DC140 Guyed Monopole

DC140 Guyed Monopole

Designer

Dynamic Concepts

Structural Engineer

Woolgar Hunter

Steelwork Contractor

M & S Engineering Ltd

Main Contractor

Dynamic Concept (International) Ltd

Client

Crown Castle International Ltd

The DC140 guyed monopole is a most elegant and distinctive design. Available in a range of five standard heights, it is equally suited for greenfield sites, rooftops and urban settings. It resolves the visual problems of lattice towers by eliminating a large number of bracing components – its unique structure consists of a single CHS spine, with a series of cast steel arms linking this spine to three tensioned guy-rods (the number of “tiers” of cast arms depending on the height of the tower). This hierarchy of components produces an unusual and graceful form – the resulting silhouette is visually akin to that of a monopole, yet the structure is capable of reaching a height of 40 metres. The cast steel arms fulfil both structural and aesthetic functions as their sculptural forms, with cutouts to allow light to pass through, give the mast its distinctive visual identity.

The concept of the guyed monopole originally evolved from combining aesthetic simplicity of the traditional monopole with guyed lattice technology; however the way its structure performs is quite unique. Unlike guyed lattice towers, the central CHS spine of the DC140 has a fixed base that attracts bending moments, and horizontal cast steel arms at frequent intervals connecting the spine to the tensioned Macalloy tie-rods. The end of each horizontal cast arm is restrained by the guy rod, thus bending moments are attracted through to the central spine and distributed throughout the structure. The result is a base moment considerably less than that of a simple monopole structure. This fixed base moment imparts a high level of stability to the tower allowing the angle of the guys to be reduced from the normal 30 to 40 degrees to a mere 3.5 degrees from vertical on the DC140. With this, the footprint of the guyed monopole is reduced to an absolute minimum.

The DC140 is designed to provide for up to five telecoms operators, each using a full compliment of cellular panel antennae and microwave link. The monopole is cost-efficient and has advantages over more traditional towers in terms of speed of assembly. The central spine is formed from standard sizes of circular hollow section, and Macalloy bars provide an appropriate and readily available component for tie rods. Steel casting has proved to be an economical method of producing the structural arms, once the price of the initial moulds is absorbed the costs are far less than the equivalent fabricated component. While the DC140 weighs more than a lattice tower, its small number of components means that time spent on-site during construction and maintenance is dramatically reduced – for example, a 25 metre tower can easily be assembled within a few hours.

The guyed monopole has already proved to be extremely successful for sites where planning consent for more traditional towers has been refused, thanks to its distinctive architectural form.

Judges’ Comment

Radio coverage affects the whole of the UK, from areas of outstanding beauty to brownfield sites and industrial estates. These two structures and their associated family of masts give operations and planning authorities a wide choice for each situation. These two examples are beautifully fabricated, practical in operation and use as little as 20% of the footprint of a conventional lattice mast.