COMPRESSED STRUCTURAL ROD

Abstract

 Compressible rod forming a closed cross-section profile that comprises in the basic structure a body, characterized in that the body (1) is filled with a filling material (2), which sets a liquid or gel with a Poisson's ratio of approximately 0.5 or lower, or an incompressible or low compressible loose material with a Poisson's ratio less than 0.5, or any combination thereof, while the body (1) on one side is ended with a sealed base (4) and on the other side with a piston (3).

Description

[0001] The invention refers to a compressed structural rod that can be used among others, in in truss structures, wherever there are elements in compression.

[0002] Where there is tension-compression in rod-like structures, buckling is an important phenomenon that often determines the load capacity and safety. Buckling is rapid, not suspected process and is characterized by a large decrease in the load capacity of the compressed element.

[0003] There are many proposals and studies related to the control of force in compressed members or the control of the buckling phenomenon, e.g.: Ting-UeiLee; Elastic buckling shape control of thin-walled cylinder using pre-embedded curved-crease origami patterns; International Journal of Mechanical Sciences Volume 151, February 2019, Pages 322-330.

[0004] Known publications concern the control of the buckling phenomenon or the control of the magnitude of the force in the compressed element.

[0005] However, the disadvantage of the known solutions is the fact that the bearing capacity is limited by the phenomenon of buckling or the need to construct supplement structural elements preventing or limiting the phenomenon of buckling. The known solutions do not directly increase the load capacity of the compressed element.

[0006] There is therefore a need to obtain a bar that achieves greater compression resistance, buckling resistance, while using typical hollow cross sections.

[0007] The essence of the invention is a structural element - a compressed bar - compressible rod, which is resistant to buckling, i.e. the loss of a straight form under axial load, which achieves a significant increase in the load capacity in compression. The invention is a hybrid rod also known as bar with increased resistance to buckling thanks to the structure being a profile with a hollow - closed cross-section filled with a filling material - a liquid or gel with a Poisson's ratio of about 0.5 or less, preferably from 0.5, or an incompressible loose material in the meaning of particulate - granular - powdery - bulk - or slightly / low compressible with a Poisson's ratio less than 0.5 or a combination/mixture of a loose material with other above-mentioned: liquid and/or gel, or a combination/mixture of liquid and gel with the following parameters: liquid or gel with a Poisson's ratio of about/approximately 0.5 or less, or incompressible loose material or a slightly - in the meaning of low compressible one with Poisson's ratio less than 0.5. Preferably, it is a liquid or a combination of loose material with the above-mentioned liquid and/or gel with above mentioned parameter for each.

[0008] The rod is preferably in the form of a hydraulic cylinder - in the case of a cylinder or other geometric spatial solid, e.g. in a cross-section of any polygonal shape, e.g. a hexagon. The body of the device is a hollow section profile, with a tight base element on one end and a piston on the other, and between these parts - inside the body - there is a filling with a filling material with the above characteristics. Thus, the space filled with the filling material is limited / tipped / ended on one side - by the piston from above and on the other side of the body - by the base element. The body therefore on one side is sealed with a tight sealed base and on the other side with a piston. The compression load acting on the rod, is transferred thanks to such a hybrid construction through the piston - further as pressure exerted on the filling, i.e. the filling material (liquid or gel or bulk material or a combination of liquids, gels and bulk materials) and then transferred to the the base as the pressure exerted by the filling - filling material. In this way, the load applied to the rod from the piston side is carried out on the base plate (and vice versa). In the rod body (hollow profile) there are only circumferential forces - in the case of filling with a liquid, e.g. water or gel - and there are additional vertical forces caused by the friction of the filling material against the walls of the rod body in the case of filling with a bulk material or a combination of liquids / gels and loose materials. In order to minimize the friction in the case of a filler material containing bulk material between the filler material and the body, it is preferable to introduce on the inner surface of the body a separation layer or layers reducing the friction of the filler material against the inner walls of the rod body. The separation layer or layers are thus made between the inner side of the body and the filling material and can be made of polymers. Reducing the vertical forces in the body of the member significantly reduces the negative impact of buckling on the load capacity.

[0009] The bearing capacity of the rod is determined by the bearing capacity of the rod body, e.g. a pipe section under the pressure inside. However, when using filling materials transferring the vertical load to the surface of closed/hollow profile by friction - all of the above-mentioned combinations with loose material - i.e. except for liquids and gels - this effect should preferably be taken into account in the load capacity assessment. If the effect of friction has a significant negative impact on the load-bearing capacity of the bar, then it is preferable to use an additional layer or a system of separation layers mentioned above on the inner surface of the closed profile - the body, reducing the effect of friction on the body walls.

