PROTECTIVE CABLE NETS SYSTEM (PCNS)

Abstract

A combined net structure is disclosed that comprises a non-planar coarse net with a grid-like structure comprising a plurality of coarse cables wherein longitudinal coarse cables intersect with latitudinal coarse cables to form a plurality of coarse cells and cutouts of a fine net attached to the coarse net, wherein the fine net comprises a plurality of adjacent fine cables. Each non-edge fine cable is attached to two adjacent fine cables on each of its sides at a plurality of locations along their lengths forming attachment points, wherein the fine net is arranged in a form of an array of fine quadrangular cells with said attachment points constituting the vertices of the fine quadrangular cells. System that comprises the combined net structures are disclosed as well.

Claims

1. A combined net structure comprising: a non-planar coarse net with a grid-like structure comprising a plurality of coarse cables wherein longitudinal coarse cables intersect with latitudinal coarse cables to form a plurality of coarse cells; cutouts of a “fine net” attached to said coarse net, wherein said “fine net” comprises a plurality of adjacent fine cables (forming a fine cable net); a fabric; a membrane (soft or solid); solid tiles; stuffed hollow tiles; fluid filled hollow tiles; wherein each non-edge fine cable is attached to two adjacent fine cables on each of its sides at a plurality of locations along their lengths forming attachment points, wherein said fine cable net is arranged in a form of an array of fine quadrangular cells with said attachment points constituting the vertices of said fine quadrangular cells.

2. The combined net structure according to claim 1, wherein each “fine net” cutout is substantially coextensive in shape with one or more coarse cells.

3. The combined net structure according to claim 2, wherein all the coarse cells are attached to “fine net” cutouts.

4. The combined net structure according to claim 2, wherein the “fine net” cutouts are connected to the coarse net such that portions of a fine cable net or edges of the fabric, the membrane (soft or solid) or the solid tiles of said “fine net” cutouts are attached to corresponding portions of a coarse cable of the coarse net by means of connecting elements that hold said “fine net” and said coarse cable together.

5. The combined net structure according to claim 1, wherein the coarse net further comprises connecting elements that connect the intersecting longitudinal coarse cables with the latitudinal coarse cables at the intersecting points.

6. The combined net structure according to claim 1, wherein the fine quadrangular cells are square or rhombic cells.

7. The combined net structure according to claim 1, wherein the distances between two adjacent attachment points of two adjacent non-edge fine cables are substantially the same; and wherein the imaginary line which bisects and is perpendicular to the imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables passes through an attachment point of one of said two adjacent non-edge fine cables with its other adjacent fine cable.

8. The combined net structure according to claim 1, further comprising one or more edge cables attached to the perimeter of the coarse net.

9. The combined net structure according to claim 8, wherein the diameter of the edge cables is between 15 mm and 50 mm.

10. The combined net structure according to claim 1, wherein the diameter of the coarse cables is between 8 mm and 40 mm.

11. The combined net structure according to claim 1, wherein the diameter of the fine cables is between 3 mm and 6 mm.

12. The combined net structure according to claim 6, wherein the square or rhombic cell diagonals are between 20 mm and 60 mm.

13. The combined net structure according to claim 1, wherein the longitudinal coarse cables and the latitudinal coarse cables have predetermined lengths and are attached to each other at pre-calculated locations marked along their lengths.

14. The combined net structure according to claim 13, wherein the predetermined lengths are such that the coarse net formed comprises a 3-dimensional structure.

15. The combined net structure according to claim 6, wherein an imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables is parallel to the longitudinal coarse cables or to the latitudinal coarse cables.

16. A system comprising: at least one column; the combined net structure according to claim 1; plurality of anchors; wherein the combined net is attached to said column and to said plurality of anchors.

17. The system according to claim 16, wherein the combined net structure is quadrangular and one of its vertices is attached to the column, and wherein said system comprises three anchors and three vertices of said combined net structure are each attached to one of said anchors.

18. The system according to claim 16, wherein the column is height adjustable.

19. The system according to claim 16, wherein the anchors are concrete blocks.

20. The system according to claim 16, wherein the system comprises one or more additional combined net structures; wherein the one or more additional combined net structures are attached to the column and to the plurality of anchors.

