INTO THE STRENGTH OF WROUGHT-IRON PLATES. 
691 
found necessary, as the metal gave indications of weakness in consequence of the lap 
being rather narrow. Another reason for enlarging the lap was a desire at the com- 
mencement to begin with the least possible quantity, and by direct experiment to 
ascertain the maximum distance which the plates should overlap each other in the 
joints, and to determine the strongest and best form of uniting them. To these points 
every attention was given, for the purpose of collecting the facts on which are founded 
the tabulated results on that part of the subject which treats of the comparative dimen- 
sions of rivets and extent of the lap in reference to the thickness of the plates. In this 
department of the inquiry will be found the depth of lap, diameter and length of rivets, 
and the distances of holes for nearly every description of joint ; also the thickness of 
the plate, with a column of strengths as deduced from the experiments. 
If we examine the nature of the fracture in the foregoing experiments, it will be 
found that the machine-riveting is superior to that done by the hammer ; the mean 
of the three first experiments being to the mean of the fourth and fifth as 5 ; 4. In 
the eighth and ninth the strengths are nearly the same. 
On comparing the strength of plates with their riveted joints, it will be necessary 
to examine the sectional areas taken in a line through the rivet-holes with the section 
of the plates themselves. It is perfectly obvious, that in perforating a line of holes 
along the edge of a plate, we must reduce its strength ; and it is also clear, that the 
plate so perforated, will be to the plate itself nearly, as the areas of their respective 
sections, with a small deduction for the irregularities of the pressure of the rivets 
upon the plate ; or in other words, the joint will be reduced in strength somewhat 
more than the ratio of its section, through that line, to the solid section of the plate. 
For example, suppose two plates, each 2 feet wide and three-eighths of an inch thick, 
to be riveted together with ten f-inch rivets. It is evident that out of 2 feet, the length 
of the joint, the strength of the plates is reduced by perforation to the extent of 7^ 
inches; and here the strength of the plates will be to that of the joint as 9:6T87, 
which is nearly the same as the respective areas of the solid plate, and that through 
the rivet-holes, namely, as 24 : 16’5. From these facts it is evident that the rivets 
cannot add to the strength of the plates, their object being to keep the two surfaces 
of the lap in contact, and being headed on both sides, the plates are brought into 
very close union by the contraction or cooling of the rivets after they are closed. It 
may be said that the pressure or adhesion of the two surfaces of the plates would add 
to the strength ; but this is not found to be the case, to any great extent, as in almost 
every instance the experiments indicate the resistance to be in the ratio of their 
sectional areas, or nearly so. 
If we take the ultimate strength of the Yorkshire plates in Tables Land II., it will 
be found that the mean breaking weight of eight specimens, each with a sectional 
area of '46 inch, is 26,168, and the strength of the single joint*, of the same descrip- 
tion of plates with an area of '44 inch, is 18,591 ; this reduced gives the ratio of the 
* I use the term single joint to distinguish it from the double riveted joint, w'^hich will be treated of hereafter. 
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