To reliably cover a garage door 3 meters wide, the minimum permissible section of a steel corner is a profile of 100x100x8 mm or 120x80x10 mm, provided there is no additional central support. The use of thinner rolled products, for example the common angle 75x75 mm, without installing a vertical post in the middle of the opening will lead to critical deflection of the structure under the weight of the brickwork and can cause destruction of the gate leaves. Engineering calculations show that it is on spans over 2.5 meters that a sharp increase in bending load begins, requiring the use of powerful rolled metal or the introduction of additional reinforcing elements in the form of trusses.
The choice of a specific standard size directly depends on the height of the planned brickwork above the opening and the type of gate itself. If you are building a permanent garage made of solid brick with a wall height above the lintel of more than 1 meter, you absolutely cannot save on metal, since the weight of one linear meter of masonry half a brick thick is hundreds of kilograms. At the same time, for light frame structures or gates made of corrugated sheets, the requirements may be slightly reduced, but the margin of safety should remain significant.
When planning the construction of a garage, many site owners make the fatal mistake of relying on a visual assessment of the thickness of the metal, rather than on calculated bending resistance data. Gate closing - this is not just a decorative element, but a load-bearing structure that must withstand the weight of the wall, wind loads and vibrations when opening heavy doors. An incorrectly selected corner will lead to the fact that after a few months of operation you will notice cracks in the masonry above the opening or, even worse, jamming of the gate due to misalignment of the frame.
The key factor determining which profile to take is the free span length, which in your case is 3 meters. This is a significant distance, requiring a serious approach to choosing rolled metal. Standard solutions for window openings are not suitable here, since the load is distributed differently, and the dynamic effects on the gate frame are much higher. It is also necessary to take into account the method of supporting the ends of the angle on the walls, since the depth of embedding affects the overall rigidity of the system.
Calculation of loads and selection of profile sections
Determining whether what corner do you need? for a specific opening, begins with an analysis of static loads. For a span of 3 meters, the main enemy is the force of gravity of the brickwork, which creates a distributed load along the entire length of the lintel. If we take into account that 10-15 rows of bricks can be erected over the lintel, the total weight per linear meter can reach 300-400 kg, not counting the weight of the metal profile itself and possible snow loads on the roof if the garage is pitched.
To ensure the necessary rigidity and prevent deflection, which is visually noticeable and structurally dangerous, the metal cross-section must have a high moment of inertia. Steel corner works in bending, and its lower flange experiences tension, and its upper flange experiences compression. The use of paired corners, welded with flanges to each other or backs, allows you to create an I-section that resists deformation much more effectively than a single profile.
⚠️ Attention: Using a corner less than 100 mm as a single lintel for a 3-meter opening under a solid brick wall is a violation of building codes and can lead to collapse.
When choosing a material, it is important to pay attention not only to the geometric dimensions, but also to the steel grade. Ideal for construction purposes steel St3sp, which has good weldability and sufficient strength. If you plan to use used rental steel, you must carefully check it for corrosion and residual deformation, since rusty metal loses its load-bearing capacity.
Single corner or twin design
When deciding which profile to use, many are faced with a dilemma: install one powerful corner or use two smaller sections. For a span of 3 meters, the most rational and reliable solution is to use paired corners. This design, often called a composite beam, distributes loads more evenly and simplifies installation because two lighter angles are easier to lift and install by hand than one solid beam.
There are two main ways to connect corners into a single beam. The first option is to weld the corners with flanges to each other, which forms a closed box-shaped profile. The second, more common option is back welding, which creates an analogue of an I-beam. The second method is preferable for brick garages, as it allows you to easily lay bricks between the shelves of the corners, ensuring perfect binding and eliminating the formation of cold bridges.
- 🏗️ Twin angles 80x80x8 mm provide sufficient load-bearing capacity, subject to high-quality welding and the absence of high dynamic loads.
- 🔩 A single corner 120x120x10 mm can be used, but requires special equipment for lifting and installation due to its heavy weight.
- 🛡️ A composite beam made of two corners 100x100 mm is superior in reliability to a single profile of similar mass due to stress distribution.
To do this, they are welded every 50-70 cm with transverse plates or a continuous seam, if access allows. This prevents delamination of the beam and ensures that both elements work together under load. Welds must be made with high quality, without burns or lack of penetration, since they transfer forces from one part of the profile to another.
Load Limit Table
The table shows the approximate permissible deflection load of 1/250 for various sections of angles for a span of 3 meters. The data is for reference only.
Technology for installing lintels in a brick wall
Installing a lintel is a critical step on which the geometry of the entire gate opening depends. Before starting work, it is necessary to prepare support platforms on the walls. The depth of support of the corner on the brickwork should be at least 250 mm on each side for brick garages and at least 300 mm for walls made of foam block or aerated concrete. Failure to comply with this requirement may result in the jumper being turned outward under the action of spacer forces.
The installation process begins with laying the mortar pad on the prepared supports. The corner (or paired structure) is laid on the mortar, after which its horizontalness is checked using a building level. Any distortions must be corrected immediately, since it will be almost impossible to correct them after the mortar has hardened and the laying has begun without the risk of damaging the structure.
☑️ Check before laying
After leveling the metal beam, you can begin laying bricks. It is recommended to lay the first rows of bricks with special care, filling all voids with mortar. If a paired corner is used, laid with shelves up, the bricks are placed between them, which creates a tray effect and prevents the mortar from slipping. During the laying process, it is important not to allow impacts on the structure that has not yet been strengthened, since the mortar gains full strength within 28 days.
