You bring the drinks, we'll bring the balustrades
The Insight
Australians have always appreciated a good verandah. Who can go past a BBQ on the deck or drinks on the balcony?
Our enjoyment is typically connected to the view, the fresh air and the people with us. Little thought is given to the balustrades that play a big part in our ability to enjoy these spaces. Firstly, they provide a psychological safety barrier that helps us feel safe. Secondly, they provide a physical safety barrier, largely to protect us from ourselves.
While the balustrades are not significant to the overall structure – a failed balustrade does not lead to a building collapse – they are significant for safety. They need to be designed to appropriately withstand prescribed structural loads and human behaviour.
The Impact
Protecting us from ourselves is a tough job. Balustrade heights are set at a level to prevent us from inadvertently toppling over. The design loads to be applied are there to prevent failure and vary depending on the risk innate to the use of the area (and our probable level of stupidity).
For instance, a verandah in a typical residence will need a balustrade with a top rail designed to withstand 0.75 kN/m horizontal and 0.75 kN/m vertical loads. This is equivalent to approximately 75 kg/m in the horizontal direction (for people leaning on or pushing against the top rail) and in the vertical direction (for people sitting or climbing on the top rail).
These vertical top rail values are the same across most applications, however the horizontal top rail values increase significantly as areas become susceptible to overcrowding such as for grandstands and bars. This increases to 3.0 kN/m horizontally – approximately 300 kg/m.
Failure of a balustrade to withstand required loads is a structural failure with virtually no structural impact, but potentially catastrophic safety ramifications. An under-designed balustrade can still fulfil our psychological needs, but physically it leaves us vulnerable. It is up to engineers to ensure that the reassurance provided by the presence of balustrades is justified.