US2402090A - Ground mat - Google Patents

Description

June 11, 1040. F H UPPEL 2,402,090

GROUND MAT Filed May 31, 1943 2 Sheets-Sheet l 2 Sheets-Sheet 2 ..........m o I m w wu H r vj F. H. RUPPEL GROUND MAT Filed May 31, 1945 June 11, 1946.

Patented June 11, 1946 OFFICE GROUND MAT Frederick H. Buppel, Pasadena, Calif.

Application May 31, 1943, Serial No. 489,125

3 Claims.

1 This invention relates to openwork metal mats to be laid on the ground for forming aeroplane runways, roads, gun foundations, etc., and con-l stitutes a further development of mats disclosed in my pending applications, Serial No. 452,681, filed July 29, 1942, now Patent No. 2,369,412, issued February 13, 1945, and Serial No. 455,859, filed November 17, 1942.

The present mat, like those disclosed in my prior applications, consists of two sets (upper and lower) of elongated members, all the members of one set being parallel to each other but at right angles to the members of the other set, each member being riveted to the members of the other set at their points of crossing.

An object of the present invention is to increase the effectiveness of mats of the general type described, for supporting heavy loads on soft, yielding ground.

Another object is to provide a mat that is capable of supporting heavy loads, and yet maintains itself at the surface of soft ground instead of embedding itself deeply into the ground.

Still another object is to provide a mat that is particularly effective when reinforced with concrete, asphalt, stabilized earth, etc.

Other more specific objects and features of the invention will appear from the description to follow, of certain specific embodiments of the invention.

In the mats of my prior applications referred to, the elongated members consist of relatively small channel sections positioned back to back so that the edge flanges of the upper set provide a non-skid surface for engagement with the wheels of the vehicles moving thereover, and the flanges of the lower set dig into the surface of the earth and increase the frictional resistance of the mat to lateral movement with respect to the ground. Those prior structures provide relatively small contact with the earth, that is to say, the ratio of the area of the mat members in contact with the earth to the total surface area of the mat, is relatively small. They depend largely for their load-supporting ability on the tensile strength of the mat members and the frictional resistance to lateral movement of the mat with respect to the earth. Thus those mats may, under a heavy load applied to the middle thereof, sirlc appreciably below the surface of the earth so that the mat becomes a catenary suspended from the edge portions On each side of the load. They have the great advantage that where it is possible to employ a mat of small ground-contacting area, it can be of relatively light construction,

2 thereby facilitating transportation and handling, and economizing in the use of steel.

However, I have discovered that under certain conditions of service, particularly those involving the moving of relatively heavy loads over unusually soft ground, that it is sometimes desirable to employ a mat having relatively greater rigidity or resistance against bending, and having suflicient bearing with the earth to support the load without extending the mat large distances to each side of the line of traflic, as may be necessary when relying upon the catenary action of the mat. The present invention consists of a novel mat construction providing this increased rigidity and greater ground-bearing surface, and frictional efiiciency, together with other advantages which will be fully explained later on.

Briefly, the mat construction in accordance with the present invention dilfers essentially from those of my prior application in that, instead of employing shallow channel sections as the lower members of the mat, it employs angle sections or T sections having downwardly extending legs of substantial depth, which penetrate into the ground and contact therewith over a surface that may be comparable to or greater than the total horizontal area of the mat itself. However, the depth of these members provides great rigidity and strength against bending under heavy loads, and much greater bearing efiiciency than if the same amount of material were employed in a solid or perforated fiat sheet of metal adapted to be laid on the surface of the earth.

Another distinguishing'dilference between the present construction and those of my prior applications, is that whereas the earlier constructions related to unit mats of approximately square shape the mat units in accordance with the present invention are relatively narrow in the direction at right angles to the lower angle members, and the mats are laid transversely with respect to the direction of trafiic. I find that this construction is highly advantageous in that it reduces the tendency of the mat units to cup or curl up at the edges, under the strains of trafiic rolling thereover.

A full understanding of the invention may be had from the detailed description to follow, which refers to the,drawings in which:

Fig. 1 is a plan view of a mat unit in accordance with the present invention, shown in collapsed position for shipment and handling;

Fig. 2 is a plan view showing the mat unit fully extended;

Fig. 8 is a plan view of a portion of a landing field composed of fully extended unit mats in accordance with Fig. 2;

Fig. 4 is a plan view of a portion of a trafiio base composed of mat units that are only partially opened;

Fig. 5 is a plan view of a section of road formed of fully extended mat units;

Fig. 5A is a plan view of a section of road formed of partly extended mat units;

Fig. 6 is an enlarged detail plan of a portion of the field shown in Fig. 3, illustrating one manner of attachment of individual mats to each other;

Fig. 7 is a detailed vertical cross-section of the mat construction. the section being taken on line VII-VII of Fig. 6 perpendicular to the lower (angle section members of the mat;

Fig. 8 is a detailed vertical cross-section taken on line VIII-VIII of Fig. 6 at right angles to the upper (channel) members of the mat;

Fig. 9 is a detailed plan showing a connector for interconnecting two mats; and restraining mats from partial collapsing or shifting sideways under certain stresses when used as roadways expedients; and

Fig. 10 is an elevation view partly in section, of the connecting structure of Fig. 9.

