Walkway System

1. Purpose

The perimeter walkway provides dry-foot operator access around all four sides of the processing tray without wading through chemical solution. It serves four access functions:

• Near walkway (pinhole wall side) — access to electrical panel, battery bank, spray-bar, tilt-swing adjusters, and valve manifold.
• Far walkway (film plane wall side) — access to film plane carriage clamps, rail end-stops, and far-side spray bar pole slot.
• Left walkway (cargo door end) — access to hinged light-trap panel latches and revolving drum. Removable for panel transport.
• Right walkway (IBC end) — access to IBC valves, filter skid, and pump manifold. Carried on a cantilever rectangle off the IBC frame to clear the IBC stack below.

All four sections share a common 130mm deck height (115mm bracket arm, L-angle, or floor-leg arm + 15mm grating) and 300mm standard width, creating a level perimeter walking surface. There are two sections that punch out to allows easier access of the lightrap and around the battery stack.

The design enforces zero processing tray contact — all walkway supports are either wall-mounted, carried on the cantilever rectangle off the IBC frame, or placed outside the tray footprint. This prevents chemical contamination of walkway structures and avoids disrupting the tray's watertight seal.

Interactive 3D model — the four removable grated sections, the wall-cantilevered near/far brackets (with exterior reinforcing plates + M12 through-bolts), the right walkway on its cantilever rectangle (closed 40×40 SHS frame on 2 center arms off the IBC frame, with combined corner plates shared with the bottom film rail), the removable left lift-out grate on 5 floor-leg cantilever brackets (posts on bare floor outside the tray, arms cantilevering over it), and the processing tray, inside a ghost of the container. Drag to orbit, scroll to zoom.

TBS-001 Walkway Model by alvin91403 on Sketchfab

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2. System Specifications

Parameter	Value
Standard walkway width	300mm
Deck height (floor to grate top)	130mm (raised +50 to clear the floor-level spray bar)
Grating	15mm molded GRP (fiberglass), vinyl-ester, grit top (thin grate, lowered deck; corrosion-proof in the chemistry zone)
Grating bearing bars	15×3mm at 34.2mm pitch
Bracket arm height	115mm above finished floor
Bracket spacing (near/far)	457mm (18") — aligned to container rib spacing
Container rib spacing	457mm (18") — ISO standard corrugation pitch
Near walkway widened section	500mm at X≈1,155–2,629mm
Open processing area	3,859×1,762mm = 6.80 m²
Spray bar slit width	30mm (near and far walkways)
Total walkway sections	4 (all removable)

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3. Near and Far Walkways — Wall-Cantilevered

The near (pinhole wall) and far (film plane wall) walkways run the full length of the processing tray zone, from the left walkway butt joint at with the left and right walkways.

3.1 Cantilever Bracket Design

Each bracket is a three-piece welded 8mm steel plate assembly:

Component	Dimensions	Function
Vertical mounting plate	8×150mm (height), flat against wall rib	Bolted to container corrugation rib interior face
Horizontal arm	8mm plate, 300mm cantilever (500mm in widened zone)	Supports grating
Triangular gusset	Right triangle, 70mm reach from wall	Braces arm from below; reach stops before tray rim

Attachment: 3× M12 through-bolts per bracket in a triangular pattern, passing through the full wall assembly: hex head → reinforcing plate (6mm) → exterior panel (1.6mm Corten) → air gap → rib interior face (1.6mm) → bracket vertical plate (8mm) → nut. Two lower bolts straddle the 8mm gusset plate at ±27mm from the plate centerline in X (centered between plate edge and gusset). One upper bolt (just above the bracket arm, near the top of the mounting plate) is centered on the gusset centerline. The container corrugation ribs are hollow — each bolt bridges the air gap inside the rib. A 6mm reinforcing plate (100×180mm) is welded to the exterior panel face to provide a bearing surface for the bolt heads and washers. See View B for the bolt pattern detail.

Spacing: Brackets mount at every container rib — 457mm (18") centers.

3.2 Near Walkway Widened Section

The near walkway widens from 300mm to 500mm, extending past the spray bar slit to the next rib position. This widened section provides additional standing room in front of the electrical panel, battery bank, and through the spray bar slit zone. These wall-mounted equipment items require front access for operation and maintenance, and the wider platform gives the operator full-width standing room during spray bar passes.

Four brackets in this zone use a heavier design to support the 500mm cantilever arm. The bracket positions align to container corrugation ribs. Extending the widened zone past the slit ensures 500mm-arm brackets support the grating on both sides of the slit, eliminating unsupported overhang.

