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Right Walkway — Cantilever Support Study

Status: ADOPTED (rev12) — decision record. The right walkway is now the wall-/IBC-cantilevered design; the ceiling-hung scheme it replaced is retired. The as-built version (refined into a closed cantilever rectangle) is in Walkway Report §4; this page records why the change was made and the first-order load check behind it.

1. Why

The right walkway was originally ceiling-hung — five M10 rod-pairs from the deck up to the roof. The film-plane rework (wall-seat saddles, rails now running the full width) exposed a conflict: those vertical rods sit in the film plane's X-footprint (X4329–4629 ⊂ X150–4649) and in the volume the tilting plane sweeps — the plane's right corner reaches Yd1760 at 28° swing and Yd1575 at 40° tilt, colliding with the hangers at Yd1828/1371 — plus the rods sit in the optical band (shadow risk). See Film Plane Report and the corner analysis.

Key insight: the deck itself was never the problem — it sits at Z130, tucked under the film-frame bottom (Z150). Only the vertical rods intrude. Remove the rods and the film-plane conflict disappears, with no reduction in film size and the same swing range on both sides.

2. The clearance that makes this possible now

The earlier design went ceiling-hung because there was thought to be no room for floor/wall support. That changed:

Element Z Note
Tray rim 50
Spray-bar gantry (top) ~54–85 Ø32 wheels + 40×25 SS beam, rides the raised/sloped floor — low
Clear band under the grate ~30mm (worst, far-left) see Walkway Routing Sections §H-H
Walkway grate 115–130
Film-frame bottom rail 150 deck clears it by 20mm

Plus a 45mm gap (X4629–4674) between the tray's right edge and the IBC frame face. So there's now both vertical and horizontal room the old layout lacked.

3. The design — hybrid anchor (IBC frame + side walls)

As-built (rev12): refined into a closed cantilever rectangle — see Walkway Report §4. The support strategy below is what was built: cantilever off the IBC frame + wall anchors, no ceiling rods.

The IBC stacking frame only has uprights at the corridor (Yd 1046 / 1266, at X4654) — there is nothing at the perimeter (Yd0 / 2362) to bolt to. So the support is split:

  • 2 inner cantilever arms — off the IBC corridor uprights (X4654, deep-box front upright). A U-clamp grips each upright with 2× M12; the arm (40×40 SHS) reaches ~325mm back to the deck's left edge (X4329).
  • 2 outer wall-mounted ledgers — on the near (Yd0) and far (Yd2362) container walls, each through-bolted (interior + exterior plate, 2 bolts) at 2 X stations along the deck width. These carry the deck's ends, where the frame can't reach.
  • 2 longitudinal bearers (Yd-running, at X4329 + X4629) ride the arms + ledgers; the grate spans the ≤1,046mm between supports.
  • All members sit at Z70–115 — ~10mm above the spray-bar top at the (low-side) cantilever stations, below the film frame (Z150). No ceiling rods. Nothing into the tray. Nothing in the optical band above the deck.

3D study model: src/models/generate_right_cantilever_study.py (scenes: Combined / Anchors (frame + walls) / Clearance / Labeled — the Anchors scene shows both the upright U-clamps and the wall ledgers).

4. Load check (first-order — favorable)

Quantity Value Notes
Deck self-weight ~0.45 kN right walkway ≈ 46 kg (Weight Dist. §3.2)
Live load (one person) 1.0 kN ~100 kg
Worst cantilever arm 325mm person at the far deck edge, over one arm
Worst single-arm moment ~0.33 kN·m 1.0 kN × 0.325 m (conservative; normally shared 2 arms)
Arm bending stress (40×40×3 SHS, Z≈4.0 cm³) ~81 MPa vs 250 MPa yield → SF ≈ 3 (upsize to 50×50 for SF≈5)
Added stress on IBC upright (50×50×3, Z≈7.9 cm³) ~41 MPa small vs the frame's stack duty
Anchor bolt force (2 bolts @ ~100mm) ~3.3 kN/bolt vs ~15–20 kN M12 capacity → SF ≈ 5

The IBC frame already carries the 2×2 IBC stack and is anchored to floor + walls; the added ~0.33 kN·m cantilever is minor. Recommend a structural sign-off on the gusset connection, but first-order it's comfortable.

5. What it resolves / what stays separate

Resolved: the film-plane ↔ walkway conflict (no rods in the sweep or optical band); film plane keeps full width (X150–4649) and the same tilt/swing range on both sides; ceiling de-cluttered on the right.

Resolved as follow-ups (rev12): the chem prep shelf was moved left of the tap (X3129–3729 / Yd300–600) to clear the film-plane swing envelope, and the sump pickup + tray-drain plumbing return riser was rerouted into the grate gap with a Yd twist to clear the new right-walkway beam.

6. Comparison

Ceiling-hung (former) Cantilever off IBC frame (adopted, rev12)
Rods in film-plane sweep / optics yes (the conflict) none
Forces film-size reduction? (else yes) no — full width, symmetric swing
Tray / spray-bar intrusion none none (arms at Z70–115, above the gantry)
Adds load to roof ribs IBC frame (2 inner arms) + near/far walls (2 ledgers); minor — needs connection sign-off
Cost 5 rod-pairs + 10 roof plates 2 arms + 2 wall ledgers + clamps/bolts (≈ neutral)

7. Implementation (rev12 — complete)

Adopted and built per Walkway Report §4: the cantilever rectangle replaced the ceiling hangers in the walkway + overview 3D models, the 2D walkway diagram + component-dependency-map were updated, and the BoM/cost and weight models were rebased (ceiling-hanger hardware → cantilever arms/gussets — roughly neutral). The chem-shelf shift and sump reroute followed (§5).

8. See Also