US2767627A

US2767627A - Bridge gratings

Info

Publication number: US2767627A
Application number: US307278A
Authority: US
Inventors: Joseph C Lynn; John A Rau
Original assignee: ALLISON STEEL Manufacturing CO
Current assignee: ALLISON STEEL Manufacturing CO
Priority date: 1952-08-30
Filing date: 1952-08-30
Publication date: 1956-10-23
Anticipated expiration: 1973-10-23

Description

J. C. LYNN ET AL BRIDGE GRATINGS 2 Sheets-Sheet 2 Filed Aug. 30, 1952' FIG. 2

INVENTORS. JOSEPH C. LYN/V JOHN A. RAU

ATTORNEY United States Patent BRIDGE GRATINGS Joseph C. Lynn, Berkeley, Calif., and John A. Ran,

Phoenix, Ariz.; said Ran assignor to Allison Steel Manufacturing Company, Phoenix, Ariz., a corporation of Arizona Application August 30, 1952, Serial No. 307,278

1 Claim. (Cl. 94-30) This invention is concerned with metal gratings, particularly heavy gratings of the type used for decks. Such gratings are used as flooring for bridges, viaducts, etc., and can be used in open condition or filled with concrete to form a solid deck. Gratings of this general type have been approved by the U. S. Corps of Engineers for military bridges, but heretofore all gratings acceptable to the Corps have had manually welded joints. This adds greatly to the cost of the gratings and the manual Welding requirement has been a bottleneck that has restricted production of the gratings.

As a result of our investigations we have developed a deck grating of adequate strength which requires relatively little manual welding and in which the great majority of the joints are welded automatically by the resistance technique. The design of the grating is such that it acts as a unit, rather than as its individual members, under stress.

The grating of our invention comprises three sets of metal (say steel) members, with the members of each set spaced from each other. The members of the first or upper set provide the wearing surface of the grating or deck and are called rods in the following, although they can also be bars or for that matter, any long members. They are spaced side by side in the upper plane of the deck and overlie a first set of bars. These bars are preferably parallel to each other and set on edge and are spaced from each other, extending transverse to the rods. The rods are fastened to the upper portions of the bars of the first set, this being accomplished by a resistance-Welding technique in which the rods are pressed against the upper portions 0f the bars while electric current flows through the several junctions between the rods and bars. These junctions oifer a high resistance and the current softens the metal at the intersections or junctions, so that the rods are forced into the upper portions of the bars while the junctions are plastic. During this resistance-Welding operation the rods are pressed into the bars, preferably to a depth greater than half the rod thickness. This achieves a mechanical lock at each junction of rods and bars which is almost sufficient for the loading. But in addition to this mechanical lock, the resistance-Welding causes the rods to be soundly welded to the first set of bars at the several junctions.

No notches are made in the rods on the first set of bars at the junctions prior to welding, both bars and rods being of original full section at the junctions. They are joined by the heat and pressure applied during the resistance-welding step, the excess metal forming a pronounced fillet at each junction, adding greatly to the strength of the grating. All of the welds in between the rods and first set of bars in a given grating unit are formed simultaneously, thus reducing time of manufacture to but a small fraction of that formerly employed in making satisfactory bridge gratings.

A second set of bars runs in the direction of the rods. These bars are also set on edge and are substantially deeper than the bars of the first set. These bars of the second set have their upper edges substantially abutting the bottoms of neighboring rods but are spaced from each other by at least twice the rod spacing, so that there are some rods, at least half, which are not accompanied by bars of the second set. The bars of the second set are notched where they cross the bars of the first set, and the bars of the first set are fitted in these notches to give other mechanical locks, with the upper edges of the bars of the second set substantially abutting the companion rods. The bars of both sets are fastened together at the several mutual intersections of the three types of members by fillet welds, preferably made manually, for example by an operator employing a welding rod. These fillet welds are much fewer in number than those first described. Consequently the amount of labor employed in forming the grating is much reduced, with attendant savings in cost and time, but with no loss in strength.

Preferably the bars of the second set are of inverted T section, with a heavy but relatively narrow flange at the bottom. This inverted T may or may not have reinforcement thickening or longitudinal rib in the web, below the intersection of the first set of bars.

The notches in the bars of the second set are on the upper edge of the bars and preferably are just wide enough to accommodate the bars of the first set, except adjacent the upper edge, Where space is left on both sides for the metal of the fillet-resistance weld. In this way a strong three-Way joint between rod, the bar of the first set, and the bar of the second set is assured.

At present, round rods are preferred, although rods of other cross section may be employed. By way of example, the upper surface of the rods may be roughened to give a good tread.

These and other aspects of the invention are described in detail in the following and illustrated by the accompanying drawings in which:

Fig. 1 is a fragmentary plan view of a presently preferred form of the grating of our invention;

Fig. 2 is a side view of the grating of Fig. 1;

Fig. 3 is an enlarged fragmentary plan View taken in the area 3 on Fig. 1; a

Fig. 4 is an enlarged fragmentary sectional view of the grating taken on line 44 of Fig. 3, showing how the hand fillet Welds are employed to fasten rod to bar to bar;

Fig. 5 is an enlarged fragmentary sectional view of the grating taken on line 55 'of Fig. 1;

Fig. 6 is a detail showing how the first set of bars in the grating of the foregoing figure is notched during the fusion welding; and

Fig. 7 is a detail showing how the second set of bars of the grating of Figs. 1 to 6 is notched before welding.

The essentials of the presently preferred form of the invention are best seen in Figs. 4, 5, 6 and 7. Thus Figs. 4

and 5 show that the top of the grating is formed by a set of round rods 10 lying parallel to and spaced from each other in a level plane. The rods rest on a first set of bars 11 disposed at right angles to the rods. These first bars are of elongated rectangular section with their sides vertical and at each intersection of rod and bar, the bars are joined by fusion welding.

