structures built about the same tire as the two mentioned have given no 

 particular worries. That doesn't mean, however, that they will not give 

 trouble as time goes on and it is believed that all these structiares should 

 be carefully -/ratched for some years to come and a special inspection has 

 been instituted in regard to tViem that will do just that. Concrete hulls 

 for other structures such as floating dry docks and barges of which the 

 Bureau has a considerable number have in general p:iven remarkably little 

 trouble in a period of about seven years of active service and as regards 

 them, a statement made oreviously in this talk is again made, namely, 

 that if our water front structures are built in strict accordance v.'ith 

 our latest concrete standards they v/ill be ^ood structures. Hull mainte- 

 nance costs on these concrete floating structures in comparison Y;ith steel 

 are very low, possibly in the order of 20/o, For this reason, in new designs 

 for such structures, the Bureau is going just as far as possible in the use 

 of concrete. 



In these ne\i studies of the use of concrete for floating structures concrete 

 is being given every possible break in the Y:ay of taking advantage of the 

 possibilities of precasting and orestressing the concrete, decreasing 

 coverage for reinforcing steel, using mes'^- reinforcement in lieu of bars, 

 etc. This is all design, however, which should be left to others on the 

 program but it is mentioned because it has to do with possible later 

 deterioration problem. At the end of the war, two experimental concrete 

 barges were constructed, one largely of precast concrete box construction 

 and one of prestressed concrete construction. These barges have novir been 

 in constant normal water front use for a period of about seven years and 

 both have been satisfactory, and maintenance costs on them have been very 

 low. It is significant to note here that the prestressed concrete one 

 which might be expected to have a minimum of cracks, has the greater number 

 of cracks and there is some indication th.at some prestressed elements or 

 areas are no longer in the original condition. If this is the case, pre- 

 stressed concrete loses a lot of its appeal from the maintenance point of 

 viev; because the main thing sovight in such construction was more insurance 

 against salt water attack on reinforcing steel and other embedded metals. 

 In the present state of t^e art of prestressin? in this country, claimed 

 economies from prestressed concrete are considered decidedly futuristic. 



Many more things could be touched on in a talk like this if time allowed. 

 It is thought, however, that the best -/ay to follow up the points men- 

 tioned as needing further study is by conferences, exchange of data and 

 perhaps sometimes by correspondence. The Bureau is always glad to share 

 in these activities as previously indicated, and delegates are invited to 

 follow up particular interests v/ith the Bureau at this present meeting 

 or at any future time. 



D - 10 



