192 PRESENT STATUS OF THE CONCRETE SHIP. 



forced concrete oil tanks then in service indicated that mineral oils had no deleterious 

 effects on concrete which was cured before contact with the oil. The series of tests 

 now under way confirms this conclusion and shows that certain organic oils do have 

 a destructive effect on the concrete used. 



The penetration tests are being made with oil under a maximum head of i6 feet. 

 The penetration into 1-2-4 concrete for the lightest oil used {y^.J Baume) was 

 about 1.6 inch in 40 days, and for the heaviest oil (95.5 Baume) it was about 0.27 

 inch. Preparations are being made for tests under a head of about 25 feet. 



Tests are under preparation to determine the relative advantages, for taking 

 stress, of placing slab reinforcement parallel to and at an angle with the direction of 

 the span. No results for these tests are available as yet. 



In a beam having large variation in the area of the cross-section there is uncer- 

 tainty as to how much of this area is fully effective in resisting the tensile and com- 

 pressive stresses. Analysis indicates that, if the entire area is available, the use of 

 properly designed haunches in ship frames may permit a reduction in the weight of 

 ship frames of from 20 to 30 per cent of the weight required on the basis of existing 

 standards. A series of tests to obtain information on this question is now under 

 way, but no results are yet available. 



The unit stresses now employed in the structural design are as follows : — 



CONCRETE. 



1. Maximum unit compressive stress in the extreme fiber in 



flexure IjSOO lbs. per sq. in. 



2. Maxijnum unit compressive stress in the extreme fiber in 



flexure, adjacent to support of a continuous or fixed ended 



beam 1,700 lbs. per sq. in. 



3. Maximum unit compressive stress in stanchions 1,000 lbs. per sq. in. 



4. Maximum unit shearing stress in tee beams and in 



bjd 



shell or other slabs 500 lbs. per sq. in. 



In isolated beams 300 lbs. per sq. in. 



5. When the maximum unit shearing stress is less than 50 lbs. per sq. in., the con- 



crete may be considered to carry all the shear. 



6. When the unit shearing stress is greater than 50 lbs. per sq. in, reinforcement 



should be provided as follows: — 



(a) In the design of thin slabs, used as the webs of beams, with the shearing action 

 perpendicular to any local shearing stress such as the shell, provide shear rein- 

 forcement according to the formula and the diagram prepared by W. A. 

 Slater, and a formula for combining shear and local stresses. 



(&) In all other cases provide shear reinforcement to carry the full amount of the 

 shear. 



