seventy-two feet long, to span the avenues of those respective widths; the
principle of the construction is the same in each. The top rail (if it may
be so called) of the truss is formed with two pieces of [L section] iron
placed back to back [double L sections], and the bottom rail with two flat
bars [parallel flat bars], the total depth being three feet; at the ends
these bars are riveted on to cast-iron standards, and the intermediate
distance is divided into eight-feet lengths by other cast-iron standards,
to which the bars are also riveted, and thus a framework of rectangles is
formed. In the trusses forty-eight feet span there are, therefore, six such
divisions in the length, and nine in those of seventy-two feet span. These
are then divided in the direction of ONE of the diagonals by a flat bar
passing between and riveted to those forming the top and bottom rails. This
completes the constructional part of the truss; but to render the
appearance more uniform with that of the cast-iron girders, a flat bar of
wood (shown by the dotted lines) is made to form the other diagonal of the
rectangles.
[Illustration: DIAGRAM OF 48-FEET GIRDER.]
The trusses for a span of seventy-two feet are cambered or bent upwards
about ten inches, which both adds to their strength and improves the
appearance. The form and arrangement of these roof-trusses may be clearly
traced in several of the views of the interior which are presented to the
reader. The weight, when completed, of each of the trusses of seventy-two
feet span is about thirty-five cwt., and of those of forty-eight feet span
about thirteen cwt.
It has been already mentioned that four of the roof-trusses vary from the
rest on account of the greater load they have to sustain. The depth of
these exceptional trusses is six feet, and their length seventy-two feet,
or the width of the main avenue, which they bridge over. The principle of
their construction is similar to that employed in the lighter trusses; but
the arrangement of the parts is somewhat modified. The top rail consists of
two pieces of [L section] iron, placed, as before, back to back; but they
are further connected on the top by a flat piece [double L sections with
flat]. The lower rail is formed by two flat bars placed upright [parallel
flat bars], and these are riveted at the ends to standards of cast-iron,
which, however, are considerably heavier in construction than those before
described; and they have also in the centre, at (_a_) two slots, or
sinkings, into which the ends of two of the diagonal bars are riveted. The
whole length is then divided into three equal parts, each 24 feet long, by
strong CAST-iron standards at (_b_) the ends of which are riveted between
the rails, and these spaces are again subdivided into three eight-feet
lengths by WROUGHT-iron standards at (_c c_). The top of each standard is
next connected with the foot of the next but one to it by diagonal flat
bars, which, together with the short pieces fastened into the slots at
(_a_), complete the figure of the whole, forming a kind of trellis-work,
two diamonds in depth. In the diagram only half the length of the girder is
shown.
[Illustration: DIAGRAM OF ONE-HALF OF 72-FEET GIRDER.]
The dimensions of the different bars of iron in this piece of construction
are proportional to the amount of strain they have to bear. The two heavier
out of the four trusses just described weighed when completed eight tons
each, and the other two, which are of rather lighter construction, six tons
each.
The riveting together of the wrought-iron trusses was performed on
horizontal supports, on which the curve that they were to be made to was
marked out. The bars having been previously cut to the requisite lengths,
and punched and drilled with holes for the rivets, were laid out on the
stages in the proper forms with the cast-iron standards, which were
temporarily kept in place by bolts passed through some of the rivet-holes.
The whole framework was then riveted up with red-hot rivets supplied from
small portable furnaces, several sets of men being employed upon each
truss, by which means as many as sixteen were completed in one day. The
whole of the trusses, three hundred and seventy-two in number, required for
the building were put together on the ground, and several ingenious
mechanical contrivances were made use of to facilitate and hasten the work.
To form some idea of the amount of labour that had to be performed, it may
be mentioned that each of the trusses forty-eight feet in length, or the
smallest, is held together by more than fifty rivets, requiring more than
twice that number of holes to be made in bars of iron varying in thickness
from a quarter of an inch upwards. About 25,000 rivets were thus required
for the whole of the work.
Iron Drilling Machine.