Parameter	Standard bracket	Widened bracket
Plate thickness	8mm	10mm
Vertical leg height	150mm	200mm
Arm reach	300mm	500mm
Gusset reach	70mm	70mm (tray rim constrained)
Bolt pattern	3x M12 triangular (2+1)	4x M12 rectangular (2+2)
Reinforcing plate	100x180x6mm	120x220x6mm

The gusset reach remains 70mm on both bracket types — limited by the processing tray rim. The widened bracket compensates with heavier plate, taller vertical leg for greater wall engagement, and the additional bolt for higher moment capacity.

Attachment: 4× M12 through-bolts per bracket in a rectangular pattern, passing through the full wall assembly: hex head → reinforcing plate (6mm) → exterior panel (1.6mm Corten) → air gap → rib interior face (1.6mm) → bracket vertical plate (10mm) → nut. Two lower bolts straddle the 10mm gusset plate at ±32mm from the plate centerline in X (centered between plate edge and gusset). Two upper bolts (30mm above the grating deck) at the same ±32mm X offset. The container corrugation ribs are hollow — each bolt bridges the air gap inside the rib. A 6mm reinforcing plate (120×220mm) is welded to the exterior panel face to provide a bearing surface for the bolt heads and washers. See Sheet 7, View B for the bolt pattern detail.

Width transition: At the two transition brackets, the grating changes from 300mm to 500mm width (or vice versa). Both the narrow and wide grating sections rest on the same 500mm bracket arm. A 40×500×5mm flat bearing plate is welded to the bracket arm top surface at each transition, providing a wider landing surface so both grating sections have adequate bearing. The narrow section occupies the inner 300mm of the plate; the wide section occupies the full 500mm. Stainless hold-down clips retain each grating section independently on either side of the transition.

3.3 Spray Bar Slit

A 30mm wide slot is cut through both near and far walkway grating at the beam center X position, providing clearance for the spray bar telescoping pole to pass through the walkway during processing operations.

On both walkways, the slit extends from the inner walkway edge inward only to the processing tray lip — not the full walkway depth. The remaining grating between the tray lip and the wall stays solid, maintaining structural continuity across the slit.

Walkway	Inner edge (Yd)	Tray lip (Yd)	Slit depth	Solid remaining
Near (widened)	500mm	80mm	420mm	80mm
Far (standard)	2,062mm	2,280mm	218mm	82mm

See Processing Tray & Spray Bar for pole assembly details.

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4. Right Walkway — Cantilever Rectangle

The right walkway at the IBC end cannot use wall-cantilevered brackets because the IBC stack occupies the floor below.

4.1 The Cantilever Rectangle

A closed rectangular frame of 40×40×3mm SHS sits directly under the deck:

• Two long beams run the full container width, with the 300mm grating spans between them.
• Two short end beams (≈300mm) close the near and far ends, joining the long beams into a torsionally stiff closed rectangle (no free bearer ends to droop).

4.2 Center Cantilever Arms

Two 40×40×3mm SHS arms cantilever inward off the IBC corridor uprights and pick the rectangle up at mid-span. Each arm is half-lapped (cross-halved) where the long beams cross it, so the beams seat down into the arm and the two members share a flush top face. The arms carry the central span that the corner supports alone would leave to sag; the rectangle bounces well under the design footfall (≈0.35 kN·m peak moment at the arm root — see the cantilever study).

4.3 Corner Supports

Corner	Support	Fixing
Left, near + far	Wall cleat — 8mm steel back-plate + exterior reinforcing plate + a shelf the long beam lands on	M12 through-bolts (sandwich the wall, sealed)
Right, near + far	Combined corner plate — a single 10mm plate that carries BOTH the walkway right beam AND the bottom film rail (BR/TR)	4× M12, permanently bolted (interior + exterior plate sandwich the wall)

The combined corner plate is the key coupling: the walkway's right long beam and the film plane's bottom (and top) rail terminate at the same position, so a single plate seats both — the walkway beam on a 70mm seat, the film rail on a 150mm seat.

4.4 Design Rationale

The cantilever rectangle achieves three goals:

1. Zero floor contact — clears the IBC stack entirely; no legs on the floor in the IBC zone.
2. Zero tray contact — the rectangle floats above the processing tray.
3. Consolidated film-rail anchor — the combined corner plate does double duty, removing a separate BR saddle.

The pipe-routing space under this walkway — past the IBC frame feet, the tray rims, and the cantilever arms — is detailed in the Walkway Routing Sections.

