Girders Sentence Examples
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.
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.
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.Advertisement
The middle girders are 120 ft.
The main suspension chains are carried across the centre span in the form of horizontal ties resting on the high-level footway girders.
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.Advertisement
The anchor ties are connected to girders embedded in large concrete blocks in the foundations of the approach viaducts.
The two bascules are each constructed with four main girders.
Over the river these are lattice girders, with transverse girders 12 ft.
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.Advertisement
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.
The walls thus supported no load but their own weight, and were tied to the inner cage formed by the wall columns, interior columns, girders, and floors by anchors arranged to provide for the shrinkage of masonry in drying out which always occurs to a greater or less extent.
In such metal framework the beams and girders shall be riveted to each other at their respective junction points.
If pillars made of rolled iron or steel are used, their different parts shall be riveted to each other and the beams and girders resting upon them shall have riveted or bolted connexions to unite them with the pillar.Advertisement
If cast-iron pillars are used, each successive pillar shall be bolted to the one below it by at least four bolts not less than three-fourths of an inch in diameter, and the beams and girders shall be bolted to the pillars.
At each line of flooror roofbeams, lateral connexion between the ends of the beams and girders shall be made by passing wrought-iron or steel straps across or through the cast-iron column, in such a manner as to rigidly connect the beams and girders with each other on the direction of their length.
These straps shall be made of wrought-iron or steel, and shall be riveted or bolted to the flanges or to the webs of the beams or girders.
The bracing is accomplished by the introduction at the angles of the columns and girders or beams of gusset plates or knee braces, or by diagonal straps or rods properly attached by rivet or pin connexions.
For girders of small spans " I " beams or channels are generally used, but for greater spans girders are built of riveted work.Advertisement
In girders and beams the maximum fibre stress is usually limited to 16,000 lb.
In very short girders the shear must be computed, and in long girders the deflexion, particularly the flexure from the variable load, since a flexure of more than of the length is liable to crack the plastering of the ceilings carried by the girders.
The same necessity for computing shear and flexure applies to the floor beams. The floors between the girders are constructed of " I" beams, spaced generally about 5 ft.
Sometimes the beams rest upon the girders, and are riveted through the flanges to it; in this case the abutting ends of beams are spliced by scarf plates placed on each side of the webs and secured by rivets.
It is usual in both girders and beams to provide not only for the safe support of the greatest possible distributed load, but for the greatest weight, such as that of a safe or other heavy piece of furniture which may be moved over the floor at its weakest points, the centres of the girders and beams. It must always be borne in mind that the formulae for the ultimate strength of the " I " beams only hold good when the upper chord or flange is supported laterally.
The Broad Flange Differdange Beams are claimed by the manufacturers to be stronger and to minimize weight for use as girders; they are made in twenty-one different sizes with flanges from 88 to i 2 in.
The arrangement of the building and floor framings is in a great measure governed by the architectural effect sought and by the arrangement and proper planning of the interior according to the intended uses; the positions of columns, girders and floor beams are usually the result of particular requirements, and unless complicated and expensive framing is to be expected the distance between columns must be kept within the limits of simple girder construction.
The position of the columns having been determined, the girders must next be located; these serve to support the floor beams which transfer the loads direct to the columns, and also to brace the columns during erection.
Truss rods, portals, or lattice or plate girders constitute the more definite types of wind-bracing ordinarily employed; the bracing must reach to some solid connexion at the ground.
The filling between the girders and floor beams consists of segmental arches of brick, segmental or flat arches of porous (sawdust) terra-cotta, or hard-burned hollow terra- - cotta voussoirs, or various patented forms of con crete floors containing ties or supports of steel or iron.
In flat forms of masonry floor construction the level of its bottom is placed somewhat below the bottom of the " I " beams and girders, so that when it is plastered a continuous surface of at least an inch of mortar will form a fire-proof protection for the lower flanges of the beams and girders.
Girders projecting below the floor are usually encased in from z to 2 in.
It is important in all fire-proofing of columns and girders, and in all floor construction, furring and partitions, that there shall be no continuous voids, either vertical or horizontal, which may possibly serve as flues for the spread of heat or flame in case of fire.
The Dynamic Avon The single cable forms a graceful curve to support bridge girders without blocking the view creating a gorgeous landscape.
Later, wrought-iron box girders gave way to plate girders.
When the chains were in place vertical suspension rods were added before the two huge girders were added by two mammoth cranes.
The hand rails are bolted to the main girders.
The struts of the high girders, which plunge down from the top like the tracks of a rollercoaster, are not absolutely straight.
An 1876 drawing of the River Avon Bridge, showing the original ornate lattice girders.
The earliest iron truss bridges were evolved from the plate girders which came into use all over Great Britain in the railroad age.
The floor system is built on the customary method of heavy cross girders and longitudinal stringers.
The Ordish bridge built at Prague in 1868 had oblique chains supporting the stiffening girders at intermediate points of the span.
These results are for the centre deflections of main girders, but Stone infers that the augmentation of stress for any member, due to causes included in impact allowance, will be the same percentage for the same ratios of live to dead load stresses.
A purely empirical allowance for impact stresses has been proposed, amounting to zo% of the live load stresses for floor stringers; 15 for floor cross girders; and for main girders, io% for 40-ft.
In a three-span bridge continuous girders are lighter than discontinuous ones by about 45% for the dead load and 15% for the live load, if no allowance is made for ambiguity due to uncertainty as to the level of the sup ports.
