112 Mr Fairbairn on Fireproof Warehouses. 
boards (three-inch plank), securely nailed to sleepers em- 
bedded in concrete: this plan would give additional security, 
by the transmission of the impinging force over a larger 
surface; and, under these circumstances, the concussion 
would be made, in the first instance, on a soft elastic sub- 
stance, before it could act upon the more rigid materials of 
iron beams and brick arches. 
In order, however, to remove all doubts as to security, it 
will be advisable to have stronger iron beams and columns 
in the two lower floors; and having computed these strengths, 
they will probably be found nearly correct in the ratio of 12 
to9. If, on this data, we take the breaking weight of a beam, 
as suitable to the upper stories of a warehouse, at 22 tons, 
those of the lower stories would require to be 29.32, or near- 
ly 30 tons; and the columns, although less liable to fracture, 
will, nevertheless, be greatly improved by the introduction 
of a proportionate thickness of metal. 
Having, to the best of our ability, established the fact of 
perfect security in the use of iron beams and arches, the 
next point of inquiry will be as to the strength and propor- 
tion of the columns ; but before treating of this part of the 
subject, it may be proper to advert to the tie-rods, which are 
built into the walls and arches, and should unite the walls 
and girders as a species of net work. These tie-rods are of 
great value, as they resist the strain of the arches, which, 
acting through their line of tension, not only secure the walls 
from being thrust out, but also retain the beams in the posi- 
tion best adapted to sustain the load. The usual practice in 
these districts is to leave five lines of $-square rods in a 
width of 30 feet ; two lines are imbedded in the wall, and the 
remaining three built into the arches. This is considered a 
perfectly secure building ; but it must be borne in mind that 
cotton mills are not subjected to heavy loads, and instead of 
five tie-rods of -inch square, a warehouse should have seven 
lines of rods, each 14-inch square. This will give a sectional 
Parliament for the regulation of fireproof buildings does not admit of any 
timber whatever. In such case, I would advise the beams so to be made 
one-half stronger. 
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