ice covers while smaller interior bays and lakes become completely ice-covered. The ice is never
stationary but moves in response to winds and currents.
Ice exerts forces on structures in several ways. Moving sheets or floes press horizontally against
vertical structures like walls and pilings. Slender structures such as piling can be heavily damaged under
these conditions. If the ice sheets adhere to the structure, sudden changes in water level can cause
considerable vertical loads. A decrease in water level can force pilings deeper into' the bottom, while a
rise will tend to jack the piles upward while soil collapses beneath the tip and prevents the pile from
returning to its original position.
Structures located on the lakes and some bays, therefore, must withstand heavy ice loadings
(horizontal) if they extend into the water. Vertical loadings are also important on the lakes. Protective
measures might include air bubbler systems, pile sleeves, and use of floating structures.
Availability of Materials
Structures should be designed and built with locally available materials when possible. In some
areas, such as the Pacific Northwest, timber is plentiful and somewhat less expensive than other
materials. Rock is available in most areas, as are scrap tires and concrete. Some proprietary devices,
however, are fabricated only in certain places, and their use may require high transportation costs. An
alternative should be chosen only after comparison of different designs utilizing a range of available
materials.
Vandalism and Theft
A final factor is the susceptibility of the structure to vandalism. If this is a problem, materials
should be selected which cannot easily be cut, carried away, dismantled, or otherwise damaged. For
instance, sand-filled fabric bags are easily slashed by knives, small concrete blocks can be stolen, and
wire mesh baskets can be opened with wire cutters and the contents scattered.
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