21. The system according to claim 20, wherein the one or more additional combined net structures are quadrangular; wherein one of the one or more additional combined net structure vertices is attached to the column and the other one or more additional combined net structure vertices are attached to the anchors.

22. The system according to claim 16, comprising two columns and two anchors; wherein the combined net structure is quadrangular comprising a first vertex, a second vertex, a third vertex and a fourth vertex; wherein said first vertex is attached to a first column and said second vertex is opposite to said first vertex and is attached to a second column, and wherein said third vertex and fourth vertex are each attached to one of said two anchors.

23. The system according to claim 22, further comprising one or more additional quadrangular combined net structures, two columns and two anchors; wherein each of said one or more additional combined net structures is quadrangular and comprises a first vertex, a second vertex, a third vertex and a fourth vertex; wherein the one or more additional quadrangular combined net structures first vertex is attached to the column; and wherein the one or more additional quadrangular combined net structures second vertex is opposite to said first vertex and is attached to a second column; and wherein said third vertex and fourth vertex of said one or more additional quadrangular combined net structures are each attached to one of said two anchors.

24. A system comprising: a. two intersecting arc structures; b. two parallel arc structures; c. one arc structure; d. any combination of arches and columns a combined net structure according to claim 1; wherein the combined net structure is spread over said two intersecting arc structures, two parallel arc structures, one arc structure, any combination of arches and columns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The present invention is illustrated by way of example in the accompanying drawings, in which similar references consistently indicate similar elements and in which:

[0092] FIG. 1A illustrates an embodiment of the fine net of the present invention.

[0093] FIGS. 1B-1C illustrate an embodiment of the construction of the fine net of the present invention.

[0094] FIG. 2A illustrates an embodiment of groups of cells of the coarse net of the present invention.

[0095] FIG. 2B illustrates an embodiment of cutouts of the “fine net” of the present invention. The cutouts can be made from fine cable nets; membranes (soft or solid); fabric; solid tiles; stuffed hollow tiles; fluid filled tiles or any combination thereof.

[0096] FIG. 2C illustrates an embodiment of groups of cells of the combined net of the present invention.

[0097] FIGS. 3A-3B illustrate an embodiment of the one column system of the present invention.

[0098] FIGS. 4A-4B illustrate an embodiment of the one column system of the present invention.

[0099] FIGS. 5A-5B illustrate an embodiment of the two-column system of the present invention.

[0100] FIGS. 6A-6B illustrate an embodiment of the intersecting arcs system of the present invention.

[0101] FIGS. 7A-7B illustrate examples of the flat steel pieces used according to an embodiment of the present invention.

[0102] FIG. 8A Prior art—Skylight example: crossed circular arches on structural frame.

[0103] FIG. 8B Prior art—The force density method for a bar element.

[0104] FIG. 8C Prior art—FORCE DENSITY METHOD FOR A MEMBRANE ELEMENT.

[0105] FIG. 8D Prior art—THE GRID METHOD.

[0106] FIG. 8E Prior art—RECTANGULAR SKYLIGHT.

[0107] FIG. 8F Prior art—A SIMPLE CABLE NET.

[0108] FIG. 8G-FIG. 8H Prior art—SKYLIGHT DIMENSIONS FOR EXAMPLE 8B

[0109] FIG. 8I Prior art—COMPUTED PRESTRESS ON ⅛ SKYLIGHT STRUCTURE.

[0110] FIG. 8I (I) Prior art—COMPUTED FINAL CABLE FORCES.

[0111] FIG. 8J Prior art—(a) PLAN OF THE ‘HYPERBOLIC PARABOLOID’ CABLE NET.

[0112] FIG. 8K Prior art—(B) SCHEMATIC OF THE HYPERBOLIC PARABOLOID CABLE NET.

[0113] FIG. 8L Prior art—EDGE CABLE FOR THE HYPERBOLIC PARABOLOID CABLE NET.

[0114] FIG. 8M Prior art—NODE MAP FOR THE HYPERBOLIC PARABOLOID.

