Joints of multisided poles: flange, telescopic joint, hatch, anchor cage — what to state for the designer

Which joints we cover

The shaft of a multisided pole is a truncated pyramid with six or more faces, bent from sheet and welded with one longitudinal seam. Everything else is joints, and each has its own responsibility. The table below puts them together; each is covered in more detail further down.

The joints depend on each other: the flange holes must match the anchors of the cage, and the flange size together with the bottom diameter of the shaft must fit the galvanizing bath.

Flange connection: design, bolts, tightening

Flange connections on bent multisided poles are made with bolts on a circle or on the outline of a rectangle. They join the sections to each other and the shaft to the foundation. The main property of a flange joint: the height of the erected shaft matches the design height exactly.

The bottom diameter of the shaft equals the flange diameter, so it is chosen for the type and size of the foundation. The foundation for 6–10 kV line poles is made as a pipe with a flange, and for 220 kV as a steel pipe joined to the bottom section by flanges. The hole in the flange is only slightly larger than the bolt, so in a request what matters is not the diameter of a single hole but the relative position of all the holes.

Catalogue examples: the park pole PMO-7 is fixed with four M24 bolts at a hole spacing of 220 mm, the floodlight mast PM-20 with twelve M30, PMV-20 with sixteen M36, a 25–40 m telecom tower with 12–20 bolts M36–M42. For comparison, the European standard EN 40-2 gives, for a square flange with four holes, a row of bolt-axis spacings from 200 to 550 mm, but our series have sizes by our own catalogue and do not always match that row, so replacing a pole with one from another maker without the flange drawing is not advisable.

The welds that attach the flanges are made with full penetration and checked by non-destructive testing, most often ultrasonic; in the shop we check welds by visual inspection and ultrasound, and we do not carry out radiographic testing. For lighting poles EN 40-2 limits the deviation of the flange from the perpendicular to the shaft axis to 1°; for line poles and masts the limit is taken from the project.

Bolts, tightening and checking

The class of bolts and nuts, their pairing and coating are chosen by the joint calculation, not by what is in stock: the article on fastener strength classes explains how the bolt class relates to the thread and to galvanizing. On tall masts the bolts in a flange joint are high-strength and tightened to a controlled torque, with no gaps left between the flanges.

In our installation recommendations the mounting bolts are tightened to not less than 15 kgf·m, but the final value is set by the project and the pole drawing. The tightness is checked by the method of the project or of the manufacturer’s instructions; a practical technique is tapping with a 0.4 kg hammer (the bolt does not vibrate or move) and a 0.3 mm feeler gauge (a technique from the former DSTU B V.2.6-200:2014, withdrawn on 02.02.2026). All the nuts are tightened before the slings are removed, and a lock nut keeps the anchor nuts from backing off. On galvanized poles the nuts are tightened once more after a week, because the zinc compresses, and on tall masts the tightening is repeated after the first period of service.

Plumbing and grouting

There are two installation schemes: the pole is set on an already levelled foundation or plumbed during erection with the support nuts. When plumbing with nuts, the flange rests on levelling nuts and the gap is grouted with non-shrink mortar. The shaft is put on the bolts with the control mark on the flange aligned with the mark on the cage.

The pole is lifted when the foundation concrete has reached the strength set by the project: in our installation recommendations this is not less than 50 %. If a bolt has drifted, this is corrected before the pole arrives, and the flange is not fitted by force on site. Details are in the articles on assembly and erection of poles and anchor bolts.

Telescopic joint of sections

A pole taller than 12 m is assembled from several sections. The sections are joined by flanges or telescopically, when one section enters another. A telescopic joint holds by wedging when pulled together, and the sections are not welded to each other on site, since that would damage the zinc. Thanks to the taper, the pulling load creates a tight joint that transmits the bending moment without slip.

The joint length in the project is taken at roughly one and a half to two diameters of the sections joined, that is about 1.8 of the mean diameter. The tolerance on the joint length is 10–12 %, so the actual height of the shaft may differ from the design height, and this is allowed for in the calculation. Example: with a mean diameter in the joint zone of 0.4 m, the joint length is 1.8 × 0.4 = 0.72 m, and the deviation at the upper limit of tolerance reaches about 86 mm per joint. In a telescopic joint the sum of section lengths exceeds the shaft height by the length of the joints: for 24 m with sections up to 12 m three sections are needed, 25.44 m in total.

