488 
ME. W. H. BAELOW 0'S THE EESISTAXCE OF FLEXUEE EN' BEAAIS. 
Tabulated Eesults. 
Number of 
1 Hodgkinson’s 
series. 
Upper flange. 
Lower flange. 
Thickness 
of centre 
web. 
Deptli of 
Breakine 
Breaking 
Computed 
Breadth. 
Depth. 
Breadth. 
Depth. 
girder. 
distance. 
weight. 
Talue of f. 
inches. 
inch. 
inches. 
inch. 
inch. 
inches. 
ft. 
in. 
lbs. 
lbs. 
1 
1-75 
•42 
1-77 
•39 
•29 
4 
6 
6,678 
14,578 
2 
1-74 
•26 
1-78 
•55 
•30 
4 
6 
7,368 
14,128 
3 
1-07 
•30 
2-10 
•57 
•32 
Mean. 
H 
4 
6 
8,270 
14,005 
4 
No upper flange. 
2-27 
•52 
•405 
4 
6 
8,720 
13,868 
9 
1-05 
•34 
3-08 
•51 
•305 
H 
4 
6 
10,727 
14,765 
11 
1-60 
•315 
4-16 
•53 
•38 
4 
6 
14,462 
14,832 
12 
1-56 
•315 
5-17 
•56 
•34 
5f 
4 
6 
16,730 
14,181 
15 
2-35 
•29 
5-43 
•537 
•35 
t;.5 
4 
6 
16,905 
13,918 
19 
2-33 
•31 
6-67 
•66 
•266 
4 
6 
26,084 
15,4, 4 
23 
2-25 
•33 
6-00 
•74 
•40 
4-1 
7 
0 
13,543 
16,720 
24 
2-25 
•35 
6-00 
•77 
•34 
5-2 
7 
0 
15,129 
13,612 
30 
2-10 
•27 
6*14 
•77 
•27 
Mean. 
9 
0 
28,672 
14,606 
34 
No upper flange. 
2-27 
•44 
•37 
4 
6 
8,792 
15,374 
35 
No upper flange. 
2-26 
•47 
•352 
4 
6 
9,044 
15,980 
In the preceding investigation the breaking weight is given from which to determine 
the tensile resistance ; but the usual practical question is, to find the breaking weight, 
having first ascertained the tensile strength, which is of course simply to reverse the last 
operation. In the case of small beams, of the kind employed in the foregoing experi- 
ments, a sufficiently near approximation, it will be seen, may be obtained by assuming 
14,500 or 15,000, except in peculiar kinds and mixtures of iron ; these will generally 
require a higher number, which must be previously determmed. 
But it appears from the results of experiments by Mr. Hodgkixsox, given at page 111 
of the ‘Appendix to the Report of the Commissioners on Raihvay Structiu'es,’ and others 
by Lieut.-Colonel James, R.E., page 251, &c., that a much lower value of f must be taken 
when the thickness of the casting becomes 2, 2-| or 3 inches, as in large railway gii'ders. 
Mr. Hodgkinsox found, that bars of 1, 2 and 3 inches square, broken on props ha'sing the 
same relative distances, manifested a decrease of strength in the proportion of 1, '780. 
•756 ; and Colonel James’s experiments gave a still greater decrease, riz. of 1, -794, -624. 
and which, by other experiments, he traces to an imperfect crystallization of the inte- 
rior particles, in consequence probably of the more rapid cooling of the exterior parts. It 
appears, therefore, that in those large castings commonly employed for railway bridges, 
it would not be safe to assume t at more than 10,000 lbs. 
The large girder broken and reported at page 94 by Mr. Hodgkixsox, treated as in 
the preceding cases, gives 10,533 lbs. Its length was 45 feet; depth, 29-| inches; 
the thickness of the lower flange, 2j^ niches; and its weight, 18,000 lbs. 