Referring first to Fig. 2, there is disclosed a unit mat having a plurality of relatively short upper members 2!] overlying and extending at right angles to a plurality of relatively long lower members 2!, and pivotally interconnected therewith at the cros-over points by rivets or bolts 22. By virtue of the fact that the members are pivotally, connected together, the mat can be collapsed into the condition shown in Fig. 1, for convenience in shipping and handling, or, if the ground conditions are so bad as to justify it, to increase the load-supporting ability of the mat.

The upper, short members 20 are preferably channel or strip members having their flanges uppermost as shown in Fig. 8, and all of the members may be of the same size; but I prefer to form the end members ZUI of somewhat larger channels than the intermediate members 20, in order to strengthen the connections between individual mats. The intermediate members may be x and the end members 2! may be 1" x /2". The channels may be spaced l /z" apartcenter to center when the mat is fully extended as shown in Fig. 2, so that that particular mat would have an over-all length of approximately 12' 1" and a width of 3' 1..

The lower, long members 2| are preferably angle members and may all be of the same dimensions, but, as shown in Fig. 7, I prefer to make the edge members 2!! smaller than the intermediate members. Thus the members 2 may be 1" on a side, whereas the intermediate members 2| may be 1 /2" on each side, or larger if additional rigidity and bearing surface is required. If the angles are larger than 1 /2" x 1 /2 th horizontal plate may be smaller than the vertical plate. Thus the horizontal plate may be 1 /2" and the vertical plate 2" ormore.

It is possible and desirable to make the edge angles smaller than the intermediate angles, because as shown in Fig. '7, the edge angles of two adjacent mats are positioned close together, and, therefore, providea reater bearing at that point. In general, it is desirable to make the efiective bearing at the edges substantially the same a at intermediate points, and this result can be approximated by using edge and intermediate anles of the approximate dimensions shown.

It is desirable to face successive angles oppositely insofar as is possible, so that each pair of adjacent angles form a symmetrical structure. This compensates for the inherent tendency of angles to skew to one side when a load is placed thereon parallel to one member. In the particular construction shown in Fig. 2, there are an odd number of angles, so it is not possible to have the two angles of each adjacent pair opposed to each other in all instances, but it is done insofar as possible.

It is to be understood that it is not essential that the under members be of angle section; the important thing is to have relatively deep vertical webs extending into and having large surface contact with the earth, and angle sections seem to provide this most economically. However, as an alternative shape, a T-section might be employed. T-sections have the advantage of symmetry, in that there is no tendency to lateral skewing in response to vertical bending, but T- sections would not lend themselves so readily to riveting as the angle sections.

It is desirable to join the different unit mats together at relatively closely spaced points in order that the stresses on the connectors will not be excessive and will be evenly distributed. Various types of connectors can be employed, but one that has proved satisfactory is disclosed in Figs. 6 and 'I. It consists of a U member 23 which fits down over the two adjacent members of the mats to be joined and is locked in place by inserting a cotter pin or nail 24 through suitable apertures provided in the flanges of the U member 23. After the cotter pin 24 is inserted, its outer ends are bent apart. The cotter pins are preferably made of relatively hard steel so that they do not have to be of excessive size in order to have sufiicient strength to prevent spreading of the connectors.

In some instances I find it desirable to employ much longer U members 25 as shown in Figs. 9 and 10, these members extending almost the full distance between channel members, and havin their flanges interconnected by one or more cotter pins 2 1. The end portions of the bases of the U members 25 may be extended upwardly to form ears 25! adapted to abut against adjacent channel members 20 and limit the collapsing or shifting movement of the mats.

The individual mats such as shown in Fig. 2, and designated generally by the reference numeral 26, may be combined to form large mat areas of any desired shape and size. Ordinarily, where the ground is not to soft and the load to be borne is not too heavy, the units will be fully expanded into rectangular shape as shown in Fig. 2, and joined together as shown in Fig. 3, to form a large area such as a landing field, or as shown in Fig. 5, to form a road. In the large structure shown in Fig. 3, the individual mats are staggered like brick work, to afford maximum strength at the joints. In all instances, the mats are preferably laid with their long dimension transverse to the direction of traffic, so that the wheels of the vehicles roll on the short upper channel members 20 and Zlll in the same direction as the latter. The spacing of the channel members 28 is preferably less than the width of the tires on the ve hicles that will use the mats, so that the weight will be applied directly to the upper channel members and transferred from those members to the lower angle members which have the major bearing contact with the earth. Application of the loads directly to the upper members and indirectly to the lower members, reduces the strains on the rivets joining the upper and lower members.