[0010] The base of the bar - rod and the piston on the outer side of the bar are preferably equipped with e.g. a steel bearing for axial load transfer.

[0011] The hybrid bar - rod is optionally equipped with a shut-off valve for filling, pressure control or length regulation (specially in case when the filling is liquids or gels ).

[0012] The body of the rod, i.e. a profile with a hollow section, which is filled with a filling material and which is closed with a base on one side and a piston on the other, can be made of any materials with appropriate tensile strength, e.g. metals or synthetic materials, preferably FRP composites - reinforced with fibres, etc. FRP composite pipes are preferably used to make the profile - the body of the rod. Such pipes are characterized by high resistance to internal pressure (circumferential tension) and much lower resistance to compressive, external axial load acting on the profile of such a pipe. This is due to the anisotropy of the composite, which is the cause of a significant reduction in the compressive capacity in relation to the stretching. Using such a solution, it is possible to significantly increase the compressive load capacity of composite bars, especially cylindrical ones, e.g. Pipes. The base is made of, for example, steel or composites. A piston is made of, for example, metal, steel, aluminum or plastics, composites, polymers.

[0013] The invention is described in more detail in examples and shown in the drawing.

[0014] The construction of the rod is shown in Fig. 1, Fig. 2 and 3 that set photos of the prototype of the invention in a given implementation, for which the effectiveness of the invention was checked.

[0015] Designations in the drawing:

1. Body of bar/rid - hollow/closed profile - cylinder in the example - with a cylindrical cross-section

2. Filling material in the interior of the closed profile limited by a base and a piston with a filling material - liquid and/or gel and/or loose material - e.g. granulate or a combination of liquid, gel and/or loose material - granulate, i.e. filling material - liquid or gel with a Poisson's ratio of about 0, 5 or less, or incompressible or slightly compressible loose material with a Poisson's ratio of 0.5 or less.

3. Piston

4. Base of bar/rod

5. Seals used in the embodiment

6. Separating layer or layers reducing friction - optional depending on the filling material

7. Bearing ensuring axial load transfer

[0016] Filling 2 is interchangeably referred to as filling material 2, bar - rod.

Example 1

[0017] The bar is in the basic structure - is essentially a profile with a hollow circular cross-section, which is filled with a filling 2 - liquid 2 - in this case with Poisson's ratio v equal to 0.5 and this liquid is hydraulic oil in this example. The filling 2 in body profile 1 is closed on one side with a movable piston 3 and on the other side with a base plate 4 in the form of a bottom. Body 1 is made of steel, i.e. S460, the base is made of S460 steel, and the piston is made of the same steel. Additionally, between body 1 and piston 3, there are hydraulic seals 5 made of a polymeric material typical for hydraulic seals, eg polyurethane or neoprene composites.

[0018] In addition, there are elements ensuring axial load transfer 7, i.e. in this example, a steel bearing 7 made of S460 steel fixed in a standard way to the piston 3 from the outside, or it can be made entirely with the piston, i.e. constitute an integral part of the piston, and steel bearing 7 made of S460 fixed in a standard way permanently to the base 4 from the outside, or it can be made entirely with the base 4, i.e. constitute an integral part of the base. The whole can be optionally equipped with a valve to regulate the pressure or the length of the rod - the valve connects the device to the control or pressure control system. This valve is permanently attached to the body profile 1.

[0019] The bar made in this way provides increased resistance to buckling in compression compared to other bars without new additional design features - load transfer from the piston to the base through the filling is described above. This was demonstrated by additionally testing the prototype described in Example 6 and shown in Figures 2 and 3.

[0020] In this example, no additional separation layer 6 was made.

Example 2

[0021] The bar is constructed in a similar way as described previously, except that S420 steel is used to make the steel elements, and granulate, i.e. loose material, is used as the filling material. The increase in load capacity depends on the coefficient of friction between the filling granules and the internal walls of the body. In order to minimize friction in the case of a filling material containing loose material along the entire length - the inner surface of the body 1, a single separation layer 6 was made to reduce the friction of the filling material against the internal walls of the body 1. The separation layer 6 is made between the inner side of the body 1 and the filling material 2 and made it's made of PTFE - a fluoropolymer.

[0022] The base part of body 1 is a profile with a hollow circular cross-section filled with granulate 2, i.e. sand - in this case with a Poisson's ratio of about 0.3, The filling 2 in body 1 is closed on one side with a movable piston 3 and on the other side with a base 4 in the form of a bottom. The body 1 is made of steel - in this example S420, the base 4 is made of steel ie S420, the piston is made of steel ie S420. Additionally, mechanical seals 5 made of elastomer are mounted between body I and piston 3. In addition, in this example, bearings 7 were introduced, i.e. elements ensuring axial load transfer, i.e. in this example in the form of conical elements. Bearings 7 are made similarly as described in example 1.

