Technical Requirements for Steel Power Line Poles and Substation Gantries: Design, Welding, Galvanising

Which document covers what

The requirements for a steel power line pole or switchyard gantry come from several documents, not one. The PUE (2026 edition) cover loads, design cases, earthing and clearances in open switchgear. Steel members are designed to DBN V.2.6-198:2014, the execution of the structure (geometry, welding, bolted joints, inspection) is described in DSTU EN 1090-2:2019, and the zinc coating in DSTU EN ISO 1461:2024.

The specific figures for your pole are written by the design, and the shop fabricates to the KMD drawings. We prepare KM and KMD drawings or take them from the customer (KMD drawings). If a needed figure is missing from the design, we do not invent it but ask the designer. The table below shows what goes into the KMD and where each topic is covered in detail.

Tolerances and the extent of inspection for a particular pole are set by the design; the figures in our articles are guidance taken from current standards and production data.

Loads and design

The size of the shaft and foundation of a power line pole is governed by horizontal loads: wind on the structure, wind and ice on conductors and earth wires, conductor breakage. Design cases and the return period of loads are taken from the PUE (2026 edition). For poles and foundations the return period depends on the reliability class, which is set by the line voltage, and grows from 30 years for lines up to 1 kV to 500 years for lines of 500–750 kV. The cases and classes are covered in Loads on overhead lines and poles, and wind regions in the article on wind regions of Ukraine.

Poles and foundations are designed by the limit state method (PUE, cl. 2.5.25), and steel members are checked to DBN V.2.6-198:2014. Table A.1 of Annex A of this DBN puts overhead line poles in category A III, which directly affects the choice of steel. The consequence class of the facility is stated by the design or the customer; we do not set it (Consequence classes CC1–CC3).

The purpose of a pole (suspension, tension, angle, terminal) sets the loads and so the structure: Power line pole types by purpose. Typical lattice poles were designed to standards that have been updated since, so for a new line they are checked by calculation and the joints are strengthened where needed (Typical lattice poles). A multi-sided pole is designed for the specific line.

Shaft and sections of a multi-sided pole

The shaft of a multi-sided pole is a truncated pyramid with six or more faces. It is bent from plate on a 2000 t press (plate up to 25 mm thick, bend length 12 m) and welded with a longitudinal seam. A shipping section is normally no longer than 12 m: that is easy to transport and passes through the press and the galvanising bath. A shaft up to 12 m is one section, a taller one is built from several.

Sections are joined by flanges or by a telescopic joint. With flanges the height of the erected shaft matches the design exactly. In a telescopic joint the sections slide into each other and are held by wedging, so the sum of section lengths exceeds the height by the joint lengths. The joint length, its tolerance and the wedging marks are stated in the KMD (Joints of multisided poles).

How the shaft is fixed depends on the pole series. In our series it is as follows.

Foundation, protection of the buried part and the hatch

When a pole is set in a drilled pit, the backfill is sand-gravel or sand-cement mix. The buried part of the shaft is coated with bitumen at least 3 mm thick or another insulating coating: over 3.5 m from the butt for 35 kV lines and 4.5 m for 110 kV lines.

We design the foundation as a separate order and for a separate fee, or only pass on the loads while the customer designs it (Foundations for masts, towers and power line poles). We supply the anchor cage with its bolts both together with the pole and separately from it (Foundation anchor cages FPO, FPM, FKM).

A reinforced frame is welded into the hatch of power poles, and its thickness is set by the design. The hatch cuts out part of the wall, so the section in its zone is calculated as weakened.

Steel for poles

The steel grade and class are stated by the design: they are chosen by the purpose of the member, the structure group and the design temperature of the region. The lower the temperature, the stricter the impact toughness requirements. In an order the strength class and the grade to the standard are written together, and replacement with an equal-strength steel is agreed with the design organisation.

The designation «St3» without an index is incomplete. St3kp belongs to class S235, which under Table G.1 of DBN V.2.6-198:2014 is not allowed in structure group 2, and for line poles also not in group 3. Rolled products for steel building structures are supplied to DSTU 8539:2015. The step-by-step choice with tables is described in How to choose a steel grade to DBN.

Welds and their inspection

Pole welds are made to an approved procedure by qualified welders. Quality requirements for fusion welding are set by the DSTU EN ISO 3834 series, and permissible imperfections in a weld by the quality levels of DSTU EN ISO 5817:2022. The required quality level and execution class (EXC) are stated by the design: the execution class is determined under Annex U of DBN V.2.6-198:2014 as amended by Amendment No. 1.

The joint type, leg size, weld length and place of making (shop or site) are written into the KMD; the shop does not choose them in place of the designer (Weld joint types). Welds attaching flanges are made with full penetration.

In the shop all welds are inspected visually, including the longitudinal seam of the shaft. Internal defects are found by ultrasonic testing, which we carry out ourselves. We do not carry out radiographic testing, so it is better to mention such a requirement before the contract is signed.

Cracks in welds are not allowed: the defective section is gouged to sound metal, re-welded and re-inspected. What exactly we check in production is described in Quality control of steel structures.

Bolts, flanges and anchor cages

Flange joints of shafts work in tension, so the bolt class, hole type, tightening method and force are written into the KMD and not left to the erectors. Under DBN V.2.6-198:2014, bolts of class 10.9 or higher are used in flange joints with preload (cl. 7.8 as amended by Amendment No. 1). We supply fasteners together with the structures, so the class and coating are stated in the order.