On our line poles the lower and middle sections have stiffening diaphragms at the top, which prevent the telescopic joint from crushing under design load. On tall flagpoles the lowest joint is the longest, the top one the shortest, and the length of each is set by the designer; a shaft with other joint sizes must not be used without agreement.

Assembly and checking of the joint

Before assembly the surface in the joint zone must be clean and free of unevenness, and the sections lie in turn on wooden supports levelled horizontally. The sections are pulled together with a rising load until mutual movement stops; the recommended pulling load is not less than 10 t. They are pulled with jacks or hoists by special lugs on the sections, and without lugs with a winch whose cable runs inside the shaft. During pulling, the evenness of the load is watched: skew and premature wedging are hard to correct.

The joint length is checked by marks within which the wedging must occur. The marks are usually applied by the manufacturer; if there are none, the erectors apply their own following the assembly instruction that the plant includes in the accompanying documents. During lifting the sections must not slide apart, so the joint is fixed at the lugs with temporary devices or slung in a special way.

Hatch: purpose, size, position

The hatch serves to bring in the cable and to install a protective device. It is made at the bottom of the pole above the ground. On flagpoles an electric panel and the lifting drive sit behind the hatch, and on masts with a mobile crown the hatch is locked with a security bolt. The basic set of a lighting pole is a galvanized shaft with an inspection hatch; there is no cable entry in the supply, and additional hatches and holes are agreed when ordering and made to an individual design.

According to EN 40-2 in our summary, the hatch is placed parallel to the bracket on the side opposite the direction of traffic. The lower edge of the hatch must be at least 300 mm above the ground, about 600 mm is recommended. The hatch is flush with the surface, without sharp edges; in metal poles the corner radius of the hatch is not less than 20 mm or half its width. Typical sizes in the standard are from 132 × 38 to 600 × 130 mm, the size tolerance is +10/−0 mm, the protection degree is IP 3X up to 2.5 m above ground, and the type impact test is to class IK08.

Our own hatch sizes are given in the catalogue tables of the series: the height and width of the hatch and its distance to the base of the pole.

From the catalogue «Structures for outdoor lighting». For masts of other heights and for individual poles the hatch size is set by the drawing. The position of the hatch relative to the bracket and the road is stated in the request.

Weakening of the section and reinforcement

The hatch cuts away part of the shaft wall, and at the bottom of the pole the bending moment is greatest. In the section calculation the weakened section is taken in the hatch zone. On load-bearing poles a reinforced frame is welded into the hatch and its thickness is set by the project; on other poles the need for reinforcement is shown by the calculation for the particular pole, not by habit. The rounded corners of the hatch under EN 40-2 are not for looks: a sharp corner concentrates stress and a crack can start there. In pole inspections, cracks around the hatch are among the places that are checked.

The hatch and the cable opening are cut before galvanizing: cutting on the finished coating damages the zinc. The edge is cleaned to bare metal. A plate around the hatch is welded with a continuous double-sided weld so that acid and flux do not stay in the gap.

Anchor cage

Anchor bolts are not set in concrete one by one: they are assembled into a cage in which templates hold the bolts in the design position until the concrete gains strength. The cage is cast into the foundation in advance, and the pole is then set on the bolts without fitting. In the catalogue the cages are divided by purpose: FPO for lighting poles, FPM and FPMV for floodlight masts and lightning rods, FKM for catenary poles. The size tables are in the article on foundation anchor cages, and the choice of bolts in the article on anchor bolts.

The choice starts with the pole, not with the cage. The diameter, number and spacing of the bolts must match the holes in the flange. A few examples: PMO-7 (four M24 bolts, spacing 220 mm) on the FPO-1000-1 cage, the PM-20 mast (12 M30 bolts) on FPM-570-950, the PMV-20 mast (16 M36 bolts 1,200 mm long) on FPMV-810-1200. A larger cage must not be taken «just in case»: it simply will not fit under the flange.

We make the cages of steel S245/S345 to DSTU 8539:2015 and supply them without coating. Whether the thread above the concrete needs protection, and which, is decided by the foundation design. Before concreting, the cable duct and the earthing lead-out must be in place, and the cage is braced so that the pressure of the mix does not move it. Each bolt is measured and the result is entered in the as-built diagram.

