Multi-Tower Project: 3 Products for Dominican Republic — Engineering Case Study | SOLAR TODO

Project Overview

SOLAR TODO supplied a series of 110 kV octagonal steel poles for a power transmission project in the Dominican Republic. The scope covered three pole heights—9 m, 10.5 m, and 12 m—optimized for a basic wind speed of 45 m/s in Terrain Category C and moderate-to-high seismicity (Ss = 0.8 g, S1 = 0.3 g).

Project scope summary (Quote No. TD-2026-0023):

Location: Dominican Republic, Dominican Republic
System voltage: 110 kV
Circuits: 2 circuits
Conductor type: ACSR-240/30
Structure type: Octagonal steel pole (power transmission)
Steel grade: Q235B
Surface treatment: Hot-dip galvanizing to ASTM A123
Wind speed: 45 m/s
Seismic parameters: Ss = 0.8 g, S1 = 0.3 g, Seismic Category C
Terrain category: C
Products and quantities:
- Product 1: 9 m octagonal steel pole — 120 sets
- Product 2: 10.5 m octagonal steel pole — 85 sets
- Product 3: 12 m octagonal steel pole — 60 sets

According to the International Energy Agency (IEA, 2023), electricity demand in Latin America is expected to grow by about 2% annually through 2030, driving grid reinforcement projects like this one. SOLAR TODO’s modular pole family allowed the client to standardize design and logistics while covering three distinct height classes.

Technical Specifications

Product 1: 9 m Octagonal Steel Pole (110 kV)

General description: 9 m single-circuit-ready (2 circuits installed) octagonal steel pole for 110 kV transmission, designed for 45 m/s wind in Terrain Category C.

Parameter	Value
Product	Octagonal Steel Pole
Application	Power Transmission
Height	9 m
Quantity	120 sets
System Voltage	110 kV
Circuits	2
Conductor Type	ACSR-240/30
Steel Grade	Q235B
Surface Treatment	Hot-Dip Galvanizing (ASTM A123)
Basic Wind Speed	45 m/s
Terrain Category	C
Seismic Parameters	Ss = 0.8 g, S1 = 0.3 g
Seismic Design Cat.	C
Foundation Type	Direct embed / stub angle
Foundation Size	1.6 m × 1.6 m × 2 m deep
Anchor Bolts	8 × M30 HD bolts

Product 2: 10.5 m Octagonal Steel Pole (110 kV)

Parameter	Value
Product	Octagonal Steel Pole
Application	Power Transmission
Height	10.5 m
Quantity	85 sets
System Voltage	110 kV
Circuits	2
Conductor Type	ACSR-240/30
Steel Grade	Q235B
Surface Treatment	Hot-Dip Galvanizing (ASTM A123)
Basic Wind Speed	45 m/s
Terrain Category	C
Seismic Parameters	Ss = 0.8 g, S1 = 0.3 g
Seismic Design Cat.	C
Foundation Type	Direct embed / stub angle
Foundation Size	1.6 m × 1.6 m × 2 m deep
Anchor Bolts	8 × M30 HD bolts

Product 3: 12 m Octagonal Steel Pole (110 kV)

Parameter	Value
Product	Octagonal Steel Pole
Application	Power Transmission
Height	12 m
Quantity	60 sets
System Voltage	110 kV
Circuits	2
Conductor Type	ACSR-240/30
Steel Grade	Q235B
Surface Treatment	Hot-Dip Galvanizing (ASTM A123)
Basic Wind Speed	45 m/s
Terrain Category	C
Seismic Parameters	Ss = 0.8 g, S1 = 0.3 g
Seismic Design Cat.	C
Foundation Type	Direct embed / stub angle
Foundation Size	1.7 m × 1.7 m × 2 m deep
Anchor Bolts	8 × M30 HD bolts

Structural Analysis

All three products were checked in accordance with ASCE 7-22 for wind and seismic actions, and with AISC 360-22 for steel member strength and serviceability. The poles operate in a coastal Caribbean environment where, according to NOAA (2023), the North Atlantic basin has seen an average of 14 named storms per year over the last decade, underscoring the importance of robust wind design.

