Eco-friendliness is the watchword of architecture today. And aluminium clearly stands out as the right choice for the purpose. The recyclability of aluminium saves almost 170 million tonne of greenhouse gas emissions per year. It has excellent UV and sea water resistance.
Also aluminium allows architects and structural engineers more creative liberty owing to its wonderful formability and unlimited colour options. Moreover, aluminium’s ability to form alloy with many elements like manganese, magnesium, zinc et al, makes aluminium alloy delightfully versatile. Its physical and mechanical properties can be varied widely and thus used for a vast range of applications.
All this makes aluminium alloy the most important component of facade works. It is an essential component for both framework and ACP. The alloys which are used today are: AA1100/ AA3105/ AA5005/ AA6063.
Ideally we should stick to the earlier norm of taking into account the chemical properties of these alloys rather than their mechanical properties. But many do the reverse which isn’t the right way of going about it.
Majorly all of these are magnesium and silicon based alloys. The amount of magnesium decides the anti-corrosiveness, and silicon decides its ability of being moulded into different shapes.
|AA1100||0||Fe+Si = 0.9|
|AA 3105||0.2 – 0.8||0.6|
|AA 5005||0.2 – 1.1||0.3|
|AA 6063||0.45 – 0.9||0.2 – 0.6|
These alloys are given the required tensile strength, thickness and shape according to their chemical properties. We should decide usage of these alloys considering their applications.
AA 6063 have the properties for extrusion and when we anodize it or powder coat it, its life in exterior becomes long enough because of the amount of Magnesium. AA 6063 is used in the framework of facades.
Two things that we need to check before installing the framework are:
Maximum Stress: Z > (w*l2)/(8*δ%0.2)
Deflection: L/200 > 5*w*L4 /E*I*384
Z: cross section module of bottom construction (mm3)
W: Wind Load (N/m)
L: support interval (mm)
E: Elastic Module (N/mm2)
I: Moment of Inertia (mm4)
δ%0.2: %0.2 Stress Endurance (N/mm2)
This would enable us to calculate the frame interval, L, according to wind load and mechanical properties of the alloy.Also, when we calculate the panel size of the ACP, alloy is the major factor as it is the one which would take the wind load of the entire panel.
Maximum stress that can be withstood by a panel can be calculated from the tensile load of the alloy. So, to calculate the panel size, we would calculate the maximum stress being applied on the panel, and if that is less than the maximum allowable stress that can be borne by the panel, only then can it be the exact panel size.
Applications of AA 1100, AA 3105 and AA 5005 alloys are decided in the similar way as discussed above. The chemical properties of an alloy decide the cost of it. The alloy with minimum chemical properties, as regards being used for ACP, is given the lowest tensile strength and the alloy with higher chemical properties is given a higher tensile strength. AA1100 gives us 120 N/mm2 to 140 N/mm2, AA 3105 gives us 150 N/mm2 to 180 N/mm2 and AA 5005 gives us 180 N/mm2 to 220 N/mm2.
The panel size is according to the wind load and stress which a panel can take:
δ max: β x w x b2/t2
where δ max is stress taken by panel
β coefficient from panel size ratio and connection type
w: wind pressure (N/mm2)
b: Length of shorter side (mm)
t2: (Panel Thickness3- LDPE Thickness3)/ Panel Thickness