NZ Landscaper Magazine
THE SUBSTANCE OF BEING HOLLOW
Thanks to uniform stress, a hollow tree doesn’t always mean a weak tree. This is worth considering if a client has asked you whether a tree should be removed because it is hollow or has a hole in it
As you read this, you’re probably sitting in a building with walls and hollow internal spaces called rooms. You could be in your work vehicle; a hollow structure with outside walls and an inside space called the cab. You may well be drinking from a cup, can or bottle; a hollow vessel. You push a wheelbarrow, drive a car, ride a bicycle - all connected to the ground with tyres; hollow rubber things filled with air.
Every day you are surrounded by, use and/or depend on hollow things. These hollow things are not just hollow, as in mostly empty on the inside, but they are also structural.
Hollow load-bearing things that support hollow structures that hold hollow things – if you think about it, many of the things that we consider to be solid are not entirely solid. A wall of concrete is just an outer shell used to create a space. We literally live in hollow things. So why am I pointing out the obvious, and why should you care?
HAVING NOTHING ON THE INSIDE, (BEING HOLLOW) IS UNIMPORTANT AS LONG AS THE OUTSIDE CAN HANDLE THE LOAD.
APPLY YOUR KNOWLEDGE TO THE NATURAL WORLD
Being surrounded by hollow engineered structures is one of those instances where we know something at one level, but don’t use that
insightful email they entered their office through a door – a large hole in a wall. They sent their letter of concern to a person, who upon reading it, gazed out through a hole in the side of their building (a window) in despair and thought ‘heck there is a big hole in the side of a tree and the tree will fall down because there is a hole in it.’
So not only are we surrounded by hollow things that don’t fall down, but many of the hollow things that don’t fall down have holes in them too. Who would have thought?
So, how are you going to use this insightful bit of information that you already knew? How are you going to apply your knowledge in a way that might be useful?
The next time you find a tree with a big hole in it or you tap a tree and it sounds hollow, don’t instantly assume that it will fall down. It might, but it might not.
UNIFORM STRESS MATTERS
In nature, strength is created through uniform stress (the axiom of uniform stress). Engineers have been learning from nature and they too design structures that are incredibly strong yet hollow by applying the concept of uniform stress. It’s all about the shape and thickness of the shell wall – the outside layer that supports everything.
If you are so inclined and still retain a sense of balance (I don’t necessarily recommend you do this), place an empty aluminium can upright on flat ground (the can will have to be empty, but otherwise undented or misshapen in any way), then with grace and elegance place one foot on top of the can, then slowly and smoothly lift your other foot off the ground so all of your weight is transferred onto the foot that is on top of the can. It’s possible that an