Profile pipes used as structural parts and building elements are made in the form of hollow rods with a square or rectangular section. The profile pipe is similar in its qualities metal bar, but due to its lighter weight and four stiffening ribs, it is more widely used. When bending, the main load acts on the extreme parts of the product, and the core of the beam is not subjected to significant deformations, so the bending strength of the profile pipe does not differ from that of a solid product of a similar section.
Profile pipes produced with a square section have the same resistance to bending force, which is directed perpendicular to any of the faces. Rectangular pipes are more resistant to bending along the wide side.
The closedness of the cross section increases the resistance of this type of profile to torsion, which makes it possible to use profile pipes when creating arched vaults, steep roofs and ribbed domes.
Comparison of strength indicators of round and square pipes
Profile pipes have a number of advantages over round ones when used as load-bearing element structures. The use of square pipes allows to reduce the surface area of the structure and reduce the weight of the product, which ensures their effective use as part of connecting and frame parts buildings and makes it possible to create more complex engineering structures with minimal cost material.
The determination of the bending strength index is carried out taking into account transverse moment inertia. Due to the uniform distribution of metal along the perimeter of the profile, square pipes are characterized by high radii of gyration in relation to their cross-sectional area, which ensures the efficiency of their use for the manufacture of compressed-bent and compressed rods.
With equal indicators of the cross-sectional area, diameters and wall thickness, more effort is required to bend a square pipe. Under the condition of equal strength of materials and equal specific gravity of products on running meter indicators of bending strength of the section of square and round pipes have comparable values, while the radius of gyration of the circular section exceeds this indicator for the square section.
What is preferable to use as corrugated fence posts? 99% will answer this question unequivocally - a metal pipe. And absolutely right. steel pipe- the most economical and durable material with sufficient strength for bending (primarily) loads.
The next question is: which pipe is better to use - round or square? Everything is not so clear here. Opinions are divided roughly evenly. In this article, we present our vision of this issue. We leave the issues of aesthetics and design outside the brackets - "There are no comrades for taste and color," as they say ... The issues of strength calculation of fence posts are discussed in detail in another article.
So, a square pipe has, undoubtedly, a large bending strength. Its moment of resistance is approximately 1.7 times larger than a round pipe with similar parameters (outer diameter and wall thickness). This is if you put the pole parallel to the plane of the fence, as 99% of developers do. (By the way, if you put the posts diagonally - at an angle to the plane of the fence, the increase in the moment of resistance will be only 1.2 times compared to a round pipe.)
However, this method of installation has a rather significant drawback: In the place where the log is attached to the pole, a corrosion center is inevitably formed, which is almost impossible to stop or prevent. The fact is that in the place where the pipes overlap, a windproof cavity is formed where moisture is constantly present (after rain) and excellent access to oxygen. And these are two conditions under which the metal corrodes extremely quickly. The presence of a weld only exacerbates the problem. In a few years, the welded joint is completely destroyed and the fence needs to be repaired or replaced. The most annoying thing is that this place cannot be defended or at least slow down the rate of destruction. Metal corrodes from the inside!
Many people get out of the situation by cutting the fence lags to a multiple of the step of the fence posts and welding them end-to-end to each post. However, in addition to significantly greater labor costs (and the cost of such installation), the stiffness of the load-bearing structure in the fence plane and its strength are sharply reduced. The main loaded elements of such a design are just welds, and this is wrong from an engineering point of view. In winter, the forces of frost heaving can raise some of the pillars. Welded joints are destroyed and work like hinges (do not work). Among other things, high quality welding work, because it is necessary to provide a sealed weld to avoid corrosion problems already inside the joist pipe.
Many mistakenly believe that a corrugated sheet gives additional structural rigidity. Unfortunately, it is not. When the fence is skewed, the sheet is simply torn at the fastener points.
In addition to the above main drawback of square pillars, others should be noted:
- The complexity of the installation increases: in addition to ensuring verticality, it is necessary to ensure that one face of the square is in the same plane as the fence line.
- The high cost of a square pipe - a pipe weighs 30% more than a similar round pipe, and costs about 35% more
- The presence of a weld. Pipes of square (rectangular) section are produced only by welded technology. On one side there is a welded seam for the entire length of the pipe. The pipe begins to actively corrode, and the coloring practically does not prevent the occurrence of corrosion along the weld.
