RAILWAY BRIDGES.

11

D.—No- 6c,

The present order is to include only two lines of girders to support the cart road. These ara to be 15 feet 4 inches centre to centre, resting on cast-iron bed plates, secured to the capsills with bolts 18 inches centre to centre, so as to clear the heads of the piles. As the roadway lies on the tops of these girders, they will require lateral bracing from the bed plates, and the horizontal bracing must be attached to the top web rather than the bottom. The joists, 5 x 12 inches, and 29 inches centre to centre, are to be secured to the girders by f inch clip bolts. For convenience of erection, the girders are to be connected in lengths of three, before being rolled to their place, and these lengths may then be joined by coupling plates with oblong holes to allow for contraction and expansion. The 3rd line of girders and its horizontal bracing will form a subsequent order, but provision must now be made for attaching the bracing of this 3rd lino of girder, which will be 7 feet 8 inches ceutre to centre from the middle line. Each line of girders will consist of 110 spans of 33 feet, that is 220 girders under the present order. The erection will be commenced from the South end, and the 3rd line of girders will be placed to the East of those now ordered. Schedule for one pair of Girders, 33 feet span, 14ft. Bin. centre to centre. Tons cwts. qrs. lbs. 2 wrought iron plate girders ... ... ... 4 7 1 14 Horizontal bracing ... ... ... ... 0 2 2 8 Lateral bracing to the ends ... ... ... 0 0 1 12 4 connecting plates ... ... ... ... 0 2 0 14 2 cast iron bed plates ... .... ... ... 0 5 0 22 Bolts, viz.—4 bed plates to capsill, 1-7 xl^ — 374 lbs. 8 girders to bed plates 5^ x ■£ = 14J 14 horizontal bracings to girders 2| x $• = 18J 2 bracings to each other If x -f- = 2 Lateral bracing to girders 2f x -f = 4 72 to coupling and bearing plates 2f x f= 97 12 to girder ends 2-J- x £ = 15 188 lbs. = 0 1 2 20 24 clip Bolts to secure joists to girders 0 0 2 0 Extra Bolts ... ... ... 0 0 0 22 Weight per pair of Girders... ... ... ... 5 0 0 0 110 Spans at 5 Tons each ... ... ... 550 0 0 0 Note.—2 extra cast iron bed plates and holding-down bolts will be required with the last pair of girders. TV. B. Beat, Ist April, 1871. District Engineer.

Enclosure 1 in No. 15. TVaitaki Bridge. Present Order. Estimate of Cost of Iron Girders for cart bridge. 110 Spans at 5 ton per Span=sso tons at £13 ss. ... ... £7,287 10 0 Freight on 550 tons at 30s. ... ... ... .. 825 0 0 £8,112 10 0 Future Order. Estimate of 3rd line of Girders for Bailway. 110 Spans at 2 tons 10 cwt. 3 qrs.=279 tons 2 cwts. 2 qrs. Say 280 tons at £13 ss. ... ... ... ... £3,710 0 0 Freight on 280 tons at 30s. ... ... ... ... 420 0 0 £4,130 0 0 The weights of the above ironwork are the same as in the particulars furnished us of the iron work sent per " Crusader," omitting the cross girders and bolts not required, and adding to the weight where required for the TVaitaki bridge. TV. B. Beat, Ist April, 1871. District Engineer. 3