To increase the reliability of the structure, the ends of the corners are often additionally fixed in the wall. This can be done by laying the ends into the masonry of the piers or by using anchor bolts if the piers have already been erected. Anchoring prevents longitudinal displacement of the lintel and increases the resistance of the entire doorway system to wind loads.
Strengthening the structure for heavy gates
If you are planning to install a solid metal gate with a wicket door or an automatic sectional door with a heavy drive, a standard lintel may not be enough. In such cases, it is recommended to apply additional reinforcement measures. One effective way is to use farms - a spatial structure made of angles or pipes, which has significantly greater deflection rigidity at the same weight.
A truss for covering a 3-meter opening can be made from a 60x40 or 80x40 mm profile pipe. This structure is welded on the ground in the form of a triangle or trapezoid, and then installed in place. Using a truss allows you to reduce the height of the lintel, which can be important if the height of the garage is limited, and at the same time increase the load-bearing capacity.
| Construction type | Material | Max. load (kg/m) | Weight 1 l.m. (kg) |
|---|---|---|---|
| Single corner | 100x100x8 | ~400 | 12.2 |
| Twin corners | 2x80x80x8 | ~600 | 19.0 |
| Truss (pipe) | 60x40x3 | ~800 | 8.5 |
| I-beam (beam) | №10 | ~1200 | 10.0 |
Another reinforcement option is to install a central support or column in the middle of the opening, if the gate design allows it (for example, for swing gates with a central post). This radically solves the problem of deflection, turning one 3-meter span into two 1.5-meter spans, which allows the use of a much lighter and cheaper rolled metal.
Main conclusion: For a 3-meter opening under a brick, paired corners 80x80x8 or 100x100x8 mm with a support depth of at least 25 cm are optimal.
Protecting metal from corrosion and destruction
The metal lintel, being inside the brickwork, is exposed to moisture, which can penetrate through microcracks in the mortar or condense due to temperature changes. Metal corrosion leads to a decrease in its cross-section and, as a consequence, to a decrease in load-bearing capacity. To avoid this, the corner must be carefully treated before installation. anti-corrosion composition.
The optimal solution is to use rust primers, which can be applied even to slightly corroded areas, followed by painting with oil or alkyd paint. If the lintel is completely hidden in the masonry, one or two layers of high-quality soil are sufficient. However, if part of the corner remains visible or is in contact with the atmosphere, a full paint coating is required.
⚠️ Attention: Do not use nitro paints or other compounds that form a vapor-permeable film, as moisture may accumulate under them, accelerating the rusting process.
Particular attention should be paid to the ends of the corners that go into the wall. It is recommended to weld them or close them with plastic plugs to prevent moisture from getting inside the profile. Moisture trapped inside the corner can expand when it freezes and cause the metal to rupture or damage the adjacent masonry.
Expert advice: For better paint adhesion, degrease the surface of the corner with solvent or Galosh gasoline before treatment.
Common mistakes when installing jumpers
One of the most common mistakes is insufficient support depth. Many builders, wanting to save material or time, seal the ends of the corner by only 10-15 cm. For a span of 3 meters, this is critically small: under the weight of the wall, a significant torque arises, which can tear the jumper out of its socket. The minimum permissible embedment depth for such spans is 25 cm, and better - 30-40 cm.
Another mistake is using metal that is rusty, warped, or too thin. An attempt to save on rolled metal by purchasing a used corner with residual deformation or a flange thickness of 5 mm instead of 8 mm can lead to the lintel bending immediately after removing the formwork or starting to lay the top rows. Deflection lintels are unacceptable, as they violate the geometry of the gateway.
- ❌ Lack of level alignment leads to gate skewing and opening problems.
- ❌ Poor quality of welds when assembling a composite beam reduces its load-bearing capacity.
- ❌ Ignoring anticorrosive treatment reduces the service life of the structure significantly.
Temperature gaps are also often forgotten. Metal and brick have different coefficients of thermal expansion. With strong heating in summer, the metal lintel can lengthen and put pressure on the masonry walls, causing cracks. To avoid this, a small gap should be left between the end of the corner and the brick in the depth of the wall or a layer of soft insulating material should be laid.
FAQ: Frequently asked questions
Is it possible to use a channel instead of a corner to cover 3 meters?
Yes, a channel (for example, No. 10 or No. 12) is an excellent option for covering a 3-meter opening. It has a high moment of inertia and resists bending well. However, a channel is heavier than an angle and may cost more. When using a channel, it is important to correctly orient its flanges (usually down or up, depending on the method of laying the brick) and ensure reliable support.
Is it necessary to make a concrete lintel over a metal corner?
In most cases, garage doors do not require a separate concrete lintel on top of the metal angle, as long as the angle is selected correctly. The metal profile takes on the main load. Concreting may be required only in specific cases, for example, when the height of the masonry above the opening is very high or when using lightweight aerated concrete blocks that do not hold the bearing load well.
How to calculate the number of corners if the masonry is 2 bricks?
When laying 2 bricks (51 cm), the load on the lintel doubles. In this case, the use of single corners, even of large cross-section, is not recommended. It is best to use a paired structure of powerful corners (100x100x10 or more) or use a ready-made reinforced concrete lintel in combination with a metal corner to support the outer layer of brick. You can also consider installing a central support.
What to do if the corner still bends after installation?
If the deflection is small and the masonry has not yet been erected, you can try to straighten the corner using a jack and stops, after preheating the bend (if the thickness of the metal allows). However, the safest thing to do is to strengthen the structure: weld additional reinforcement or profile pipe from below, creating a truss, or install a central vertical post that will split the span into two parts.