Wtc 7 what was in it

The secondary conclusion of our study is that the collapse of WTC 7 was a global failure involving the near-simultaneous failure of every column in the building.

Project Info Lead Researcher s J. Project Summary This is a study of the collapse of World Trade Center Building 7 WTC 7 — a story building that suffered a total collapse at PM on September 11, , following the horrible events of that morning. For 4 weeks receive unlimited Premium digital access to the FT's trusted, award-winning business news. Digital Be informed with the essential news and opinion.

Delivery to your home or office Monday to Saturday FT Weekend paper — a stimulating blend of news and lifestyle features ePaper access — the digital replica of the printed newspaper. Team or Enterprise Premium FT. Pay based on use. Does my organisation subscribe? NIST protected the integrity of the original videos at all times. Many of these videos are available online. For the WTC 7 story model for structural response to fire effects, why did NIST model the girders without shear studs, given that articles published in the open literature showed drawings of typical floor framing plans of WTC 7 with shear studs on the girders?

The source documents used for developing the structural analysis models of WTC 7 were the structural drawings prepared by the structural engineer of record Irwin G. Cantor, Structural Engineers and the erection drawings prepared by the steel fabricator and erector Frankel Steel Limited. A structural drawing showing modifications to Floor 10 Structural Drawing S to accommodate increased floor loads in certain areas did indicate shear studs for the girders in the affected areas, though the additional load was not identified on the drawing.

The modification also indicated reinforcing some floor connections and adding new plates on the bottom flanges of some north and south floor beams. A paper by J.

Salvarinas that was published in the Canadian Structural Engineering Conference Proceedings contained "Figure 5 - Typical Floor Framing" that showed shear studs on the girders, although no reference was cited for the information presented in the figure. The number of shear studs indicated on the floor plan by Salvarinas is similar to, but not exactly the same as, the number of studs indicated on the modified framing plan for floor For typical floors 8 to 20 excluding floor 10 , both structural and erection drawings of WTC 7 obtained by NIST are not consistent with Figure 5 in the Salvarinas paper.

What was the purpose of the partial floor model of the northeast section of WTC 7 Section 8. How were these analyses used in the final WTC 7 story model? Were there any discrepancies between the results of the partial floor model and the story model? The detailed finite element model of the partial northeast floor framing was developed to evaluate its response to elevated temperatures and to confirm which failure modes needed to be accounted for in the story ANSYS model, i.

This detailed model consisted of shell elements to model the steel wide flange sections and plates and the concrete floor slab, and the model was capable of capturing both local and overall member buckling. Shear studs were modeled explicitly as were bolts. Contact interfaces were employed between different components to model, for example, the girder resting on the seats at both column 44 and column Temperature-dependent material properties were defined and appropriate boundary conditions were prescribed.

Gravity loads were applied to represent service loads and uniform, monotonically increasing temperatures were applied to the floor beams and girder, to cause both thermal expansion and degradation of mechanical properties. 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.

Differences between the results of the partial floor model and the story model are to be expected. Reasons for these differences include:. What improvements to building safety have been recommended as a result of the WTC 7 investigation? NIST made one new recommendation and reiterated 12 recommendations from its investigation of the collapses of the WTC towers. The new recommendation involves explicitly evaluating buildings to ensure the adequate fire safety performance of the structural system.

Of particular concern are the effects of thermal expansion in buildings with one or more of the following characteristics:. Typical floor span lengths in tall office buildings are in the range of 40 feet to 50 feet. This range is considered to represent long span floor systems. Thermal effects e. The earlier recommendations encompass increasing structural integrity of buildings, enhancing structures' endurance when exposed to fire, creating new methods for increasing fire resistance in structures, improving active fire protection, improving some aspects of emergency response, and increasing education and training.

Are there hundreds or thousands of unsafe tall buildings with long span supports that must be retrofitted in some way? How would one retrofit a building to prevent this problem? While the partial or total collapse of a tall building due to fires is a rare event, NIST strongly urges building owners, operators, and designers to evaluate buildings to ensure the adequate fire performance of structural systems.

Of particular concern are the effects of thermal expansion in buildings with one or more of the following characteristics: long-span floor systems, connections that cannot accommodate thermal effects, floor framing that induces asymmetric forces on girders, and composite floor systems, whose shear studs could fail due to differential thermal expansion i. Engineers should be able to design cost-effective fixes to address any areas of concern identified by such evaluations.

Several existing, emerging or even anticipated capabilities could have helped prevent the collapse of WTC 7. The degree to which these capabilities improve performance remains to be evaluated. Possible options for developing cost-effective fixes include:. NIST is recommending that building standards and codes be strengthened beyond their current intent to achieve life safety to prevent structural collapse even during infrequent building fires like those in WTC 7 when sprinklers do not function, do not exist or are overwhelmed by fire.

Some people have said that a failure at one column should not have produced a symmetrical fall like this one. What is NIST's answer to those assertions? WTC 7's collapse, viewed from the exterior most videos were taken from the north , did appear to fall almost uniformly as a single unit.

This occurred because the interior failures that took place did not cause the exterior framing to fail until the final stages of the building collapse. The interior floor framing and columns collapsed downward and pulled away from the exterior frame. There were clues that internal damage was taking place prior to the downward movement of the exterior frame, such as when the east penthouse fell downward into the building and windows broke out on the north face at the ends of the building core.

The symmetric appearance of the downward fall of WTC 7 was primarily due to the greater stiffness and strength of its exterior frame relative to the interior framing. In a video, it appears that WTC 7 is descending in free fall, something that would not occur in the structural collapse that you describe.

How can NIST ignore basic laws of physics? In the draft WTC 7 report released Aug. This time period is 40 percent longer than the 3. During the public comment period on the draft report, NIST was asked to confirm this time difference and define the reasons for it in greater detail. To further clarify the descent of the north face, NIST recorded the downward displacement of a point near the center of the roofline from first movement until the north face was no longer visible in the video.

Numerical analyses were conducted to calculate the velocity and acceleration of the roofline point from the time-dependent displacement data. The instant at which vertical motion of the roofline first occurred was determined by tracking the numerical value of the brightness of a pixel a single element in the video image at the roofline.

The analyses of the video both the estimation of the instant the roofline began to descend and the calculated velocity and acceleration of a point on the roofline revealed three distinct stages characterizing the 5. This analysis showed that the 40 percent longer descent time—compared to the 3. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below.

This is consistent with the structural analysis model, which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. However, the final NIST report downplays both scenarios, concluding that the diesel fuel stored in tanks and intended to power backup generators did not burn long enough or hot enough to account for structural failures. And, while debris damage to WTC 7's southern exterior was considerable and initiated the destructive fires , the collapse originated in the northeast portion of the building.

In fact, the report concludes: "Even without the structural damage, WTC 7 would have collapsed from fires. The report determines that the actual culprit in the collapse was the combustion of ordinary building furnishings: "These uncontrolled fires had characteristics similar to those that have occurred previously in tall buildings. A key factor in the collapse, NIST concluded, was the failure of structural "connections that were designed to resist gravity loads, but not thermally induced lateral loads.

Spurred by conspiracy theorists' questions, investigators did look specifically at the possibility that explosives were involved. NIST's press release and other material on the report can be found here. Click here to download the full report in pdf form.