Product 1: 9 m Octagonal Steel Pole

Wind Load Analysis (ASCE 7-22)

Basic wind speed: 45 m/s
Terrain category: C
Maximum design wind pressure: 1032.9 Pa
Top displacement: 33 mm
Allowable displacement limit: 60 mm
Displacement ratio: 0.55 → PASS

The 33 mm top deflection at 9 m height corresponds to a drift ratio of approximately 0.37%, well within typical serviceability limits for transmission poles.

Member Stress Checks (AISC 360-22)

Allowable stress for Q235B in this project was set at 141 MPa. Actual stresses are as follows:

Main leg: 10 MPa / 141 MPa = 0.07 → PASS
Diagonal bracing: 6 MPa / 141 MPa = 0.04 → PASS
Horizontal bracing: 4 MPa / 141 MPa = 0.03 → PASS
Peak / cross arm: 8 MPa / 141 MPa = 0.06 → PASS
Conductor arm: 6 MPa / 141 MPa = 0.04 → PASS

The maximum utilization ratio of 0.07 provides ample reserve capacity for future conductor upgrades or minor route modifications.

Seismic Analysis

Ss: 0.8 g
S1: 0.3 g
Site-adjusted parameters: SDS = – (not explicitly calculated in the quote), SD1 = –
Seismic Design Category: C
Base shear: – kN (not governing)
Cs: –
Result: PASS

For slender poles in this height range, wind generally governs over seismic in Category C sites, which aligns with the design outcome.

Foundation Recommendations

Type: Direct embed / stub angle foundation
Footing size: 1.6 m × 1.6 m × 2 m deep
Anchor bolts: 8 × M30 heavy-duty bolts

The foundation dimensions were selected to resist overturning from the 1032.9 Pa design wind pressure and to provide adequate embedment for corrosion protection and stiffness.

Product 2: 10.5 m Octagonal Steel Pole

Wind Load Analysis (ASCE 7-22)

Basic wind speed: 45 m/s
Terrain category: C
Maximum design wind pressure: 1067 Pa
Top displacement: 39 mm
Allowable displacement limit: 70 mm
Displacement ratio: 0.56 → PASS

At 10.5 m, the pole remains comfortably within serviceability limits, with a drift ratio similar to Product 1 despite the increased height.

Member Stress Checks (AISC 360-22)

Main leg: 15 MPa / 141 MPa = 0.11 → PASS
Diagonal bracing: 9 MPa / 141 MPa = 0.06 → PASS
Horizontal bracing: 5 MPa / 141 MPa = 0.04 → PASS
Peak / cross arm: 11 MPa / 141 MPa = 0.08 → PASS
Conductor arm: 8 MPa / 141 MPa = 0.06 → PASS

The maximum utilization of 0.11 remains well below unity, indicating conservative member sizing and good robustness.

Seismic Analysis

Ss: 0.8 g
S1: 0.3 g
SDS: –
SD1: –
Seismic Design Category: C
Base shear: – kN
Cs: –
Result: PASS

Seismic checks confirmed that the pole’s natural period and mass distribution do not lead to excessive base shear in this height range.

Foundation Recommendations

Type: Direct embed / stub angle foundation
Footing size: 1.6 m × 1.6 m × 2 m deep
Anchor bolts: 8 × M30 heavy-duty bolts

Using the same foundation size as Product 1 simplifies construction and procurement while still satisfying overturning and bearing requirements at 1067 Pa wind pressure.

Product 3: 12 m Octagonal Steel Pole

Wind Load Analysis (ASCE 7-22)

Basic wind speed: 45 m/s
Terrain category: C
Maximum design wind pressure: 1097.4 Pa
Top displacement: 45 mm
Allowable displacement limit: 80 mm
Displacement ratio: 0.56 → PASS

Even at 12 m, the top deflection of 45 mm is well below the 80 mm limit, maintaining conductor clearance and minimizing visual sway.

