Analysis of availability, weight, cost, shipping, and structural capacity
Aluminum extrusion presses have physical limits. The key constraint is the circumscribing circle diameter of the cross-section — the smallest circle that fully encloses the profile. For a 16″-tall I-beam with, say, 6–8″ flanges, the circumscribing circle is roughly 17–18 inches.
| Press Size | Max Circumscribing Circle | Availability |
|---|---|---|
| Standard large press | 12–14 inches | Common in USA & China |
| Very large press | 16–18 inches | Rare; a few exist in China, fewer in the West |
| Mega press (e.g., China Zhongwang) | 20–25+ inches | Very few worldwide; custom orders only |
| Profile | Height | Flange Width | Weight (lb/ft) | Alloy |
|---|---|---|---|---|
| Aluminum Assoc. I 12 × 11.7 | 12.00″ | 7.00″ | 11.7 lb/ft | 6061-T6 |
| Aluminum Assoc. I 10 × 8.65 | 10.00″ | 6.00″ | 8.65 lb/ft | 6061-T6 |
| Aluminum Assoc. I 8 × 6.18 | 8.00″ | 5.00″ | 6.18 lb/ft | 6061-T6 |
| Approach | Pros | Cons |
|---|---|---|
| Welded plate girder (5083 plate) | Any size; proven marine practice; available from many yards | Welding reduces strength in heat-affected zones (~60%); heavier design needed |
| Custom extrusion (China mega-press) | Efficient cross-section; no weld HAZ | High die cost; long lead time; minimum order ~5–10 tons |
| Two 8″ I-beams stacked & bolted/welded | Uses standard profiles | Connection is a weak point; adds weight |
| Aluminum truss from smaller extrusions | Very light for the stiffness; standard parts | More fabrication labor; many joints |
Extrusion lengths are limited by:
Since a 16″ aluminum I-beam isn't a standard catalog item, let's estimate based on scaling and comparable steel beams.
Aluminum density is about 169 lb/ft³ (roughly 1/3 of steel). An aluminum I-beam with the same cross-sectional dimensions as a W16×26 would weigh:
26 lb/ft × (169/490) = ~9.0 lb/ft
However, since aluminum's modulus of elasticity is about 1/3 of steel's (10.0 vs 29.0 Msi), and yield strength (5083-H116) is about 33 ksi vs steel's 36–50 ksi, in practice you'd often need a somewhat heavier section for equivalent stiffness. A practical marine aluminum 16″ I-beam would likely weigh 9–14 lb/ft depending on the flange/web proportions chosen.
| Scenario | Approx. Weight per Foot | Weight for 40 ft beam | Weight for 60 ft beam | Weight for 80 ft beam |
|---|---|---|---|---|
| Light (same dims as W16×26) | ~9 lb/ft | 360 lb | 540 lb | 720 lb |
| Medium (stiffened for deflection) | ~12 lb/ft | 480 lb | 720 lb | 960 lb |
| Heavy (wider flanges) | ~16 lb/ft | 640 lb | 960 lb | 1,280 lb |
| Item | Estimate | Notes |
|---|---|---|
| Standard 6061-T6 I-beam (12″ or smaller), per lb | $3.50 – $5.50/lb | Off-the-shelf from distributors like Metals Depot, Ryerson, etc. |
| Custom extrusion die (16″ profile) | $15,000 – $40,000 | One-time cost; amortize over total order |
| Custom extruded 6061-T6 I-beam, per lb | $3.00 – $5.00/lb | At quantity (5+ tons) |
| 5083-H116 welded plate I-beam, per lb | $5.00 – $8.00/lb | Includes fabrication; marine yards |
| Source | Material Cost | Die Cost (amortized) | Total per Beam (approx) |
|---|---|---|---|
| USA standard 6061 (if 12″ max) | $1,700 – $2,600 | N/A | $1,700 – $2,600 |
| USA custom extrusion 6061 | $1,440 – $2,400 | +$1,500–$4,000 (over 10 beams) | $2,940 – $6,400 |
| USA welded 5083 plate girder | $2,400 – $3,840 | N/A | $2,400 – $3,840 |
Chinese aluminum extrusion is significantly cheaper, especially for custom profiles:
| Item | China Estimate | Notes |
|---|---|---|
| Custom extrusion die | $3,000 – $10,000 | Much cheaper than USA |
| 6061-T6 extruded I-beam, FOB China, per lb | $1.50 – $2.50/lb | At 5+ ton order |
| 6061-T6 extruded I-beam, FOB China, per kg | $3.30 – $5.50/kg | |
| 5083 extruded (if press available), FOB China, per lb | $2.00 – $3.50/lb | Limited suppliers for large 5083 extrusions |
| Item | Cost |
|---|---|
| Material (480 lb × $2.00/lb) | $960 |
| Die (amortized over 10+ beams) | $300 – $1,000 |
| FOB China per beam | $1,260 – $1,960 |
You're absolutely right that beams under 40 feet that fit in containers are far more practical and economical to ship.
