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inches, and the struts 2 inches, deep ; the rib in both casesbeing £ inch, and the top table £ inch in thickness.
The tie-rods are 1 inch round, the king-rod £ inch, andthe queen-rod £-inch.
The fourth example is for a span of 60 feet, and consistsof rafters and tie-rad, suspended at five points by a king andfour queen-rods, two on either side. The four struts springfrom the feet of the inner suspension-rod to the head of theouter.
The rafters are formed in the same manner as in the secondexample, of two parallel plates of bar-iron, with plankbetween ; the scantlings are, however, somewhat heavier, thedepth of the bar-iron being 4 inches, and its thickness fj.The struts are of T iron, the top table being 3 inches wideand 1 inch deep, and the rib 3£ inches deep and £ thick.
The tension-rod is of round iron, and is, from the extremityto the first suspension-rod, 1£ inch thick, thence to the secondrod If inch, and thence to king-rod l£ inch. The king-rodis If- inch round, the intermediate £ inch, and the outermost£ inch. The fifth example is for the same span, and consistsof rafters and tension-rod, suspended at five points by king-rod and four queen-rods, placed closer together than in thelast example. There are six struts placed as above, but thelast on either side buts against the rafter where there is noqueen-rod.
The entire roof is of malleable iron, the rafters of the T-form measuring 3 inches across the top table, which is f inclithick, and 3£ inches in the depth of the rib, which is £ inchin thickness. The struts are also of T iron, the inner onesbeing 2£ inches wide over the top table, which is § inch thick,and 3£ inches in the depth of the rib, which is £ inchthick. The outer struts are 2£ inches wide over the top table,and 2£ inches in the depth of the rib, the former being f inchthick, and the latter £ inch.
The tension-rods are If inch round near the springing, 1£inch in the middle, and If near the king-rod.
In all such roofs, it is necessary to strengthen them withiron tie-rods, passing obliquely from the springing to theridge across one bay, and secured on the under side of thepurlins. The distance between the principals varies from 5to 7 feet.
The roof over the Museum of Practical Geology, Picca-dilly, of which Mr. Pennethorne was architect , is entirely ofcast-iron, which is somewhat differently applied to anyinstance we have alluded to. The total width of the buildingis 67 feet, but there is an intermediate bearing on either side6 feet from the external wall, thus making the clear width ofthe roof 55 feet. Each rib is composed of five separate piecesor girders, securely bolted together at the ends ; the firstpiece, one end of which rests upon the wall, and the other onthe intermediate bearing, is of a triangular form, with a per-forated spandrel; the lower side is horizontal, resting uponthe supports, the upper taking the slope of the roof, and theinner one springing from the inner support, with a curve of
5 feet radius, to range with the curvature of the other partof the roof, the radius of which is 48 feet. This girder is 1foot 6 inches in depth, with a rib on either side in the centre.The next girder is of the same depth throughout, viz. 1 foot
6 inches, and in the cross section has a rib in the centre, andone of less projection at the lower edge : this portion iscovered with slate slabs, £ inch thick. The central girderdiffers from the rest, being 2 feet in depth, with a flanche attop and bottom, the girder between being perforated for thesake of diminishing the weight: this portion is covered withglass. Each of the girders have abutment plates at the end,by means of which they are bolted together. The total riseor versed sine of the roof is about 12 feet.
■ 1 "0
The roof over the palm-house, Kew Gardens, is a ^ e i e ga"*of description, on account of its exceedingly light a f e et °appearance. The total length of this house is fee 1
inches in the clear, the central portion measuring c j el) r.6 inches long, and 100 feet wide, by 63 feet high 1I1 w .j n g 3 s reexclusive of the lantern, which is 6 feet. _TheWi l7fe e«
each 112 feet 6 inches long, and 50 feet wide, aDa ,^ e to°high from the floor to the bottom of the lantern- g v,ei n 5is in this case entirely of wrought iron, the main _ ^ j l0 llo^
formed of 9 inch deck-beam iron of circular sec *
at the core, with four double flanges at righteach other. These ribs are
obtained in lengths , longh'i
ang le3of a
W ut
, j e ngu
12 feet, and are welded together to the req |11 j' e re q U jsi t(iabout 42 feet, and then bent upon a template to thecurvature.
The roof of the wings is of a single span,-h® - c ixcurved of a semicircular form, the extremities of ' v '' ot j,ito afrom the ground on either side of the plan, and 0 j (J [liesolid block of granite, upon a concrete foundation- t' i°
main or central building this semicircle is 4lV ' 4e . t , n ent> ^quadrants, which cover the aisles of this coinp® 1 tl>®
lower ends being bedded upon granite, as a ^ fe ’„ 3 id 1 '* 1upper ends into the tops of strong cast-iron UI j n to th*’® 8divide the width of this portion of the building ^ ^.yuh 11 !aisles. From the top of the same columns spring 8 _„nun te:
rib, similar to that in the wings, which is again c oIu° |,1 (fby a lantern 6 feet in height. From the top obrackets project, which on one side carry a g al ’ 0 i\iet sl nround the bottom of the upper roof, and mi ^ col 0 ! 11 ,serve to assist in the strengthening of the ribs. ^ sca nt ^jheads are connected by a continuous curb of 81011 ‘ ae thet*°to the ribs, and the whole of the ribs are brace c!lS t-itp gstrutted by wrought-iron tie-rods, passing 111101 ponied 0 ^tubes, which act as purlins. These purlins a 16 j en gtbs>round bar, l£ inch in thickness, welded in i°!'” uoU s°tens'® ^passing through the ribs, so as to form a contm ^ ^ stI ‘ ll t . ( lrod all round the house at each purlin, with nl ®‘ j s co v ’ e !„ing them as tight as possible. This ten . slon " exa ctlyor enclosed in a tubular bar of wrought-iron, O ppo sl ebetween the ribs, and acting as distance-pieces^.^ gtJ -uctto the strain of the tension-rods : thus is the & r>°® j 5
compacted together. The distance between t i p e6 t. , lt12 feet 6 inches, and between the purlins 9 01 n j s iiin£^ lois in every respect a very elegant roof, and as o ,
for so great a span. _ Htion at | 0 uS
The iron roof erected over the railway 8 ^ ^ ing er ^ n jsstreet, Liverpool, is of great span, and of nov nconstruction. The area roofed over in p [ '^ ct 0 vetfrom the fagade in Lime-street to the via ^ gg o 3Hotham - street passes, and from the i ,ine , p a rcel 0 g'-l
offices to about the middle of tl* e 0 leng 11 j 9 ts> -strew 6 ^ c0 ns ls
receiving
feet, and^the ’ * ilus making the extreme
of a series of sesrrn ! * eet 6 inches. The rootv afs of 21 ffieffi ®' 1 f P rir >oipals, or girders, fixed at gf0
Supported on one sidl? f '°' n cemre t0 centre: tbe fyr a*they extend and th U P on tlle w alls of the offices, » f e et4 inches, upon a ^ t0 the viaduct, a distance o f theother side thev • ox " beaiJ i of wrought-iron, ivhfis . mIs
a f e made to w ^ a ser *es of radiating 8t * a ’a# aflf
diagonal braces • h ,£° n tliem b ? lining the tie* } . lC edover tiie radhtlL f m ' e tn,ssed laterally by t hen>’
as Well as by diocZ St . rilts = an d intermediately of
^ radiating 2f extending from the ^ in
tke adjoining nrin • °, t le to P ot ‘ tl,e corresponding ne etedwith i>kin,?Zy ? 1 T, ‘ ese ^sonal braces are co*» ^
° P , by a bar of the same scantling.