Description of Setting and Associated Townscape and Landscape.
Please see Stage 2 spiral bound submission, page 2: Architecture, Urbanism and Symbolism.
The Spire will be fabricated in sections in the fabrication workshop. The construction sequence has been designed to maximise prefabrication and minimise construction activity in O’Connell Street. Foundation works in O’Connell Street will proceed in parallel to the off-site spire fabrication. The 11-20 metre spire sections will then be assembled on the ground and erected in a 2 lift sequence which has been determined through detailed discussions with erection experts. The works on site will be limited to a secure compound and phased in order to limit disruption to trade and access in O’Connell Street, while ensuring the safety of Dublin’s citizens. Main lift operations, during which no traffic alongside the compound will be possible, will be executed at pre-determined times chosen to minimise inconvenience.
The spire will be fabricated from stainless steel grade 316L (L denoting low carbon content) manufactured and supplied in accordance with EN 10088. This is a material with great longevity due to its resistance to corrosion. Corrosion resistance is a particularly important consideration in Dublin where the structure will be affected by industrial and traffic pollution and the marine environment. Every effort will be made to ensure that corrosion will not be introduced to the structure during the manufacture. All fabrication operations including cutting and welding will be carried out under conditions of strict quality control. In addition the spire sections will receive a thorough post-fabrication clean before leaving the fabrication works.
The spire surface will be given a shot peened finish. This involves the use of stainless steel and glass beads to create a lightly textured surface. The shot peening process enhances further the corrosion resistance of the spire and retains the surface shine over a prolonged period. The effects of light on the surface are much softer than with a conventional brushed finish. The spire will reflect the changing light conditions of the streetscape and offer soft focus reflections of people touching its surface.
The base will be cast in bronze with a surface profile designed to prevent slipping. The techniques of casting a non-slip surface in bronze have been thoroughly researched. The bronze surface finish has a proven track record in its application to stair treads in rail and underground stations and other public buildings where safety is a priority. Bronze has the additional quality of improving in its chromatic and textural qualities as it weathers.
A series of fabrication and finishes samples have been produced by fabricators to the specification of Ian Ritchie Architects in order to examine their workmanship. Agreed samples will form part of the contracts between Dublin Corporation and contractors in order to ensure the required quality is met.
Conceptually the structure is simple. It is a conical spire which tapers from 3 metres diameter at the base to 0.1 metres as it cantilevers to the pinnacle at 120 metres height. Quality control in the process of fabrication will eliminate potential fatigue problems. The structural integrity of the spire has been studied over a 500 year fatigue loading analysis. Structural modifications, notably an internal `damping’ mechanism, resulting from this analysis have been incorporated in the design.