Abstract:
A lightweighted weldless grating comprising a plurality of substantially parallel, longitudinally extending primary load bearing members, a plurality of secondary load bearing members, and a pan member positioned between the primary load bearing members and supported on the flanges adapted to contain wet concrete, the pan member having a portion thereof extending upwardly against the lower edge of the secondary load bearing member to maintain the secondary load bearing members in web slots in the primary load bearing members, thereby forming the weldless grating.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to grids or gratings useful for open or filled bridge decks, walkways, drain gratings and the like and more particularly, this invention relates to grids or gratings that are constructed and held together without welding. 
     In making prior gratings for bridge decks, whether the deck is open or filled with concrete, a certain amount of welding is performed to hold or bind the individual components together. That is, if the grid is used for open grating or open bridge deck, the main load bearing members, secondary load bearing members and tertiary load bearing members are welded together, usually by puddle welding, to hold the members together and give the deck or grating strength. Even if the grid or deck is to be encased in concrete, still some welding is required to hold the assembly in a rigid configuration until the concrete hardens. If only minimal welding is performed, then the deck or grid work when encased in concrete has a decreased level of strength. Thus, for peak bridge strength, the various components of the grating or bridge deck must be fastened together to perform as a unit. 
     Various deck or grating systems have been proposed in the art, and the members comprising the grating deck are welded together. For example, U.S. Pat. No. 3,260,023 discloses a bridge floor and surfacing component. The bridge floor comprises parallel bearer bars and cross bars. The cross bars are pressure welded into the tops of the bearer bars. 
     U.S. Pat. No. 4,865,586 discloses a method of assembling a steel grid and concrete deck wherein the primary load-bearing bars are formed with openings to receive slotted secondary load-bearing bars that are passed through the primary load-bearing bars. However, the patent discloses that tack welds are used to temporarily hold the grating in its desired configuration. A concrete component encases at least the top surface of the grating base member and secures the elements of the grating base member together. 
     U.S. Pat. No. 2,128,753 discloses a steel floor construction having a series of parallel main bars in spaced relationship. Each of the main bars is provided with a plurality of rectangular-shaped openings. The openings are designed to permit the insertion thereon and the positioning of two cross bars. A third set of bar is placed in slots in the cross bars. After the members are assembled, the entire construction may be welded together to maintain the different parts in position. 
     U.S. Pat. No. 2,190,214 discloses a grating wherein a desired number of parallel spaced apart main bearer bars with intermediate bearer bars of less depth are placed between the main bearer bars. The main bearer bars and intermediate bearer bars are connected at their tops by cross bars secured thereto by electric pressure welding. Carrier bars which pass through slots in the main bearer bars are welded to the intermediate bearer bars. Also, carrier bars are welded to the main bearer bars. 
     U.S. Pat. No. 2,645,985 discloses an open floor grating having a plurality of longitudinal primary members, a plurality of transverse secondary members welded to and extending between the primary members. A plurality of tertiary members are welded to the secondary members. A rod is inserted through holes in the webs of the primary members and welded thereto. 
     U.S. Pat. No. 2,834,267 discloses a grating comprised of a plurality of spaced parallel main longitudinal bars and a plurality of spaced parallel lacing bars and tertiary longitudinal bars intermediate the main bars. Bottom bars are inserted through holes in the webbing of the main bars. The intersection between the lacing bars and the tertiary bars are welded and the bottom bar is welded to the webbing of the main bar. 
     U.S. Pat. No. 4,452,025 discloses a self-interlocking grille consisting of a plurality of metallic or plastic strips or flats or bars with certain types of notches and holes disposed along the length of the strip or flats or bars in a regular interval, which are used together with a plurality of rods in assembling a variety of interlocking grills. 
     U.S. Pat. No. 4,780,021 discloses an exodermic deck conversion method for converting a conventional grid deck to an exodermic deck. Tertiary load-bearing bars are placed on top of the grating parallel to and between the primary load-bearing bars. A plurality of shear connectors, such as vertical studs, are welded or attached to the surface of the grating. It will be seen from the above that in gratings and bridge decks, usually some form of welding or cement is used to hold the assembly together. 
