The design, structure and environmental considerations of Alba di Milano
Conceptually the structure is simple. It consists of three main elements; 2 cantilever tubular members, a cable net and a base foundation. The tubular members taper from 1.5m at the base to 0.5m as it cantilevers to the tip at 42m. They are fabricated from mild steel. The cable net is assembled using small diameter stainless steel cables. Overall the structure is a balanced cantilever. The overturning moments due to the wind and snow are resisted by a combination of bending action and the self weight of the reinforced bases.
The angled cantilever is wrapped in light emitting fiber optic fabric.
The foundations are sculpted to form seating for people to gather and rest beneath DAWN.
Fiber Optic Fabric
DAWN is wrapped in a textile woven from fiber optic threads. Each 1.5mm glass fiber is encased in plastic Megalon material. The fibers are then woven into a fabric. The weaving process causes the glass fiber threads to partially ‘break’, forming points from which light is diffused. When connected to a light box the fabric glows across its surface. Megalon glass is PVC free, will not degrade under ultra violet light, extreme temperatures or pollution or be damaged by attack from insects or birds. The textile can be woven with an additional stainless steel thread which will sparkle in daytime. No electrical current passes through the fabric.
Light flows through the fiber optic fabric from 72 LT100-MH-CW Metal Halide lightsources enclosed in an IP65 housing situated within the superstructure frame. A chromatic disc in the lightsource generates waves of coloured light which flows through the fabric, creating a plane of bright fluidity.
The lightsources are powerful enough to render the fabric bright during daytime. However the fabric will be particularly radiant during evening and night.
Heat from the lightsources is naturally ventilated. There is no heat build up in the fabric.
The superstructure consists of two tubular steel corrosion resistant grade 55C members embedded into the concrete foundations. The tubular members taper from 1.5m diameter at the base to 0.5m at the tip.
The cantilever is fabricated from steel using conventional techniques and can resist loads both perpendicular and parallel to the plane of the fabric.
The cable net structure spans between and transfers the fabric weight, wind and snow loads to the cantilever trusses. The cable net consists of 10mm diameter stainless steel cables at 1200mm centres spanning between the trusses. Running parallel to the trusses the stainless steel weft thread of the fabric is utilised and is an integral part of the cable net. The cable net has been designed as a `loose fit’ allowing the fabric to react to the wind and snow loads.
The superstructure is locked into reinforced concrete foundations. No load is applied to ground above the underground passage but is instead dispersed either side. The bases are sculpted reinforced concrete. They are cast on top of the existing ground slab but straddle the areas with restricted loading. The bases are located over the `strong’ points of the structure below. Further investigation into the existing structure will be required.
Concrete grade C40 with high yield, fy = 460N/mm2, reinforcement is to be used for the substructure elements. High cement content, low water cement ratios, increased cover and care during curing will be used to ensure a good quality durable material.