For riveted girders E is about 17,500,000 lb per sq.
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?
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 Warren type, either with two sets of bracing bars or with intermediate verticals, affords convenient means of supporting the floor girders.
The girders are independent polygonal girders.
The cross girders, stringers and wind-bracing are wrought iron, the rest of mild steel.
It is available for spans greater than those practicable with independent girders; in fact, on this system the spans are virtually reduced to smaller spans so far as the stresses are concerned.
An internal viaduct of lattice girders carries a double line of rails.
The girders over the second and fourth spans are extended as cantilevers over the adjoining spans.
The girders are of the Whipple Murphy type, but with curved top booms. The bridges.
The two side span girders are 420 ft.
The side girders rest on the cantilevers on 15-in.
The reason given for this change of form was that it more conveniently allowed the lower the lattice girders above.
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.
Cast iron was about the same time used for arches, and some of the early railway bridges were built with cast iron girders.
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.
Lastly, some bridges are composed of cantilevers and suspended girders.
In the Ordish system a certain number of intermediate points in the span are supported by oblique chains, on which girders rest.
There are three chains on each side, of one and two links alternately, and these support wrought iron stiffening girders.
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.
There are four cables, one on each side of the two main trusses or stiffening girders.
The roadway girders are lattice, 17 ft.
The lattice girders of the side spans were first rolled into place, so as to project some distance beyond the piers, and then the arch ribs were built out, being partly supported by wire-rope cables from (3) Draw or Bascule Bridges.
In closed position the main girders rest on a bed plate on the face of the pier 4 ft.
Transverse girders and bracings are inserted between the main girders at 12 ft.
The main girders rest on the revolving platform, and the ends of the bridge are circular arcs fitting the fixed roadway.
Each bascule consists of two main girders with cross girders and stringers.
The main girders are hung at each side on a horizontal shaft 8a in.
The girders weighing 2000 tons carry a double track for trains between the girders and on each side on cantilevers a trolley track, roadway and footway.
The supporting structure is a cable suspension bridge with stiffening girders.
A car is suspended from the bridge, carried by a trolley running on the underside of the stiffening girders, the car being FIG.
Riveted plate girders are used up to 50 ft.
When girders form the superstructure, the resultant pressure on the piers or abutments is vertical, and the dimensions of these are simply regulated by the sufficiency to bear this vertical load.
The convenience of erecting girders on shore is very great, but there is some risk in the floating operations and a good deal of hauling plant is required.
In some cases hauling tackle is used, in others power is applied by levers and ratchets to the rollers on which the girders travel.
The girders of the side spans were rolled out so as to overhang the great span by 105 ft., and formed a platform from which parts of the arch could be suspended.
Bridges would then be designed for these selected loads, and the process would be safer in dealing with flooring girders and shearing forces than the assumption of a uniform load.
This increment is larger on the flooring girders than on the main ones, and on short main girders than on long ones.
Dead Load.-The dead load consists of the weight of main girders, flooring and wind-bracing.
It is generally reckoned to be uniformly distributed, but in large spans the distribution of weight in the main girders should be calculated and taken into account.
The weight of main girders increases with the span, and there is for any type of bridge a limiting span beyond which the dead load stresses exceed the assigned limit of working stress.
Let k(Wt+Wf) be the weight of main girders designed to carry We+Wf, but not their own weight in addition.
Let w 1, w 2 be the weights of main girders per ft.
From some known examples, C varies from 1500 to 1800 for iron braced parallel or bowstring girders, and from 1200 to 1500 for similar girders of steel.
This fact was forced on my attention nearly twenty-five years ago by the fracture of a number of girders of ordinary strength under a five-minutes' train service."
This result is modified if the action of the load near the section is distributed to the bracing intersections by rail and cross girders.
If the load is in the bay D'E' and is carried by a rail girder which distributes it to cross girders at D'E', the part of the influence line under this bay is altered.
But if the load is distributed to the bracing intersections by rail and cross girders, then the shear at C' will be greatest when the load extends to N, and will have the values wXADN and -wXNEB.
Let P be the cost of one pier; G the cost of the main girders for one span, erected; n the number of spans; 1 the length of one span, and L the length of the bridge between abutments.
Cost of piers (n-1) P. Cost of main girders nG.
The cost of the main girders for one span will vary nearly as the square of the span for any given type of girder and intensity of live load.
Differentiating and equating to zero, the cost is least when dC _ LP +La =o, dl = l2 P=ale=G; that is, when the cost of one pier is equal to the cost erected of the main girders of one span.
Taking K for steel girders as 7200 to 9000, Limiting Span in Ft.
For parallel girders when r = 10, the limiting span is 1070 ft.
For parabolic or bowstring girders, when r =8, the limiting span is 1280 ft.
Frames are much used as girders, and they also give useful designs for suspension and arched bridges.
The majority of bridges not of great span have girders with parallel booms. This involves the fewest difficulties of workmanship and perhaps permits FIG.
Most braced girders may be considered as built up of two simple FIG.
When all the forces are vertical, as will be the case in girders, the polygon of external forces will be reduced to two straight lines, fig.
The method of sections already described is often more convenient than the method of reciprocal figures, and the method of influence lines is also often the readiest way of dealing with braced girders.
The class of simple frames includes many of the frameworks used in the construction of roofs, lattice girders and suspension bridges; a number of examples will be found in the article BRIDGES.