4H NOTES ON DOCKS AND DOCK CONSTRUCTION. 



the highest water level, B b the level of the sill, and e the lowest 

 level of the outer water. Then A B == D, and E B = d. Make B b 



2 P 



= , draw b F parallel to A B, and complete the triangle A F I-]. 



The figure B A F b will then graphically represent the vertical dis- 

 tribution of the pressures or forces acting on the gate. The area of 

 the figure B A F 6 will represent the whole pressure, and if O 0' be 

 any part of the line A B, the portion of the pressure acting between 

 O O' is represented by that portion of the area B A F b which lies 

 between the horizontal lines O X and O' X'. Also the intensity at 

 any point O is represented by X, the portion of the horizontal line 

 through O, lying between A B and A F b. 



The diagram (Fig. 361) showing the value of the forces acting 

 on a dock gate is taken from Mr. Brown's paper on " Dock Gates." 1 



All questions of form and material are left out of consideration. 



FIG. 3d. 



A. pair of gates is taken as simply consisting of two rigid rods 1 inch 

 thick, supporting the water pressure, and meeting at the mitre. 



s = span of lock. 



r = rise. 



I = length of either gate. 



w = water pressure in tons per inch run. 



The dimensions are taken in inches, because the stress is alsvnys 

 measured in tons to the square inch. 



Then taking one gate as A B (Fig. 3G1), the forces acting upon 

 it are 



The water pressure, equivalent to w X I acting at the centre or 

 the middle point of the gate. 



The reaction at the mitre-post. This by symmetry will ac< dircd 1 y 

 across the lock in the direction of A. 



The reaction at the heel-post, which by ihc Iri.-inglr of I 



1 M.r.T.C.K., vol. xxxi. p. 318. 