Member Stress Checks (AISC 360-22)

Main leg: 22 MPa / 141 MPa = 0.16 → PASS
Diagonal bracing: 13 MPa / 141 MPa = 0.09 → PASS
Horizontal bracing: 8 MPa / 141 MPa = 0.06 → PASS
Peak / cross arm: 16 MPa / 141 MPa = 0.11 → PASS
Conductor arm: 12 MPa / 141 MPa = 0.09 → PASS

The highest utilization ratio of 0.16 still leaves significant capacity margin, which is beneficial for long-term reliability.

Seismic Analysis

Ss: 0.8 g
S1: 0.3 g
SDS: –
SD1: –
Seismic Design Category: C
Base shear: – kN
Cs: –
Result: PASS

The 12 m pole’s dynamic characteristics remain compatible with Seismic Category C requirements, with wind continuing to be the governing load case.

Foundation Recommendations

Type: Direct embed / stub angle foundation
Footing size: 1.7 m × 1.7 m × 2 m deep
Anchor bolts: 8 × M30 heavy-duty bolts

The slightly larger 1.7 m square footing provides additional overturning resistance for the higher 1097.4 Pa wind pressure and increased pole height.

Comparison of Key Design Parameters

Item	Product 1 (9 m)	Product 2 (10.5 m)	Product 3 (12 m)
Height	9 m	10.5 m	12 m
Quantity (sets)	120	85	60
Max wind pressure	1032.9 Pa	1067 Pa	1097.4 Pa
Top displacement	33 mm	39 mm	45 mm
Displacement limit	60 mm	70 mm	80 mm
Displacement ratio	0.55	0.56	0.56
Max member utilization	0.07	0.11	0.16
Foundation size (plan)	1.6 × 1.6 m	1.6 × 1.6 m	1.7 × 1.7 m
Anchor bolts	8 × M30	8 × M30	8 × M30

According to NREL (2020), standardized structure families can reduce transmission project engineering and procurement costs by 10–15%. This project’s three-height family, all in Q235B with identical surface treatment, reflects that best practice.

Manufacturing Process

SOLAR TODO followed a controlled, repeatable manufacturing workflow tailored to octagonal transmission poles. All three products share the same process, with dimensional variations by height.

Raw material preparation
- Q235B steel plates are sourced with mill certificates to EN 10204 3.1.
- Plate thickness and chemistry are verified upon receipt.
Plate cutting and beveling
- CNC plasma cutting forms the tapered octagonal plate patterns.
- Edge bevels are prepared to meet AWS D1.1 welding groove requirements.
Forming of octagonal shells
- Plates are cold-formed into octagonal segments using press brakes.
- Dimensional tolerances follow EN 1993-3 recommendations for towers and masts.
Longitudinal seam welding
- Automatic submerged arc welding (SAW) closes the octagonal shells.
- Weld procedures are qualified (WPS/PQR) to AWS D1.1.
Section assembly and flange welding
- For each height, sections are matched and flanges/connection plates welded.
- Bolt hole patterns are drilled and checked with go/no-go gauges.
Fitting of cross arms and attachments
- Cross arms, climbing steps, and earthing lugs are welded or bolted as per design.
- All attachments are positioned to maintain conductor clearances.
Surface preparation for galvanizing
- Degreasing, pickling, rinsing, and fluxing are performed to ASTM A123 process guidelines.

Manufacturing Process

According to the World Steel Association (2022), modern fabrication and corrosion protection can extend steel structure service life beyond 50 years in many environments, which aligns with SOLAR TODO’s design philosophy for transmission assets.

Surface Treatment

All three products use hot-dip galvanizing in accordance with ASTM A123, ensuring consistent corrosion protection across the pole family.

Hot-Dip Galvanizing Process

Pre-cleaning
- Oil and contaminants are removed by alkaline degreasing.
- Acid pickling removes mill scale and rust.
Fluxing
- A zinc ammonium chloride flux promotes metallurgical bonding between steel and zinc.
Galvanizing
- Poles are immersed in a molten zinc bath at approximately 450 °C.
- Coating thickness is controlled to meet ASTM A123 minimums.
Cooling and inspection
- Visual inspection checks for runs, bare spots, and drainage.
- Coating thickness is measured using magnetic gauges.

