Where the rail-gauge is narrow and great weight is not desired, blocking girders are provided across the under side of the truck; these are arranged so that, by means of wedges or screws, they can be made to increase the base.
The principal component parts of a traveller are the main cross girders forming the revolving bridge, the two end carriages on which the bridge rests, the cranes.
Running wheels which enable the end carriages to travel on the longitudinal gantry girders or runway, and the crab or jenny, which carries the hoisting mechanism, and moves across the span on FIG.
With Edward Cooper (son of Peter Cooper, whom Hewitt greatly assisted in organizing Cooper Union, and whose daughter he married) he went into the manufacture of iron girders and beams under the firm name of Cooper, Hewitt & Co.
The inspections made by the officers of the Board of Trade under this act are very complete: the permanent way, bridges, viaducts, tunnels and other works are carefully examined; all iron or steel girders are tested; stations, including platforms, stairways, waiting-rooms, &c., are inspected; and the signalling and " interlocking " are thoroughly overhauled.
Where the depth to rail-level was too great for cut-and-cover methods, ordinary tunnelling processes were used; and where the trench was too shallow for the arched roof, heavy girders, sometimes of cast iron, bridged it between the side walls, longitudinal.
31), the earliest form, consisted of a single row of columns supporting two lines of longitudinal girders carrying the rails, the lateral stability of the structure being obtained by anchoring the feet of the columns to their foundations.
32) has two rows of columns connected at the top by transverse girders, which in turn carry the longitudinal girders that support the railway.
From 1880 onwards) it has wholly superseded the latter except for girders of less than 100 ft.
In the former the main supporting member or members may be an arch ring or arched ribs, suspension chains or ropes, or a pair of girders, beams or trusses.
The suspension bridge dispenses with the compression member required in girders and with a good deal of the stiffening required in metal arches.
It can be stiffened by girders and bracing and is then of mixed type, when it loses much of its advantage in economy.
In the simplest case the main girders are supported at the ends only, and if there are several spans they are discontinuous or independent.
In the Ordish system a certain number of intermediate points in the span are supported by oblique chains, on which girders rest.
About 1850 it was perceived that a bridge stiff enough to carry railway trains could be constructed by combining supporting chains with stiffening girders suspended from them.
The two stiffening girders are plate girders 3 ft.
The stiffening girders of the main span are 40 ft.
P. 258; also " Suspension Bridges with Stiffening Girders," by Max am Ende, Proc. Inst.
These girders are supported by the cables over the centre span but not in the side spans.
There are two high-level footways for use when the bascules are raised, the main girders of which are of the cantilever and suspended girder type.
The middle girders are 120 ft.
The suspension chains are constructed in the form of braced girders, so that they are stiff against unsymmetrical loading.
Transverse girders are hung from the chains at distances of 18 ft.
There are fifteen main transverse girders to each shore span, with nine longitudinal girders between each pair.
The anchor ties are connected to girders embedded in large concrete blocks in the foundations of the approach viaducts.
Over the river these are lattice girders, with transverse girders 12 ft.
Apart, and longitudinal and subsidiary transverse girders dividing but usually the time taken is one and a half minutes.
- The main supporting members are two or more horizontal beams, girders or trusses.
The girders carry a floor or platform either on top (deck bridges) or near the bottom (through bridges).
For railway bridges it commonly consists of cross girders, attached to or resting on the main girders, and longitudinal rail girders or stringers carried by the cross girders and directly supporting the sleepers and rails.
In the girders of bridges the horizontal girder is almost exclusively subjected to vertical loading forces.
But girders may have curved chords and then the stresses in the web are diminished.
Itl ' At first girders had soli or plate webs, but for spans o 9 over ioo ft.
With pin connexions some weight is saved in the girders, and erection is a little easier.
It consists of a pair of tubular girders with solid or plate sides stiffened by angle irons, one line of rails passing through each tube.
The spans were in fact designed as independent girders, the advantage of continuity being at that time imperfectly known.
The vertical sides of the girders are stiffened so that they amount to 40% of the whole weight.
Wrought iron and, later, steel plate web girders were largely?
1?Y area of the cellular top flange of the large-span girders is 648 sq.
As no scaffolding could be used for the centre spans, the girders were built on shore, floated out and raised by hydraulic presses.
On the other hand a framed or braced web afforded opportunity for much better arrangement of material, and it very soon became apparent that open web or lattice or braced girders were more economical of material than solid web girders, except for small spans.
In America such girders were used from the first and naturally followed the general design of the earlier timber bridges.
Now plate web girders are only used for spans of less than ioo ft.
It was a bridge for two lines of railway with lattice girders continuous over three spans.
Not only were the bracing bars designed to calculated stresses, and the continuity of the girders taken into account, but the validity of the calculations was tested by a verification on the actual bridge of the position of the points of contrary flexure of the centre span.
There were four girders, two to each line of way.
The girders after erection.
22 shows girders erected in this way, the dotted lines being temporary members during erection, which are removed afterwards.
The girders are independent polygonal girders.
The cross girders, stringers and wind-bracing are wrought iron, the rest of mild steel.