Dublin's design pinnacle
The Spire of Dublin's simple elegance belies the complex design and engineering process behind its construction Dublin has a new monument - a slender spire at the heart of the city which soars 120m above the rooftops. By day, the stainless steel spire reflects the city's changing light and shadow; by night, the base glows gently while the illuminated tip shines out like a beacon over the city.
The concept and design is by Ian Ritchie Architects, the winner of an international competition for a monument to celebrate the third millennium and to be the centrepiece of wide-scale urban improvements.
Its position - on O'Connell Street at the junction with Henry Street and North Earl Street - is significant in Dublin's history.
This was the site of Nelson's Pillar, a memorial built in 1808 and blown up in 1966 by the Irish Republican Army. It is also next door to the General Post Office, the headquarters for the Easter Rising in 1916 and a place of pilgrimage for Republicans everywhere.
The spire is a stainless steel cone, tapering from 3m in diameter at the base to 150mm at the tip. Ritchie's inspiration for the spire's form evolved from a study of standing stones and obelisks and from an ambition to create a monument which would be as slender and vertical as possible as it escaped the roofline of Georgian Dublin - and, crucially, would capture the light of Ireland's skies.
'The spire reintroduces a vertical counterpoint to the prevailing horizontal nature of O'Connell Street's buildings, without visually interrupting the streetscape, ' says Ritchie. It was decided that the maximum desirable base diameter should be 3m and this led to a proportion of base width to height of 1 in 40 - an elegant but technically challenging specification.
The spire was fabricated in eight sections (see pages 42-43) from stainless steel grade 316L (L denoting low carbon content) manufactured and supplied in accordance with EN 10088. This grade is extremely resistant to corrosion, a necessary factor in an environment where traffic pollution and wind-borne marine salts are both present.
The stainless steel surface was given a shotpeened finish, a process which uses stainless steel beads to create a lightly textured surface that enhances corrosion resistance and diffuses light. The effects of light on a peened surface are much softer than with a conventional brushed finish. The top 12m of the spire is perforated with approximately 12,000 holes to allow light to escape and to illuminate the upper surface of each hole.
The spire rises from foundations below ground and passes through a 7m diameter bronze base plate set at pavement level.
Bronze was chosen for its historical associations with the development of art in Ireland and for the fact that it weathers well. An elegant logarithmic spiral design was machined into the surface of the 16 bronze plates to produce an anti-slip surface.
In concept and basic structure, the spire is extremely simple - a cone which tapers from 3m to 150m at the pinnacle in a simple cantilever. But the research undertaken into the materials, finishes and structural implications (see structural description below) belies the simple elegance of the final result.
CREDITS ARCHITECT Ian Ritchie Architects:
Ian Ritchie, Robin Cross (project architect), Gordon Talbot, Phil Coffey CLIENT Dublin City Council STRUCTURAL AND SERVICES ENGINEER Arup QUANTITY SURVEYOR Davis Langdon & Everest LIGHTING Ian Ritchie Architects/La Conch MAIN CONTRACTOR SIAC/Radley Engineering joint venture SUPPLIERS Steel forming Barnshaw Steel Bending