x86 THE IMPROVEMENT OF RIVERS. 



Sheathing Plates. These may be of buckled or of flat plates. The former are prefer- 

 able, as they possess much more strength than the flat plates, and permit of wider panels 

 between the beams without requiring vertical stifTeners. Their actual strength is a matter 

 of experiment, as it cannot be calculated. The following values were found for plates 

 3 feet square, well bolted down on all sides.* 



Tki..i._. Safe Load per Sq. Foot 



(Onc-fuurth Broking L.d). 



\" 1 1 20 Ibs. 



,V" '540 " 



f" 2240 " 



Where the plates are supported on four sides, but not bolted or riveted down, 

 the above loads are to be reduced one-half. If two sides only are supported the loads 

 are to be reduced in the proportion of 8 to 5. 



The resistance of flat plates under conditions such as exist when they are em- 

 ployed as skin plates is likewise a matter of uncertainty. The most recent and prob- 

 ably the most reliable experiments in this field are those of Professor Bach of Stutt- 

 gart, who gives the following formula for flat rectangular plates, subject to fluid 

 pressure: 



t =cb 



in which t = the thickness of the plate in inches ; 



c = a constant = 0.6 1 for a plate riveted down all around; 



a = length of plate between supports in inches ; 



b = breadth of " 



p = intensity of fluid pressure in pounds per square inch ; 



/ = maximum allowable tensile stress in the metal in pounds per square inch. 

 The spacing of the rivets in the plates, as regards securing water-tightness of the 

 joints, need not be closer than 6 inches, and examples are in use where the spacings 

 were made 9 inches, and have proved perfectly tight under heads of 14 to 1 6 feet. 



Single and Double Sheathing. The use of double sheathing for gates, that is, of 

 plates on both up-stream and down-stream sides, has been chiefly confined to very 

 wide locks. The object of the double plating is to provide water-tight compart- 

 ments near the bottom of the leaf so as to secure buoyancy and consequent reduction 

 of weight. This lessens the strain on the anchors, and facilitates maneuvers. In 

 practice, however, they have hardly proved an unqualified success. It has been 

 found difficult to keep the chambers free from leakage, and when the water gets in 

 Ihe gate loses its buoyancy, and the second skin merely acts as an additional and useless 

 load, defeating the very purpose for which it was put on. This style of gate, where 



* Pocket Companion Carnegie Steel Co., 1900. 