Surface Treatment

According to ISO (ISO 14713-1:2017), hot-dip galvanized steel in medium corrosivity environments can achieve 30–50 years to first major maintenance. This is particularly important in the humid, saline conditions typical of Caribbean coastal regions.

Quality Control

SOLAR TODO applies a multi-stage quality control regime to ensure structural integrity and compliance.

Material and Documentation

Mill certificates: Verified to EN 10204 3.1 for Q235B plates.
Traceability: Heat numbers tracked from plate to finished pole.

Welding Quality

Welding standards: Procedures and welder qualifications to AWS D1.1.
NDT: Ultrasonic and magnetic particle testing on critical seams and attachment welds.
Visual inspection: Weld profiles, undercut, and porosity checked against AWS acceptance criteria.

Dimensional and Fit-Up Checks

Pole straightness and taper: Verified against design drawings and EN 1993-3 guidance.
Flange flatness and bolt holes: Checked with calibrated gauges and templates.
Assembly trials: Random poles are trial-assembled in the factory to confirm fit.

Galvanizing Quality

Coating thickness: Verified to ASTM A123 using calibrated meters.
Adhesion and continuity: Visual and hammer tests on representative samples.

Structural Compliance

Design verification: Per ASCE 7-22 and AISC 360-22.
Documentation: Inspection records compiled into a quality dossier for each shipment.

An expert structural engineer from SOLAR TODO summarized the approach: “By aligning our internal QC with AWS D1.1, ASTM A123, and AISC 360-22, we ensure that every pole leaving the factory is fully traceable and structurally compliant over its intended service life.”

Production Timeline

The three products share an identical production schedule, optimized for batch processing.

Product 1: 9 m Pole (120 sets)

Design and detailing: 2 days
Procurement of raw materials: 5 days
Fabrication (cutting, forming, welding): 7 days
Galvanizing: 3 days
Inspection and testing: 2 days
Packing and loading: 2 days
Total production time: 21 days

Product 2: 10.5 m Pole (85 sets)

Design and detailing: 2 days
Procurement of raw materials: 5 days
Fabrication: 7 days
Galvanizing: 3 days
Inspection and testing: 2 days
Packing and loading: 2 days
Total production time: 21 days

Product 3: 12 m Pole (60 sets)

Design and detailing: 2 days
Procurement of raw materials: 5 days
Fabrication: 7 days
Galvanizing: 3 days
Inspection and testing: 2 days
Packing and loading: 2 days
Total production time: 21 days

According to McKinsey (2020), well-structured industrial supply chains can reduce lead times by 20–30%. SOLAR TODO’s standardized 21-day cycle for three different pole heights illustrates this efficiency.

Installation & Erection

Field installation procedures were designed to be straightforward and repeatable across all three pole types.

Site preparation
- Surveying and staking of pole locations.
- Excavation of foundations to specified dimensions (1.6 × 1.6 × 2 m or 1.7 × 1.7 × 2 m).
Foundation construction
- Placement of reinforcement (if required by local design) and anchor bolt cages (8 × M30).
- Concrete pouring and curing to local code requirements (e.g., IBC 2024 references).
Pole assembly
- On-site assembly of pole sections and cross arms where shipped in segments.
- Torqueing of flange bolts to specified values.
Erection
- Lifting using cranes with appropriate capacity and rigging.
- Plumb adjustment using anchor bolt nuts and shims.
Conductor and hardware installation
- Installation of insulators, hardware, and ACSR-240/30 conductors.
- Tensioning and sagging per IEEE and utility standards.
Final inspection
- Verification of clearances, bolt tightness, and earthing connections.
- Documentation of as-built conditions.

Installation

A senior field engineer commented: “The consistent geometry and bolt patterns across the 9 m, 10.5 m, and 12 m poles significantly reduced installation learning curves and minimized on-site errors.”