Basics for Thermal Expansion on Facade Components
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions1. The dimensional change is calculated by a coefficient (α) which means unit expansion against each unit temperature difference (∆T=T2 -T1).
Facade components such as aluminium profiles, metal cladding, glass, gaskets, fiber cement boards etc. also effected by daily or season outer temperature differences, sun heating effects, inner air condition factors etc. In spite of different type effects, linear and area expansion situation considered for facade. All the materials have their own coefficient of expansion and behave as an individual part. This means the design must be suitable to compensate this natural movements for each material.
Daily temperature differences are important but to decide the limits we need to work with winter and summer lowest and highest limits. But if the material is opaque and the sun heating is so strong, we need to consider very hot surface heating.
Aluminium profile has a big expansion coefficient (24.10-6/K) and this requires special solutions considering insulation and expansion situations together. In general, only mullion profiles are considered for thermal expansion effect. This is a common understanding as a result of the phenomenon which explain longer elements expands longer. But transoms, aluminium window frames, aluminium decorative profiles, finishing materials etc. also effect by temperature differences.
Mullion profiles are fixed on an upper or lower beam (concrete, steel wood etc.) and other connections are designed free in linear direction. Lower or upper beam selection changes according to the deflection limits of the beam in general, lower limits are better for fixing. But if there are doors are located in curtain wall, lower fixing will be better.
Another critical point is the different kinds of materials which fixed each other such as aluminium & steel. Steel is used as a reinforcement material or sub-construction for aluminium solutions in general. The connections must be designed suitable with expansion properties and structural requirements. For example; connections may be slotted according to expansion direction, or hole diameters maybe bigger on aluminium component which let enough movement.