Logs to such pillars are overlapped with two short seams at the top and bottom of the log. The connection turns out to be purged, easily protected from corrosion by paint and serves for many years and decades. The welded seam has sufficient tensile strength (more than 1.5 tons per one log). This is 15 times the load caused by a storm wind (25 m/s, for a 2 m high fence with a post spacing of 2.5 m). Due to the fact that the logs are not cut, the load-bearing structure of the fence is as rigid as possible and prevents a single column from sticking out of the ground. The pillar, in fact, is kept from bulging by two neighboring ones.
The most optimal, perhaps even the best, solution is to use tubing pipe fence posts. It is thick-walled and seamless, made of high-strength steel (yield strength reaches 116 kgf/mm2, which is 5.5 times higher than conventional pipes). Due to the high strength of steel, such poles are much stronger than a commensurate square one, and they cost about 2 times cheaper. Fences 4 meters high or more can be installed on tubing poles!
Prices for tubing poles and other materials for the construction of the fence:
The best basis is metal pipes for the fence - durable, easy to install and durable. On metal frame you can easily fix any enclosing material - wood, profiled steel sheet, mesh, cellular polycarbonate, asbestos or cement - particle sheets.
Budget developers are often stopped by the high price of metal. However, comparing the life of a metal fence with a wooden one, you will see the opposite.
metal poles and the veins will last at least 50 years while wooden frame fence for this period you will have to replace 3-4 times with all the ensuing costs.
From the point of view of science that studies the resistance of materials (sopromat), the most advantageous is the round section of the pipe. With a minimum of material, it provides maximum rigidity.
If we take into account the ease of installation, then round pipes are inferior to profile ones. Rectangular racks and girders are more convenient to cut and join by welding. Flat surface contact allows you to fix all the elements of the fence more densely and more rigidly than round.
As we have already said, a round pipe with the same weight is stronger than a profile pipe for bending. Therefore, if you decide to buy round-section racks for the fence, you will save money by reducing the weight of the metal. In addition, it is more convenient to install a round pipe in soft soil by screwing it in with a collar.
The reliability of the entire fence structure directly depends on the material of the supporting frame.
Put wooden posts, and the fence on your site will last no more than 10 years. Wood, even antiseptic, is susceptible to decay.
Concrete is a more reliable option. But when installing such a design, difficulties arise with fastening the runs.
Drilling a reinforced pole is not easy, and not all developers can install mortgages in it with high quality.
The pitch of the fence posts is of great importance. Optimal - 2.5 meters. In an area with strong gusty winds, it should be reduced to 2 meters.
For low fences (less than 1.5 meters), a square pipe 40x40x2 mm or 60x60x2 mm with veins with a section of 30x20x2 mm or 40x20x2 mm can be used.
A little about the rectangular pipe
GOST R 54157-2010 "Steel profile pipes for metal structures", this standard applies to round, square, rectangular, oval and flat-oval pipes for metal structures made of carbon and low alloy steel.
Dimensions of rectangular profile pipes:
– 20x10, 28x25, 30x15, 30x20, 40x25, 40x28, 50x20, 50x25, 50x30, 50x40
– 60x30, 60x40, 80x40, 80x60, 100x50, 100x60, 100x80, 120x60, 120x80
- 140x60, 150x100, 160x120, 160x80, 180x125, 200x100
A big plus of steel rectangular pipes is the effective ability to interact with the planes of a symmetrical surface, which can significantly expand the scope of use in general. The rectangular section of the pipes increases the range of functional orientation of the product of the final raw material, but it is worth immediately excluding those areas in which pipes with a similar section are not used, and this is, first of all, the transportation of gaseous substances, plumbing and other systems.
Main areas and applications:
– Small-scale construction (less often - large-scale)
– Mechanical engineering
– Installation work both outdoor and indoor type
– Steel structures of a wide profile
– Production of consumer goods
Scheme of installation of a tubular frame fence
The profile pipe used for racks must be turned with the wide side perpendicular to the cladding. This will maximize the rigidity of the posts with respect to the wind tending to bend the wide "sail" of the fence.
Unlike a solid fence made of profiled sheet, the installation of a frame made of pipes for a steel mesh fence is less responsible. Even a hurricane wind is not terrible for this design, because the mesh does not create a lot of aerodynamic resistance.
Here main task is to ensure the stability of the base, therefore, sufficient penetration into the ground and concreting of the pillars are mandatory conditions for the stability of the entire structure.
