What causes natural movement in architectural façades?
Various environmental and physical factors can cause façades to move which must be considered in the design stage.
In a nutshell:
• Weather conditions can cause significant movement and structural stress.
• Changing climates can cause façades to thermally expand and contract which causes movement.
• Fluctuating live loads (people/vehicles) adds weight onto floor slabs which impacts façade fixings.
• Traffic, construction, and other activities cause micro-movements that can affect building stability over time.
• Movement joints (expansion gaps) help absorb structural stress, preventing façade failure.
• FEA predicts how façades will respond to different conditions, ensuring durability and safety.
You may be surprised to know that buildings can move in response to various physical factors such as thermal expansion and wind loads. This naturally affects architectural façades which are consequently at risk of failing due to added stress caused by movement.
Weather
Wind loads are a large contributing factor as to why buildings move and architectural façades fail. Not only can wind cause buildings to shake and façades to weaken, but it can also cause façades to be lifted off buildings. Many believe that when a façade breaks due to wind loads, it's because the façade has been ‘blown off’ the building when in reality it's due to suction. It happens because when wind impacts a building, it creates low pressure and suction behind the façade causing it to ‘lift off’.
Snowfall also creates additional loads on façades and buildings. Heavy snowfall in particular can weigh down façades and cause them to move and shift if not accounted for.
Fluctuations in temperature can also cause façades to expand and contract, creating movement. On a hot, sunny day a façade will thermally expand causing structural stress and warping whereas on a cooler day, it will contract which can cause cracking.
Live loads
As well as external loads, façades will experience internal live loads (people and vehicles) that will constantly change day-to-day, particularly car park façades. When vehicles enter a car park, this adds loads onto the flooring slab causing it to move, which then adds stress onto the brackets attaching the façade to the steelwork substructure. Therefore, car park façades must be able to accommodate the various weights and movements of numerous cars throughout their lifespan.
Ground activity and vibrations
Although earthquakes are incredibly rare in the UK, other activities can cause the ground to move such as vibrations from traffic and construction which, over time, can cause micro-movements.
Ways to account for natural movement in façade design
During the design stages, there are many measures a façade company can take to prepare their design for natural movement.
One method is incorporating a movement joint within the façade system to allow for natural movement. A movement joint, sometimes called an expansion joint, is a gap between façade elements that absorbs structural stress caused by moving elements.
Another precautionary measure is undertaking structural calculations such as finite element analysis. FEA is a form of desktop simulation that can predict how systems will perform under various conditions and help designers identify any weaknesses in their design.
To accommodate for live loads, façade companies typically liaise with respective clients who will advise on the predicted maximum deflection of the floor slab.