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5. Left Walkway — Removable Lift-Out

The left walkway at the cargo door end cannot use wall-cantilevered brackets because the hinged light-trap panel occupies the end wall and swings ~56° about the pivot for transport (its sweep passes over this zone). Its inner edge sits over the processing tray, so it cannot be supported from below either. The left walkway is therefore a removable lift-out grate carried by 5 floor-leg cantilever brackets — each a post standing on the bare floor outside the tray with an arm that cantilevers over the tray to the grate inner edge. The +50mm deck raise lifts these arms clear of the floor-level spray bar.

5.1 Support System

Component	Specification	Position
Floor-leg cantilever bracket (×5)	50×50×3mm steel SHS post (~115mm, floor to grate bottom) + 40×40×3mm SHS arm (40mm deep) + 128×60×8mm foot plate	5 brackets (outside the tray)
Floor anchors	4× M10 wedge anchors per foot plate (20 total)	Sealed penetrations into the container floor
Standard arm reach	Arm reaches the grate inner edge	2 brackets
Extended arm reach	Arm extends under the drum-exit punch-out	3 brackets

The grate rests on the cantilever arms and lifts straight out — no fasteners, no kerb. The operator load travels grating → 40×40×3 cantilever arm → 50×50×3 post → foot plate → floor anchor, with zero tray contact: the posts stand on bare floor outside the tray and the arms cantilever over it. The arm bottom clears the floor-level spray bar by 15mm and the tray rim by 25mm. Because the brackets stand entirely outside the panel's transport-swing footprint, the grate simply lifts out before the panel swings; the floor-bolted posts stay put.

Load path / hand-check. The longest cantilever is the punch-out arm. With a ~1kN footfall at the arm tip, the 40×40×3 SHS arm and 50×50×3 SHS post carry the moment with margin and the foot plate's 4× M10 anchors react the overturning. This is a hand-check, not a signed analysis; the brackets bolt to the floor permanently and only the grate lifts out for transport. This floor-leg cantilever supersedes the earlier full-width edge-beam scheme — it is simpler and lighter and needs no through-wall seats.

5.2 Drum-Exit Punch-Out

The operator steps out of the revolving-door light lock at its interior face, but the standard 300mm walkway ends — leaving only ~20mm of landing in front of the drum opening, with the processing-tray basin immediately beyond. The left walkway is therefore deepened to 600mm over the drum-opening span — a ~600 × 760mm landing centered on the exit (the same approach as the near-walkway widened section on the pinhole side).

Optical clearance. The punch-out is inside the active image zone (X≥150mm) — so it was checked against the optical cone. At the drum-exit depth the cone's left boundary, so the punch-out is entirely left of the cone: every pinhole sight line through it lands ~113mm clear of the image edge. Confirmed by generate_line_of_sight.py (no equipment intersects the cone).

Support. The 600mm punch-out is carried by the 3 middle floor-leg brackets — the same posts that carry the standard left walkway, but with their arms extended to X=770mm. Each arm cantilevers the full ~630mm over the tray from its post on bare floor, with zero tray contact, and lifts out with the rest of the left walkway for transport. No separate sub-frame, edge beam, or bearing strip is needed.

Sheet 9 — Detail E: Drum-Exit Punch-Out Support (plan). How the deeper landing is supported — the 3 middle floor-leg brackets with arms extended, cantilevering over the tray with zero tray contact. See also Sheet 6 (Detail D) for the floor-leg bracket itself.

5.3 Floor-Leg Cantilever Bracket Detail

Each of the 5 brackets is a post standing on the bare floor outside the tray, with an arm cantilevering over the tray to carry the grate. No wall seats and no tray contact.

Component	Specification
Post	50×50×3mm steel SHS, ~115mm tall (floor to grate bottom), on bare floor at X=140mm
Foot plate	128×60×8mm steel plate, with 4× M10 wedge anchors into the container floor (sealed)
Arm	40×40×3mm steel SHS, reaching X=470mm (2 brackets) or extended to X=770mm (3 brackets, under the punch-out)
Overturning reaction	reacted by the foot-plate anchors; ~1kN footfall at the arm tip is the worst case

The grate simply rests on the cantilever arms — located laterally by butting the near/far grate edges, free to lift straight out (no fasteners, no kerb). Demountable for transport: the grate lifts out before the panel swings; the floor-bolted posts stay in place. No through-wall hardware at all.

5.4 Panel Transport Clearance

Parameter	Value
Panel transport motion	SWING ~56° about the Ø89 pivot
Swing sweep reach (near-walkway zone)	X≈1,395mm
Butt joint / near-far walkway start	X=470mm
Panel / cage bottom edge	Z=130mm (grate-top level)

The left walkway grate — together with the door-end near-deck lift-out section — must be lifted out before the panel can swing (the 5 floor-leg posts stay bolted to the floor). As the panel + drum swing ~56° about the pivot, the cage sweeps past the butt joint into the vacated zone, riding the Z=130mm floor gap over the Z115 door-end brackets — so no walkway bracket is struck (the swing clears). The relevant standing clearance is vertical: the panel/cage bottom edge sits at the grate-top level, clearing the tray rim and the bracket tops.