[0115] FIG. 8N Prior art—PATTERNING STRIPS FOR THE ⅛ SKYLIGHT EXAMPLE.

[0116] FIG. 8O Prior art—PATTERNING STRIPS FOR ¼ HYPERBOLIC ARABOLOID.

[0117] FIG. 8P Prior art—NUMERICAL DESCRIPTIONS OF STRIPS.

DETAILED DESCRIPTION OF THE INVENTION

[0118] The present invention relates to a protective cable net system (PCNS) for preventing anti-tank missiles, rockets, bomblets, shells and other artillery or aerial ammunition and drones, with or without explosive, from causing fatalities and destruction at required areas.

[0119] The strength calculation, geometrical prediction and patterning into shape of the protective cable net system, comprised of both a coarse net structure and a “fine net” structure, is new and inventive and in view of solid geometrically nonlinear structural theory as depicted in the aforementioned book by Levy and Spillers, 2003.

[0120] The present invention Protective Cable Nets System (PCNS) is a tensile structure which is light weight, erectable, ready to use, easy to repair, easy to transport, foldable and movable system that can protect required zones against direct hits of munitions such as missiles, rockets, shells, mortars, cluster bombs, anti-tank missiles, and other artillery or explosive objects. The PCNS can also protect required areas from small and mid-sized drones. Because of its lightweight and excessive strength, the PCNS can cover large areas.

[0121] The structure of the PCNS can initiate the munitions with frontal super quick (SQ) fuses or the first fuse of double sequential warheads (the second warhead may be initiated by an additional internal net) at a safe distance from vulnerable areas such as school yards, residential houses, critical infrastructures, hazardous materials, ammunition storage, military bases, radar and antennae facilities, open grounds for troop gathering, military vehicles and aircrafts. The munitions explosion is caused on impact with the PCNS. The PCNS can withstand multiple hits of munitions with super quick (SQ) fuses, bomblet hits (exploded or unexploded), and can stop small and mid-sized drones due to its configuration, structural strength and redundancy (as will be explained hereinbelow).

[0122] The PCNS can be erected in populated areas, power and other facilities, or military zones. In populated areas or facilities where structures are in existence some of the PCNS supports may be the structural elements of the buildings and facilities themselves such as reinforced concrete columns and plates. For example, when protecting military base yards, the existing buildings can act as anchors. Normally, one or two PCNS columns per module will be vertical on base plates, stabilized by oblique steel cables (preferably four per column for net redundancy) anchored to massive concrete units or fixed foundations. The net may be erected horizontally, vertically or slanted. When existing buildings provide four anchors, with one anchor being at a feasible different elevation than the other three, no additional columns will be necessary for that particular PCNS.

[0123] In military zones where structures or heavy and stable military vehicles exist some of the PCNS supports may be anchored to the structural elements or the vehicles.

[0124] The PCNS can therefore be used for: [0125] 1. Overhead protection against ballistic munition hits and small and mid-sized drones. [0126] 2. Side direct hits protection against anti-tank missiles, rocket propelled grenades, and other direct hit explosive munitions such as artillery shells. [0127] 3. For camouflage or deception with fabric, tiles or membranes of visual and multispectral nature.

[0128] According to an embodiment of the present invention, the present invention relates to a “fine net” comprising a plurality of fine cables (see FIGS. 1A-1C). This fine cable net is constructed as follows. Each fine cable is attached to two adjacent fine cables on each of its sides (with exception to the fine cables at the net edges which are attached to only one fine cable). Each fine cable (e.g. cable no. 1) is attached to its adjacent fine cables, 2 and 3, at a plurality of locations along their lengths, wherein the distance of one attachment point to its adjacent other attachment point (on the same two cables) is substantially the same distance along the whole length of the fine cable (e.g. attachment points 4 and 5). Each fine cable 1 is attached to its first adjacent fine cable 2 at a plurality of locations along their lengths (points 5) and to its second adjacent fine cable 3 at a plurality of locations (points 4), substantially being equally in between the lengths between the attachment points (5), with the first fine cable. The net is then spread out (FIG. 1A and FIG. 1C) in a manner such that the fine cables form a series of square or rhombic cells. The attachment points (of the spread-out fine net) are such that the square or rhombic cell diagonal is usually between 20 mm and 50 mm.