| Container Type | Internal Length | Max Beam Length | Payload Capacity |
|---|---|---|---|
| 20′ standard | 19′ 4″ (5.9 m) | ~19 ft beams | ~44,000 lb |
| 40′ standard | 39′ 5″ (12.0 m) | ~39 ft beams | ~58,000 lb |
| 40′ high-cube | 39′ 5″ (12.0 m) | ~39 ft beams | ~58,000 lb |
| 40′ flat-rack | 39′ 5″ (can overhang) | 45–55 ft with overhang | ~88,000 lb |
Anguilla has very limited port facilities (Blowing Point and Road Bay/Sandy Ground). Most cargo comes via transshipment through St. Maarten (Port of Philipsburg) or St. Thomas, USVI, then by barge or small vessel to Anguilla.
| Route Segment | Cost Estimate (per 40′ container) | Notes |
|---|---|---|
| China (Shanghai/Shenzhen) → Miami or St. Maarten | $3,000 – $6,000 | Ocean freight; varies hugely with market conditions. 2025 rates elevated vs. pre-COVID. |
| Miami → St. Maarten (transshipment) | $1,500 – $3,000 | If routing through Miami |
| St. Maarten → Anguilla (barge/feeder) | $800 – $2,000 | Short hop; limited service; cost per container |
| Port handling, customs, duties | $500 – $1,500 | Anguilla import duties vary; aluminum structural may be ~10–20% |
| Total per 40′ container | $5,800 – $12,500 |
A 40′ container internal width is 7′ 8″ and internal height is 7′ 10″ (or 8′ 10″ for high-cube). A 16″ tall I-beam with ~6″ flanges could be stacked and packed efficiently:
| Beams per container (est.) | Total weight | Shipping cost per beam |
|---|---|---|
| 20–30 beams (at 480 lb each) | 9,600 – 14,400 lb | $200 – $625 per beam |
Weight is well under container limits; you're volume-constrained, not weight-constrained with aluminum.
Simple beam, supported at both ends, uniform load w (lb/ft) along entire span. We'll evaluate both bending strength (will it break?) and deflection (will it sag too much?).
| Max bending moment | M = wL²/8 |
| Bending stress | σ = M / Sx |
| Max deflection | δ = 5wL⁴ / (384 × E × Ix) |
Where: L = span, Sx = section modulus, Ix = moment of inertia, E = modulus of elasticity
| Property | 6061-T6 | 5083-H116 |
|---|---|---|
| Yield strength (σy) | 35,000 psi | 33,000 psi |
| Allowable bending stress (with safety factor ~1.65) | ~21,000 psi | ~20,000 psi |
| Modulus of elasticity (E) | 10,000,000 psi | 10,300,000 psi |
| Span (ft) | Allowable Total Load (Strength-limited, lb) |
Total Load for L/240 Deflection Limit (lb) | Governing Limit | Allowable Uniform Load (lb/ft) | Approx. Allowable Total Load (lb) |
|---|---|---|---|---|---|
| 20 | 26,900 | 46,300 | Strength | 1,345 | 26,900 |
| 30 | 11,950 | 9,150 | Deflection | 305 | 9,150 |
| 38 (container-fit) | 7,430 | 4,480 | Deflection | 118 | 4,480 |
| 40 | 6,720 | 3,860 | Deflection | 97 | 3,860 |
| 50 | 4,300 | 1,975 | Deflection | 40 | 1,975 |
| 60 | 2,985 | 1,143 | Deflection | 19 | 1,143 |
| 80 | 1,680 | 482 | Deflection | 6 | 482 |
Let's also look at a beefier custom 16″ beam with wider, thicker flanges:
| Span (ft) | Allowable Total Load (lb) — deflection-governed | Allowable Uniform Load (lb/ft) |
|---|---|---|
| 20 | 42,300 (strength governs) | 2,115 |
| 30 | 14,750 | 492 |
| 38 | 7,220 | 190 |
| 40 | 6,220 | 156 |
| 50 | 3,180 | 64 |
| 60 | 1,840 | 31 |
| 80 | 776 | 10 |
Even with the heavier beam, 60–80 ft spans with a single I-beam are impractical. The loads are too low.