The holes for the rivets were made partly by drilling and partly by
punching. In the machine used for the former the bar to be bored was laid
upon a flat surface forming part of the solid cast-iron stand of the
machinery; the drilling-point worked vertically, and could be moved in that
direction to suit the different thicknesses of iron brought under its
operation. It was suspended at one end of a lever, with a counterpoise at
the other. This lever was also connected by a rod and crank, with another
near the ground, one end of which was formed into a tread to be worked by
the foot. The workman, when he had arranged the iron in the right position
under the drill, pressed his foot upon the tread; thus raising the
counterpoise end of the upper lever, and pressing the point of the drill,
which was of a spear-head form, down upon the iron. Underneath the iron to
be drilled was placed a piece of wood to protect the point of the drill
when it had passed through the iron. It was also necessary to moisten the
iron during the operation, in order to keep the drill-point cool. Three men
were required to attend to this work, which was not so rapid as the other
method of making the holes by punching.
[Illustration: THE DRILLING-MACHINE.]
The Punching Machine.
[Illustration: THE PUNCHING-MACHINE AND SHEARS.]
The enormous power exerted by this piece of machinery renders it necessary
that the stand containing the punch, &c., should be exceedingly solid, and
it is formed accordingly by a heavy mass of cast-iron, in which there are
two indentations, as seen by the engraving. In the lower of these the
punching operation is performed, and in the upper there are shears for
cutting off the ends of the bars when required. The motion is communicated
to each of these by means of a cogged wheel at the back; but both the punch
and the shears work in a vertical direction, slowly moving up and down with
irresistible force. There is no sudden blow or jerk, which makes the effect
the more striking, as the unpractised eye has no means of discovering the
amount of the force which is being put in operation. It is, however, so
great that, although the punching of a hole scarcely occupies two or three
seconds, the iron becomes quite hot from the effect of the pressure. In
using this machine, the workman arranges the iron bar on a solid rest,
placing it so that when the punch descends it makes the hole in the
position required. As soon as the punch has passed through the bar, the
action of the machinery is reversed, and the instrument ascends again;
during which time the bar is re-arranged, and the operation is thus
continually repeated. This piece of machinery also requires three men to
work it, if the bars to be punched are of considerable length, so as to
require the ends to be held up; otherwise, one alone is sufficient; and in
the course of a ten-hours day about three thousand holes can be punched
out--the number, of course, varying according to the thickness of the bars.
Neither of the mechanical contrivances just described are novel inventions,
though they are thus, perhaps, brought for the first time under the notice
of many of our readers, to whom they may be so far rendered interesting
from their being connected with the execution of THE building of the day.
The Adzing and Planing Machine.
[Illustration: THE ADZING-CUTTERS.]
At the Chelsea Saw-mills, where the reader has already seen the Paxton's
gutters shaped out, another interesting piece of machinery was in use for
these works, for the purpose of finishing planks to a certain size and
thickness, called the adzing and planing machine. An adze is a tool used by
carpenters to remove any unevenness in the surface of a board in a
particular spot. In this piece of machinery two cutters are fixed to a
revolving arm, under which the plank is made to pass; and as it does so the
cutters remove a certain thickness from the whole of the surface. The
arrangement of these cutters is very plainly shown in the annexed
engraving. On the under-side of the same bench to which this apparatus is
fixed, three planes are set, each at an angle of about 5 degrees, by which
the under-side of the plank is brought to an even face, while the upper
surface is operated on by the adzing-cutters, and in this manner the plank
is reduced to an even thickness throughout. As it passes on it is brought
between two circular saws, which are adjusted to the width which it is
desired to give to the plank. It is dragged forward towards the planes and
cutters by means of an endless chain, composed of open links; which chain
passes over a wheel provided with projecting pegs, so arranged as to fit
into the links. The plank is kept down upon the planes, and otherwise held
in position, by pressure-rollers.
[Illustration: THE ADZING AND PLANING MACHINE.]
The Columns and Connecting Pieces.
[Illustration: SECTION OF COLUMN.]
