The need to quickly dismantle and reassemble a metal structure often occurs when organizing a seasonal carport or building a greenhouse in a summer cottage. The collapsible frame from the profile pipe solves the problem of mobility, allowing you to transport the assembled structure on a conventional trailer or even in the back of a truck without the use of heavy special equipment. Unlike welded analogues, such a system requires accurate calculation of loads on the joint nodes, since bolt joints are critical points during wind and snow impacts. Errors in the choice of fasteners or metal thickness lead to deformation of the racks and violation of the geometry of the entire structure in the first year of operation.
The main advantage of using profile-pipe It has a high resistance to torsion and bending at relatively low weight. Rectangular or square cross-section allows you to easily dock elements in one plane, which simplifies the installation of polycarbonate or profnatile skin. However, to create a really reliable collapsible node, it is not enough just to drill holes and insert bolts. Special connectors such as crab systems, flanges or complex docking plates are required, which distribute the force over a larger area of metal. Ignoring this rule leads to local crumpling of the pipe walls around the fastening hole.
Designing such a design begins with the definition of dimensions and the selection of a section of the profile that will withstand the design load without sagging. For spans up to 4 meters, the optimal solution is considered to be a pipe with a cross section of 40x40 mm or 40x60 mm with a wall thickness of at least 2 mm. The thinner metal can be deformed by tightening bolts or under the weight of the roofing material. It is also important to consider the method of anticorrosion treatment, since in drilling and docking areas, the protection is broken, requiring additional measures of insulation from moisture and oxygen.
Selection of materials and calculation of profile cross-section
The foundation of durability of any metal building is the correct selection of raw materials. Profile tube It is made of various steel grades, and for street structures exposed to atmospheric influences, the most suitable steel grade St3sp or St3ps. These materials have sufficient ductility for processing and good weldability, if individual units are still decided to make inseparable. When buying metal at a metal warehouse, it is important to check quality certificates, since a handicrafted profile can have an uneven wall thickness, which is critical for design loads.
The calculation of the cross section directly depends on the width of the span and the step of installing the pillars. If a small visor is enough pipe 20x20 mm, then for a full-fledged carport More powerful beams are needed. Farms that provide roof rigidity are often made of a pipe of smaller cross-section than the main columns to reduce the overall weight of the structure. However, you can not save on material for racks: they take the bulk of snow and wind gusts.
⚠️ Note: The use of a profile pipe with a wall thickness of less than 2 mm for load-bearing columns with a height of more than 2.5 meters is strictly not recommended. Thin-walled metal is prone to local loss of stability (crumbling) in the places of attachment of bolts.
To protect against corrosion, it is best to purchase an already galvanized profile or pipe with a factory polymer coating. If ferrous metal is used, high-quality primer and painting in several layers before assembly is required. Particular attention is paid to the ends of the pipe, which are open gates for moisture, leading to the destruction of the metal from the inside. Cover the ends can be special plastic plugs or brew them if the design allows partial welding.
Types of collapsible joints and fasteners
The key point in creating a collapsible design is the choice of the type of connection that will provide the necessary rigidity and allow you to disassemble the unit repeatedly without losing strength. The simplest option is a cross-plug connection, when one pipe is superimposed on another and fixed by bolts through the wall. However, this method requires precise fitting and often looks unaesthetic. A more professional solution is to use docking-plate Or the cups that are put on the ends of the pipes and tightened by bolts.
For connecting pipes at an angle, for example, when installing roof trusses, special crab systems are used. These are stamped or welded elements of sheet steel, repeating the geometry of the joint. They cover the pipes on three or four sides, providing reliable fixation. When using such elements, it is important to choose the right length of bolts: they must pass through all the walls of the connected parts, but do not protrude too much, interfering with the installation of the skin.
- 🔩 Flange connection: ideal for docking vertical pillars with horizontal beams, provides high rigidity of the unit.
- 🔩 Glass connection: a pipe of smaller diameter or cross-section is inserted inside a larger one, fixed with a bolt, suitable for increasing the length.
- 🔩 Crab systems: universal clamps for cruciate and t-shaped joints, simplify assembly without welding.
The choice of fasteners also plays a critical role. Conventional black bolts quickly rust, so you need to use zinc coated metals (strength class is not lower than 4.8, and for load-bearing nodes - 8.8). Under the head of the bolt and under the nut, wide washers are necessarily installed to increase the area of fitting and prevent the pipe metal from being squeezed during tightening. The use of growers (spring washers) is mandatory to prevent spontaneous unwinding under the influence of vibration.
Tools and training required
Assembly of the frame from the profile pipe with your own hands does not require the presence of complex industrial equipment, but the toolkit should be complete and high-quality. The main tool for cutting metal is a grinding machine (Bulgarka) with metal cutting discs. To obtain a clean roar without barbs, it is recommended to use 1 mm thick discs, although they serve less, but provide better accuracy. An alternative is a metal saber saw, which gives fewer sparks and a more even end.
To drill holes under bolts will require a high-power electric drill or, preferably, a drilling machine. Using a hand tool often results in skewed holes, making it difficult to assemble on site. The drills should be cobalt or with solid alloy braids, as ordinary high-speed steel quickly blunts against the profile pipe. The diameter of the drill is selected 1-2 mm larger than the diameter of the bolt to compensate for possible distortions during installation.
Do not forget about personal protection. Working with metal involves the presence of a large amount of sharp shavings and sparks. Safety glasses, tight gloves and workwear made of non-combustible materials are mandatory. When working at height, if the frame is assembled immediately at the installation site, you will need a reliable ladder or scaffolding. All cutting edges of the pipes after cutting must be cleaned with a file or petal disc to exclude injuries during installation.