     However, welding gratings or deck structures have the problem that toxic fumes are released into the atmosphere causing health hazards to the welders and pollution of the environment. Welding of structures such as bridge decks results in curling or deforming of the deck as the welds cool. Thus, the design of the deck is complicated in that the curling or deforming must be accommodated in the design. Further, welding has the disadvantage that it is time consuming and often is the rate-determining step at which decks can be built. Welding also requires that the gratings or deck assemblies be maintained in jigs prior to starting the welding process. This is an additional, undesirable step in the process of making a bridge deck. Further, welds on bridge decks have the problem of cracking either with use or as the temperature cycles between winter and summer. It is desirable to rustproof gratings by galvanizing. However, because galvanizing is destroyed by welding, the welded grating or deck is often galvanized as a unit. However, this also results in temperature cyclization and warping of the bridge deck with the result that welds often break, detrimentally affecting the integrity of the deck. 
     Thus, it will be seen that there is a great need for an improved bridge deck or grating which will eliminate these problems and will provide for an improved deck or grating structure. The present invention provides such a structure. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved grating. 
     It is another object of the invention to provide a grating suitable for use on bridge decks. 
     It is a further object of the invention to provide an interlocking grating fastened together without need for welding. 
     Still, it is another object of the invention to provide an interlocking grating which may be used for open bridge decks or may be utilized with a concrete component that encases at least a top portion of the grating. 
     Yet, it is a further object of the invention to provide an interlocking grating for bridge decks and the like employing a primary load bearing member and a secondary load bearing member securely held together without welding. 
     And yet, it is an additional object of the invention to provide an interlocking grating for open or concrete encased bridge decks and the like employing a primary load bearing member, a secondary member and a tertiary load bearing member held together without welding. 
     These and other objects will become apparent from the drawings, specification and claims appended hereto. 
     In accordance with these objects, there is provided a lightweighted weldless grating comprising: (a) a plurality of substantially parallel, longitudinally extending primary load bearing members having an upper portion, a lower portion and a web located between the upper portion and the lower portion, the primary load bearing member having a plurality of spaced-apart openings in the web, the openings in each of the primary load bearing members being aligned with the openings in adjacent primary load bearing members, the openings having web slots extending upwardly towards the upper portion, the primary load bearing members having flanges in the lower portion extending towards adjacent primary load bearing members; (b) a plurality of secondary load bearing members having an upper edge and a lower edge, the secondary load bearing members provided with first slots extending downwardly through the upper edge to provide top slots and with upwardly extending slots through lower edge to provide bottom slots located substantially opposite the top slots, the bottom slots extending into the secondary load bearing members a distance greater than the bottom slots, the secondary load bearing members positioned in the aligned openings in the web of the primary load bearing members, the secondary load bearing members moved into the web slots, the web slots forming a locking engagement with the secondary load bearing members, the top and bottom slots in the secondary load bearing member forming a locking engagement with the web surrounding the openings in the primary load bearing members; and (c) a pan member positioned between the primary load bearing members and supported on the flanges adapted to contain wet concrete, the pan member having a portion thereof extending upwardly against the lower edge of said secondary load bearing member to maintain said secondary load bearing members in the web slots, thereby forming the weldless grating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a grating in accordance with the invention showing a secondary load bearing member locked in the web of a primary load bearing member. 
     FIG. 2 is a perspective view showing the parts of the grating of FIG. 1 in unassembled relationship. 
     FIG. 3 is an end view along the primary load bearing members showing a pan mounted on upper ribs of the primary load bearing members to contain wet concrete. 
     FIG. 4 is an end view along the primary load bearing members showing a pan mounted on lower ribs of the primary load bearing members to contain wet concrete. 
     FIG. 5 is a perspective cutaway view of a grating utilizing a deep web with concrete encasing the top portion of the grating. 
