A joint is the place where two different portions or pieces of a
structure meet or unite, and it consequently forms the division
or union between them, as well as a
factor of the structure it helps to consolidate.
A joint is
either simple or compound, fixed or movable, and however perfect
it may be it is almost invariably a source of weakness.
light the monolithic description of concrete is superior to
masonry; but, as an opposite instance, the superiority of a beam
sawn asunder down the middle, reversed, and bolted together
again, over a jointless one, is worthy of note.
As a general
rule all parts of a joint should be equally strong, the strength
of the entire joint equal if possible to that of the parts
joined, and its form, when used in framing or other analogous
combination, such as to direct the pressures, as far as skill
will allow, along the axes of the component pieces.
joint should never be of a complicated nature, but its parts,
reduced to the smallest practicable number, ought to be so
devised as to resist in the most scientific manner the
particular kind of stress that each will be tried by.
By a simple joint is meant one consisting of nothing beyond the
contact of meeting surfaces, such as an abutting joint in
carpentry, without fastenings of any kind - though it may
otherwise ill-devisedly be of an elaborate and intricate
By a compound joint is meant one which a
cementing medium, or some kind of attachment, in used to assist
weight or pressure in keeping the contiguous parts from moving
or racking—the first step towards separation and ruin.
joint forms a common illustration of the latter class, for the
mortar not only binds the bricks together, but before setting
affords a conveniently yielding bed to enable each brick to take
its bearing, so to speak, and thus to be in its best position to
resist external forces.
Such a joint is necessarily a compound
one, since the mortar joint proper between any two bricks is
compounded of the two joints formed by the adhesion of the
intervening mortar to the surface of both bricks. Either a
compound or a simple joint may be fixed or movable, the sliding
joint in joinery affording a familiar instance of the simple