WO2001044596A2

WO2001044596A2 - Combined structural element

Info

Publication number: WO2001044596A2
Application number: PCT/IL2000/000844
Authority: WO
Inventors: Yosef Karta
Original assignee: Advanced Pneumatic Structures Ltd.
Priority date: 1999-12-19
Filing date: 2000-12-18
Publication date: 2001-06-21
Also published as: AU1882601A; IL133593A0; WO2001044596A3

Abstract

A combined structural element comprising at least two components, one of said two components (3) having a higher Young modulus value than the second component (2), wherein said first component (3) is embedded in said second component (2), whereby said first component (3) provides reinforcement to said second component (2) imparting the combined structural element improved load resistance.

Description

COMBINED STRUCURAL ELEMENT

FIELD OF THE INVENTION

This invention relates to structural elements, and more particularly it relates to a structural element that is reinforced by a strengtheπer enhancing the load resistance of the structural element and providing it with improved physical strength properties.

BACKGROUND OF THE INVENTION

Many structural elements such as rods, tubes, sheets and beams are made in solely from plastic materials. Plastic materials are used extensively in industry due to their physical and mechanical properties. Chemical stability, durability, corrosion resistance, low conductivity, texture, relatively low cost, flexibility, color and strength are part of the qualities that make thermoplastic polymers one of the commonly used materials in the world nowadays. Another property that makes thermoplastic materials appealing to industry is the ability to melt the polymer by heating. This permits molding the melt to a structure required by engineering and/or styling considerations.

The main drawback of using plastic materials as structural elements that have one dimension much longer than the others is the lack of stiffness. The Young modulus (elastic modulus), which measures the resistance of the material to stretching, is relatively low. Flexibility or semi-flexibility renders plastic material susceptible to bending failure along the axis of constancy and to buckling under transverse loading normal to that axis.

Another drawback of thermoplastic materials when used as structural elements is the creeping phenomenon, a time-dependent property of polymers. When the plastic material is subjected to constant stress, the strain of the material changes with time. In order to harden a structural element made from plastic material or other yielding material, it is customary to add supporting bushes. The supporting bushes contribute to the physical strength of the structural element by providing it with the strength needed, but they do not improve the intrinsic properties of the structural element itself.

It is the purpose of the present invention to provide a structural element combined with a reinforcing member. The structural element is preferably made from a material capable of hindering the breakdown of the structure but has a relatively small Young modulus (yielding material, such as plastic). The reinforcing member, preferably made of a hard material having a relatively larger Young modulus such as metal, enhances the stiffness of the structural element.

It is another purpose of the present invention to strengthen the combined structural element in the direction susceptible to possible buckling failure while saving weight and cost.

It is another purpose of the present invention to provide a combined structural element having a basic structural element made from a thermoplastic material with much greater resistance to creeping.

BRIEF DESCRIPTION OF THE INVENTION

It is thus provided, in accordance with a preferred embodiment of the present invention a combined structural element comprising at least two components, one of said two components having a higher Young modulus value than the second component, wherein said first component is embedded in said second component, whereby said first component provides reinforcement to said second component imparting the combined structural element improved load resistance. Furthermore, in accordance with a preferred embodiment of the present invention, said second component is made from plastic material and provides a casing for said first component, and wherein said first component is made from an inorganic material.

Furthermore, in accordance with a preferred embodiment of the present invention, said first component is made from material selected from the group consisting of aluminum, steel, magnesium and titanium or alloys of these metals.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component is made form material selected from the group consisting of polycarbonates, polyesters and polyvinyls. Furthermore, in accordance with a preferred embodiment of the present invention, said first component is fixed to said second component by the frictional forces existing between the components.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component is in the form of a cylinder and said first component has cruciform cross-section.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component is in the form of a hollow cylinder.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component is in the form of a solid cylinder. Furthermore, in accordance with a preferred embodiment of the present invention, said first component is inserted into said second component forcefully.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component is provided with serrated edges enhancing the friction between the components.