[0129] FIG. 1A illustrates a portion of a fine cable net 10. The fine net 10 comprises a cable 1 connected to cable 2 (being on its left side) at a plurality of attachment locations 5. The distances between two adjacent attachment locations 5 of cables 1 and 2 are equal, i.e. the diagonal (of the quadrangle formed between the attachment locations 5) distances are equal and the sum of the two continuous sides of the quadrangle formed between the attachment locations 5 (from cable 1 and 2) are equal. Cable 1 is also connected to cable 3 (being on its right side) at a plurality of attachment locations 4. The distances between two adjacent attachment locations 4 of cables 1 and 3 are equal, i.e. the diagonal (of the quadrangle formed between the attachment locations 4) distances are equal and the sum of the two continuous sides of the quadrangle formed between the attachment locations 4 (from cable 1 and 3) are equal. The imaginary line connecting attachment locations 5 is parallel to the imaginary line connecting attachment locations 4. The imaginary line which bisects and is perpendicular to the section connecting two adjacent attachment locations 5 passes through one of attachment locations 4.

[0130] The fine cables are preferably made of a material selected from the group consisting of steel, high strength steel, stainless steel, Fiber reinforced plastics, or Fiber reinforced polymers (FRP). The diameter of the fine cables is usually between 3 mm and 6 mm.

[0131] The fine cables are attached at the aforementioned attachment points by pre-threading pairs of cables through cylindrical steel rings and pressing the rings. The rings usually have a thickness of between 0.8 mm and 2 mm. The width of each ring is usually between 5 mm and 12 mm.

[0132] An alternate method for attaching the fine cables of the aforementioned attachment points is by pressing and bending a flat steel piece into a cylindrical shape that holds the two cables together. The flat steel pieces usually have a thickness of between 0.8 mm and 2 mm. The width of the flat steel pieces is usually between 5 mm and 12 mm. The length of the flat steel pieces is usually between 18 mm and 36 mm. According to a preferred embodiment of the present invention, an example of the flat steel piece used in the present invention, is as found in the catalog of Carl Stahl Gmbh of 2006 on page 139, e.g. the embodiments in photos “a” and “b” (shown in FIGS. 7A and 7B respectively). It should be noted that other attachment elements/connecting elements may also be used.

[0133] The fine net is constructed such that its total spread-out net length is usually between 10 m and 20 m. Its total spread-out net width is usually between 1.5 m and 3.0 m.

[0134] FIG. 1B shows the construction of the fine cable net comprised of fine cables. At the first step, pluralities of pairs of parallel individual cables (e.g., of 50 meters) are spaced apart and in parallel to one another, close to one another. One steel cylindrical ring of a first group of rings is threaded through each pair, bonding the pair cables together, each pair having a left cable and a right cable. The bonding rings (of the first group of rings) are positioned along a first imaginary line 100.

[0135] At the second step, other than the net outmost cables, the other cables (herein also referred to as non-edge fine cables) are paired consecutively such that each right cable of the former pairs of cables is paired and bonded to the left cable of its former adjacent pair (from its right side). One cylindrical steel ring of a second group of rings is threaded through each new pair, bonding the new pair cables together, each new pair having a new left cable and a new right cable. The bonding rings (of the second group of rings) are positioned along a second imaginary line 200.

[0136] At the third step, the cables (including the net outmost cables) are paired according to the pairing in step 1. One cylindrical steel ring of a third group of rings is threaded through each pair, bonding the pair cables together, each pair having a left cable and a right cable. The bonding rings (of the third group of rings) are positioned along a third imaginary line 300.

[0137] At the fourth step, the cables (excluding the net outmost cables) are paired according to the pairing in step 2. One cylindrical steel ring of a fourth group of rings is threaded through each pair, bonding the pair cables together, each pair having a left cable and a right cable. The bonding rings (of the fourth group of rings) are positioned along a fourth imaginary line 400. This process is continued etc., Mutatis Mutandis, wherein if the step number is odd the cable pairs of that step are according to step 1, and if the step number is even the cable pairs of that step are according to step 2. The process continues until the net length is exhausted.

