The present invention relates to a composite beam resistant to bending.

Background of the Invention

Beams are structural members that carry transverse loadings. In other words, beams are structural elements that carry forces acting perpendicular to the longitudinal axis. The main purpose of these structural members is to carry the transverse loadings with less bending-displacement and without breaking. In the state of the art, some of the application areas of the beam structural members are as follows:

- Spectacle frames are a type of system of beams that can hold and carry the spectacle lenses at the eye level.

- Our arms are a kind of cantilever beams that we frequently use in daily life.

- Tennis rackets are also a kind of cantilever beams that resist the impact load applied by the tennis ball.

- B -pillars which are used in vehicles and which are extremely important for safety of life in case of side collisions are examples of beam structures.

- Aircraft wings and fuselage are also a kind of cantilever beams subjected to the lifting force of the wind.

- Helicopter propellers are also a kind of beam structures due to the fact that they are exposed to transverse loadings such as lifting force of the wind.

- Submarine and ship propellers are also wide and short beam panels that resist the driving force applied by the water. - The bridges of bridged-tanks, which are a different type of tanks enabling tanks to pass through valleys such as ditches or rivers, are also a kind of beam structure.

- The towers and blades of wind turbines, which are an important component of the energy sector, are also a good example of long span beams.

- Bridges are huge structures that are able to carry tons of weight by means of their beams.

- When horizontal forces such as wind and earthquake act on the buildings, the columns of the buildings also serve as structural beams to provide sufficient resistance against bending. In this respect, it is possible to define the columns of high-rise buildings such as skyscrapers as structural beam members, which are expected to withstand these horizontal forces.

- The roofs in buildings are beams bearing snow load. In addition, the systems that hold and carry the floor we step on at our home or office are also beams.

In the state of the art, the beams are designed using various materials (steel, concrete, wood, composite polymers, etc.). Reduction of the weight of the said beams is demanded by many engineering disciplines such as civil, mechanical and aeronautical engineering. For example, aircraft wings or automobile beam structures are required to be lightweight in order to save energy. Another example is that by means of reducing the weight of the beams to be used in buildings, the civil engineers will be able to build much higher skyscrapers or bridge structures with much longer spans in the future. In the state of the art, the beam structures are designed using a plurality of materials in order exhibit a high bending strength, and such beams are called composite beams. The most common problems experienced with composite beam structures can be defined as shear cracks, delamination failures, slipping problems (due to inadequacy of interfacial bonding force or friction force between the materials), and flexural cracks. In the state of the art, composite beams can be produced as laminated composite beams. These laminated composite beams, as the name implies, are formed by arranging composite laminae of certain thicknesses one on top of another using epoxy or resin mixtures. Various materials can be used in each lamina of the laminated composite beams, and the bending strength of the composite laminated beam varies according to the strength properties of the materials used. For this reason, generally carbon material-based laminae are used to produce a laminated beam with high bending strength. The most important problem of these laminated composite beam structures is the delamination failure of these superimposed laminae during load bearing. If these delamination failures between the laminae occur prior to compressive or tensile failures during the flexural performance of the laminated composite beams, they cause the system not to reach the actual bending capacity. Therefore, it is known in the literature that the most important disadvantage of the laminated composite beams is delamination (see D. Wilkins et al. 1982; F. Javidrad 2000; A. Ricco et al. 2017). Another disadvantage of laminated composite beams is that their self-weights are not at the desired low levels, because many engineering branches require a beam system with beams having low specific bending strength. This specific bending strength of the beams is directly related to their self-weights; and the specific bending strength is calculated to be the ratio of their bending strength to their density.

In the state of the art, composite sandwich panel structures are produced in order to reduce the self-weight of the laminated composite beams. In this context, much more lightweight materials (such as foam) are used in the core of the sandwich beams in order to reduce their self-weight without decreasing the bending strength so much. There are provided carbon fiber reinforced structures in the top and bottom sheets of this type of beams. The said structures can carry more loads in proportion to their density than the laminated composite beams. However, in these sandwich panel structures, shear cracks occur in the core material (see W. Ferdous et al. 2018), del ami nation occurs as a result of separation of the bottom or top sheets from the core (see A. Henao et al. 2010) and indentation failures occur with the sudden collapse of the top sheet (see FM Shuaeib and PD Soden 1997). Therefore, unfortunately, the specific bending strength of these sandwich beams cannot be increased to the desired extent. In the state of the art, honeycomb structures are used to further reduce the weight of the core parts of the sandwich beams. However, the indentation failures, which are produced by the sudden collapse of the top sheet of honeycomb composite sandwich structures under load, may hinder achieving a specific bending strength of desired levels (see SM Lee and TK Tsotsis 2000; A. Petras and MPF Sutcliffe 2000; M. Hussain et al. 2019).