The columns in the building perform three important offices. They support
the roof and the galleries, and serve as pipes to convey the rain-water
from the roofs. Their form, which is beautiful, both mechanically and
artistically, was suggested by Mr. Barry; it is a ring, eight inches in
diameter externally, the thickness varying in the different columns,
according to the weights they have to support respectively. Four flat
faces, about three inches wide, are added on the outside of this ring, so
that when the column is in its place, they face nearly north, south, east,
and west. The column may therefore be considered as a hollow tube, of the
section just described, and of the same form at each end, having at its
extremities horizontally projecting rings called SNUGS, through which the
bolts are passed, to fasten the columns to the connecting-pieces and
base-pieces. That the hollow form adopted for the columns is that best
suited to obtain the greatest strength with the least amount of material
has been abundantly shown by experiments, as even two straws placed in an
upright position will bear a very considerable weight; it is that also seen
in the structure of the bones of animals. Of these columns there are 3,300
in the whole building.
Those portions of the height of the columns which correspond with the depth
and position of the girders form separate lengths, which are called
connecting-pieces, as they unite the lengths of columns of the different
storeys. These connecting-pieces have the same sectional form as the
columns themselves, and, like them, are the same at each end, where there
are projections cast on, which serve to support the girders, and which are
provided with holes through which the bolts pass to connect them with the
columns. These holes alternate with the projections to receive the girders,
which projections are so formed that they clip others cast on to the ends
of the girders, which will be hereafter described. In the centre of each
projection there is formed a small notch which receives the key or wedge
for fixing the girders.
The meeting faces of the columns and connecting-pieces were all turned in a
lathe, in order that, when set up, they might fit so precisely as not to
require any packing to adjust them in an upright position; and only in the
cases of those columns which serve as water-pipes is any such packing
introduced. In those a piece of canvass, with white lead, is put into the
joint. An enormous amount of additional labour was involved by this
proceeding, as no less than twelve hundred of such faces had to be operated
on; but this did not deter the enterprising contractors, who were fully
alive to the importance of the object to be attained. When fixed, the
projecting "snugs," with the bolts passing through them, were covered by
ornamental caps and bases of cast-iron, fixed after the rest of the work
was completed.
The Base Pieces.
The lower storey of columns in every case stands upon base-pieces of which
the upright portion is a continuation of the column, with "snugs" at the
top, to correspond with those of the column, and standing on a horizontal
bed-plate, from which "shoulders" rise to strengthen the upright portion.
These bed-plates vary in size from three feet by two feet to one foot six
inches by one foot, in proportion to the weight which the several
superincumbent columns have to sustain. The longest dimension of the
bed-plate is in the transverse direction of the building, in which the
greatest overturning strain might be expected to act upon the columns. From
the vertical portion of the base-pieces, sockets six inches in diameter
project, in the direction of the length of the building, into which are
fitted the cast-iron drain-pipes, which convey away the water brought down
by the columns from the roof. The height of the base-pieces varies to suit
the different levels at which the floor is supported above the ground.
These levels had therefore to be determined in every individual instance
previous to the castings being made. It was done, however, with such
precision that, when they came to be used, they were all found to be of the
exact length required for their situation. Of these base-pieces, 1,074 were
required for the building.
[Illustration: BASE-PIECE.]
Cast-iron Girders.
It has been mentioned that the columns supported girders at three different
heights, dividing the greatest altitude of the building into three storeys;
and that the lower tier of girders, where the building consisted of more
than one storey, served to support a gallery.
These gallery girders are all twenty-four feet long and three feet deep,
the upper and lower "flanges" or rails having a [T section] formed section
with standards at the ends of similar section. The rectangular space
between them is then divided into three equal parts, by uprights having a
[+ section] form of section, and the three smaller spaces thus obtained
have diagonal "struts" in each direction. The girder thus described forms a
double truss, in which the diagonal braces are subjected both to the strain
of compression and tension. At the top and bottom of the end-standards
small projections are cast on, by which the connecting-pieces hold the
girders; and at each end of the flat portion of the top and bottom rails
small sinkings are cast, by means of which the girder is keyed up to its
position. The flat portion of the upper and lower "flanges" of the girder
is swelled out in width from the ends towards the centre, in order to
increase the quantity of metal in that part where the strain is greatest.