[0138] The distances between imaginary ring lines 100 and 200, 300 and 400 etc. are equal. The result is a net of given width which is opened and rolled ready for transport. An alternate method for attaching the fine cables is by pressing and bending flat steel pieces (instead of the rings) into cylindrical shapes that hold the cables together.

[0139] The present invention further comprises a predesigned and pre-calculated three-dimensional coarse net comprising a plurality of coarse cables forming a coarse net structure. The coarse net is then connected to a “fine net” structure comprised of corresponding predesigned and precalculated cutouts. Examples of coarse nets that may be used appear in Levy and Spillers, 2003 and described hereinabove. Both the coarse net structure and the “fine net” structure are independent in the structural sense and are safe and stable to carry loads. Cutouts of a “fine net” may be comprised of a fine cable net, fabric, membranes (soft or solid), solid tiles, stuffed hollow tiles or fluid filled hollow tiles that are attached to the course net which supplies the structural strength and stability of the system. Membranes and tiles may be comprised of ballistic resistant composite materials, polycarbonate, metal sheets etc. Additional materials such as wood, chain-link or welded metal or non-metal fencing may be used as tiles.

[0140] The coarse net structure comprises a plurality of coarse cables in the form of an array of (typically approximately straight on the longitudinal axis) longitudinal coarse cables intersecting with latitudinal coarse cables, such that the intersection of the longitudinal and latitudinal cables creates a series of quadrangular cells, wherein each cell is bounded by the intersecting coarse cables. The angles of the quadrangular cells may vary for different coarse nets. The longitudinal coarse cables and the latitudinal coarse cables have predetermined lengths and are attached to each other at pre-calculated locations marked along their lengths to result in a net of coarse cables forming a series of quadrilateral cells. It should be noted that the term “intersecting” is used herein as lying across, i.e. the longitudinal coarse cables lie across the latitudinal coarse cables (write above/beneath them and touching them) forming contacting points at the intersections.

[0141] According to a most preferred embodiment of the present invention the coarse cables are connected to each other (after a pre-calculation) in a manner such that the quadrangular cells formed have a non-planar curved surface. The projection of the non-planar Three-dimensional cells is a quadrangle. The plurality of the non-planar three-dimensional cells together form a three-dimensional coarse net. This is achieved by the predetermined lengths and pre-calculated locations of connection (i.e., attachment points) between the longitudinal and latitudinal coarse cables. The structure of this embodiment is such that a segment of a certain coarse cable between two attachment points is not coplanar with the attachment points forming an arc-like connection between the attachment points, and thus provides the 3-dimensional effect. A plurality of such segments between attachment points enable to form the desired 3dimensional shape of the coarse net.

[0142] It should be understood that the general directions of the intersecting coarse cables remain latitudinal and longitudinal, only with an arc-like non-planar curve between the connection points. Therefore, the general cell shapes formed between the intersecting cables remain, but the segments connecting between the vertices of the cells are not coplanar with the vertices, forming an arc-like connection between the vertices. Therefore, it should be understood that the term “substantially quadrangular cells” may also mean cells with the segments connecting between the vertices of the cells, being not coplanar with the vertices forming an arc-like connection between the vertices.

[0143] The segments of the coarse cells connecting between the vertices of the coarse cells are usually between 250 and 1000 mm.

[0144] The coarse net preferably comprises steel edge cables (preferably of 8 mm to 50 mm in diameter) attached to the perimeter of the coarse net at predesigned edge locations obtaining a 3-dimensional coarse net structure. Thus, the cells at the periphery of the coarse net (the peripheral coarse cells) may not be quadrangular. The edge cables may be connected at the edge intersecting points or to an edge of a coarse cable. Moreover, the course net may be comprised of other than steel cables such as aramid ropes having diameters between 12 mm to 50 mm.