     FIG. 6 is a perspective view illustrating partial locking of secondary load bearing members into primary load bearing members. 
     FIG. 7 is a side view of the secondary load bearing member in FIG. 6. 
     FIG. 8 is a side view of the primary load bearing member with openings in the web for receiving primary load bearing members. 
     FIG. 9 is a perspective view of the pan of FIG. 3. 
     FIG. 10 is an end view of the pan of FIG. 3. 
     FIG. 11 is a perspective view of a three-member weldless grating employing a primary load bearing member and a secondary load bearing member or cross-rail. 
     FIG. 12 is a side view of a secondary load bearing member which is used with the primary load bearing member in FIG. 16. 
     FIG. 13 is an end view of the primary load bearing members and side view of the secondary load bearing members in assembled relationship. 
     FIG. 14 is a side view of a secondary load bearing member which is used with primary load bearing member shown in FIG. 15. 
     FIGS. 15 and 16 are side views of primary load bearing member having different shaped openings in the web thereof. 
     FIG. 17 is an end view of an assembled grating similar to FIG. 13 except a flat pan is utilized between primary load bearing members. 
     FIG. 18 shows an end view of a pan configuration useful in the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is shown a grating in accordance with the present invention. Grating or grid 2 is comprised of a plurality of primary load-bearing bars 4, a plurality of transverse secondary bars 6, a plurality of tertiary bars 8 shown running substantially parallel to the primary load-bearing bars 4. A rod 10 is shown laced through web 12 of primary load-bearing bar 4 and through tertiary bars 8. 
     In FIG. 2, the primary load-bearing bars 4 and transverse or secondary load bearing bars 6 are shown in partial unassembled relationship along with tertiary bars or tertiary load bearing members 8 and rod 10. It will be seen that primary load-bearing bars 4 have openings 14 (see FIG. 8) cut out to receive secondary bar 6. Openings 14 can have different configurations, one of which is shown in FIG. 8. Thus, each primary load-bearing bar 4 has a plurality of openings 14 to receive each secondary load-bearing bar 6. Further, each secondary load-bearing bar 6 has a plurality of slots 16 and 17 (see FIG. 8) that align with openings 14 in primary load-bearing bar 4 when assembled. 
     With respect to secondary load bearing members 6, these are shown having a generally rectangular cross-sectional configuration for convenience. However, other cross-sectional shapes may be utilized. Secondary load bearing members 6 are shown in FIG. 7 in a preferred embodiment having three slots 16 and 22 on top surface 15 and two slots 17 on bottom surface 19. Slots 16 and 17 are positioned opposite each other so as to engage web 12 of primary load bearing member 4 when secondary load bearing member 6 is turned to a vertical position, as explained later. Further, secondary load bearing member 6 is provided with a slot 22 to engage tertiary load bearing member 8 when the grating is assembled. Slots 16, 17 and 22 are formed to provide a snug fit then engaged or locked with web 12 and tertiary load bearing member 8. Further, these slots may be tapered from edge, e.g. 15, to the bottom of the slot to provide for improved engagement and minimize play between the mating members. 
     Primary load bearing member 4 is generally rectangular in cross-section and may have ribs or flanges projecting from either or both sides. FIG. 7 shows a side view of a primary load bearing member 4 showing openings 14 formed in web 12. Two openings are shown for illustration purposes. For purposes of locking secondary load bearing member in primary load bearing member 4, secondary load bearing member 6 is inserted on its side into primary load bearing member 4 as illustrated in FIG. 6. Thus, extent b of opening 14 must be at least slightly larger than height b of secondary load bearing member 6. Also, extent c of opening 14 must be just slightly larger than the thickness of secondary load bearing member 6. When opening 14 has these dimensions, then secondary load bearing member 6 can be inserted on its side through opening 14 until alignment with slots 16 and 17 are reached, as shown in FIG. 6. 
