121
OF ENGINEERING FOBMULÆ.
6
9
12
15
I’ebmanent Loads on Bbidges, &c.
For rough calculations the weight of the bridge
itself may be assumed to be (ia wrought-iron
bridges) :—
For 30 feet spans single line 5 cwt. per foot run
„ 60 ~
„ 100
„ 150
„ 200 . . ..
Dense crowds average 120 lbs. per square foot.
For flooring 1J to 2 cwt. per square foot, exclusive
of the weight of the flooring, is generally allowed.
In store-houses from 2 to 4 cwt. per square foot.
Safe Load in Structures, including Weight
of Structure.
In cast-iron columns .. .. = | breaking weight.
Wrought-iron structures .. = |
In cast-iron girders for tanks = }
In ditto for bridges and floors = a „
In timber (live load) .. .. „
„ (dead load) .. ., = i „
Stone and bricks__________= i ,,
To Cut the best Beam fbom' a
Log.
Divide the diameter, a b} into 3
equal parts, a f, f e, and e b, and
from e and /—draw the lines f c,
e d, at right angles to a b—join a c,
a d,b c, and b d, then a c b d is the
cross-section of the strongest beam.
To cut the stiffest beam, divide
the diameter into 4 instead of 3
parts, as shown.