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6. Corner Joints

All four corners use butt joints (not miter joints). The near and far walkway grating sections terminate at the butt joint lines, and the left and right walkway grating sections rest on or abut the near/far bracket arms at these intersections.

Corner	Butt joint X	Design
Near-left / Far-left	X=470mm	Left walkway grate rests on the floor-leg cantilever arms; butts the near/far grate
Near-right / Far-right	X=4,629mm	Right walkway grating abuts near/far grating

Butt joints are used rather than miters for two reasons:

1. Panel clearance — near/far walkways start at X=470mm, clear of the door-end panel swing sweep, so only the left walkway + the door-end near-deck section need removal for transport mode.
2. Simplicity — each grating section lifts off independently without affecting adjacent sections.

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7. Evaporative Cooler Transport Stowage

During transport, the evaporative cooler (~20kg dry) is stowed on the near walkway grating — in the widened section, so it clears the panel swing sweep. The cooler sits on a 12mm plywood base plate that distributes load across the grating and prevents the housing from catching in grate openings. Two 25mm ratchet straps loop over the cooler and hook to near walkway cantilever bracket arms.

The 350mm cooler depth slightly exceeds the 300mm walkway width — the cooler overhangs 50mm into the processing tray zone. This is acceptable because the tray is drained and empty during transport.

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8. Grating Specification

All four walkway sections use the same grating:

Parameter	Value
Type	Molded GRP (fiberglass) grating
Thickness	15mm (5/8") — keeps the lowered deck + 15mm spray-bar clearance
Resin	Vinyl-ester (resists both alkaline developer and acidic fixer splash)
Mesh	~38×38mm square, molded
Open area	~40%
Surface finish	Grit top (slip-resistant)

8.1 Grating Retention by Walkway Section

Walkway	Retention Method	Attachment Point	Removal
Near (pinhole wall)	316 SS hold-down clips	Bracket arm top surface	Release clips, lift grating
Far (film plane wall)	316 SS hold-down clips	Bracket arm top surface	Release clips, lift grating
Right (IBC end)	316 SS hold-down clips	L-angle bearer horizontal leg	Release clips, lift grating
Left (cargo door)	Gravity (floor-leg arms)	Floor-leg cantilever arms	Lift straight up — no fasteners

Near and far walkways use 316 SS hold-down clips that clamp the GRP panel down onto the bracket arm (a stainless clamp clip — not a TEK screw driven into a steel bearing bar, since FRP isn't screwed through). Clips are spaced at every other bracket (~914mm centers).

Right walkway uses the same stainless hold-down clips, but they clamp to the horizontal leg of the 25×25×5mm L-angle bearers rather than the bracket arms.

Left walkway uses gravity retention only. The grate rests on the 5 floor-leg cantilever arms (Yd 250/800/1180/1560/2110) and is located laterally by butting the near/far grate edges. No fasteners are used because the left walkway must be removed quickly for hinged panel transport mode — lift straight up and carry out; the floor-bolted posts stay put.

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9. Load Considerations

The walkway must support an operator (~100kg) plus portable equipment. The critical load case is the widened near walkway section (500mm cantilever) with an operator standing at the outer edge.

The standard 8mm steel plate gusset brackets at 457mm centers provide substantial structural capacity. Each standard bracket is a rigid triangle (vertical leg + horizontal arm + gusset) with 3x M12 through-bolts to the container rib. The four widened brackets use 10mm plate with 4x M12 rectangular bolt patterns and 200mm vertical legs for the increased moment demand of the 500mm cantilever arm.

The right walkway is a cantilever rectangle. A closed 40×40×3mm SHS frame is picked up at mid-span by two arms cantilevering off the IBC corridor uprights and at its four corners by wall cleats (left) and the combined corner plates (right). The governing case is the arm root, where the design footfall produces a peak moment of only ≈0.35 kN·m — comfortably within the ≈1.6 kN·m elastic capacity of 40×40×3 SHS (see the cantilever study). The closed rectangle resists twist far better than the previous free-ended bearer angles, so the deck bounces noticeably less than the rod-hung version it replaces.