     In opening 14, the extent or dimension represented by &#34;a&#34; is smaller than the dimension represented by &#34;b&#34; in order than secondary load bearing member locks in web 12. Further, the &#34;a&#34; dimension is preferably slightly larger than the &#34;d&#34; dimension in secondary load bearing member 6 which extends from the bottom of slot 16 to the bottom slot 17. However, the closer the tolerance maintained between these two dimensions, the more rigidity is maintained in the grating. It will be appreciated that there is a balance in the tolerances of all the slots and thickness of material inserted therein and ease of assembly of the grating. That is, the tighter the tolerances maintained, the more rigid the grating. It should be noted that openings 14 are provided with a ramp or land 25 by removal of web material to permit secondary load bearing member 6 to be turned and locked in web 12. 
     For purposes of illustrating the assembly of weldless grating 2 in accordance with the invention, in one embodiment, secondary load bearing members 6 are laced through openings 14 in primary load bearing members 4. In the method of lacing secondary load bearing members 6 through primary load bearing members 4, secondary load bearing member 6 is turned on its side. That is, as shown in FIG. 6, side 7 of secondary load bearing member 6 is located underneath and side 9 is located on the top. After secondary load bearing member 6 is inserted through openings 14 to the extent where slots 16 and 17 (FIG. 7) coincide or align with web 12, secondary load bearing member 6 is rotated counter clockwise (FIG. 6) where sides 7 and 9 are in a substantially vertical position. In this position, web 12 is engaged by or inserted into slot 16 on top edge 15 of secondary load bearing member 6. Also, concurrently therewith, web 12 is engaged by or inserted into slot 17 (FIG. 7) on bottom edge 19 of FIG. 7. Thus, web 12 is engaged by or locked into slot 16 on the top of edge 15 of secondary load bearing member 6 and also engaged by or locked into slot 17 on bottom edge 19 of secondary load bearing member 6. While secondary load bearing member 6 is maintained in an upright position as shown in FIGS. 1 or 2, then the top 21 and bottom 23 of primary load bearing member 4 is prevented from moving in the direction of adjacent primary load bearing member 4. In this embodiment of the invention, secondary load bearing member 6 is maintained in a substantially vertical position by use of tertiary load bearing member 8 (FIGS. 1 and 2). 
     It should be noted that different shapes may be used for opening 14 and different methods of assembly may be used. For example, secondary load bearing bar 6 may be turned clockwise instead of counterclockwise. Further different methods of interlocking may be employed. All of these are contemplated within the purview of the invention. 
     Tertiary load-bearing bars 8 are provided with a plurality of slots 24 for alignment with slots 22 (FIG. 2). In one embodiment of the assembly, slots 24 line up with slots 22 so as to provide a planar surface, if necessary. To provide a planar surface, slots 24 and 22 should have a depth equal to half the depth of tertiary load-bearing bar 8. However, as explained earlier, if it is desired to have tertiary load-bearing bar 8 project above edge 20, then slot 22 may be shallower. Also, as explained earlier, any combination of slot depths may be used to provide either a planar surface or a ridge or rough surface for traction. Similarly, slots 22 may be eliminated if slots 24 are sufficiently deep in member 8. 
     Thus, it will be seen that in assembly, primary load-bearing bars 4 are first placed or fixed in position and then secondary load-bearing bars 6 are placed on their side and laced through openings 14 of primary load-bearing bars 4. When slots 16 and 17 are in alignment with web 12, primary load-bearing member 4 is turned counter clockwise to a vertical position to ensure that slots 16 and 17 engage web 12 to lock it in position and prevent lateral movement. It should be noted that if either slots 16 or 17 are missing, then the grating loses rigidity. Thereafter, tertiary load-bearing bars 8 are placed across secondary load-bearing bars 6 with slots 22 and 24 being aligned for engagement. 