Example 3:

[0023] The rod is constructed similarly to how it was described in the previous Example 2, with the only difference being that a mixture of liquids and granules mentioned in Example 1 and 2 is used as the filling material in a 1:1 ratio.

Example 4:

[0024] Confirmation of the invention's effect.

[0025] The effects of the invention were tested on a compression rod with a hybrid tubular cross-section, which means a solid body filled with liquid as described in Example 1. Calculations were performed to determine the load-bearing capacity of the rod according to the invention when perfectly compressed and hinged at the supports. Basic calculations were conducted for a tubular steel cross-section made of S460 steel with a strength of R = 460 MPa.

Parameters;

Rod length: 1 = 5 m,

Tubular cross-section diameter: ϕ = 70 mm,

Body wall thickness: t = 3.2 mm,

Moment of inertia of the tubular cross-section: J = 375,000 mm⁴.

[0026] Calculation of the load-bearing capacity under compression according to Euler's formula:
The critical force under pure compression is:

[0027] Calculation of the load-bearing capacity using the invention:
In the case of using the rod in a hybrid construction, where it is filled with the liquid described in Example 1, the rupturing of the tubular profile (body) is determined by the pressure of the liquid, considering the given Poisson's ratio coefficient.

[0028] The approximate bursting pressure of the tube is:

where the piston area is At = 3177 mm2.

[0029] The load-bearing capacity of the hybrid rod at rupture is: P_pc = C * At, P_pc = 147 kN.

[0030] Conclusion: A hybrid rod constructed with a tube of ϕ = 70 mm and t = 3.2 mm, having a length of 1 = 5 m and filled with liquid with a Poisson's ratio coefficient of 0.5 or less, theoretically increases the load-bearing capacity under compression by nearly five times compared to a conventional compressed rod with the same circular cross-section. This confirms the effectiveness of the invention. Based on this, it can be inferred that when using granular filling material with a Poisson's ratio coefficient less than 0.5, or a mixture of liquids with a Poisson's ratio coefficient of 0.5 or less, in combination with granular material and/or gel, similar characteristics can be achieved, especially when a separating layer is applied as described in Example 2.

Example 5:

[0031] Prototype testing - Fig. 2 and 3.

[0032] The effects of the invention described in Example 1 were examined.

[0033] A prototype rod was constructed in accordance with the description provided in Example 1.

[0034] The load-bearing capacity under compression was evaluated for a rod made of a steel tube with dimensions ϕ57/7.1 mm and a length of 1 = 6.07 m. The hybrid rod was hinged at both ends within supporting structures. The force in the rod was increased by raising the liquid pressure internally using a hydraulic pump equipped with a pressure gauge. The load-bearing capacity under compression achieved nearly 2.31 times greater than the buckling capacity. The experiment was terminated due to deformations (rotation) of the rod mounting from the piston side.

[0035] The theoretical critical force for a tubular rod according to Euler's formula is Pk = 19.38 kN, while the force obtained in the experiment was Pp = 45 kN.

Claims

1. Compressible rod forming a closed cross-section profile that comprises in the basic structure a body, characterized in that the body (1) is filled with a filling material (2), which sets a liquid or gel with a Poisson's ratio of approximately 0.5 or lower, or an incompressible or low compressible loose material with a Poisson's ratio less than 0.5, or any combination thereof, while the body (1) on one side is ended with a sealed base (4) and on the other side with a piston (3).

2. The rod according to claim 1, wherein the body (1), ended on both sides with a base (4) and a piston (3), is constructed in such a way that the load is transmitted wholly or partially from one end to the other end of the rod through the pressure that is exerted on the filling material (2).

3. The rod according to claims 1-2, wherein in the case of filling material (2) with a loose material or a combination of loose material with a liquid and/or gel, between the filling material (2) and the body (1), an optional separating layer (6) or separating layers (6) are provided on the inner surface of the body (1) that is made of a material enabling to reduce the friction between the granular material and the body walls (1).

4. The rod according to claims 1-3, while the base (4) and/or the piston (3) are equipped with a bearing on the outer side that enable to provide axial load transmission.

5. The rod according to claims 1-4, while the filling material (2) is liquid with a Poisson's ratio of 0.5 or lower.

6. The rod according to claims 1-5, while it is equipped with a shut-off valve for filling, pressure control, or length adjustment.

Drawing