CHANOINE WICKET DAMS. 



23? 



The journal-boxes should be bored ^" to T y full, to secure easy movement and 

 prevent rusting up. 



The sectional area required in the horse for the tension T and to resist strains from 

 the chain in raising is small compared with that required to stand drift, twisting, etc., 

 and experience is consequently the best guide for proportioning it. The upper cross- 

 piece, to which the head of the prop connects, must be made strong enough to 



T f 

 support the bending moment caused by the latter, which equals X , where /= width 



between the uprights of the horse. This piece is sometimes made with ears forged 

 to and projecting above it, and provided with a pin to which the prop connects. This 

 method, however, is objectionable, as it causes a twisting strain, besides adding to the 

 cost of manufacture. Dimensions employed in actual practice will be found in the 

 next paragraph. 



Prop. The strain 5 on the prop is essentially one of compression, and should be 

 determined as for a "pin-bearing" column. A section must first be assumed, and if 

 r = its radius of gyration in inches, and / the length of the prop in feet, the ultimate 

 strength per square inch by the usual formula for columns will be in pounds. 



50,000 



i + 



i8,ooor 2 



As in the horse, the section should be made ample. Thus for the Port-a-1'Anglais 

 dam (1870) the strain allowed on the props was only 1600 Ibs. per square inch. 



The head -of the prop should be bored i" to T 3 ? " full, to allow the proper lateral 

 movement when sliding along the hurter. 



The lower portions of the props for a pass are usually forged out to a considerable 

 increase of area. The object of this is to provide a weight which the water cannot 

 easily move, and so prevent a proper seating being obtained in the hurter. In view, 

 however, of the fact that this increase has been found unnecessary on weirs under an 

 8-foot head, where the rush of water is much more violent than on passes, it would seem 

 that the additional weight given to props on the latter is somewhat superfluous. 



The following are examples of sizes used for horses and props : 



SIZES OP PROPS. 



