147 



( )nl\- tlu- i)rc-cast rectangular pile and the jirecast shell type of jacketed pile ha\e 

 been considered in this outline. These are the more conservative types and are not 

 covered by trade names or patented processes. There are a number of proprietary 

 types of both reinforced concrete and concrete jacketed piles wiiich have Ix-en used 

 successfull)- and have merit, while otlier t\pes have proved inadequate and unsatis- 

 factory for use ill sea water. The effectiveness of these proprietary types can be 

 measured by the requirements of the foregoing specifications. 



Gexkral 



The specifications here presented eml)od\- less exacting requirements, in some 

 particulars, tjian ha\'e often been achocated. This is due to a con\iction that, while 

 it is admittedly possible to produce more nearly perfect concrete than that specified, 

 the increased perfection is accompanied b>' a cost increased out of pro]iortion to actual 

 efficiency- gained; furthermore, iiroxisions requiring onerous precautions, not practi- 

 cable ill the field, are usually ignored, and the result is frequently a poorer quality of 

 work than can be obtained Ijy less exacting reciuirements well carried out. 



These specifications are an attempt to co-ordinate cost and quality, so as to 

 produce a concrete having the highest combined efficiency in sea water resistance and 

 economic cost. The resulting concretes will all test from 2000 to 3000 lbs. in 28 days, 

 the 1 to 71 2 concrete having practicalK' the same strength as the 1 to 5 when used and 

 manipulated as specified. We have ample exjierience to show that such concrete is 

 satisfactory in resisting sea water on San Francisco Bay. For the strength and quality 

 of concrete obtained, the specifications represent an economic balance in the cost of 

 cement, aggregate and manipulation, for San Francisco market conditions; and no 

 increase in any of these elements of cost is likely to produce a corresponding increase 

 in the value of concrete obtained. 



On the other hand, these specifications, in other particulars, such as placement 

 of reinforcing steel, concreting under sea water and the protection of concrete in marine 

 structures by asphaltic or other similar paint coatings, represent requirements seldom 

 thus far enforced by most engineers charged with marine concrete construction. In 

 respect to these requirements, however, a very extensive aggregate experience in this 

 Bay is conclusive that the practices specified will so greatly increase the sea water 

 resistance and, consequently, the eftective life of the resulting structures as to pay 

 many times over for any extra cost of following the requirements involved. 



In conclusion, it should be remembered that while "simple" and "composite" 

 structures are discussed separately, for the purpose of contrasting their behavior, 

 and "harbor" and "ocean" exposures are differentiated to emphasize the effect of 

 varying conditions, in design and practice no distinct line of demarkation can be drawn. 

 Between these extremes there is a wide range of practicable combination of structures 

 and a great variation in degree of exposure. Sea water exposed structures should be 

 designed by experienced engineers if the lowest ultimate cost is to be obtained, taking 

 into consideration all factors of first cost, maintenance and efficiency of operation. 

 No outline of practice, however complete, will take the place of actual experience, 

 and important structures should not be undertaken without the service of a skilled 

 engineer. 



METAL PILES 



Steel and cast and wrought iron piles have been used successfully under certain 

 conditions for many years, particularly by the U. S. Government in military and 

 lighthouse structures. The first installation in San Francisco Bay appears to have 

 been in the Quartermaster's Dock at Alcatraz Island built about 1870 with cast iron 