In the state of the art, latticed core sandwich panels or truss core sandwich beams are placed in the middle part (core) of the sandwich beams instead of a honeycomb structure. Although these beams that are developed may exhibit more specific bending strength, these systems are also observed to be subjected to types of cracks such as indentation, local bucklings and interlayer delamination (see VS Deshpande and NA Fleck 2001; G. Xu et al. 2016).

In the state of the art, reinforced concrete composite beam structures are currently frequently used in the construction industry. Although the bending strength of these structures is very high, their specific bending strength remains at very low levels due to their high self-weight. Therefore, such structures do not attract the attention of the sectors requiring lightweight and durable structures such as aerospace industry, defense industry and automotive industry. These reinforced concrete beams are a kind of composite structures, which includes steel bars as reinforcement material, and whose main material is generally concrete, that is, comprised of a combination of a plurality of materials. One of the most important problems that may occur in such composite beams is that the strength of the interfacial bonding strength between the reinforcement material and the concrete material is not sufficient and thus the reinforcement material slips in the concrete system. It is also utterly clear that a reinforcement used in a composite beam with a slipping problem will be of no use. For this reason, deformed steel bars have been formed on the surface of these steel bars, which are used as the reinforcement material, in order to prevent them from slipping in the system. Although the use of these deformed steel bars in concrete is highly successful, they are unable to resist corrosion (see Won et al. 2008; Tighiouart et al. 1998; Davalos et al. 2008). For this reason, corrosion resistant carbon or fiber glass materials are desired to be used as reinforcement (see Katz 1999; Davalos et al. 2008; Lin et al. 2013). However, no successful system has been found that can completely prevent these carbon or fiberglass reinforcements from slipping within the system. In some recent research studies (Katz 1999; Davalos et al. 2008; Baena et al. 2009; Hao et al. 2009; Lin et al. 2013), this slipping problem was desired to be solved and various techniques were applied on the carbon or fiber-glass based reinforcement materials. However, a carbon or fiberglass based reinforcement produced by these techniques does not yield as successful results as the bonding property of the deformed steel bars.

Problems Solved by the Invention

It is an objective of the present invention to provide a composite beam which is lightweight, high-strength and low-cost.

Another objective of the present invention is to provide a composite beam having higher bending strength and/or specific bending strength compared to those produced by the prior art techniques.

A further objective of the present invention is to ensure that the composite beam to be produced is a composite beam having less fatigue properties than those produced by the prior art techniques.

Detailed Description of the Invention A composite beam developed to fulfill the objectives of the present invention is illustrated in the accompanying figures, in which:

Figure 1A. is a perspective view of an embodiment of the composite beam of the present invention.

Figure IB. is a perspective view of another embodiment of the composite beam of the present invention.

Figure 2 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention.

Figure 3 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention.

Figure 4 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention.

Figure 5 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention. Figure 6 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention.

Figure 7 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention.

Figure 8 is a view of the a-a section in the X-Y plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention.

Figure 9 is a perspective view of another embodiment of the composite beam of the present invention. Figure 10 is a view of the b-b section in the X-Z plane on which are located the reinforcement materials of another embodiment of the composite beams of the present invention having different cross-sectional areas along the longitudinal axis.

The components in the figures are given within reference numbers as follows:

1. Composite beam

2. Body

21. Bottom Cover

22. Top Cover

23. Core

3. Longitudinal Reinforcement

4. Insert

5. Knot

6. Zigzagging geometric structure

7. U-shaped geometric structure

8. Hole

A composite beam (1) according to the present invention essentially comprises at least one body (2) and a longitudinal reinforcement (3) including at least one knot (5) thereon (see Figure 2). In order to increase the friction between the longitudinal reinforcement (3) materials and the body (2), the said knot (5) is formed by looping or tying the bendable reinforcements (3) on themselves or each other. These reinforcements (3) with knots (5) are disposed in the body (2) in the longitudinal axis of the body (2). The main reason for using these knots (5) is to prevent slipping of the longitudinal reinforcement (3) material in the body (2) thereby creating the desired reinforcement effect. In a preferred embodiment of the present invention; if the knots (5) tied on the longitudinal reinforcement (3) are desired to be larger, a plurality of knots (5) may be tied on the point where the knot (5) is located. In a preferred embodiment of the present invention, at least one longitudinal reinforcement (3), which is in the form of linear or curvilinear zigzags (6) to create a frictional force that prevents the longitudinal reinforcement (3) from slipping in the body (2), is arranged in the body (2) in the longitudinal axis of the body (2) (see Figure 3). In a preferred embodiment of the present invention, the longitudinal reinforcement (3), which is in the form of linear or curvilinear zigzags (6) placed in the body (2) also includes at least one knot (5) in order to further increase the friction (see Figure 4). In a preferred embodiment of the present invention, at least one longitudinal reinforcement (3), which is in a form similar to a U-shaped structure (7) to create a frictional force that prevents the longitudinal reinforcement (3) from slipping in the body (2) (see Figure 5). The longitudinal reinforcement (3) having this U-shaped structure (7) can be formed by bending at the end portions of the body (2) so as to pierce through the body (2) or remain within it. In a preferred embodiment of the present invention, the longitudinal reinforcement (3), which is in a form similar to a U-shape (7) disposed in the body (2), also includes at least one knot (5) in order to further increase the friction (see Figure 6). In a preferred embodiment of the present invention, the longitudinal reinforcement (3), which is in a form similar to a U-shape (7) arranged in the body

(2), also includes at least one linear or curvilinear zigzagged structure (6) in order to increase the friction (see Figure 7). In a preferred embodiment of the present invention, the longitudinal reinforcement (3), which is in a form similar to a U-shape (7) disposed in the body (2), also includes both at least one linear or curvilinear zigzagged structure (6) and at least one knot (5) (see Figure 8). In a preferred embodiment of the invention, it is also possible to use the longitudinal reinforcements

(3) together with various adhesive or epoxy materials in order to further increase the friction force between the body (2) and the longitudinal reinforcements (3). It may be preferred that these epoxy materials are non-brittle, i.e. more flexible and ductile, and have a high-strength thermoset or thermoplastic structure. In a preferred embodiment of the invention, the longitudinal reinforcements (3) disposed within the body (2) are made of carbon, fiberglass, kevlar, basalt and aramid based materials or mixtures and derivatives of these materials in different proportions. The flexibility of the said materials will facilitate forming knotted (5) structures in the longitudinal reinforcements (3). In a preferred embodiment of the invention, the longitudinal reinforcements (3) in the form of linear or curvilinear zigzags (6) or a form similar to a U shape (7) disposed in the body (2) are made of metal, or metal-metal alloy materials, or metal-nonmetal alloy materials. In a preferred embodiment of the invention, the cross-sectional areas of the longitudinal reinforcement (3) materials disposed within the body (2) may be of different shapes such as circular, elliptical, trapezoidal, rectangular, square, triangular and parallelogram.

In order to prevent delamination problems occurring under transverse loadings in a composite beam (1) of the present invention, the total value of the widths of the longitudinal reinforcements (3) placed in the same planar height within the body (2) is required to be smaller than the width value of the body (2) at that height (see Figure 2-8). In a preferred embodiment of the invention, inserts (4) are used by passing through the body (2) at vertical or inclined angles between the longitudinal reinforcements (3) disposed in the body (2) (see Figures 2-8). These vertical or oblique angled inserts (4) provide the composite beams ( 1 ) to have resistance against formation of both delamination and shear cracks under the transverse loadings. In a preferred embodiment of the invention, it may be preferred that the vertical or oblique angled inserts (4) are of nail or fabric structure produced of carbon-based, kevlar- based or glass-based materials. In a preferred embodiment of the invention, it is recommended that the vertical or oblique angled inserts (4), which are made of carbon, kevlar, or glass-based materials, comprise at least one knot in order to prevent slipping within the body (2). In a preferred embodiment of the invention, the vertical or oblique angled inserts (4) are used such that they are in the form of a fabric wrapped around the longitudinal reinforcements (3) disposed in the body (2).