When the applied loads are very high and the ground excessively soft or very wet, it may be desirable to have a greater bearing surface between the mats and the earth than is afforded by fully expanded mats. In such instances, the bearing surface can be increased to any desired value by only partially expanding the mats from the folded position shown in Fig. 1. A portion of a landing field formed of such partially expanded mats, is illustrated in the plan view of Fig. 4, in which it will be observed that the individual mats 26 are in the form of oblique parallelograms instead of rectangles. This same expedient may be adopted in a roadway as shown in Fig. 5A, by extending the longedges of the partially collapsed mats across the roadway at an oblique angle while maintaining the short ends of the mats parallel to the roadway.

A mat of the dimensions described, forming a rectangle 3 1" x 12' 1" when fully extended, has an area of 37.26 square feet, but has a total surface in. contact with the soil, of 32.5 square feet which is approximately 87% of the mat area. The horizonta1 area of the mat when fully collapsed is only 11.08 square feet whereas the area in contact with the earth, is approximately the same as before (32.5 sq. ft.). It will be apparent, therefore, that the ratio of the bearing area to the horizontal area may be increased to any necessary extent by partial or complete collapse of the mats.

Even where the additional bearing surface is not required, the collapsible feature of the mats has advantages, particularly in the making of roads, since bends in the road can be readily formed by partially collapsing the mats in the region of the bend.

It has been found in actual load tests that the mat construction of this invention has greater load-supporting capacity on soft ground than would be expected. This is especiall true in situations Where the ground consists of a semi fluid mass of soil and water overlaid by a drying crust. In such situations, only the crust has any load-supporting capacity, and if a vehicle breaks through the crust it is hopelessly mired. It is found that when the present mat is laid on ground of this type, it appears to greatly reinforce the crust so that it is capable of supporting ubstantial traffic for a relatively long period of time. It appears that when the mat depresses locally under a load passing thereover, it tends to partially collapse the mat, thereby bringing the embedded walls of the angle members closer together, which compresses the soil crust therebetween, thereby greatly increasing its strength and its ability to maintain a surface impervious to the semi-liquid mass therebelow.

In the same way, the mat construction is unusually efiective when reinforced by some material such as concrete, asphalt, stabilized earth, or the like. Such material may be applied under the mat, or over it, or both under and over it.

It is highly advantageous to position the individual mats with their long dimension transverse to the direction of traffic (substantially transverse when the mats are partially collapsed) because all mats of this type have a tendency to cup under rolling traffic, which cupping raises the edges of the individual mats to produce a scallop effect.

It is impossible to completely avoid this effect in any composite mat the units of which are not absolutely rigidly connected together, but I find that it can be greatly reduced by making the dimen sions of the units smaller in the direction of the trafiic.

The present mat construction, in addition to the advantages specified, has other important advantages in common to the structures of my prior applications, namely, that the mats are relatively light in proportion to the area covered, and can be collapsed into relatively compact packages for shipment and easy handling. They can also be laid rapidly, can be readily camouflaged by planting grass or other vegetation, and can be readily taken up, collapsed, and relaid.

Under ordinary surface conditions, no auxiliary material is necessary to provide suflicient bearing surface, but should exceptional conditions demand it, the mats can be reinforced with concrete, asphalt or other similar materials, as previously described, or with brush, timber, or other auxiliary material to provide a suitable foundation. When planks or logs are used as auxiliary material, they should be laid under the mat parallel with the line of traffic so that the angle members extend transversely thereacross.

Although for the purpose of explaining the invention, a specific embodiment thereof has been disclosed in considerable detail, it is to be understood that various departures from the exact structure shown can be made while still utilizing the advantages of the invention which is to be limited only to the extent set forth in the appended claims.

I claim:

I. A mat of the class described comprising a plurality of units connected together at their adjacent edges, each unit consisting of a lower set of relatively long spaced-apart parallel members and an upper set of relatively short spaced-apart parallel upper members overlying said upper members and at right angles thereto, a pivotal connection between each member of the lower set and each member of the upper set at their points of intersection whereby each mat unit may be collapsed Or expanded into various shapes in the plane of the surface on which it rests, the lower members being constructed and positioned to perform as beams and extend in a line substantially transverse to the line of travel thereover and to frictionally engage a material on which the mat is superposed, the said lower members being substantially more resistant to bending in a vertical plane than the upper members, and U- shaped connecting members adapted to overlie juxtaposed lower and upper members of adjacent units to secure individual units together.

2. A mat as described in claim 1, in which said lower members are of angle cross-section having horizontal plates riveted to said upper members, and vertical plates extending downwardly from one edge of the horizontal plate.

3. A mat as described in claim 1, in which said lower members are of angle section having horizontal plates riveted to said upward members, and having vertical plates extending downwardly from one edge of said horizontal plates, adjacent pairs of lower members being reversed with respect to each other.

FREDERICK H. RUPPEL.

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