[0145] The spread-out coarse net structure forms a 3-dimensional structure with a net having longitudinal and latitudinal members that intersect forming the cells. The attachment points are such that the projection of the three-dimensional coarse net structure may be a grid of quadrangular cells. The coarse net structure (e.g. predesigned pre-calculated contact locations between the longitudinal and latitudinal cables) may form a curved three-dimensional structure, as explained in Levy and Spillers, 2003 and described above.

[0146] The coarse cables are preferably made of a material selected from the group consisting of steel, stainless steel, and high strength steel used for prestressing and of strong non steel material such as aramid. The diameters of the coarse cables are usually between 8 mm and 50 mm.

[0147] The coarse cables are attached at the aforementioned attachment points (intersecting points) pre-calculated in order to form the 3-D structure. The intersecting coarse cables are attached by means of attachment elements/connecting elements. According to a preferred embodiment the attachment is carried out by pressing and bending a flat steel piece into a cylindrical shape that holds the two cables together. The flat steel pieces usually have a thickness of between 1.0 mm and 5.0 mm. The width of the flat steel pieces is usually between 10 mm and 20 mm. The length of the flat steel pieces is usually between 30 mm and 60 mm. The flat steel piece structure may be similar as the flat steel piece explained hereinabove with the proper size to fit the coarse cables. Non-steel cables are preferably knotted at the intersection of the attachment points.

[0148] The coarse net is manufactured by marking the intersection points on the coarse cables according to a predesign and pre-calculations and pressing and bending flat steel pieces into cylindrical shapes that hold the cables together. The cables can be also connected using off the shelf bolted connectors. Intersection points between edge cables and coarse cables are also marked and connections are similarly made.

[0149] The “fine net” structure is then attached to the coarse structure forming a combined net structure. A portion of the course net is attached to a coextensive congruent cutout portion of the “fine net”. The “fine net” comprises a set of predesigned and pre-calculated cutouts substantially coextensive and congruent in shape with one or more cells of the coarse net. An example of ‘fine net” cutouts combinations is shown in FIG. 2B—the cutouts being portions C1, C2, C3, C4 and C5. Incidentally, if the “fine net” cutouts of fine cables, fabric or membranes would have been connected together without the coarse net, they would form a 3-dimensional structure of exact geometry as the coarse net structure but will lack the benefits of redundancy, excessive strength, resilience, ease of repair etc.

[0150] The combined net is completed by attaching cutouts of the “fine net” structure onto the coarse net structure cutout by cutout. Each “fine net” cutout is connected to its corresponding coarse net portion overlapping thereon. FIG. 2A for illustration purposes in order to understand the present invention, shows groups of cells D1, D2, D3, D4 and D5 (apart from each other) of the coarse net corresponding to the “fine net” cutouts, wherein actually the coarse net is one connected structure (wherein the longitudinal cables shown adjacent to each other between each group of cells are actually the same cable, i.e. one vertical edge cable, serves two adjacent cutouts). The group of coarse cells shown form one quarter of a square coarse net structure when attached. The “fine net” cut outs are attached to the coarse net corresponding portions (the coarse net cutouts covered with tailored “fine nets”), as shown in FIG. 2C being combined portions E1, E2, E3, E4 and E5

[0151] The combined net structure is constructed by attaching portions of the “fine net” cutouts to the coarse cables by means of connecting elements. According to a preferred embodiment the attachment is carried out by pressing and bending flat steel pieces into cylindrical shaped binding elements (connecting elements) that hold the cables together or using bolt connectors. The “fine net” cutouts are connected to the coarse cables at certain locations along the coarse cables wherein the “fine net” is connected at a portion of a fine cable of the “fine net” cutouts (or by connecting a connecting element of the “fine net” to the coarse cables).

[0152] According to a preferred embodiment of the combined net, the “fine net” is arranged such that its quadrangular cells are square or rhombic cells, and an imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables is parallel to the coarse net longitudinal (or latitudinal) cables.

[0153] The combined net structure, in the structural engineering sense, is now comprised of two nets, the coarse net structure and the “fine net” structure. Both are stable and able to withstand loads independently when comprised of cable “fine net” or a fabric “fine net” or a membrane “fine net”. This implies that those “fine net” structures alone could act as a protective cable net systems but will, of course, lack the benefits of redundancy, ease of repair etc.