Furthermore, in accordance with a preferred embodiment of the present invention, an adhesive material is applied between said first component and said second component to improve the grip between them.

Furthermore, in accordance with a preferred embodiment of the present invention, a groove is provided in the second component into which the first component is inserted thus enhancing anchorage of the first and second components together. Furthermore, in accordance with a preferred embodiment of the present invention, said second component is a beam and said first component has cruciform cross-section.

Furthermore, in accordance with a preferred embodiment of the present invention, said first component has a star shaped cross-section.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component is a beam having a polygonal cross-section.

Furthermore, in accordance with a preferred embodiment of the present invention, said second component has star shaped cross-section.

Furthermore, in accordance with a preferred embodiment of the present invention, said first component is a slat.

Furthermore, in accordance with a preferred embodiment of the present invention, said first component is wavy. Furthermore, in accordance with a preferred embodiment of the present invention, said second component is U-shaped.

Finally, in accordance with a preferred embodiment of the present invention, it is provided a combined structural element comprising more than two components, some of said components having a higher Young modulus value than one other component, wherein said some of said components are embedded in said one other component, whereby said some of said components provide reinforcement to said one other component imparting the combined structural element improved load resistance.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an isometric illustration of a combined structural element in accordance with a preferred embodiment of the present invention comprising a hollow cylinder combined with a cruciform reinforcing member. Figure 2A is a side view of a combined structural element in accordance to a preferred embodiment of the present invention anchored at one end to a vertical surface.

Figure 2B is a cross sectional view of a combined structural element as the one shown in Figure 1.

Figure 3 represents simulation results for the deformation of three structural elements under stress: (1 ) a combined structural element in accordance with a preferred embodiment of the present invention; (2) structural element having a reinforcing member made from the same material as the structural element; (3) basic structural element without reinforcement; (4) reference.

Figure 4 is a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a solid cylinder combined with a cruciform reinforcing member.

Figure 5A is a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with a cruciform reinforcing member.

Figure 5B is a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a solid beam combined with a cruciform reinforcing member.

Figure 6 illustrates a cross-sectional view of a U-shaped combined structural element in accordance with another preferred embodiment of the present invention with an X-shaped reinforcing member.

Figure 7A illustrates a cross-sectional view of a cylindrical combined structural element in accordance with another preferred embodiment of the present invention with a slat reinforcing member.

Figure 7B illustrates a cross-sectional view of a cylindrical combined structural element in accordance with another preferred embodiment of the present invention with a wavy slat as reinforcing member.

Figure 7C illustrates a cross-sectional view of a cylindrical combined structural element in accordance with another preferred embodiment of the present invention with a plurality of slats as reinforcing members.

Figure 8 illustrates a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention shaped as a beam with slat as reinforcing member.

Figure 9 illustrates a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with slat serving as reinforcing member.

Figure 10 illustrates a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with supported slat serving as reinforcing member. Figure 11 illustrates an isometric view of the experimental set-up for a comparison loading experiment between two waste pipes. One of the examined pipes is a preferred embodiment of the present invention.

Figure 12A shows the results of the load resistance test on pipe deflection performed on the set-up shown in Figure 11. The graph shows the deflection results of the basic waste pipe in comparison with the results obtained from a waste pipe in accordance with a preferred embodiment of the present invention as a function of the load.

Figure 12B shows the results of the load resistance test on pipe deflection performed on the set-up shown in Figure 11. The graph shows the deflection results of the basic waste pipe in comparison with the results obtained from a waste pipe in accordance with a preferred embodiment of the present invention as a function of time in days.

