STRAINS ON GATES. 



by Mr. P. Barton l and Mr. Kingsbury, 2 all of which arc worthy of 

 careful study. 



In practically designing dock gates a largo excess of strength 

 beyond that theoretically indicated should be provided particularly 

 high np where the calculated strains are least to gnard against 

 rough usage, and to cover possible defects of workmanship or of 

 material. 



If the surface of the water in the dock is at a higher level than 

 that of the outer waterway, the pressure on the gates due to this 

 difference of level has to be withstood, and conveyed to the side 

 walls by the structure of the gates. 



If a dock gate be considered as divided by a scries of cross-sections 

 into a number of narrow vertical strips, say of 1 foot wide, the full 



a Highest Water Level A 



Lowest Water 



f Level Outside 



Sill 



FIG. 360. 



depth of the gate, then the total pressure on any such strip will be 

 the pressure per unit of length of the gate. 8 



P = total pressure on any strip or the pressure per unit of length 



of gate. 



W = weight of water per unit of measure. 

 D = depth of sill below highest water level. 

 d = depth of sill below lowest level of outer water. 



Then P = ^f(D 2 - d*) 

 2t 



If the outer water leaves the sill entirely dry d = o . 



W 



and P = D* 

 tt 



This pressure 4 is distributed throughout the whole depth in pro- 

 portion to the head of water at the various levels. In Fig. 360, a is 



1 M.P.I.C.E., vol. i. p 67. 

 Ibid., vol. Iviii. p. 157. 



8 Hid., xviii. p. 445. 

 4 Ibid., p. 158. 



