204
Molesworth’s pocket-book
Notes on Permanent Way—continued.
The action of the train increases the compressi-
bility of the timber.
The cellular tissue of soft sleepers is gradually
destroyed by too great pressure.
Distribution of weight should be effected by
increasing the bearing surface of plates and shoeri,
rather than by adopting a more rigid rail which
destroys elasticity, or by increasing the number
of sleepers which does not attain the desired end.
Soft sleepers allow of canting under lateral
pressure from compression of the timber.
The sinking of well-bedded sleepers into the
ground is insignificant.
It is estimated that thu relative value of fir to
oak is as 1 to 1£.
The coefficient to resist the drawing of spikes
is 300 lbs. per square inch of the surface of the
spike in fir, and 600 lbs* in oak if lateral pressure
is not used at the same time; if lateral pressure
is also used, the coefficient is reduced to 160 in
fir and 270 in oak.
Intermediate sleepers in fir should have two
spikes on the outside of the rail, or a small plate
to connect the inside with the outside spikes.
Joint sleepers or sleepers on sharp curves should
have shoes or bed-plates.
Holes for spikes should be bored quite through
the sleepers.
The test size for holes is half the diameter of
the spikes.
Bed-plates increase the resistance to lateral
pressure by 60 ■» 100 per cent.
The enlargement of the gauge to an extent of
i or # inch is not beyond the limits of elasticity,
and does not impair the tenacity of the spikes.