DETAILED DESCRIPTION OF THE INVENTION

Additional strength can be provided to a structural element made from a yielding material such as plastic by a reinforcing member made of a reinforcing material such as metal. The combination of the two materials having different physical properties results in a combined structural element that is stronger and withstands stress better than the basic structural element made of the yielding material alone or the reinforcing member by itself. Reference is made to Figure 1 , which is an isometric illustration of a combined structural element in accordance with a preferred embodiment of the present invention comprising a hollow cylinder combined with a cruciform reinforcing member. The basic structural element 2 is a hollow cylinder. Structural element 2 can be made of plastic, which is a material that yields under pressure. There are many advantages of using plastic materials as structural elements, especially properties such as chemical stability, corrosion resistance and low conductivity that make the use of these materials appealing. Another advantage of using plastic materials in the manufacture of structural elements is the variety of properties available by changing the polymeric backbone and the possibility of adding additives such as color pigments to the plastic material. Typical materials suitable for structural elements are polycarbonates, polyesters, polyvinyls and the like.

To provide a structural element with additional strength, a reinforcing member 3 is incorporated with basic structural element 2. Reinforcing member 3 has a cruciform cross-section. Each wing of reinforcing member 3 has a length that equals to the inner diameter of the cylinder of basic structural element 2. In this way, when reinforcing member 3 is threaded into basic structural element 2, they are contiguous. Reinforcing member 3 is made from a reinforcing material, preferably a hard metal that provides the stiffness to the combined structural element. Typical materials suitable as reinforcement are inorganic materials such as aluminum, steel, magnesium, titanium and the like or alloys of these metals or metals of similar load resistance properties.

The reinforcing member is secured to the basic structural element so that together they comprise the combined structural element. It is important that there be no relative movement between the reinforcement and the structural element. Fixing the reinforcing member to the structural element can be accomplished in several ways. A simple method is to use the frictional force between the reinforcing member and the basic structural element. This method was used for the embodiment shown in Figure 1. As indicated, the length of the arms in cruciform reinforcing member 3 equals the inner diameter of basic structural element 2 so that the reinforcing member is threaded into the structural element by applying force. It is possible also to serrate the edges on the cruciform reinforcing member that are in contact with the inner wall of the cylindrical structural element in order to improve the contact between the two and increase the friction force. Another method for fixing of the strengthener to the structural element is to use adhesive material applied between the two. The use of grooves in the inner wall of the structural element, inside which a small portion of the cruciform reinforcing member is accommodated, is also possible, thus relative movement between the reinforcement and the basic structural element is greatly reduced. Any of the aforementioned methods or a combination thereof or any other method for fixing the reinforcing member to the structural element in order to produce the combined structural element can be applied with the resulting combined structural element remaining within the scope covered by the present invention.

A comparison between the performance of a combined structural element and a prior art structural element shows higher load resistance of the combined structural element in accordance with a preferred embodiment of the present invention than the plastic-made structural element alone. Figures 2A, 2B and 3 illustrates comparative finite element analysis results. Reference is made to Figure 2A that illustrates a side view of a combined structural element in accordance to a preferred embodiment of the present invention anchored at one end to a vertical surface. The combined structural element 10 resembles the one shown in Figure 1 and is one meter long. Combined structural element 10 is attached at one end perpendicularly to a surface 11 while a force of 2.9 Kg is applied at the free end of combined structural element 10, perpendicularly to the longitudinal axis of the element as indicated by arrow 12. A cross-sectional view of combined structural element 10 and its dimensions are shown in Figure 2B. Combined structural element 10 consists of a hollow cylindrical structural element 13 and a cruciform reinforcing member 14 that is threaded into hollow cylindrical structural element 13. The physical properties of combined structural element 10 are as follows: cylindrical structural element 13 is made from polycarbonate, has an outer diameter of 25 mm, weights 468 g, and has a thickness of 5 mm; cruciform reinforcing element 14 is made from aluminum that weights 101 g and has a wall thickness of 0.5 mm. Cruciform reinforcing element 14 fits the dimensions of cylindrical structural element 13 so that when fully inserted, it contiguous to the internal wall surface of structural element 13. After applying the force on the free end of combined structural element 10, the deformation of the element was computed. The deformation magnitude is measured by the displacement of the free end, which was subjected to the force, before and after the force was applied. The displacement, Δy, is measured on the axis of the force direction 12. In the case of combined structural element 10, Δy was computed to be 67 mm.

