Two standard 4m MMC pylons spaced approximately 12–15m apart, structurally coupled by three transverse cross-beams captured through both pylon stacks. The portal frame configuration shares lateral and longitudinal loads between the pair, reducing per-pylon tubular tension to approximately 20% of the single-pylon equivalent. Used for high-voltage strain towers, river crossings, and heavy conductor loading where single-pylon capacity is exceeded — up to ±1100kV UHVDC three-bipole strain.
| Configuration | Dual-tower portal with three captured cross-beams |
| Legs per pylon | 2 (paired single-pylon stacks coupled by cross-beams) |
| Pylon spacing | ~12–15m centre-to-centre |
| Cross-beams | 3 — vertically distributed along upper pylon, each carrying one circuit/bipole |
| Beam material | Concrete box girder (preferred), steel beam (high-load), or hybrid (steel core with concrete cladding) — engineering choice per location |
| Per-pylon foundation | 1 × 4m OD ATS caisson per leg — same standard ATS caisson as MMC-TB |
| Tubular per pylon | 1 × 20" L80 13Cr API 5CT — single tubular per leg, same standard SKU |
| Voltage range covered | 330kV AC strain through ±1100kV UHVDC three-bipole strain — covers every continental transmission strain case |
| Worked PT requirement examples | 330kV AC strain: 4.6 MN/pylon · ±500kV HVDC strain: 5.6 MN/pylon · ±800kV UHVDC strain: 9.7 MN/pylon · ±1100kV UHVDC suspension: 10.8 MN/pylon · ±1100kV UHVDC 3-bipole strain: 29.6 MN/pylon (needs guys added) |
| Easement | Standard corridor — no point-source extension required (vs MMC-TB Guyed) |
| Visual signature | Modern dual-pylon portal — visually similar to a contemporary bridge pier or architectural gateway. Decorative surface treatment available via P#7 cast skin. |
MMC-TA — dual-tower portal render
SketchUp render / technical drawing — placeholder for production artwork. Replace with actual asset when available.MMC-TA solves the high-voltage strain problem using only standard production units. Two MMC-TB single-leg pylons are deployed side-by-side and structurally coupled by three transverse cross-beams that pass through both pylon stacks at engineered heights. The portal frame configuration creates moment continuity through the captured beams, sharing both lateral wind load (each pylon takes half) and longitudinal strain load (the pair couple between the two pylons).
Architecturally, MMC-TA is the answer to "what do you do when a single MMC-TB pylon's PT requirement exceeds the standard 20\" tubular's capacity?" The answer: deploy two of them, couple them with a portal frame, and per-pylon PT requirement drops to ~20% of the single-pylon equivalent. The cross-beams give clean conductor circuit separation (one bipole per beam level). The architectural simplicity is decisive — the supply chain stays single-product, the manufacturing economics stay single-product, the field deployment economics stay single-product. The only differences vs MMC-TB are the cross-beam modules and the saddle column segment (P1-S) at arm height.
MMC-TA is deployed at high-voltage strain locations across the SBC continental transmission network — corridors carrying ±800kV UHVDC and ±1100kV UHVDC. Used at strain points anywhere in the corridor regardless of easement (urban, rural, remote). Phase 0 corridor's ±500kV HVDC backbone is mostly MMC-TB, with MMC-TA at strain points where the load exceeds single-pylon capacity. Phase 1, 2, and 3 continental corridors at ±1100kV use MMC-TA as the standard strain configuration.
MMC-TA is deployed across the SBC transmission network alongside MMC-TB and MMC-TB Guyed. The full transmission deployment is described in the project pages.
The engineering of MMC-TA is documented in the MMC engineering memo series. The Models page is the catalogue — the Library is the engineering depth.
MMC-TA is covered by the Multimodal Viaduct Topside (Patent 5) — specifically the paired-pylon architecture disclosure — and the Pole and Tower Architecture (Patent 6). The patent family review has flagged the dual-tower portal with three captured cross-beams as a candidate for a continuation patent or divisional claim before the April 2027 PCT deadline. The standard ATS caisson (Patents 1, 2, 3) and the renewable tubular tension element (Patent 4) are unchanged from MMC-TB.