一一 130 — 
Mr. B. Baker, C.E., in tl Beams, Columns, and Arches,” treats of pins merely 
incidentally. He finds, that, for iron in solid circular beams, tlie average value 
of 0 is /, where / is the ultimate resistance per square inch to rupture by ten- 
sion, and 0 the difference between the apparent ultimate resistance per square inch 
to rupture by bending anti /, according to the equation F =/ 4 - 0 , F being the 
apparent ultimate resistance per squaro inch of tlia extreme fibre which first gives 
way ; and, that for steel, tho value of 0 varies between 1.7/ and 1.9/» 
Professor Burr devotes five pages of his work on li Stresses iu Bridge and 110 of 
Trusses n to the subject, of pius, ami illustrates tlie particular case of a suspension- 
bridge cablo pin, and a goneral case for ordinary truss-bridge pins. 
Professor Du Bois, in ** Strains in Framed Structures,” also gives a mathema- 
tical discussion of how to find tlie maximum bending-momeiifc. 
Table XIV. gives the working bendiug-moiueuts on all tlie iron and steel pins, 
and tlie working-sliear on all the steel pins, which will ever be required. Having 
calculated tlie beiuliug-moment, the requisite diameter for the pin can be found by 
looking down the proper column until a bentling-moment at least equal to the one 
found is reached. The diameter will bo found at either end of tho horizontal row 
thus located. The use of the column for shear will be made apparent presently. 
Tlie upper anti lower horizontal lines iu tlie table of bearings (Table XV) give 
tlie diameters of the pins ; the extreme vertical lines, tlie necessary widths of bearing- 
surface afc each end of the pins, iucliuling both cliauuel and re-enforcing plates ; and 
the other vertical lines, the permissible pressure, on the bearings. Tlie method of 
using these tables is tlie following. The pressure which the pin is to carry is to be 
taken from tho diagram of stresses. A trial diameter is then assumed. The ver- 
tical column, headed by this diameter, is to be followed down, until a number 
nearest the pressure to be carried is found. At either end of tlie horizontal row 
thus located 、vill be found the proper witltli of bearing. Knowing the width of bear- 
ing, diameter aiul pressure, tlie moment to which the pin is subjected may be at 
once calculated. Tun], then, to Table XIV, and see if this moment agree with the 
working-moment coiTespoudiiig to the trial diameter. If it does, all right: if not, 
another trial is to bo made, with a new assumed diameter. After a little experience, 
tlie first trial will be sufficient. A consideration of other details, such as wkltlis 
and depths of eye bars, etc., will frequently aid very much in these trials. 
Tablo XV can be used for bearings in members of lateral systems, portal brac- 
ing an cl vertical sway bracing by multiplying the calculated stresses by t'vo thirds. 
To find the least value of tho ratio of tlie diameter of pin to depth of eye bar 
in an iron bridge, by considering the tension in the bar, and tlie pressure between 
tlie pin anil bar, —— 
Let 
w = width of bar, 
di = depth of bar, 
d = diameter or pm, 
C = intensity of working compressive stress, 
T == intensity of working tensile stress ; 
