where heavy ice, either in the form of solid ice sheet or floating 

 ice fields may occiir, adequate precautions must be observed to insure 

 that the structure is secuj^e against sliding on its base. Ice brealcers 

 may be required in relatively sheltered water xriiere wave action does 

 not require a heavy type stnictureo 



2li5« Floating ice fields may exert a major pressture on stimctures, 

 when driven by a strong T-.jind or cxirrent, by piling up in large ice 

 packs agai.nst the obstructions » This condition must be given special 

 attention in the design of small isolated structures » However, because 

 of the flexibility of the ice field, the pressures exerted probably are 

 not as great as vrould be caused by a solid ice sheet in a confined area* 



2l+6« lee formations may at times cause considerable damage to 

 shore lines in local ar-easj but their net effects are largely beneficials 

 Spray thrown up by i-ri-nd and wave action during the td.nter may freeze 

 on the banks and stractures along the shore^, covering them with a 

 protective layer of ieec. Ice piled on shore by mnd and wave action 

 does notj in general^ cause serious dcunage to beaches^, bulkheads, or 

 protective riprap, and generally provides additional protection against 

 damage from the severe x-jinter storm wavesa Some abrasion of timber or 

 concrete structtires may be caused and individual meitibers may be broken 

 or bent due to the weight of the ice mass. Piling have been slowly 

 pulled by the repeated lifting effect of ice freezing to the piles or 

 attached obstructions su.ch as wales, and then being forced upx^j^ard by a 

 rise in water stage or wave actiono 



1IATERI.ALS 



2li7, The structural design of shore protective works must take into 

 account the effects on the materials used, of the environmental conditions 

 peculiar to the shore lire areao General modifying eritex-'ia whi.ch should 

 be applied to materials comDionly iised are discussed in the following para- 

 graphs » 



2it8, Concrete . - Concrete esq^osed to sea water, freezing and thatd-ng, 

 or other destructive agents or conditions should have an ultimate com- 

 pressive strength of 3,000 pounds per square inch» A rich, dense, stiff 

 mix is to be preferred where placement is to be done undertj-atera Cai-e 

 should be taken^ when reinforcing steel is to be used, to cover the steel 

 adequately thereby minimizing possible spelling and er^osure of the steels 

 Working stresses for those conditions may be found in the Corps of 

 Engineers Engineering Manual for Civil l^orks, Gonstrmction, Part CXXI, 

 Chapter 1, Aug-ust 19h7<i 



2^9 • Steel . - VJhere ejiposed to we at hering^ allowable wor-lcing stresses 

 must be reduced to take into account corrosive action, abrasion, or the 

 combination of both which would result in loss of effective steel area« , 

 Working stresses for reinforcing and structural st-eel may be found in the 

 preceding reference » 



123 