[0154] The present invention relates to a system comprising erectable columns. According to a preferred embodiment the columns are segmental and height adjustable. The columns preferably comprise lightweight steel or composite material and preferably have a circular cross section. The column is configured to be adjusted at different heights. The column segments are pre-connected at the site into one whole piece and lifted into position by an electric or mechanical winch. Optionally the column is a telescopic column.

[0155] FIGS. 3A and 3B illustrate a small model similar to the present invention system. According to one embodiment, the combined net structure 20 comprises a coarse net structure 20f to which is attached a “fine net” structure 20e and is quadrangle and one of its vertices 20a is connected to the column 30. The other three vertices 20b, 20c and 20d are connected to anchors 35 (e.g. by means of cables). The anchors 35 can be attached to the ground or to heavy weight and stable objects such as tanks, buildings or heavy concrete blocks. According to one embodiment the net is attached to anchors which are concrete blocks. FIG. 3B shows a top view of FIG. 3A. The system with the combined net structure with the supports (e.g. anchors and column) is referred to herein as the PCNS (Protective Cable Net Structure).

[0156] FIG. 4A illustrates a drawing of a similar PCNS system comprising a quadrangle combined net 20 structure and one of its vertices 20a is connected to the column 30. The other three vertices 20b, 20c and 20d are connected to anchors 35. The column 30 is supported by anchored steel cables 40 connected (e.g. tied) to the column 30, wherein the anchored steel cables 40 are tensioned during erection. A portion of the secure zone 50 securing from the flying explosive objects or drones is also indicated.

[0157] FIG. 4B shows a top view of the PCNS drawing of FIG. 4A, with an enlargement portion showing a cutout 21 of the combined net structure 20. This cutout 21 is shown in FIG. 2C and identified as E3.

[0158] FIG. 5A shows a small model of a PCNS embodiment of the present invention, wherein the system comprises a quadrangle (preferably square) combined net structure 120 wherein one of its vertices 120a is connected to a first column 130a, and its opposite diagonal vertex 120b is connected to a second column 130b. The other vertices 120c and 120d (at the other two opposite diagonal vertices) are connected to anchors 135. The columns 130a and 130b are supported by anchored steel cables 140 connected (e.g. tied) to the columns 130a and 130b and connected to the ground, wherein the anchored steel cables 140 are tensioned during erection. In this specific embodiment the anchored steel cables 140 are connected to the top of the columns 130a and 130b. In the preferable setup two sets of cables per column are specified. FIG. 5B shows a top view of FIG. 5A. The “fine net”, which is connected to the coarse net, is not shown in these figures.

[0159] FIGS. 6A and 6B show a small model of an embodiment of the present invention with a combined net 220 spread over two rigid intersecting arcs 230 (in this sense the intersecting may also mean intersecting on the same plane). Both models (FIGS. 5A, 5B and 6A, 6B) show coarse net structures only, wherein obviously, cutouts of “fine net” straps are tailored to the coarse nets forming the combined net structure.

[0160] According to an embodiment of the present invention, the system comprises a single or double layered structure. For the double layered structure an additional combined net is placed under the first combined net. In relation to the embodiment of FIGS. 3A-3B (and 4A4B) the system comprises an additional quadrangular combined net substantially identical to net 20. One vertex of the additional (second) combined net is connected to the column 30 at a location beneath (preferably 0.5 m) where the first net is attached to the column 30 (this embodiment not shown). The other vertices not attached to the column 30 are attached to the anchors 35. Optionally, the two combined nets are arranged such that they are substantially parallel to one another.

[0161] The double layered structures are advantageous when double fuse munitions are used, or when there is a need to capture some of the munition or the drone fragments. If the fired double fuse munitions do not explode on impact with the first net, they can explode on impact with the second net. In addition, the second net is also advantageous with one fuse munitions or drones by that it captures large fragments and blocks them from entering the secure zone.