     For purposes of locking the assembly comprised of primary load-bearing bar 4, secondary load-bearing bars 6 and tertiary load-bearing bars 8, an aperture 30 is provided in primary load-bearing bars 4 between secondary load-bearing bars 6, the aperture being formed to have an axis substantially parallel to secondary load-bearing bars 6. Likewise, tertiary load-bearing bars 8 have apertures 32 formed so as to be in alignment with apertures 30 of primary load-bearing bars 4. Rod 10 then is fitted through a first aperture 30 in a first primary load-bearing bar 4, then through apertures 32 of tertiary load-bearing bar 8 and finally through a second aperture 30 in second primary load-bearing bar 4. In this assembly, end 5 of rod 10 may be bent, fitted with a pin or nut to ensure that it does not move. Thus, after having secured rod 10, primary load-bearing bars 4, secondary load bearing bars 6 and tertiary load bearing bars 8 are locked together to form a unit grating, grid work, fence or railings without the attendant problems inherent with welding. Further, because of the additional rod used, the strength of the grating structure is improved dramatically. It will be appreciated that one rod or more can be used between each set of secondary load bearing bars 6. Further, fewer rods can be used. That is, in the present invention rods 10 can be selectively placed between secondary load bearing bars 6. For example, in the present invention, high strength grating can be obtained when rods 10 are used between every other set of secondary load bearing bars 6. 
     With respect to rod 10, it will be noted that a round bar has been illustrated. However, any cross-sectional configuration may be used. 
     In FIG. 1, primary load bearing bar 4 is shown with a lower flange 34, a web portion 12, a bulbous portion 38, and a rib 40. However, primary load bearing bars 4 can have other cross-sectional configurations that may be used. In the embodiment shown in FIG. 1, rib 40 and flange 34 provide for special features as explained herein. 
     Secondary load bearing bars 6 can have a depth generally less than the depth of primary load bearing bars 4, and tertiary load bearing bars 8 can have a depth less than the depth of secondary load bearing bars 6. Further, it should be noted that if tertiary load bearing bars 8 are sufficiently deep, then notch or slots 24 may be of sufficient depth to accommodate the full depth of the secondary load bearing bars 6 without slots 22 being provided in secondary load bearing bars 6. Rod 10 can provide sufficient resistance to sideways movement of tertiary load bearing bars 8. 
     When it is desired to encase at least a portion of the grating in concrete, a pan or sheet member 50 is positioned between primary load bearing bars 4 as shown in FIG. 3. Pan 50 is formed to extend the length of primary load bearing bars 4 and to rest on ribs 40. Thus, pan 50 is preferably shaped substantially as shown in FIGS. 9 and 10. That is, pan 50 is provided with a rib 60 which extends the length of the pan in a direction generally parallel to primary load bearing member 4. Further, preferably pan 50 is generally curved or shaped upwardly towards rib 60 as shown in FIGS. 9 and 10. Rib 60 provides for stiffness in the pan. In addition, from edge 62 to the top of ridge 60 should be controlled. That is, in the preferred embodiment, when concrete is to be used as a wear surface or to partially encapsulate grating 2, pan 50 is positioned between primary load bearing member 4 prior to secondary load bearing member 6 being turned to an upright position. Edges 62 of pan 50 rest on the upper surface of rib 40, as shown in FIG. 3, for example. When secondary load bearing member 6 is turned into locking position, bottom or lower side 9 of secondary load bearing member 6 contacts ridge 60 sufficiently to secure pan 50 in place by friction. Thus, the grating can be shipped to the job site without pans 50 moving or dropping out of the grating. It should be noted that welding pans 50 in place is undesirable because of warpage that occurs. The warpage results in uneven thickness of concrete and also in spaces between the rib and the pan which results in wet concrete seeping or dripping onto the surfaces below. The assembled grating in accordance with the invention has a rigid configuration without substantially any movement of the bars or members. Thus, for example, because primary load bearing bars do not move or wobble, the pans can be placed on or inserted between the primary load bearing bars prior to shipping. 
     If it is desired to encase substantially the depth of the grating in concrete, pan 50 can be located, as shown in FIG. 4. 
     FIG. 5 is a schematic showing concrete 56 provided in the upper portion of the grating. 
     It should be understood that while the grating of the invention has been shown encasing a top portion of the grating (FIG. 5), the concrete can extend above and below the grating, if desired. That is, the grating can be substantially encapsulated with concrete. 