For the purpose of comparison, the same simulation was performed for a structural element similar to the one shown in Figure 1 while the cruciform reinforcement is made from polycarbonate instead of metal. The wall thickness of the cylinder as well as the cruciform is 3 mm, the outer diameter of the cylinder is 25 mm and the weight of the structural element is 551 g. After applying 2.9 Kg force on the free end of a one meter long structural element as indicated in Figure 2A and explained previously for the combined structural element, the displacement Δy of the structural element was computed to be 168 mm, about 10 cm more than in the case of the combined structural element in accordance to the preferred embodiment of the present invention. Another simulation was conducted for a plastic structural element without reinforcing member. To compensate the absence of reinforcement, a thicker wall was considered for the hollow cylinder, of 6.06 mm, so that the weight of the structural element was kept 570 g, approximately the same weight as the combined structural element (569 g). A force of 2.9 Kg was applied as indicated before and the displacement of the structural element's free end was 108 mm.

Figure 3 summarizes the results of the simulation and shows clearly the effect of the force on the structural elements and on the combined structural element in accordance with the preferred embodiment of the present invention. It is obvious that the combined structural element of the present invention is the least deformed element and the combination of a reinforcing member made from the same material does not improve the performance of the structural element, instead, it is better to use a thicker structural element that deforms less.

A strength experiment was performed to verify the simulation results. Two waste pipes were first loaded with different weights and then the higher weight was left for a long period of time. The strain imposed on the pipes was measures. The experiment was performed using a set-up as shown in Figure 11. One waste pipe was made of polypropylene having an outer diameter of 75 mm, wall thickness of 2 mm and length of 2 m. The other waste pipe was the same as the first one reinforced with 2 m aluminum slat, which was 78 mm wide and 2 mm thick. The deflection of the pipes is summarized in the table hereafter and in Figures 12A and 12B.

It is clear from the experimental results that the combined structural element is much more stiff that the basic structural element and endures better high weight loads. It is obvious that the creeping phenomenon is non- existing in the combined structural element.

Reference is made to Figure 4 that is a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with a cruciform reinforcing member. The combined structural element 20 comprises a basic structural element 21 that is made from a yielding material is in the shape of a solid cylinder. The reinforcing member 22 has the shape of a cruciform and is made from a reinforcing material such as a hard metal. Reinforcing member 22 is embedded in structural element 21 , as if they were fused together. The embedded embodiment can be manufactured by placing the reinforcing member in front of the extruder from which the melt of thermoplastic material is expelled. In this way, the reinforcement is embedded in the melt and goes through the cooling process as an integral part of the melt. This effect provides the combined structural element with extra-strength so that even yielding materials that have very poor stiffness but are relatively lower in price can be used as structural elements. An example for a thermoplastic material having a low elastic module that can be used for the embedded embodiment is polypropylene (E^s1000 MPa). An aluminum reinforcement with E=74500 MPa can significantly render the material with better stress and creeping resistance. Reference is made to Figure 5A that illustrates a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with a cruciform reinforcing member. The combined structural element 30 comprises a basic structural element 31 in the shape of a hollow beam 31 made from a yielding material and a cruciform reinforcing member 32, which is made from a reinforcing material. Structural elements shaped as beams are very useful in industry since many of the designs of storage boxes, toolboxes, shelves and the likes are affixed to structural elements having straight sidewalls. Reference is made to Figure 5B that illustrates a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a solid beam combined with a cruciform reinforcing member. The combined structural element 40 comprises a basic structural element shaped as a solid beam 41 , which is made from a yielding material, and a cruciform reinforcing member 42, which is made from a reinforcing material. The fixation of reinforcing member 32 to structural element 31 can be performed by similar methods as the ones indicated for combined structural element 2. Reinforcing member 42 is embedded in basic structural element 41 so that the combination between the two is even stronger than in the hollow combined structural element 30.

In Figures 5A and 5B, the cruciform reinforcing members 32 and 42 are placed with their edges 33 and 43 pointed towards the corners of rectangles 31 and 41. In this way, the possible buckling directions of the structural element and the reinforcing member are different and the combined structural element has almost no dominant buckling direction. It is possible to position the reinforcing member in any other angular direction relative to the structural element in order to produce the combined structural element and still be covered by the scope of the present invention.