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10. Parts List

Item	Spec	Qty	Supplier	Est. cost
Molded GRP (fiberglass) grating	1" (25mm) McNichols MS-S-100, 1½×1½ square mesh, vinyl-ester, grit top, 2.60 lb/sf; ~4.5 m² (4 sections)	1 lot	McNichols / Grating Pacific	$965–$1,250
Drum-exit punch-out grating	Extra GRP landing (~0.23 m²) at the light-lock exit	1 lot	McNichols	$50–$65
Cantilever bracket — standard (near/far)	8mm steel plate: 150mm vert leg + 300mm arm + 70mm gusset, welded (5 near + 9 far at 457mm centers)	14 ea	Local fab	$420–$700
Cantilever bracket — widened (near)	10mm steel plate: 200mm vert leg + 500mm arm + 70mm gusset, welded (EP/battery/slit zone)	4 ea	Local fab	$160–$280
M12×80mm through-bolt kit	Hex bolt + 2× washers + nut, grade 8.8 (3 per std + 4 per widened)	58 ea	McMaster-Carr	$87–$145
Reinforcing plate (exterior)	6mm steel: 100×180mm std (×14) + 120×220mm widened (×4)	18 ea	Local fab	$75–$130
Transition bearing plate	40×500×5mm flat bar, welded to bracket arm top at width transitions	2 ea	Local fab	$5–$10
Right walkway cantilever frame	40×40×3mm SHS — 2 long beams (2,362mm) + 2 end beams (300mm) + 2 center arms (325mm), ~8 m	1 lot	Metal Supermarkets	$28–$40
Wall cleat (left corners)	8mm steel: back-plate + exterior plate + shelf, through-bolted to the wall	2 ea	Local fab	$20–$35
Combined corner plate (right corners)	10mm steel, 150mm wide — carries the walkway right beam AND the bottom film rail	2 ea	Local fab	$50–$80
M12 through-bolt kit (right walkway)	Wall cleats + combined plates + 2 center-arm U-clamps to the IBC uprights	24 ea	McMaster-Carr	$30–$50
Floor-leg cantilever bracket (left walkway, ×5)	50×50×3mm SHS post (~115mm) + 40×40×3mm SHS arm (2 reach X470, 3 extended to X770) + 128×60×8mm foot plate	5 ea	Local fab	$55–$95
M10 wedge floor anchors	4 per foot plate (20 total), sealed into the container floor	20 ea	McMaster-Carr	$25–$45
Grating clips	Removable spring clips, stainless	30 ea	McNichols / McMaster-Carr	$30–$50
Walkway total				$2,000–$2,975

Evap-cooler transport-stowage hardware (plywood base plate + ratchet straps, §7) is costed in the Ventilation & Cooling parts list, not here.

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11. Maintenance

Interval	Task
Before each session	Inspect all grating clips are seated; test left walkway lift-out for freedom of movement
Before each session	Check the 5 floor-leg foot-plate anchors are tight; posts standing square
Monthly	Inspect cantilever bracket bolts for tightness (3× M12 std, 4× M12 widened)
Monthly	Check right walkway cantilever-arm U-clamps to the IBC uprights and the combined-plate bolts for tightness
Monthly	Inspect GRP grating panels for cracks, delamination, or a worn grit top
Quarterly	Inspect reinforcing plates (exterior) for corrosion — touch up paint if needed
Quarterly	Inspect the right walkway cantilever-rectangle welds + wall cleats for corrosion and bolt tightness
Before transport	Remove left walkway: lift the grate straight out (the 5 floor-leg posts stay bolted to the floor)
Before transport	Verify evap cooler ratchet straps to bracket arms; check anti-slide cleats
After transport	Reinstall left walkway in reverse order; check all sections for level deck

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12. Source References

1. ISO 668:2020 — Series 1 freight containers: Classification, dimensions and ratings. Container rib spacing 457mm (18").
2. Fibergrate — Molded Grating load/engineering data — molded FRP grating load tables + chemical-resistance guide (vinyl-ester resin selection)
3. AS 1657-2018 — Fixed platforms, walkways, stairways and ladders: Design, construction and installation. 300mm minimum clear width for walkways.
4. Shurflo 2088 Series datasheet — Pump dimensions for manifold access clearance.
5. Equipment Layout Report — Component positions and access requirements.
6. Processing Tray & Spray Bar Report — Tray dimensions, rim height, spray bar slit requirements.
7. Hinged Panel Report — Panel swing sweep, transport swing, floor gap.
8. Light Trap Selection Report — Panel and drum dimensions at cargo door end.
9. IBC Stacking Report — IBC stack dimensions and floor zone clearance requirements.
10. Walkway Routing Sections — Under-walkway pipe-routing cross-sections and clearances at each junction.