     In FIG. 11 there is shown a lightweighted grating 70 in accordance with the invention comprised of primary load bearing members 4, secondary load bearing members 6 and pan member 50. The secondary load bearing members 6 are locked in position utilizing pan member 50. FIG. 13 shows secondary load bearing member 6 held in place or in locking engagement with primary load bearing members 4. That is, pan member 50 is positioned on flanges 34 and pushes upwardly on secondary load bearing member 6 to hold it in locking engagement with primary load bearing members 4. A side view of primary load bearing member 4 is shown in FIG. 15. Two substantially vertical slots 72 having a height or extent &#34;h&#34; sufficient to accept secondary load bearing member 6a are shown in web 12 of primary load bearing member 4 in FIG. 15. Typically, slots 72 have a rectangular shape. Secondary load-bearing member 6a as shown in FIG. 14 is provided with slots 74 with only two slots 74 being shown projecting downwardly through top 15. For purposes of assembly, secondary load-bearing member 6a is inserted through slot 72 until slot 74 reaches web 12. After secondary load-bearing member 6a has been laced through the required number of primary load-bearing members 4 and slots 74 line up with webs 12, secondary load-bearing member 6a is moved upwardly until slot 74 locks on web 12. Then, a pan member 50 having the shape shown in FIGS. 11 and 13, for example, is inserted underneath secondary load-bearing member 6 and holds secondary load-bearing member 4 in locking engagement with web 12. It should be understood that different configurations of pan members may be employed to maintain secondary load-bearing member in locking relationship with the primary load-bearing member. For example, a pan member 50a having the configuration shown in FIG. 18 may be employed. Pan member 51a has a flat bottom 76 and sides 78. Bottom 76 is designed to rest on flanges 34, and sides 78 are designed to hold secondary load-bearing member 6 in locking engagement with web 12 of primary load-bearing member 4. It should be understood that other designs of pan member shapes may be employed and such is contemplated within the purview of the invention. Usually, the pan members are employed to contain concrete. However, pan members of the invention provide for both locking secondary load-bearing member in the primary load-bearing member and containing wet concrete. 
     If it is desired to substantially fill the space between primary load bearing members 4, a flat pan member 50b may be employed as shown in FIG. 17. Clips 51 having the cross-section configuration of pan member 50 may be employed to maintain pan member 50b securely between primary load bearing members 4 in locking engagement with web 12, as noted earlier. 
     In another embodiment, the lightweighted weldless grating may be assembled using primary load bearing members 4a shown in FIG. 16 and secondary load bearing members 6a shown in FIG. 12 employing pan 50 as shown in FIG. 11. In this embodiment, primary load bearing members 4a are provided with openings 14a which have a generally cross-shaped configuration as represented by the dimension or extent &#34;a&#34; and &#34;b&#34;. It should be noted that the dimension represented by &#34;b&#34; is greater than the dimension represented by &#34;a&#34;. Opening 14a is shown with the longer dimension on the horizontal and shorter dimension in the vertical. However, these dimensions can be oriented in any direction as long as one dimension is longer than the other. The use of horizontal and vertical as used herein is meant to include any of these different orientations. 
     In preferred opening 14a (FIG. 16), a ramp or land 25a is provided. In FIG. 16, ramp or land 25a is generally defined by straight lines 80 and 82. Straight line 80 extends from near top 71 of vertical extent represented by &#34;a&#34; to side 73 of the extent represented by &#34;b&#34;. Further, ramp or land 82 is defined by a line extending from side 74 of horizontal extent represented by &#34;b&#34; to bottom 75 of vertical extent represented by &#34;a&#34;. Land 80 and 82 are substantially opposite each other. Land 82 sloping downwardly from horizontal extent &#34;b&#34; and land 80 sloping upwardly from horizontal extent &#34;b&#34; are important in that both ramps provide for ease of assembly of the weldless grating by ramping or guiding a secondary load bearing member as the secondary load bearing member is turned from the horizontal to the vertical position. That is, the secondary load bearing member is laced through opening 14b (FIG. 16) in the horizontal position and then turned or rotated to the upright position. This is shown in FIG. 16 where secondary load bearing member 6b is shown in the upright position in opening 14b. Secondary load bearing member 6b is shown in dotted line or outline form in the horizontal position in opening 14b of FIG. 16 and then in solid form after being rotated to the upright position. In the upright position, secondary load bearing member 6b extends above top 71 and below bottom 75 to lock secondary load bearing member 6b in web 12. 