Since plastic materials in general are fairly easy to mold, it is possible to manufacture a combined structural element having any desired cross-section shape in order to obtain a structural element that meets engineering and styling demands. The basic structural element can be designed to have a polygonal shape, a star shape or any other desired shape and still will be covered by the scope of the present invention. In the same manner, the reinforcing member can be shaped in another design other than cruciform shaped, for example star shaped strengthener, and still be covered by the scope of the present invention. Reference is made to Figure 6 that illustrates a cross-sectional view of a U-shaped combined structural element in accordance with another preferred embodiment of the present invention with an X-shaped reinforcing member. The combined structural element 50 comprises a U-shaped structural element 51 , made from a yielding material and an X-shaped reinforcing member 52, which is made from a reinforcing material. The fixation of reinforcing member 52 to structural element 51 can be performed by similar methods as the ones indicated for combined structural element 2. This embodiment can be used in cases where an opened side wall is desired in order to lead electricity wires or water pipes through the lines.

Reference is made to Figure 7A that illustrates a cross-sectional view of a cylindrical combined structural element in accordance with another preferred embodiment of the present invention with a slat reinforcing member. The combined structural element 60 comprises a basic structural element 61 in the shape of a hollowed cylinder and a reinforcing member 62, which is a slat. Reinforcing member 62 width is at least the same as the inner diameter of structural element 61 so that reinforcing member 61 is forcefully inserted into the hollow cylinder. Since the slat is made of a reinforcing material and the cylinder is from a yielding material, forced insertion of the plate into the cylinder is possible even if the width of the plate is slightly larger than the inner diameter of the cylinder. The fixation between the structural member and the reinforcing member has to be relatively firm so that there is no relative movements between the reinforcing member and the basic structural element. Since a slat has a dominant direction in which it may buckle, which is perpendicular to the slat's surface, the combined structural element bears loads effectively in any other direction except from the normal direction. The most effective direction to bear loads is indicated by an arrow 63 in Figure 7A. The fixation between basic structural element 61 and reinforcing member 62 may be performed by any of the methods discusses previously regarding combined structural element 2.

Reference is made to Figure 7B that illustrates a cross-sectional view of a cylindrical combined structural element in accordance with another preferred embodiment of the present inve ntion with a wavy slat as reinforcing member. The combined structural element 70 comprises a basic cylindrical structural element 71 and a slat reinforcing member 72. The reinforcement is wavy so that it has alternating elevations and depressions about a flat surface of neutrality. Combined structural element 70 combines structural element 71 made from a yielding material and reinforcing member 72 made from a reinforcing material that renders the combined structural element with additional strength. It was mentioned before that a slat has a surface that has a tendency to buckling failure. The construction of reinforcing member 62 as a curved surface instead of a flat one further reduces the buckling susceptibility in the normal direction. The fixation between the structural element 71 and reinforcing member 72 can be accomplished in any of the methods discusses previously regarding combined structural element 2.

Reference is made to Figure 7C that illustrates a cross-sectional view of a cylindrical combined structural element in accordance with another preferred embodiment of the present invention with a plurality of slats as reinforcing members. The combined structural element 80 comprises a hollow cylinder 81 and a plurality of reinforcing members 82 having a slat shape. Reinforcing members 82 are slats made from a reinforcing material that have varying widths. The reinforcing members are inserted into hollow cylinder 81 substantially parallel to each other. This feature renders combined structural element 80 extra strength in the direction of anticipated stress. The fixation between basic structural element 81 and reinforcing member 82 can be accomplished by any of the methods discusses previously regarding combined structural element 2.

