The Conditions are
Stability, Survivability, and Impact Loads
The stability of a dock increases as the square of its beam. A three foot wide
dock is one seventh as stable as an eight foot wide dock. Whether the dock
is wooden, made of palm fronds, or concrete, a three foot dock Is one seventh
as stable as an eight foot dock.
A dock being pushed by a wall of water (wake from an 80 footer, tidal surge or
tsunami) is being impacted by a large amount of energy, which must be
counteracted, usually by the pilings or by flex, in accordance with the material’s
design criteria or otherwise. The energy of the dock doubles when the weight
doubles, but it increases four times when the speed of the water doubles.
Try to push a nail into wood with your palm and nothing happens. But give it a
good whack with a hammer and you’ll see how “impact” amplifies the load.
Lateral impact loads can be very destructive to structural members, particularly
at the fasteners. Each flex event wears down the wood at the fasteners,
making the system unstable.