6.102 Steel . Where steel is exposed to weathering, allowable working 

 stresses must be reduced to account for corrosion and abrasion. Certain 

 steel chemical formulations are available which offer greater corrosion 

 resistance in the splash zone. 



6.103 Timber . Allowable stresses for timber should be those for timbers 

 more or less continuously damp or wet. These working stresses are 

 discussed in U.S. Department of Commerce publications dealing with 

 American lumber standards. 



6.104 Stone . Stone for protective structures should be sound, durable, 

 and hard. It should be free from laminations, weak cleavages, and un- 

 desirable weathering, and should be of such character that it will not 

 disintegrate from the action of air, sea water, or in handling and placing. 

 All stone should be angular quarrystone. Tlie greatest dimension should be 

 no greater than three times the least dimension. All stone should conform 

 to the following test designations: apparent specific gravity, ASTM C 127; 

 and abrasion, ASTM C 131. Density is in pounds per cubic foot (solid cubic 

 foot without voids). In general, it is desirable to use stone with a high 

 specific gravity to decrease the volume of material required in the struc- 

 ture. 



6.11 MISCELLANEOUS DESIGN PRACTICES 



Experience with the deterioration of concrete, steel and timber in 

 shore structures may be summarized in the following guidelines: 



(a) Within the tidal zone, the elimination of as much bracing 



as is practicable is desirable; maximum deterioration occurs in that zone. 



(b) Round members, because of a smaller surface area and better 

 flow characteristics, generally have a longer life than other shapes. 



(c) All steel 



(c) All steel or concrete deck framing should be located above 

 normal spray level. 



(d) Untreated timber piles should not be used unless protected 

 from marine-borer attack. 



(e) The most effective injected preservative appears to be 

 creosote oil with a high phenolic content. For piles subject to marine- 

 borer attack, a maximum penetration and retention of creosote and creosote 

 and coal-tar solutions is recommended in accordance with standards of the 

 American Wood- Preservers Association. 



(f) Boring and cutting of piles after treatment should be avoided. 

 Where unavoidable, cut surfaces should receive field treatment. 



(g) Untreated timber piles encased in a gunite armor and properly 

 sealed at the top will give economical service. 



6-98 



