Søgning i bogen
Den bedste måde at søge i bogen er ved at downloade PDF'en og søge i den.
Derved får du fremhævet ordene visuelt direkte på billedet af siden.
Digitaliseret bog
Bogens tekst er maskinlæst, så der kan være en del fejl og mangler.
82
HARBOUR ENGINEERING.
the range in each case being due to the limits in the coefficient or factor of
safety, which must always remain a matter of conjecture and arbitrary
sélection. The multiples, in faet, lie anywhere between | and
Another and no less essential point to be noted is that the values obtained
by these formulæ relate solely to loads imposed upon piles which are com-
pletely embedded in the ground. In so far, therefore, as a pile acts merely
as a foundation for a pier column, the foregoing estimates of its resistance to
pressure are strictly and legitimately applicable. But when a pile is only
partially embedded in the ground, the calculations for its stability are of a
dual nature: first, as a pile pure and simple up to the surface of the ground,
and secondly, above the ground level, as a column or strut.
This aspect of the case calls for careful consideration, because a framework
wharf, or pier, may fail through the flexure of its vertical members as much
as through the subsidence of their bases. The longer the unsupported length,
the less becomes the permissible load. And it follows, as an obvious
corollary, that cross and diagonal bracing should be introduced from the
lowest level at which it becomes practicable.
Failure by flexure involves an investigation of the relative values of the
resistance of a material to tension and compression. Within the limits of the
present treatise, it is not feasible to enter into all the details of so complex a
problem. Neither in the present connection is it even desirable. Gordon’s
well-known formula furnishes all the information necessary for empirically
determining the limiting load on columns, whether in the sea or ashore, and
any further information on the subject should be sought in works dealing
specially with columns and structural work generally.
Gordon’s formula for the determination of the limiting loads on long
columns or struts may be expressed as follows : —
1
where p=ultimate load per square inch of sectional area;
f — compressive stress per square inch of the material;
y=ratio of length of column to its diameter, or to its least dimension
in cross-section ;
a— coefficient given in table below.
The ultimate compressive stress (/) may be taken as follows, according to
the material of which the strut is composed :—
Timber . . 2 to 4 tons per square inch.
Wrought iron. 16 »,H
Mild steel 30 n n
Cast iron 40 » ,>
Concrete (4 to 1) . . 2 » >,
do (S to l) . . 1 >5 >5
The values of the coefficient a are given in the subjoined table,