Dynamics, Construction of Machinery, Equilibrium of Structures and the ... by George Finden Warr

Author:George Finden Warr
Language: eng
Format: epub
Publisher: Robert Baldwin
Published: 1851-03-25T05:00:00+00:00

\66 MECHANICS.

arch in thickness; those of the Nemffy figure represents an abutment of a

Bridge are one-ninth only; the piers of bridge over the river Ribble (Lancashire).

Waterloo and London Bridges under

one-sixth of the span, and Westminster ^^* 7L

and BlackfHars Bridges reach so great a

thickness as one-fourth of the span.

(62.) Great care is bestowed on the terminal sapports of bridges, or the abutments. The massiveness of the piers has been less considered, because they have been supposed to transfer the thrust, and not sustain it, whereas the abutments have no similar horizontal support; they are therefore made of

great weighty and, generally, in the best The arches are elliptical and of 120 feet

specimens of these structures, arranged span, with about S2 feet rise. The arch

with a view to convert the horizontal proper suddenly turns, as usual in these

into a vertical thrust, or to transfer arches, at A, or where the tangent to

much of the pressure to the base of the the curve is about 60® inclined to the

abutment, where means are provided for horiaonj here the internal arch B begins,

sustaining it. carrying the thrust from this point to C,

Where the abutment of the terminal or the foundation, which lies on a rocky arches of a bridge is on solid rock, little bed: a great deal depends on the set-trouble is necessary; but, as is generally tling of the masonry; hot if the settle-the case, stiould the site present a loose ment happened to be less in this addi-and compressible bed for the masonry, tional arch than the other portion of the piling and platforms must be used. The abutments, a great pressure would be material of the abutments is generally exerted on the small base which C pre-masonry or brickwork, and they are of seats: in this instance, if the settlement such a weight as to require no aid from be equal, the pressure will be divided the earth behind them. between the segment fi and the front

The thrust sustained by the abut part D of the abutment. In some

ments varies much with the form of the bridges the arch abuts on masonry with

arch; thus semicircular arches give less a face inclined similar to the arch-stone

horizontal pressure than elliptical or flat meeting it, and the feces continually

arches, and these again less than those approach to the horizontal towards the

formed of a small segment of a circle; a foundations: this is the case with London

great portion of the vertical pressure Bridge. This complete and instructive

arises from the filling in of the spandrels bridge presents a very general example

or space between the haunches of an of bridge-work; one of the abutments is

arch and the roadway. This weight can shown in the following figtn-e. The

act serviceably only in assisting the elliptical arch A is met at B by the

abutment against a sliding motion masonry of the abutment; the courses

through the thrust of the arch; other•> are gradually inclined and extended^ so

wise it acts injuriously in overloading the that at the base C D the face is

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