The description just given of the gallery girders will apply to all the
cast-iron girders throughout the building, of which there are 2,150; the
only difference between them being, that those for the roofs or other
internal portions, where no gallery is to be supported, are cast with a
less amount of metal. The form of girder just described, which is unusual,
was the result of several experiments performed under the superintendence
of Messrs. W. Cubitt, C. H. Wild, C. Fox, and other gentlemen, previous to
the commencement of the building; and the thickness of metal for the
different parts of these, as well as for all the other cast-iron work in
the building, was minutely calculated and determined by Mr. C. H. Wild and
Mr. C. Fox, under the supervision of Mr. Cubitt, the President of the
Institution of Civil Engineers, to whom the Royal Commission had intrusted
the responsible duty of the chief superintendence of the whole of the work.
[Illustration: View of Interior from the Level of Galleries.]
The Galleries.
To proceed to the gallery itself, supported by the girders just described.
The timbers supporting the floor are so arranged that the weight of each
bay of twenty-four feet square is distributed equally to the four girders
inclosing it, and in such a manner as to bear upon them at the points
immediately over the vertical standards.
In the transverse direction of the building two pairs of joists, eight feet
apart in each bay, are formed into trusses by tie-rods, 1-3/8 inches
diameter, passed through a cast-iron shoe at each end, and pressing up two
"struts," which are made to bear against the under-side of binding-timbers
running longitudinally, or crossing the joists, and immediately under them.
The cast-iron shoes for the trusses are bolted down to the girders, and
serve at the same time to receive the standard supports of the gallery
railing. The ends of the binding-timbers are secured by bolts and oak
suspension-pieces to the other two girders inclosing the square. Joists
about two feet six inches apart bear from girder to girder parallel to the
trusses, and resting on the binding-timbers. On these is laid the floor, 1¼
inches thick, grooved and iron-tongued. A light cast-iron railing, forming
a kind of trellis-work, is fixed between the columns, and is capped with a
round mahogany hand-rail. From the view at page 60 the arrangement of the
galleries will be readily understood.
Testing the Cast-iron Girders.
From the very important office which the girders perform throughout the
building, but more particularly those supporting the galleries, it was of
the utmost importance that, previously to their being fixed in their
places, the soundness of the casting should be proved; for it could hardly
be expected that so large a number of girders could be produced without
some of them being defective. The ordinary means of testing girders, by
loading them with weights, would have occupied far too much time; and
therefore an ingenious apparatus was devised by Mr. C. H. Wild for this
purpose, by the use of which the testing of a girder occupied but a few
minutes.
[Illustration: FRAME AND HYDRAULIC PRESS FOR TESTING THE GIRDERS.]
It consisted of a very strong cast-iron frame rather longer than the
girder, the bottom of which was formed by two fixed beams placed eight
inches apart, and supported a few inches above the ground. At each end of
these a cast-iron standard was firmly bolted between them and rose to a
height rather greater than the depth of the girder to be tested; on the
inner faces of these standards two "shoulders" were formed, which received
the projections cast on the ends of the girder, as before mentioned.
Between the fixed beams below, at two points dividing the whole length into
three equal parts, were placed strong cylinders, with rising pistons
connected with a forcing-pump, together with which they formed a Bramah's
hydraulic press. A girder being placed in this frame, in an inverted
position, the force applied by means of the pistons rising from the
cylinders acted upon it precisely at those points, and in the same manner,
as the load from the gallery or the roof would do when afterwards fixed in
its place.