A single I-beam — even a large one — is a poor choice for spans over ~30 feet in aluminum. The deflection problem is severe. Here's what actually works:
| Approach | Effective Depth | Weight | Span Capability | Cost |
|---|---|---|---|---|
| Aluminum truss (Warren or Pratt type from standard angle/tube extrusions) | 24–48″ | Moderate | 60–120+ ft | Medium (labor-intensive) |
| Aluminum box beam / rectangular hollow section | 16–24″ | Moderate | 30–50 ft | Medium |
| Paired I-beams with cross-bracing (like a ladder frame) | 16″ per beam, ~24″ overall | 2× single beam | 40–60 ft | Medium |
| Aluminum space frame / tubular truss | 36–72″ | Very light for capacity | 80–200+ ft | Higher fabrication cost but proven for large marine platforms |
| Steel I-beams with marine coating | 16–24″ | 3× aluminum | 60–100+ ft | Lower material cost; ongoing maintenance |
A 48″-deep aluminum truss spanning 80 feet could easily carry 20,000–50,000+ lbs of uniformly distributed load while weighing perhaps 15–25 lb/ft — far superior to any I-beam.
Assuming a triangle with ~80 ft sides (three sides = 240 ft of main beams):
| Component | China-sourced Estimate |
|---|---|
| Aluminum extrusions (tubes/angles for trusses), ~7,000 lb | $14,000 – $21,000 |
| Fabrication into truss modules (if done in China) | $5,000 – $15,000 |
| Hardware (stainless bolts, splice plates, etc.) | $2,000 – $5,000 |
| Shipping (2–3 containers, China → Anguilla) | $12,000 – $30,000 |
| Customs/duties in Anguilla (~15%) | $3,000 – $6,000 |
| TOTAL for main triangle frame | $36,000 – $77,000 |
This is for the main triangle frame only — not including legs/columns, floats, cables, decking, or any systems.
| Question | Answer |
|---|---|
| Can you get 16″ extruded aluminum I-beams? | Not off-the-shelf. Custom extrusion possible (especially from China) but expensive die. Welded plate girders are more common for this size. |
| Weight of a 16″ aluminum I-beam? | ~9–14 lb/ft depending on proportions |
| US cost per beam (40 ft)? | $2,000 – $6,000 |
| China cost per beam (40 ft)? | $1,000 – $2,500 FOB |
| Shipping China → Anguilla per container? | $6,000 – $12,500 |
| Container-compatible beam length? | ≤ 38–39 feet |
| Working load of one 16″ I-beam at 40 ft span? | ~3,900 – 6,200 lb total (deflection-governed) |
| Working load of one 16″ I-beam at 60 ft span? | ~1,100 – 1,800 lb total (nearly useless) |
| Better solution for 60–80 ft spans? | Aluminum trusses (30–48″ deep) from standard tube/angle extrusions, in bolted 38-ft modules |
These are engineering estimates for preliminary planning. A licensed structural/marine engineer should verify all calculations before construction. Prices are approximate for 2024–2025 and subject to market fluctuation. Aluminum alloy selection, welding procedures, and corrosion protection strategy should be reviewed by a marine materials specialist.