Silhouette

Ian Ritchie Architects, along with Jane Wernick Associates, engineers, and Ann Christopher, Sculptor, entered the competition ran by The Royal Institute of British Architects (RIBA) in partnership with the Department of Energy and Climate Change (DECC). There were 250 applications from around the globe and our team came in joint second. The National Grid intends progressing our design along with the Danish winner. Sara L’Esperance led the design concept at Ian Ritchie Architects.

The attenuated sectioned cone shape of the pylon exaggerates its reach to the sky. Its reflective exterior skin and matte black concave interior produce a dynamic silhouette as the viewer moves past… sometimes appearing as a full black lance and other times as a thin sliver, like a single brushstroke on a canvas.

Up close, we engage the pylon at the threshold between earth and sky, at the pivotal point where it is mirrored downwards into the earth. With its asymmetrical arms, the pylon becomes an animated character in the landscape… a line dancer, part of a series or pattern… while the convex exterior skin reflects its surroundings and makes it eternally site specific.

The landscape exists within the pylon as the pylon exists within the landscape.

SUSPENSION TOWER

Although the external appearance of the pylon is of an open conical form, regular internal linking beams are set back from the open side to form an enclosed semi-circle. These beams provide the pylon with sufficient torsional strength and stiffness.

The maximum torsion in the suspension pylon is due to the broken wire condition (case 5b in the briefing documents) applied to the wire at the end of the longer arm. Torsion is also generated by cases 1a and 3 since the line of action of the horizontal loads is eccentric to the shear centre of the section.

TENSION TOWER
The magnitude of the lateral loads parallel to the arms for the tension pylon are about 3 times those of the suspension pylon. For the design of the arms, the critical vertical load (case 2a) increases by about 15% and the critical horizontal loads (case 5b) by about 40%. The arm profile could be the same as for the suspension pylon with an increase in plate thickness. Alternatively the size of the arm cross-section could increase by 20-30% to reduce the plate thickness and weight. In order to keep the plate thicknesses of the conical tower similar to the suspension pylon the diameter should be increased by a factor of about 1.5. Preliminary analyses indicate that the magnitude of the torsion in cases 1a and 3 (due to the line of the arms being eccentric to the shear centre of the section) is less than the torsion due to the broken wire condition (case 5b). Therefore, the torsional strength and stiffness required will be about 40% greater than for the suspension pylon. This should be accommodated with the increased size, but may require a small increase in the size of the linking beams. Possible alternatives to the increased diameter would be a combination of thicker plates and modifying the linking beam structure to increase its effectiveness.

Since much of the structure is a continuous surface, not consisting of discrete beams, a finite element computer model of the structure would be used to optimise the design. Such models are increasingly used for the design of building structures and have been used for many years in the aircraft and automotive industries.

The structure will be designed to the latest Eurocodes.

STAINLESS CLAD STEEL PLATE
Clad steel plate is a composite steel plate made by bonding stainless steel plate (cladding material) to either or both sides of a carbon steel or low alloy steel plate (base metal). Only one side will be clad in Stainless steel for the P12 pylon. Clad steel not only has the necessary structural strength (base metal), but it also satisfies other requirements including resistance to heat and corrosion. (Information provided from the JFE Corporation Clad Steel) The Clad Steel would be supplied in sheet form to the UK where it would be rolled. The 316L Stainless Steel cladding material would then be polished to achieve the desired reflective finish.

CAST NOSE
316L polished Stainless Steel castings will be welded to the arms and to the top of the pylon above the earth wire to achieve the smooth round effect of the extremities.

CONCRETE BASE
The concrete base will be in C32/40 concrete.

LEIGHS PAINT – ANTI-CORROSION EPIGRIP C400V3
Epigrip C123 is a high build durable coating which offers long term corrosion protection for structural steelwork, bridges and transport infrastructure in aggressive environments. (Information provided from Leighs Paints) P12 pylon will be painted to achieve the matte-black finish on the interior face of the tower, as well as on the ladder and linking rectangular hollow sections. The paint finish will allow these elements to blend into the silhouette of the pylon producing clean, striking marks in the landscape.

INSULATOR SYSTEM
P12 pylon proposes the use of conventional glass high voltage insulators.

STRUCTURAL STEEL/BOLTS
All structural steel is to be Grade S355 steel. Bolts are to be grade 10.9.