The hole in a flange is only slightly larger than the bolt, so what matters is the relative position of the holes: it has to match the anchors of the cage. The flange is not forced into place on site; a mismatch is corrected in the foundation before the pole arrives (Anchor bolts for poles and masts).

Nuts are locked with a lock nut or another device against loosening, and welding them to the shank is not allowed. In bolted joints of line poles the thread must stay outside the plate pack (cl. 16.2.5 of the DBN). Holes in parts thicker than 6 mm that are to be galvanised are better drilled than punched, because cracks can appear near a hole after cold punching. Shear, bearing, tightening and inspection are covered in Bolted connections in steel structures.

Galvanising and corrosion protection

The main protection of line poles and gantries is hot-dip galvanising to DSTU EN ISO 1461:2024. The minimum coating thickness depends on the steel thickness: for an article over 6 mm thick it is 70 µm local and 85 µm average, for over 3 up to 6 mm it is 55 and 70 µm. The table and the order of measurements are covered in Zinc coating thickness.

The bath measures 13,000 × 1,600 × 3,200 mm, and the mass of one article is up to 7 t. A 12 m section goes in along its length, and the cross-section of the bottom section together with the flange is checked against the width and depth. Longer articles are galvanised in sections, sometimes in two dips, and this is agreed separately (Part size limits).

The structure is prepared for galvanising already at the KMD stage: holes for air and zinc drainage are provided, rib corners are cut off, and no closed cavities or lap joints without a closed weld are left (Designing for hot-dip galvanising).

Powder coating is limited by the 6 × 1 × 1.8 m chamber, so a pole is not coated whole: a section or part that fits in the chamber is. Duplex (zinc plus paint) is agreed before galvanising. A pole without zinc is protected with a paint system agreed with the customer.

Earthing of poles

Under the PUE (2026 edition), cl. 2.5.127, metal and reinforced-concrete poles of 3–35 kV lines, poles with an earth wire or other lightning protection, and poles carrying apparatus are earthed. The maximum resistance of the earthing device is given by Table 2.5.29: from 10 to 30 Ω depending on soil resistivity, and by a formula for ρ above 5000 Ω·m. The table and the details for 3–20 kV lines are covered in Earthing of poles above 1 kV under the PUE.

Reinforced-concrete foundations of poles on lines of 110 kV and above may serve as natural earth electrodes if the anchor bolts are metallically connected to the reinforcement (cl. 2.5.128). On 35 kV lines the required resistance is achieved with artificial earth electrodes (cl. 2.5.130). The designer takes values for a particular line from the current text of the PUE, and the result is confirmed by measurement after the work.

A place for an earthing bolt is provided on the shaft, but the bolt is not fitted on every product. Its place, diameter and clean contact surface are stated by the design; for powder coating this spot is masked with a plug or tape.

Switchyard gantries

Clearances on a gantry are set by Chapter 4.2 of the PUE (2026 edition), where open switchgear is called VRU (ORU in Russian-language texts). The minimum clearances in air between phases, to earthed structures and to ground are taken from Table 4.2.1 (cl. 4.2.51, 4.2.54), and for flexible busbars the swing of the conductor in wind is added (cl. 4.2.52). Values for 35, 110 and 150 kV are given in Multi-sided switchyard gantries 35–150 kV.

Multi-sided gantries are made from bent shafts that are bolted by flange to a foundation made as a pipe. There is a separate page for 220 and 330 kV (Multi-sided switchyard gantries 220 and 330 kV). Layouts and heights that are not in the tables we design individually. Switchyard lightning protection is covered separately (Switchyard lightning protection under the PUE).

Acceptance and documents

In the shop the lengths, section sizes, position and diameters of holes, perpendicularity of flanges to the axis and straightness of the axis are checked against the KMD, the welds are inspected, the zinc is measured and the marking is verified. Tolerances and the extent of inspection for a particular pole are set by the design, so we do not quote figures without it. If an anchor cage ships with the pole, it is checked against the flange already in the shop.

Together with the product the customer usually asks for the metal documents, the KM or KMD drawings, an assembly diagram with instructions, the zinc thickness results and records of weld inspection. The list is agreed before fabrication starts (Accepting multi-sided poles).

On site the foundation and anchor bolts are checked, then the sections are assembled and the pole is erected. Technical supervision is carried out by the customer, and erection by a partner construction company under a work execution plan (Assembly and erection of multi-sided poles).

Standards and validity

DBN V.2.6-198:2014 «Steel structures. Design standards» is current: the e-construction register holds an edition dated 7.04.2026, and Amendment No. 1 has been in force since 01.09.2022. DSTU EN 1090-2:2019 «Execution of steel structures and aluminium structures. Part 2. Technical requirements for steel structures» has been in force since 01.07.2020 and replaced DSTU B EN 1090-2:2014. DSTU EN ISO 1461:2024 has been in force since 12.01.2024. DSTU 8539:2015 «Rolled products for steel building structures» is current.

For welding, DSTU EN ISO 5817:2022 (quality levels for imperfections) and DSTU EN ISO 3834-2:2022 (quality requirements for welding, part 2) are current. The PUE are in force in the new 2026 edition: clauses and tables in this article follow it, and the designer checks the final values against the current text. DSTU B V.2.6-199:2014 (fabrication of steel structures) was withdrawn on 02.02.2026, so references to it in old designs and contracts no longer confirm any requirements.

Mentioning a document in this list is not a statement that a product conforms to it: the requirements of a specific order are fixed by the design and the contract. The figures in this article that are not from standards are taken from our catalogues and production data; for your pole they are confirmed by the drawing.