The fusion welding is brought about by pressing the rods against the bars in a hydraulic press while current is passed through each junction or intersection. Heating results and the several junctions become plastic or fused so that the bars are, in effect, notched at each intersection as the rods penetrate into them. The resistance-welding operation preferably is so conducted that the rods penetrate the bars to a depth substantially greater than the rod radius. The excess metal forced out of the junction forms fillets at each resistance-weld. The notched construction thus achieved gives both mechanical interlock and sound welding at each intersection or junction. Fig. 6 shows the final form of the first set of bars after the rods have been forced into them in the resistancewelding operation, the actual penetration of the rods being indicated at 12.; It will be observed that the penetration is such that the center of each rod is below the top of the bar.

In the next phase of the operation, a second set of bars 13 is attached to the grating. These bars are specially shaped T sections and are attached to the grid in an inverted position, with the heavy but short cross arm 14 of the T downward. The web 15 of the T-section bar has parallel sides and the depth of the bars of the second set is substantially greatenpreferably at least double, the depth of the bars of the first set.

The second set of bars is disposed so that there is a bar underneath and parallel to every third rod, withthese alternate rods resting on the top edges of the T bars and with two rods not directly supported by the T bars in between. The T bars are notched, as shown in Fig. 7, to accommodate the first set of bars. Thus the top of eachT bar is provided with a plurality of notches 16. These notches are just the Width of the bars of the first set, and are rectangular slots except at the top Where their corners are cut away as shown at 17 in Fig. 7 to give room for the fillet metal of the flash fusion weld. When the second set of bars is placed so that their upper edges contact the rods there is a mechanical interlock between the first and second set of bars with the first set of bars fitted into the notches 16 of the second set of. bars.

When the second set of bars has been placed in position parallel to and underlyingevery third rod, hand welding begins. The hand fillet welds may be formed in various ways. One satisfactory way is shown in Figs. 3, 4 and 5 where an upright fillet weld 20 joins the first and second set of bars at each mechanically locked intersection of the two. If desired, horizontal fillet welds 23 may be employed to join the bars of the second set to the overlying rods.

If desired, the bars of the second set may have an enlarged or reinforced rib portion 24 running longitudinally immediately below the bars of the first set. This feature is shown on one of the bars of the second set in Fig. 5, and also in Fig. 7 and is formed integrally with the bars at the steel mill during the rolling operation.

Either before or after the hand welding is done, truss rods 21 (see Fig. 5) may be run through fitting round holes 22 (see Fig. 7) in the web of the second set of T bars. These truss rods extend in the same direction as the first set of bars and preferably are welded in place.

The individual grids are made up in sections as shown in Fig. 1.

If desired, support bars 26 may be welded between webs of the second set, as shown in Fig. 2.

It is, of course, not necessary that the second set of bars be disposed underneath every third rod. As. shown at the left hand end of Fig. 2, some bars of the second set may be placed on different spacings to accommodate dimensional requirements of a platform made from the grating sections.

A specific example of a grating .of the invention employs /2" diameter rods on 2" centers. These rods may 4 or may not be deformed on their top surfaces to produce a tread.

The bars of the first set (which cross the rods) are 1 /2 deep and A" Wide. The rods project above the first set of bars by /s. The bars of the first set are disposed parallel to each other on 3 centers.

The bars of the second set are disposed under every third rod, i. e. between each of the bars of the second set there are two rods which are only supported directly by the bars of the first set. Thus the bars of the second set run parallel to the rods on 6" centers. The bars of the second set have a total depth of 4%. The flange of each of these bars is A thick and the cross on the T is A Wide, this width being maintained for and then i being reduced to the width of the web in a depth of The notches in the second set of bars in which the bars of the first set fit are wide, thus requiring a force fit during assembly. These notches have a total depth of 1, and their upper corners are cut away at an angle of 45, the cut-away corner being A deep.

It will be understood that the foregoing specific example is intended merely by way of illustration and that within the scope of the invention departures may be made in any or all of the dimensions.

As indicated at the outset, the effect of the mechanical interlock between members, plus the flash resistance welds which join the rods to the first set of bars and the hand welds which join the second set of bars, is to cause the members to act as a unitary structure, the section modulus of this structure being its own and not that of the individual members.

The bridge gratings of the invention may be produced rapidly with a great saving in labor and have a strength at least equivalent to that obtained with prior bridge gratings employing hand welding throughout.

We claim:

In a metal grating, the combination which comprises a set of rods spaced side by side in a plane, a first set of bars spaced from each other and disposed adjacent but transverse to the rods, the bars of the first set being resistance fusion-welded to the rods at each intersection of the rods and, said bars and the rods being pressed into said bars during the welding at each intersection, and a second set of bars aligned with at least some of the rods, the bars of the second set being notched at the intersections of the first and second set of bars, the bars of the first set being fitted in the notches of the second set so that the edges of the bars of the second set are in lengthwise engagement with the rods with which they are aligned, the bars of the second set being joined to the bars of the first set at the intersections of the bars of the two sets by fillet welds, and the rods and bars of the second set being joined by fillet welds.

References Cited in the file of this patent UNITED STATES PATENTS 1,973,113 Schulz Sept. 11, 1934 2,155,694 Tench Apr. 25, 1939 2,169,649 Knapp Aug. 15, 1939 2,275,105 Greulich Mar. 3, 1942 2,469,070 Greulich May 3, 1949 2,542,979 Barnes Feb. 27, 1951 2,645,985 Beebe July 21, 1953