, “NFPA 921 Guide for Fire and Explosion Investigations, 2001 Edition”, National Fire Protection Association, Inc., Quincy, MA.
12 McAllister et al., pp. 349 and 351.
13 McAllister et al., p. 527.
14 McAllister, Therese P. (2009) Errata for NIST NCSTAR 1A, NIST NCSTAR 1-9, and NIST NCSTAR 1-9A, Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7, January 30. Updated June 27, 2012.
15 McAllister et al., p. 352.
16 McAllister et al., p. 354.
17 McAllister et al., p. 353.
18 McAllister et al., p. 359.
19 McAllister et al., pp. 350 and 354.
20 McAllister et al., p. 482.
21 McAllister et al., p. 483.
22 McAllister et al., p. 483.
23 McAllister et al., p. 482.
24 NCSTAR 1-9, p. 488. "Gravity shear loads in a beam were transferred to the bearing seat primarily in the proximity of the web on the bottom flange. Therefore, when the web was no longer supported by the bearing seat, the beam was assumed to have lost support, as the flexural stiffness of the bottom flange was assumed to be insufficient for transferring the gravity loads. Under such conditions, the beam was removed." [Emphasis added.]
25 Brookman, Ronald H., A Discussion of “Analysis of Structural Response of WTC 7 to Fire and Sequential Failures Leading to Collapse”, Journal of 9/11 Studies, Volume 33, October 2012.
26 Hulsey, J.L., Quan, Z., and Xiao, F., 2020. A Structural Reevaluation of the Collapse of World Trade Center 7 – Final Report. Department of Civil and Environmental Engineering, College of Engineering and Mines, Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, AK, INE Report 18.17, 112 pp.
27 Therese P. McAllister et al., NIST NCSTAR 1-9, Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7, Washington: U.S. Government Printing Office, November 2008.
28 Michael Newman, Public Affairs Officer. "The web stiffeners shown at the end of the girder in Frankel drawing #9114 prevent web crippling. The structural analyses of WTC 7 did not show any web crippling failures. Therefore, the web crippling plates did not need to be included in the models/analyses." October 25, 2013.
29 Jim Schufreider, Director, Congressional and Legislative Affairs Office. "NIST detailed structural analysis of the girder in question indicated that web buckling did not occur under the combined effects of gravity loads and fire. Because there was no web buckling of Girder A2001, NIST did not consider the web stiffeners as a factor in the final NIST analyses." July 11, 2014.
30 McAllister et al., p. 488. "Gravity shear loads in a beam were transferred to the bearing seat primarily in the proximity of the web on the bottom flange. Therefore, when the web was no longer supported by the bearing seat, the beam was assumed to have lost support, as the flexural stiffness of the bottom flange was assumed to be insufficient for transferring the gravity loads. Under such conditions, the beam was removed."
31 McAllister et al., p. 483.
32 McAllister et al., p. 482.
33 McAllister, Therese P. (2009) Errata for NIST NCSTAR 1A, NIST NCSTAR 1-9, and NIST NCSTAR 1-9A, Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7, January 30. Updated June 27, 2012.
34 NCSTAR 1-9, p. 488. "Gravity shear loads in a beam were transferred to the bearing seat primarily in the proximity of the web on the bottom flange. Therefore, when the web was no longer supported by the bearing seat, the beam was assumed to have lost support, as the flexural stiffness of the bottom flange was assumed to be insufficient for transferring the gravity loads. Under such conditions, the beam was removed." [Emphasis added.]
35 McAllister, Therese P. (2009) Errata for NIST NCSTAR 1A, NIST NCSTAR 1-9, and NIST NCSTAR 1-9A, Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7, January 30, updated June 27, 2012.
36 https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-7-investigation. See items 27 and 28 (originally numbered 34 and 35.)