(Contribution from the Bureau of Yards and Docks) 



DESIGN FACTORS AFFECTING DEriRIOR^TION OF MARBIE STRUCTURES 



■ ■ by Ralph C. Stokes 



The engineer is acutely aware of the destructive forces which are ever 

 at work on marine structures. Liany centuries of experience have demon- 

 strated the severity of the attack which involves chemical, physical and 

 biological processes. The battle to overcome the damaging effects has 

 taken many different turns and made use of every knovm available con- 

 struction material. None of these is exempt from the ravages of all types 

 of deterioration, but each is vulnerable to one or more of the destructive 

 processes. 



Much can be done to extend the useful life of waterfront structures by 

 proper attention to arrangement of parts, selection of materials, choice 

 of optimum shapes, and the use of protective applications. The three 

 principal construction materials, timber, steel and concrete can all be 

 used effectively if the results of experience are kept in mind. The 

 purpose of this paper is to present some of the methods ^irhich have been 

 adopted by the Eureau of Yards and Docks to obtain maximum length of 

 life at a minimum overall cost. 



'Timber Construction; 



No doubt the first crude structures built to accommodate shipping were of 

 wood. The rapid deterioration which followed probably led to the observa- 

 tion that certain species were more resistant to decay than others. Per- 

 haps the next discovery- was made by the Phoenicians, who practiced the 

 charring of wood to obtain greater life expectancy. 



It is interesting to note that -;food preservation, in a modern sense, did 

 not begin in earnest until the second quarter of the nineteenth century. 

 Although the present m.ethod of injecting creosote into wood under consid- 

 erable pressure was devised by John Bethell in 1833, the method did not 

 attain commercial importance until 1875. 



Hazards to Timber Construction: 



Timber waterfront structures suffer principal damage from the hazards of 

 decay, marine borers, abrasion and fire. 



By far the greater portion of the damage done to timber results from the 

 action of decay and marine borers. If timber is continuously submerged, 

 there is no decay. However, marine borers must be considered a menace 

 at most locations on salt water. Thus for marine structures, the borers 

 threaten timber below rirater, decay is active above water, and both do 

 damage in the tide zone. 



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