Profile pipes used as structural parts and building elements, are produced in the form of hollow rods with a square or rectangular cross-section. The profile pipe has similar properties to metal beams, but due to its lighter weight and four stiffening ribs, it is more widely used. When bending, the main load acts on the outer sections of the product, and the core of the beam is not subject to significant deformation, therefore the bending strength of the profile pipe does not differ from that of a solid product of the same cross-section.
Profile pipes made with a square cross-section provide equal resistance to bending force, which is directed perpendicular to any of the faces. Rectangular pipes are more resistant to bending along the wide side.
Closedness cross section helps increase sustainability of this type profile to torsion, which makes it possible to use profile pipes when creating arched vaults, steeply sloping roofs and ribbed domes.
Comparison of strength indicators of round and square pipes
Profile pipes have a number of advantages over round pipes when used as a load-bearing element of structures. Application square pipes allows you to reduce the surface area of the structure and reduce the weight of the product, which ensures their efficient use as part of the connecting and frame parts of buildings and makes it possible to create more complex engineering structures with minimal costs material.
Determination of the bending strength index is carried out taking into account the transverse moment of 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 effectiveness of their use for the manufacture of compressed-bent and compressed rods.
With equal cross-sectional areas, diameters and wall thicknesses, more force is required to bend a square pipe. Provided that the materials are of equal strength and the specific gravity of the products is equal to linear meter bending strength indicators of square and round pipes have comparable values, while the radius of gyration round section exceeds this figure for a square section.
What is preferable to use as corrugated fence posts? The answer to this question is 99% unequivocal - a metal pipe. And absolutely right. steel pipe- the most economical and durable material, which has sufficient strength to withstand bending (primarily) loads.
Next question: Which pipe is better to use - round or square? Everything is not so clear here. Opinions are divided approximately equally. In this article we will outline our vision of this issue. We leave questions of aesthetics and design outside the brackets - “There are no comrades according to taste and color,” as they say... Questions of strength calculations fence posts discussed in detail in another article.
So, a square pipe undoubtedly has greater bending strength. Its moment of resistance is approximately 1.7 times greater than a round pipe with similar parameters (outer diameter and wall thickness). This is if you place the post parallel to the plane of the fence, as 99% of developers do. (By the way, if you place the pillars 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 installation method has a rather significant drawback: At the point where the log is attached to the pole, a corrosion center inevitably forms, 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 there is excellent access to oxygen. And these are two conditions under which metal corrodes extremely quickly. The presence of a weld only makes the problem worse. Within a few years, the welded joint is completely destroyed and the fence requires repair or replacement. The most unpleasant thing is that this place cannot be protected or at least reduced the rate of destruction. Metal corrodes from the inside!
Many people get out of the situation by cutting the fence joists in multiples of the pitch of the fence posts and welding them end-to-end to each post. However, in addition to significantly higher labor costs (and expenses for such installation), the rigidity of the load-bearing structure in the plane of the fence and its strength are sharply reduced. The main loaded elements of such a structure are the welds, and this is incorrect from an engineering point of view. In winter, the forces of frost heave can lift some poles. In this case, the welded joints are destroyed and act as hinges (do not work). Among other things, it is required high quality welding work, because It is necessary to ensure a sealed weld to avoid corrosion problems already inside the log pipe.
Many people mistakenly believe that corrugated sheets provide additional rigidity to the structure. Unfortunately, it is not. When the fence is skewed, the sheet simply breaks at the fastening points.
In addition to the above main disadvantage of square pillars, others should be noted:
- The complexity of installation increases: in addition to ensuring verticality, you need to ensure that one face of the square is in the same plane with the fence line.
- The high cost of a square pipe - the pipe weighs 30% more than a similar round one, and costs about 35% more
- Presence of a weld seam. Square (rectangular) pipes are produced only using welded technology. Along one side there is a weld along the entire length of the pipe. The pipe begins to actively corrode, and painting practically does not prevent the occurrence of corrosion along the weld.
The logs are attached to such pillars overlapping with two short seams at the top and bottom of the logs. The connection is blown through, easily protected from corrosion by paint and serves long years and decades. Weld seam has sufficient tensile strength (more than 1.5 tons per joist). This is 15 times the load caused by storm winds (25 m/s, for a fence 2 m high with a post spacing of 2.5 m). Due to the fact that the logs are not cut, the strength structure of the fence is as rigid as possible and prevents an individual post from protruding from the ground. The pillar, in fact, is kept from protruding by two neighboring ones.
The most optimal, perhaps even the best, solution is to use fence posts made from tubing pipes. It is thick-walled and seamless, made of high-strength steel (yield strength reaches 116 kgf/mm2, which is 5.5 times higher than that of conventional pipes). Due to the high strength of steel, such poles are much stronger than a comparable square one, and cost about 2 times less. Fences with a height of 4 meters or more can be installed on tubing poles!
Prices for tubing poles and other materials for fence construction:
The best reasons are metal pipes for the fence - durable, easy to install and durable. On metal frame You can easily fix any fencing material - wood, profiled steel sheet, mesh, cellular polycarbonate, asbestos or cement-bonded sheets.
Budget developers are often stopped high price metal However, comparing the service life metal fence with wood, you will see the opposite.
Metal poles and the veins will last at least 50 years while wooden frame During this period you will have to replace the fence 3-4 times with all the associated costs.
From the point of view of science that studies the resistance of materials (resistance), the most advantageous is the circular cross-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 posts and purlins are more convenient to cut and join by welding. Flat surface contact allows you to fix all elements of the fence more tightly and rigidly than a round one.
As we have already said, a round pipe with the same weight is stronger than a profile pipe in bending. Therefore, if you decide to buy round fence posts, you will save 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 using 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 rotting.
Concrete is a more reliable option. But when installing such a structure, difficulties arise with fastening the purlins.
Drilling a reinforced pole is not easy, and not all developers can install embedded parts in it efficiently.
Great importance has a pitch of fence posts. Optimal - 2.5 meters. In areas 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 cross section of 30x20x2 mm or 40x20x2 mm can be used.
A little about the rectangular pipe
GOST R 54157-2010 "Profile steel 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
The big advantage of steel rectangular pipes is the effective ability to interact with symmetrical surface planes, which can significantly expand the areas of use in general. Rectangular section pipes increases the range of functional orientation of the final raw material product, but it is worth immediately excluding those areas in which pipes with a similar cross-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 external and internal type
– Wide-profile metal structures
– Production of consumer goods
Installation diagram of a tubular frame fence
The profile pipe used for the racks must be turned with its wide side perpendicular to the cladding. This will maximize the rigidity of the posts in relation to the wind, which tends to bend the wide “sail” of the fence.
Unlike a continuous fence made of corrugated sheets, installing a frame made of pipes for a fence made of steel mesh chain-links are less responsible. This design is not afraid of even hurricane winds, because the mesh does not create much aerodynamic resistance.
Here the main task is to ensure the stability of the base, therefore, sufficient penetration into the ground and concreting of the pillars is prerequisites stability of the entire structure.