In order to increase the specific bending strength of a composite beam (1) according to the present invention, it is necessary to reduce its density, i.e. total weight in the same outer-volume. In this context, holes, cavities or clearances (8) having a square, rectangular, trapezoidal, circular, elliptical, triangular, or parallelogram cross-section extending along the longitudinal axis of the body (2) are provided at planar heights having no longitudinal reinforcement (3) (see Figure 9). In a preferred embodiment of the invention, the body (2) is made of polymer materials or recycled polymer materials so that the composite beam (1) can be sufficiently lightweight. In a preferred embodiment of the invention, in order to attract the interest of particularly the construction sector, the body (2) may also be made of concrete -based materials for structures whose bending strength is more important than the specific bending strength.

The composite beam ( 1 ) according to the present invention preferably has a body (2) in the form of a square prism (a three-dimensional prism structure having a cross- sectional area where its width is equal to its height) or a rectangular prism (a three- dimensional prism structure having a cross-sectional where its width is not equal to its height) (see Figure 1A, Figure IB, Figure 9). In a preferred embodiment of the invention, the body (2) may be of different geometric shapes in the longitudinal axis of a composite beam (1) of the present invention (see Figure 10). For example, a composite beam (1) according to the present invention may be a three-dimensional structure having different cross-sectional areas along its length, as the blades of the wind turbines (see Figure 10). In order for such a composite beam to have a high bending strength, if the horizontal reinforcements (3) disposed in the body (2) in the longitudinal axis of the body (2) are preferred to be used at the tension region of a three-dimensional composite beam (1) having cross-sectional areas varying along its length, the horizontal reinforcements (3) should extend parallel to the outer surface of the composite beam (1) at the tension region. Furthermore, if the said reinforcements (3) are preferred to be used at the compression region of a three-dimensional composite beam (1) having cross-sectional areas varying along its length, the said horizontal reinforcements (3) should be arranged parallel to the outer surface of the composite beam ( 1 ) at the compression region. In order for the composite beam (1) of the present invention to have less fatigue property compared to those produced with the prior art techniques, the longitudinal reinforcements (3) disposed in the body (2) along the length of the body (2) should be selected from among materials capable of exhibiting linear behavior in their stress vs. strain curves.

A composite beam (1) according to the present invention can be produced by three different methods. The first one of these methods is the process of heating the composite beam (1) in a suitable mold in order to obtain the desired geometry. For this method, in the first step, a mold is prepared which is suitable for the composite beam (1) to be produced. In the second step, the longitudinal reinforcements (3), which are planned to be used in the body (2), and which are to be used in the longitudinal axis of the body (2), are placed in the mold. In addition, if inserts (4) to be placed in the body (2) at vertical or oblique angles are desired to be used, these inserts (4) must be placed in the mold. In the third step, the polymer type materials selected as the main material for the body (2) are poured or placed into the molds in solid state. In the fourth step, the mold and the product therein are heated together in an oven or autoclave oven to melt the added polymer material. In the final step, the mold is taken out of the oven and the mold is removed to obtain the designed composite beam (1). In a preferred embodiment of the present invention, the vertical or oblique angled inserts (4) can also be placed in the composite beam (1) after the production is completed. In this context, the vertical or oblique angled inserts (4) are placed in the composite beam (1) upon being driven (e.g. with hammers) at the locations where they are planned to be used. In a preferred embodiment of the present invention, the vertical or oblique angled inserts (4) are placed in cavities to be opened in the composite beam ( 1 ) with the help of epoxy after the production is completed.

The production of a composite beam (1) according to the present invention by means of the second method can be carried out by using plastic forming methods. In this context, as a first step, the longitudinal reinforcements (3) planned to be disposed in the longitudinal axis of the body (2) are placed in the molds, and polymer materials belonging to the body (2) are added into the mold using one of the plastic forming methods such as the plastic injection method. In the next step, if desired, vertical or oblique angled inserts (4) are placed in the product by being driven (e.g. using hammers) at the locations where they are planned to be used on the composite beam

(1) after all the mold parts are removed. In a preferred embodiment of the present invention, if desired, the vertical or oblique angled inserts (4) are placed in holes to be opened in the composite beam (1) with the help of epoxy after the production is completed.