The embodiments of combined structural elements 60, 70 and 80 shown in Figures 7A, 7B and 7C may be constructed also by using solid cylinders as the structural element instead of hollow cylinders. Utilizing solid cylinders as the structural elements provides the combined structural elements with further strength due to the fusion effect between the reinforcement and the structural element and better fixation between the two. Reference is made to Figure 8 that is a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention shaped as a beam with slat as reinforcing member. The combined structural element 90 comprises a basic structural element 91 in the shape of a solid beam and reinforcing member 92 having a slat shape. The solid beam is made from a yielding material and the strengthener is from a reinforcing material. Reinforcing member 92 provides combined structural element 90 with further strength to bear stress especially in the direction indicated by arrow 93. Reference is made to Figure 9 that is a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with slat serving as reinforcing member. The combined structural element 100 comprises a hollow beam 101 and reinforcing member 102 having a slat shape. This combined structural element has also a preferred stress resistance direction as directed by arrow 103. In order to provide combined structural element 100 with better fixation of the reinforcement to the combined structural element it is preferable to provide structural element 101 with two longitudinal rims 104 along two opposite inner walls of the structural element, as indicated in Figure 10. Each couple of the longitudinal rims 104 defines a groove between them so that reinforcing member 102 is inserted into basic structural element 101 while it is held in both sides by the rims.

It is optional to provide a full screen connecting two opposite rims so that the slat is provided with further support from both sides. Reference is made to Figure 10 that illustrates a cross-sectional view of a combined structural element in accordance with another preferred embodiment of the present invention comprising a hollow beam combined with supported slat serving as reinforcing member. The screens 113 from both sides of reinforcing member 112 are shown. Several reinforcing members as the ones indicated in Figures 9 and 10 can be inserted into the combined structural element, especially if the beam is a relatively wide rectangle. It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope as covered by the following Claims.

It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the following Claims.

Claims

C L A I M S

A combined structural element comprising at least two components, one of said two components having a higher Young modulus value than the second component, wherein said first component is embedded in said second component, whereby said first component provides reinforcement to said second component imparting the combined structural element improved load resistance.

The combined structural element according to Claim 1 , wherein said second component is made from plastic material and provides a casing for said first component, and wherein said first component is made from an inorganic material.

The combined structural element according to Claim 1 , wherein said first component is made from material selected from the group consisting of aluminum, steel, magnesium and titanium or alloys of these metals.

The combined structural element according to Claim 1 , wherein said second component is made form material selected from the group consisting of polycarbonates, polyesters and polyvinyls.

5. The combined structural element according to Claim 1 , wherein said first component is fixed to said second component by the frictional forces existing between the components.

6. The combined structural element according to Claim 1 , wherein said second component is in the form of a cylinder and said first component has cruciform cross-section. 19

7. The combined structural •alement according to Claim 6, wherein said second component is in the form of a hollow cylinder.

8. The combined structural element according to Claim 6, wherein said second component is in the form of a solid cylinder.

9. The combined structural element according to Claim 1 , wherein said first component is inserted into said second component forcefully.

10. The combined structural element according to Claim 5, wherein said second component is provided with serrated edges enhancing the friction between the components.

11. The combined structural element according to Claim 1 , wherein an adhesive material is applied between said first component and said second component to improve the grip between them.

12. The combined structural element according to Claim 1 , wherein a groove is provided in the second component into which the first component is inserted thus enhancing anchorage of the first and second components together.

13. The combined structural element according to Claim 1 , wherein said second component is a beam and said first component has cruciform cross-section.

14. The combined structural element according to Claim 1 , wherein said first component has a star shaped cross-section.

15. The combined structural element according to Claim 1 , wherein said second component is a beam having a polygonal cross-section.

16. The combined structural element according to Claim 1 , wherein said second component has star shaped cross-section.

17. The combined structural element according to Claim 1 , wherein said first component is a slat.

18. The combined structural element according to Claim 1 , wherein said first component is. wavy.

19. The combined structural element according to Claim 1 , wherein said second component is U-shaped.

20. A combined structural element comprising more than two components, some of said components having a higher Young modulus value than one other component, wherein said some of said components are embedded in said one other component, whereby said some of said components provide reinforcement to said one other component imparting the combined structural element improved load resistance.