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have been thus used in ^■arious San Francisco Bay structures. In i)uiliUng Pier 29 in 

 1916, for example. (iri\en reinforced concrete (liles 20 inches square and 106 feet long 

 were used. For the outer 200 feet, ho\ve\er, the depth was so great that a single pile 

 length would not suffice and clusters of from 6 to 9 timber piles were driven to lielow 

 mud line, upon which reinforced concrete cylinder cohinms were superimposed. 



Strksses 



Piling is usually required to sustain only vertical loading. It may, however, be 

 calletl upon to resist horizontal forces, as for example when serving in retaining, or 

 bulkhead walls, dolphins, fender lines or ferry slip construction. Retaining or bulkhead 

 walls resist a constant static load, and are usually strengthened by brace piles and ties. 

 In other cases mentioned the function of the pile is to create a spring to absorb the 

 impact shock of boats striking the structure. This is illustrated in the case of ferry 

 slips where speedy operation is recjuired. The ferryboats must enter the slips cjuickly; 

 the first contact is with the fender piles, which resist the impact until they come in 

 contact with the back structure, which in turn is flexed and the boat brought to rest, 

 the fender and wharf piles thus taking up the shock gradually, so as not to injure the 

 boat. Current and wave action exert great forces on solid substructures, but as far as 

 actual stresses created in piling is concerned they seldom need be considered. Their 

 adverse effect is upon the material which goes to make up the piling. 



All elements c;f a pile must be capable of functioning imder these stresses without 

 rupture of any part. Concrete cannot be used where flexibility is required; and if 

 timber is used, its protections against marine borers must adjust themselves to flexure 

 without deterioration. 



Handling Piles 



All precautions against adverse influences after placement of piling may be nulli- 

 fied by careless handling before and in the placing. This would seem an obvious fact, 

 common to every material and form of construction, and yet all evidence shows that 

 it is far from fully appreciated in regard to timber piling. Especially after having the 

 piling preservatively treated is it equally important that it be carefully handled from 

 the treating plant to the job. Once the outer protective shell is penetrated, the value 

 of the pile is largely destroyed, except for possible repair; the borers, especially Lim- 

 voria. will take advantage of the smallest openings to the untreated interior wood. 

 The danger is increased by the fact that such damage due to mishandling may not be 

 apparent until some time after the construction is completed. 



Of the creosoted piles driven in structures of the Long Wharf, 13,000 pieces, or 

 about 93 per cent were treated at the Southern Pacific Creosoting Plant at West 

 Oakland and, therefore, received a minimum of handling to the job, yet an average of 

 about 30 per cent of the piles in the structure were subjected to attack by marine 

 borers on account of physical damage to the protective shell. The extent of damage is 

 likely to be in direct relation to the extent to which it is necessary to handle the piles. 

 On San Francisco Ba>-, at present, it is necessary to purchase all of these materials 

 from distant plants, involving a maximum amount of transportation and handling 

 and consequent damage. Being so far from the source of supply, it is necessary to keep 

 creosoted piling on hand at all times, which also adds to its chances of being damaged 

 before being used. All of this handling and storage makes it very diflicult to avoid 

 damaging piles. 



The survey of wharf substructures made by the Board of State Harbor Commis- 

 sioners in 1922, which has already been cpioted, showed that the dog is by far the worst 