The production of a composite beam (1) according to the invention by the third method is based on the process of assembling all the parts of the beam (1) after productions thereof. In this context, in cases where the longitudinal reinforcements (3) to be placed in the body (2) in the longitudinal axis of the body (2) are desired to be located in both the tension and compression regions of the composite beam (1), the composite beam (1) is produced in at least three different parts. These parts are called Bottom Cover (21), Top Cover (22), and Core (23). All the parts that are designed to be assembled are produced by using plastic forming means or by melting polymer materials in the mold with the help of heat. In order for these parts to fit to each other and to be assembled in a compatible manner, all the parts to be produced must include at least one set of male-female slot compatible with each other. Furthermore, prior to assembly of these parts to each other, using thermoset or thermoplastic epoxy mixtures, the longitudinal reinforcements (3), which are planned to be used in the composite beam (1), are placed in suitable cavities already present in the core (23). Then all parts are assembled to each other with thermoset or thermoplastic epoxy mixtures. In a preferred embodiment of the invention, in cases where the longitudinal reinforcements (3) to be disposed in the body (2) in the longitudinal axis of the body

(2) are desired to be located only in the tension zone of the composite beam (1), the Top Cover (22) and the Core (23) parts are produced as a single integrated piece. In addition, all the parts to be assembled to each other also have a set of male-female slot compatible with each other. In a preferred embodiment of the invention, after all of the parts are assembled, if desired, the vertical or oblique angled inserts (4) are placed in the product by being driven (e.g. using hammers) at the locations where they are planned to be used on the composite beam (1). In a preferred embodiment of the present invention, if desired, the vertical or oblique angled inserts (4) are placed in cavities to be opened in the composite beam ( 1 ) with the help of epoxy after all of the parts are assembled.

The production of a composite beam (1) according to the invention at a lower cost than those produced by prior art techniques is based on using smaller amount of volumes for reinforcement (3) materials. For example, an engineer who wishes to design a beam that will have both high bending strength and high specific bending strength generally utilizes laminated composite beams in today's world and does not prefer other composite beam structures. This is because although the sandwich composite beams, which are among the other composite structures, have high specific bending strength due to their very low density, their bending strength can remain very low and is not very suitable for a long-span beam design. In addition, even though the truss core sandwich beams or latticed core sandwich beams have higher specific bending strengths, they are underutilized by the engineers today since they do not have the desired level of bending strength and the desired standard deviations in mass production. In this context, the fact that the ratio of the volume of the reinforcement materials used in a laminated composite beam, which has both high bending strength and high specific bending strength, to the volume of the entire beam is about 50% to 80% causes a considerable material cost. However, this ratio is about 1% to 30% for a composite beam (1) according to the present invention. This low ratio makes it possible for a composite beam (1) of the present invention to have a low material cost. Another aspect which enables a composite beam (1) according to the present invention to be produced at a lower cost than those produced by the prior art techniques is the ease of production. That is, the knotted structures (5) or zigzagged structures (6) or U-shape-like structures (7) desired to be used for the longitudinal reinforcements (3) used in the abovementioned production techniques can be easily formed, and this ease causes the general production expenses to remain at low levels.

A number of methods are proposed for easily forming and producing said various shaped structures (knotted, zigzagged, U-shaped and others) of the longitudinal reinforcements (3) passing through a composite beam (1) of the present invention. There are basically two different methods that can be discussed for forming knots (5) in the reinforcements (3). In the first method, if the reinforcement (3) has a flexible structure when dry (not cured with epoxy) like a carbon fiber material, knots (5) are tied on the said reinforcement (3) by machine or by hand at desired intervals and thereafter becomes ready for use in the abovementioned techniques. In the second method, the reinforcement (3) material, whether flexible or not, is first impregnated with resin or epoxy mixtures, and then knots (5) are tied by machine or hand. It is then cured in a suitable mold in order to acquire a solid state parallel to the surface of the composite beam (1) of the present invention. Then these reinforcements (3) become ready for use in the abovementioned techniques. In order to form a zigzag structure (6) in the reinforcements (3), a suitable mold is prepared and the reinforcement (3) materials are cured in this mold using resin or epoxy, and then they become ready for use in the abovementioned techniques. In order to form a U-shape- like structure (7) in the reinforcements (3), a suitable mold is prepared and the reinforcement (3) materials are cured in this mold using resin or epoxy, and thus they are made ready for use in the abovementioned techniques. If it is desired to form U- shape-like structures (7) by using the reinforcement (3) materials in dry state, then the molds to be used in the said production techniques must include some special vertical parts, because the longitudinal reinforcements (3) to be placed in the molds will be able to acquire “U” shape (7) by passing around these vertical structures. References:

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