110 Mr Fairbairn on Fireproof Warehouses. 
be calculated to resist the greatest load when operated upon 
by a dead weight, but the effects of impact produced by a 
body falling through a given space upon the floor. These 
calculations should apply to the two first floors of every 
warehouse, as the heavier description of goods are almost in- 
variably deposited in the lower stories. 
Mr Hodgkinson, in searching experimentally for the strong- 
est section, found that the old practice of making beams with 
equal ribs—such as recommended by former writers—ex- 
ceedingly defective ; he proved a proportional between the 
top and bottom flanges, and the strain being less towards 
the ends of the flanges, it was reduced to the parabolic form, 
in order to give equal strengths throughout the whole length 
of the beams. This was an important discovery, and as 
warehouse and factory beams are intended to be equally 
strong in every part, and to sustain the load uniformly dis- 
tributed, it is necessary to adopt the parabola in the form of 
the ribs, and to mark their relative properties with the body 
of the beam, and with each other. In discussing these pro- 
portions, Mr Hodgkinson demonstrates the curvature of the 
ribs as follows :— 
«« Suppose the bottom ribs to be formed of two equal pa- 
rabolas, the vertex of one of them, A C B, being at C; 
i Noss eee, 06 ign Nob bere 
. ae 
ad Cc 
when by the nature of the curve, any ordinate dc is as 
Ac x Be; the strength of the bottom rib, therefore, and 
consequently that of the beam at that place, will be as this 
rectangle. It is shewn, too, by writers on the strength of 
materials, that the rectangle A ¢ x Bc is the proportion of 
strength which a beam ought to have to bear equally the 
same weight every where, or a weight laid uniformly over 
i: 
From this it would appear that the forms laid down by 
Mr Hodgkinson were rightly devised, and a great saving, 
