# WTC6 upper steel: local evidence and corrected levels

26 September 2026. Source review only; model implementation belongs to the integration worker. No archive messages or orders were sent.

## New concrete findings

The positively titled Custom House EL-1 and EL-2 elevator sheets contain **actual local upper steel evidence**, even though a complete upper-floor framing plan remains unacquired. EL-2 shows two overhead beam axes in the northwest service-elevator C9 machine room, plus trolley/hoist beams in the southeast C10 and passenger-elevator sections. These justify a source-detail reconstruction with representative I-sections. They do not identify the entire upper column grid or the steel member schedule.

The high-resolution EL-2 review also corrects three earlier elevation readings:

| Level | Exact source elevation | Previous reading |
|---|---:|---:|
| Eighth floor | **413 ft 6 in** | 415 ft |
| Finished machine-room floor | **430 ft 6 in** | 430 ft |
| Local bulkhead roof | **440 ft 6 in** | 440 ft |

The eighth-floor correction is independently supported by the **13 ft 6 in** dimension above seventh-floor EL400 in both service-elevator sections. Passenger section C-C agrees. First through seventh remain EL310, 332, 352, 364, 376, 388 and 400. The service machine platform is EL431 ft 6 in. These are source datums, not a statement of uniform whole-building roof or equipment-floor extent.

Source: `sources/PANYNJ-12673-WTC.pdf`, one-based PDF706/EL-1 and PDF707/EL-2. EL-2 is titled *U.S. Custom House — Elevator Sections & Service Elevator Machine Room Plans*, contract date6December1968, with1992receivedstamp. Original SHA256 is preserved in the JSON.

## Actual local beams

| Detail | What is supported | Limit |
|---|---|---|
| Northwest service C9 plan | Two labelled overhead beam-axis strips, **7 ft clear to underside** above finished machine floor; underside **EL437 ft 6 in** | Profiles, support endpoints and site placement are not scheduled |
| Southeast service C10 section B-B | Trolley beam, **7 ft 8½ in** clearance; underside **EL438 ft 2½ in** | Plan axis not uniquely assigned in this review |
| Passenger section C-C | Trolley beams, **7 ft 4½ in** clearance; underside **EL437 ft 10½ in** | Plan axes not uniquely assigned in this review |

[Annotated C9 source](wtc6-upper-evidence-20260926/c9-hoist-beam-annotated.png) shows the two recoverable plan axes. The C9 room has written dimensions **10 ft 11¼ in ×21 ft 8 in**; its width is not10ft1¾in. The JSON records approximate room-local axes at0.78ft and9.88ft from the room's inside left edge. Displayed spans are bounded by the dimensioned room; the actual beam support center/end positions are unspecified. Allow about±0.2ft for these local drawing-axis readings. A representative I-section should be anchored at its source underside, with section depth identified as a visual choice.

The existing SKA55 plaza shaft zones provide contextual shaft locations, but they do not independently fix the upper machine-room orientation or offsets. EL-1 is an elevator layout rather than a building-wide survey drawing. Therefore the recovered C9 beams should first be shown in a **local source-detail inset**. Do not assign these approximate axes to a supposedly verified global position or turn the surrounding machine-room walls into new verified steel columns.

Review assets preserve complete EL-1/EL-2 renders, uncropped title-bearing sheets, level-label crops, width dimensions and the annotated C9 plan. No source PDF was edited.

## WTC6-specific perimeter-frame evidence

[Hamburger and Whittaker, *Modern Steel Construction*, March2004](https://www.aisc.org/globalassets/modern-steel/archives/2004/03/2004v03_blast.pdf), PDF2, expressly describes **one-bay moment frames around WTC6's perimeter**. Hamburger participated in the FEMA/ASCE building assessment; the author's related2006 [AISC Higgins paper](https://www.aisc.org/globalassets/aisc/awards/tr-higgins/past-winners/alternative-methods-of-evaluating-and-achieving-progressive-collapse-resistance.pdf), PDF4/Figure5, likewise identifies approximate frame locations on a damage photograph. This supports the structural-system type independently of copying WTC5. It gives no dimensioned bay coordinates or WTC6 member schedule.

The official web-reader text was acquired. Original binary and screenshot requests returned403; **the actual AISC figure was not visually inspected or traced**. The paper's approximate overlay therefore supplies no accepted geometric coordinates here. Its2006date is corroborated by the [official award listing](https://www.aisc.org/awards-and-honors/awards-and-honors/tr-higgins-lectureship-award/).

## Photographs and whole-upper reconstruction limits

The locally acquired [FEMA403Chapter4](https://www.fema.gov/pdf/library/fema403_ch4.pdf), PDF8/Figures4-8,4-9 andPDF9/Figure4-10 were visually inspected. The aerial photograph corroborates the stepped WTC6 outline; the damaged facade shows surviving multistory exterior structure. Damage, debris and perspective prevent a complete intact member count or setback measurement. Photographs are corroboration, not a replacement framing plan.

FEMA's detailed framing discussion principally concerns WTC5 and assumes applicability to its neighbors while warning that configurations differ. Its W27pairs, W16beams, column trees and15ftcantilevers must retain analogy status for WTC6. The paper's explicit WTC6 perimeter-frame type is a useful additional constraint, but unsupported continuations, interior beam arrangements, floor perimeters, sizes and connections still require provisional labels.

A useful next whole-building input remains the Custom House drawing index and upper/roof framing sheets in State Archives21693, MichiganMS2010-5/project6211 or PR415FilesU. Those retrieval leads are already documented; this pass did not reacquire or falsely claim the repository-held folder list.

[Machine-readable constraints and asset hashes](wtc6-upper-constraints-20260926.json)