     It should be noted that in secondary load bearing member 6b shown in FIG. 12, two slots 17b and 17c are provided substantially opposite each other. In a preferred embodiment, slot 17c is longer or deeper than 17b for purposes of moving secondary load bearing member 6b upwardly during assembly. That is, as will be noted with respect to opening 14a in FIG. 16, top 71 is recessed upwardly to provide a slot 77. Upon rotation of secondary load bearing member 6b to the upright position, secondary load bearing member 6b is forced into slot 77 which serves to anchor secondary load bearing member 6b in the upright position. Further, slot 17b and 17c form a locking engagement with web 12 which anchors secondary load bearing member 6b in primary load bearing member 4a. Secondary load bearing member 6b is held in slot 77 by a pan member 50, as shown in FIGS. 11 and 13. Further, it should be noted that because slot 17c is deeper than slot 17b, secondary load bearing member 6b can be moved upwardly into slot 77, and yet slot 17c still forms a locking engagement with web 12 of the primary load bearing member 4. 
     To assemble a grating comprised of primary load bearing members 4a as shown in FIG. 16 and secondary load bearing members 6b (FIG. 12), primary load bearing members 4a are first aligned in a jig with opening 14a aligned with openings in corresponding primary load bearing members. A pan member 50 having the cross-section configuration shown in FIG. 13 is then placed on flanges 34. Rib 60 of pan member 50 should extend upwardly sufficiently to push secondary load bearing member 6b into slot 77. Secondary load bearing member 6b is laced horizontally (extent b) through opening 14a. When slots 17b and 17c appropriately line up with web 12, secondary load bearing member 6b is rotated counter clockwise to an upright position. Leverage force may have to be applied to rotate secondary load bearing member 6b against the resistance of ridge 60. That is, ridge 60 is forced downwardly (as secondary load bearing member 6b is rotated) and then springs back as secondary load bearing member 6b slides into slot 77. 
     Because of the friction fit between pan member 50 and the bottom of secondary load bearing member 6b, grating can be shipped to the job site without pan members having to be welded to flange 34 and the attendant problems of welding. Thus, it will be seen that as with other embodiments of the grating, concrete can be used to encase a substantial portion of the grating, the concrete can extend above and below the grating as desired. 
     It will be seen that gratings in accordance with the present invention overcome the disadvantages of welded gratings referred to earlier. However, even though welds can be applied to the grating of the present invention, welding is believed to be more detrimental than advantageous because welding tends to cause embrittlement and, therefore, provides a site for failure such as fatigue failure. However, the term weldless as used herein can include minor welding, for example, if such were used to hold rod 10 in place, and such is contemplated within the purview of the invention. 
     Further, while the invention has been depicted showing primary load bearing bars having flanges, the invention contemplates gratings fabricated using plain bars for all three load bearing bars; and in certain gratings, the three bars can have the same dimensions. 
     The gratings of the invention can be fabricated from metals such as steels, carbon steel, stainless steels and aluminum alloys or from plastics such as fiberglass-reinforced plastics. 
     In the present invention, if steel bars are used, they may be galvanized prior to assembly or after assembly. If galvanized before assembly, touch up may have to be used to cover scratches resulting from assembly. Further, in the present invention, the slots should be dimensioned to provide for a snug fit to minimize collection of debris such as salts that cause corrosion, particularly in open gratings. 
     While the invention has been described in terms of preferred embodiments, the claims appended hereto are intended to encompass other embodiments which fall within the spirit of the invention.