[0162] With regard to FIGS. 5A-5B, the present embodiment comprises the structural features of this embodiment with the addition of the following feature. The system comprises an additional second quadrangle combined net beneath combined net 120. Two vertices of the lower net are attached to the columns 130a and 130b at locations beneath (preferably 0.5 m) where the first net vertices are attached to columns 130a and 130b while the other two vertices of the second additional net are connected to the anchors 135.

[0163] According to another embodiment, the system comprises three or more nets. The additional net(s) are added beneath the second net (explained hereinabove) in a manner similar to the addition of the second net in relation to the first net, mutatis mutandis.

[0164] According to an embodiment of the present invention, the PCNS system is erected as follows: [0165] 1. The column segments are connected together forming a unified element. [0166] 2. The PCNS is attached to the pre-constructed attachment locations (e.g. in the embodiment of FIGS. 3A-3B, 4A-4B, the combined net vertex 20a is attached to the column 30 and the other vertices to anchors 35), obtaining an attached loose PCNS laying on the ground.

[0167] The column is then pulled to its vertical position slowly by using an auxiliary cable attached to a winch. The anchoring steel cables are tightened as the position of the vertical column progresses. This erection of the column causes pre-stressing in the combined net. Finally, all the anchoring steel cables are tightened into position. In case of two columns (e.g. FIGS. 5A-5B) both columns are erected and positioned in sequence one at a time.

[0168] Another advantage of the present invention is its redundancy, robustness and resilience. If the combined net absorbs a blast, the whole combined net system remains intact and the damaged portion is contained and amended. In case where only the “fine net” is damaged due to exploded munition, a piece of “fine net” is attached manually as a patch to the existing “fine net” structure to cover the hole created by the explosion (typically, a new “fine net” cutout, with the size and shape of the coarse net cell surrounding the damaged “fine net” portion, replaces it). The patch is large enough to cover the hole and is attached to the quadrangle cell of coarse cables surrounding it. A plurality of locations on the fine cables of the “fine net” patch are attached to corresponding locations on the coarse cables (of the coarse net) surrounding the hole area of the “fine net”, by means of connecting elements (e.g. flat steel pieces or bolted connectors as explained hereinabove). If a coarse cable is damaged, an additional coarse cable having the length larger than the damaged (missing) portion (overlapping it) is attached to the edges of the missing portion by means of connecting elements (e.g. flat steel pieces as explained hereinabove), bolted metal connectors or cable ties.

[0169] In case of a column being hit it is simply replaced and erected into position. Optionally the column comprises an outer layer. The outer layer is larger but similar in shape to the inner main column portion, and there is space between said inner and outer portions. The outer layer portion absorbs the blast if hit, while the inner portion remains functioning erecting the PCNS.

[0170] Optionally, the columns of the PCNS may be supported by 2, 3, 4, or more tensioned anchored steel cables, thus if one of them is hit by a blast, the other/s remain functioning.

[0171] The PCNS thus enables easy construction of a protection net and its fast assembly.

[0172] Thus, even when hit, the PCNS remains strong, robust, stable and resilient.

[0173] While some of the embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried into practice with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of a person skilled in the art, without departing from the spirit of the invention, or the scope of the claims.

REFERENCES

[0174] Argyris, J. H., Angelopoulos, T., and Bichat, B., “A General Method for the Shape Finding of Lightweight Tension Structures”, Computer Methods in Applied Mechanics and Engineering, 3, 135-149, 1974. [0175] Haber, R. B., and Abel, J. F., “Initial Equilibrium Solution Method for Cable Reinforced Membranes. Part 1—Formulation”, Computer Methods in Applied Mechanics and Engineering, 30, 263-284, 1982. [0176] Otto, Frei (editor), Tensile Structures, MIT Press, Cambridge, M A 1973. [0177] Schek, H. J., “The force density method for form finding and computation of general networks”, Computer Methods in Applied Mechanics and Engineering, 3, 1974, pp 115-134. [0178] Siev, A., and Eidelman, J., “Stress Analysis of Prestressed Suspended Roofs”, Proc. ASCE, 90, ST4, pp. 103-121, August 1964. [0179] Zienkiewicz, O. C., The Finite Element Method, 3 rd edition, McGraw-Hill, N Y, 1977.