We prepare the foundation design to a separate order and for a separate fee; often we only pass on the loads to the foundation and the customer designs it. We also supply cages separately from poles, for example when the foundation is prepared in advance.

Earthing of the pole

A place for the earthing bolt is provided on the shaft. According to the project an additional earth connection is attached to the pole contact with an M16 bolt; this is only a connection point, and the pole is earthed when it is connected per the project and the resistance is measured. For lighting poles EN 40-2 in our summary requires an earthing clamp that resists corrosion, is clearly visible and easy to reach, with a bolt of the fixed part of not less than M8. The place of the bolt on the shaft, its height and side, is stated by the project; the bolt is fitted not on all products.

The surface under the earthing bolt must be clean. It must not be tightened on a dirty or painted surface, so for powder coating this place is closed with a plug or heat-resistant tape and marked on the drawing.

The cage can also be a link in the earthing. Under the PUE (2026 edition), on overhead lines up to 1 kV metal poles on reinforced concrete foundations must have a metal connection between the metalwork and the foundation reinforcement (cl. 2.4.33). For poles of lines of 110 kV and above, reinforced concrete foundations can be used 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 must be achieved with artificial earth electrodes (cl. 2.5.130). These are requirements for the line project, and the designer takes the values from the current text of the PUE. In detail: earthing of metal poles and earthing of overhead line poles above 1 kV.

Galvanizing of joints and drainage holes

A pole section is usually not longer than 12 m, so it passes through the 13,000 × 1,600 × 3,200 mm bath by length. The cross-section of the bottom section together with the flange must also fit the bath; this is allowed for when choosing the base diameter and the flange size. About the sizes for all the operations see the article on part size limits.

In long hollow sections (over 6 m) the holes for air and zinc drainage are made larger or more numerous. Near the base plate make at least two drain holes diagonally between the anchor-bolt holes, as close to the shaft wall as possible, and cut the corners of stiffening ribs near the plate: in a corner with three planes the flux evaporates before the zinc gets there. In plates and flanges that close a hollow section provide holes for air and zinc. Plates are welded with a continuous double-sided weld.

Provide points for lifting and hanging: lifting lugs. Bolt holes are sized with the coating in mind, because zinc reduces the diameter, and the thread of nuts is run through after galvanizing. Bolts, nuts and washers for assembling galvanized structures must be galvanized with a coating thickness of not less than 42 µm. The rules for holes are covered in detail in the article on designing for hot-dip galvanizing. Holes, flanges and hatches should be cut before galvanizing, not after.

What to state in the KMD and in the request

We prepare the KM and KMD drawings from which the pole is made or receive them from the customer (KM and KMD design). For the joints to agree with the foundation and the erection, the drawing and the request state:

Where mistakes are most common

• the holes in the flange do not match the anchors: the bolt in the concrete has drifted or the holes were marked not to the cage layout. The flange must not be fitted by force, the foundation is corrected;
• the cage is taken «with a margin», of a larger size;
• the height of a shaft with a telescopic joint is counted as the sum of the sections and it is forgotten that the sum is longer by the length of the joints;
• a section joint without marks and without an assembly instruction: erectors wedge the sections at random;
• the slings are removed before the nuts are fully tightened, and lock nuts are not fitted;
• the hatch is cut without a calculation of the weakened section, with sharp corners;
• plates and flanges that close a hollow section without holes for air and zinc;
• the earthing bolt is tightened on a painted surface, and the earthing lead-out from the foundation is forgotten before concreting;
• the flange together with the bottom diameter of the shaft does not go into the galvanizing bath.

Standards and validity

The design and detailing of steel poles, including flange and bolted joints, is done under DBN V.2.6-198:2014 «Steel structures. Design standards» (current, with Amendment No. 1). The earthing of overhead line poles is described by the PUE (2026 edition): the clause numbers above are given as in our articles on earthing, and the designer checks the final values against the current text. Hot-dip galvanizing is covered by DSTU EN ISO 1461:2024 (current); recommendations for the designer by ISO 14713-2:2019.

The dimensions and tolerances of lighting poles (hatch, earthing clamp, flange) are set out in the European standard EN 40-2:2004; we give it as a reference, not as a statement of conformity of our products. The validity of the national equivalent of EN 40-2 is checked separately before it is cited in a project. The figures in this article that do not relate to standards come from our catalogues and installation recommendations; for your pole they are confirmed by the drawing.