The essential parts of the Bramah's press may be thus briefly described. It
consists of two cylinders, the diameter of one being considerably larger
than that of the other. The smaller cylinder is fitted with a solid plunger
or piston, by means of which water may be forced from it into the larger;
this being also fitted with a rising piston, the force is communicated by
it to the weight which it is desired to raise. The power obtained by means
of this apparatus arises from the distributive power of fluids and the
practical incompressibility of water, and it is proportioned to the
difference of the diameters of the two cylinders; so that if a pressure of
one pound per square inch be applied on the surface of the piston in the
smaller cylinder, and the piston in the larger cylinder present a surface
ten times greater, the power is multiplied by that number; whilst, in
addition, the lever power used in applying the pressure to the smaller
piston is obtained. The cylinders are fitted with valves, so arranged as to
prevent the return of the water from the larger to the smaller, while the
apparatus is in action, and thus the power is accumulated in the former.
In the instance before us, the two 3-inch cylinders already alluded to in
the proving-frame took the place of the larger cylinder of the ordinary
apparatus; and they were connected with the forcing-pump by a strong metal
tube. When a girder had been fixed in the frame for proving, the force-pump
was worked till the pistons underneath the girder carried it off its lower
bearings and pressed it upwards against the "shoulders," by which it was
firmly held, and the pressure was then continued until the amount
previously fixed upon as necessary for proof had been obtained. This was
ascertained by means of a self-adjusting apparatus attached to the
hydraulic press.
An iron cylinder 1½ inches diameter was placed in communication with the
pipe connecting the pump and the press, so that the pressure obtained in it
was, in proportion to its diameter, the same as that in the large cylinder;
and it was fitted with a piston-rod, working in a vertical direction. This
piston-rod was connected with a lever, from the end of which a scale-pan
was suspended, at a distance from the fulcrum ten times greater than that
of the point of attachment of the piston from the same. The weight of the
scale-pan and lever were balanced by a large mass of iron at the other end.
In the scale-pan a certain weight was placed, proportioned to the proof
desired to be obtained; and the action of the pump was continued until the
water, rising in the iron cylinder just described, forced up the lever, and
with it the weight attached; and thus indicated that the pressure to which
it was desired to subject the girder had been reached. The weight to be
placed in the scale-pan was thus determined: the diameter of the lever
cylinder being 1½ inches, and that of each of those in the proving-frame
three inches, the pistons or "rams" in the latter presented together eight
times the surface of that in the lever cylinder; which being multiplied by
the difference of length of the two parts of the lever, determines the
weight for the scale-pan to be one-eightieth of that to which it was
desired to prove the girder.
The ordinary gallery girders were tested with a pressure equivalent to a
weight of fifteen tons; but it was calculated that, when fixed, the
greatest weight they would have to sustain would be seven-and-a-half tons.
In one instance, for the sake of experiment, the pressure was continued
beyond the proof weight of fifteen tons, to see what amount of strain the
girders would bear without fracture, and it was found that a strain of
thirty tons produced no injurious effect; but the girder broke with an
additional weight of half a ton.
Roof of Transept.
We will now return to describe that portion of the roof which varies in
form and arrangement from the rest, namely, the semicircular covering of
the transept. This is supported by arched ribs, placed twenty-four feet
apart, and constructed of Memel timber, in three thicknesses; the
centre-piece four inches thick, with a 2-inch piece on each side of it.
They are formed in lengths of about nine feet, placed so as to break joint;
that is, the joints of the outer pieces fall upon the centre of the inner
one. The thicknesses are fastened together by bolts passing through them
about two feet six inches apart, besides being nailed at other points. On
the inner circumference of the rib thus constructed there is then placed a
piece of timber moulded to correspond with the form of the columns; and on
the outer circumference two boards, each one inch thick, are bent round and
attached to the rib with strong nails. On both the outer and inner
circumference a flat bar of iron is secured by bolts passing through the
whole depth of the rib, which, thus finished, measures eighteen inches in
depth by eight inches in thickness. The ends of the ribs are fitted into
sockets, formed by the upward continuation of the columns, to which they
are attached by iron straps.
The ribs, which are supported by the trusses over the main avenue, have
their ends bolted down upon a piece of timber secured on the upper portion
of the truss; and they are further fixed in their places by oak brackets,
forming a spreading foot on each side upon the same piece of timber.