168 
The number found at the intersection of a diagonal with a weight re- 
presents in tons the strain produced in the diagonal by the weight in 
question. The sign + prefixed to a strain signifies that it is compres- 
sive; the sign — that it is tensile. 
The 10th and 11th columns contain the maximum strain of both 
kinds, compressive and tensile, which the moving load can produce. 
These are obtained by adding the numbers in the several rows—first, 
those expressing compressive strains; and, secondly, those expressing 
tensile. 
The last. column contains the strains which the load produces when 
distributed uniformly all over. These are obtained by adding algebrai- 
cally the strains in the several horizontal rows; or, more simply, by 
taking the difference of the two preceding columns. 
The table, on examination, will be found to corroborate what has been 
already stated, viz., that the maximum strains in the diagonals occur 
when the passing load covers, not the whole girder, but one segment 
merely. 
Thas, in the 6th row from the top, we find that weights 1, 2, and 8, 
in the left segment, produce compression in diagonal 6, while all the 
weights in the right segment produce tension. If, however, the load 
cover the whole girder, the resulting strain is equal to the difference be- 
tween the sum of the tensile and the sum of the compressive strains, 
i.e. is the same as would occur if weights 4 and 5 alone rested on the 
beam. 
The preceding method is the usual one; if, however, we wish to ex- 
press the maximum strains by formule, we must divide Girders into two 
classes :— 
Class A. 
Girders in which the first loaded apex is distant one whole bay from 
the abutment. 
Let there be loaded apices between any given diagonal and the 
abutment. The strain produced by the weight at— 
The Ist apex = = sec 0. 
2nd apex = 2 = sec 0. 
3rd apex=3 sie sec 0. 
W 
n apex =n —see 0, 
y 
The maximum strain is equal to the sum of these separate strains, 
Hence— 
Max. strain=(142+3+.... m) 2000, 
Max. strain = (1 + 7) av sec 0. (IV.) 
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