Step-by-step instruction for assembling the frame
The installation process begins with the preparation of the base. The racks of the collapsible frame should be based on a flat, concrete or asphalt platform, or on specially prepared foundation blocks. If the frame is installed on the ground, it is mandatory to install concrete "heels" under each rack, which will prevent uneven subsidence of the structure. The first stage is always the installation of vertical supports, which are set strictly in level and temporarily fixed by stretch marks.
After installation of racks horizontal beams and farms are installed. Assembling farms is more convenient to produce on the ground, twisting all elements into a single flat design, and then lift the finished assembly up. This allows you to control the geometry and perpendicularity of the angles. The lifting of heavy farms is carried out with the help of a winch or by several assistants. At this stage, it is important not to tighten the bolts completely, but only to make them in order to be able to adjust the position of the elements.
| Work phase | Action | Reference parameter |
|---|---|---|
| 1. Preparation | Open the pipes, drilling holes, primer | Dimension accuracy ± 2 mm |
| 2. Installation of racks | Vertical installation, stretching fixation | Verticality by plumb |
| 3. Farm assembly | The clumping of the elements on the ground | Planar design |
| 4. Roof installation | Lifting and installing farms on racks | Horizontality of the upper belt |
| 5. Final assembly | Tightening all bolt joints | Moment of key tightening |
The final stage is the final tightening of all bolt connections. It is produced diagonally, starting from the center of the structure to the edges to avoid distortions. After the tightening, the level of all elements is checked again. If the structure is assembled from a galvanized profile, the cutting and drilling sites are necessarily treated with an anti-corrosion composition (for example, zinc-containing paint or "Hummerright") to prevent the development of rust in places of violation of the protective layer.
Structural reinforcement and wind loads
Collapsible structures inherently less rigid than welded, so the issue of wind stability should be given special attention. Wind creates not only vertical, but also horizontal load, as well as the force of separation. To compensate for these forces, diagonal bonds (swings) are used, which turn the rectangular cells of the frame into rigid triangles. Without such connections, the frame can form like a house of cards with a strong gust of wind.
As slanting, you can use the same profile pipe of a smaller cross section or steel cable with tension talreps. Cable stretch marks are lighter and cheaper, but require periodic tension checks. Hard slanting from the pipe is more reliable, but increase the weight and wind sailing of the structure itself. When calculating the number of connections, the construction region is taken into account: in windy areas, the slanting step should be minimal.
⚠️ Attention: When installing a frame in an open area (field, shore of a reservoir), the wind load may exceed the standard calculated values. In such cases, it is recommended to increase the number of attachment points to the foundation.
An important element of strengthening is the correct attachment of the bottom of the pillars to the foundation. Even if the frame is collapsible, its base should be fixed as rigidly as possible. Use anchor bolts, hammered into concrete, or welded plates with holes that are attached to the foundation parts. Only the upper parts of the pillars or spans between the columns remain removable, while the "shmoks" remain fixed forever.
Maintenance and seasonal conservation
One of the main advantages of the collapsible frame is the possibility of its dismantling for the winter period, which is especially important for greenhouses or light canopies in regions with heavy snowfalls. Before disassembly, it is recommended to conduct an audit of all connections: check the bolts for corrosion, replace damaged elements if necessary and lubricate threaded connections with graphite lubricant to facilitate unwinding in the next season.
When storing dismantled elements, it is important to ensure their protection from moisture. Pipes should not be stored directly on the ground; it is better to use wooden pallets or shelving. Farms and long runs are kept in a horizontal position to avoid curvature under their own weight. Small details, such as bolts, nuts and connecting plates, it is better to pack in sealed packages indicating which node they belong to, so as not to waste time in the spring on the selection of fasteners.
In the spring, before assembly, all elements are cleaned of dust and dirt, checked for defects. Particular attention is paid to the places of the previous attachment of bolts: if the holes are deformed or rusted, they are drilled or, in extreme cases, digest new plates. Timely maintenance allows you to operate a collapsible frame from a profile pipe for decades, preserving its functionality and appearance.
Which pipe is better to choose for the frame: round or profile?
For collapsible structures, a profile (square or rectangular) pipe is preferable to a round one. It has flat faces, which greatly simplifies the docking of elements and installation of fasteners. A round pipe is more difficult to connect without welding, requiring special clamps of complex shape. In addition, the profile pipe has a large moment of inertia, which makes it more resistant to bending.
Can I use a used pipe for construction?
Use of used pipe is possible, but requires thorough defects. It is necessary to check the metal for the presence of through corrosion, especially inside the profile. If the pipe was painted, the old paint will have to be completely removed (sandjet or brushes), which is time-consuming. The savings can be questionable due to the cost of preparation and the unpredictable residual life of the metal.
Do I need to cook knots if the frame is collapsible?
In a fully collapsible frame, welding is not used, since it deprives the design of mobility. However, welding of the constituent elements of farms on the ground is allowed if their dimensions allow them to be transported in assembled form. In this case, welded seams are necessarily cleaned and painted to protect against rust.
What is the optimal diameter of the bolts for connecting pipes 40x40?
For a pipe 40x40 mm optimal is considered a bolt diameter of 8 mm (M8) or 10 mm (M10). The M6 bolt will be weak for load-bearing structures, and the M12 may require a too large hole to weaken the pipe wall. It is important to use high-strength bolts (Class 8.8 and above).