Anchors for concrete are special fasteners necessary for reliable fixation of various objects and elements on concrete structures. Fastening elements are used where the strength of the walls does not allow the use of screws or nails. Usually, equipment and furniture are attached to walls in this way; they are also relevant for installing doors and windows.
Externally, a concrete anchor looks like a bolt. It is made of galvanized or stainless steel in the shape of a cylinder with a cone-shaped extension at the end of the fastening. The spacer part opens into the concrete after installation and ensures maximum density between the elements and guarantees reliability.
The concrete anchor is installed in a hole of the required size. The high holding capacity of the anchor is ensured by the force of friction, gluing using a special composition, and the interaction of the thrust element with the inner walls of the hole.
Working principle and application
Concrete is a porous material with a heterogeneous structure. And in the places of fastening, various forces appear - twisting, bending, shearing, shearing, compression, tearing. The concrete anchor takes over them, distributing them together with the supporting structure.
Basic principles of operation of concrete anchors:
- At the moment of interaction between the base material and the anchor, a frictional force appears - the expansion is carried out with dowels and metal collets.
- When, at the depth of anchoring, the material provides resistance to fracture or crushing - due to collet bushings on the fasteners, the curved shape of the rod, and expansion.
- Loads at the point of contact between the base and the rod are compensated by tangential stresses during embedding or gluing - this is how smooth, adhesive anchors work.
Anchors for concrete can be of different designs, types, sizes. They are made from special steel according to GOST and coated with a layer of anti-corrosion agent. The rod can be 6-20 millimeters in diameter and up to 220 millimeters long.
Any anchor includes the following parts:
- The bolt itself
- Cone with a layer of thread inside
- Bushing with special cutouts
Anchors perform a constructive or load-bearing function. The load-bearing function is implemented in cases of connecting floor slabs, beams, columns, balcony consoles, landings and flights, finishing and wall panels, engineering equipment, communications, hoods, ceiling lamps, etc. Anchors are also used for installing joists on concrete or hollow-core floors. They are used to attach electrical equipment and hanging furniture to walls.
Structural fasteners are used to counteract the displacement of parts of the assembly if their stability is guaranteed by their own weight; anchors are also relevant when straightening in construction.
Design features
The anchor bolt can have different sizes, but structurally consists of the following main elements:
- threaded rod (has a cone-shaped head at the end);
- outer sleeve;
- lock nut;
- washer.
The inner rod is threaded to established standards and looks like a regular bolt. The main difference is its head. It is made under a cone, which makes it easier to expand the lower part of the sleeve. Its dimensions are determined by the requirements for the reliability of fastening of specific products (their dimensions and weight).
The bushing is made in the form of a cast rod. It has longitudinal slits that resemble petals. Thanks to them, during the fastening process, this part of the sleeve expands, which significantly increases the effect of adhesion of the anchor to the hole. The sleeve is made of metal. Like the entire anchor, it is covered with an anti-corrosion layer. It ensures its durability.
The lock nut has a hexagonal design. Some designs use a nut with a pressed washer.
The operating principle of such a device is to create the effect of reliable fastening in a pre-prepared hole. This can be achieved due to the fact that during the process of tightening the nut of the inserted anchor, the petals of the stud expand. It fits tightly to the walls of the hole, which significantly increases the friction force. The permissible load on the entire structure increases many times over. To prevent excessive deepening of the nut, a special lock washer is used.
To more accurately select the dimensions of the required anchor bolt, a special table has been developed. It shows the dimensions of the products and their main technical characteristics. Before installing the anchor, it is necessary to develop a drawing of the future fastening. With its help, the type, its diameter and length of the anchor bolt are selected.
Types and types of anchors and methods of their fastening
Anchors for concrete can be very different, using one or more acting forces - emphasis, intermolecular bonding during the gluing process, friction, bending, compression, etc. Depending on their purpose, concrete anchors can be frame, ceiling, foundation or universal. In shape - curved and straight, with a prefabricated or solid structure.
The surface of the anchor can be corrugated or smooth. There are different types of fasteners depending on the contact area - those that are used for porous materials and those that are used for dense ones. According to the installation method, anchor fasteners for concrete may involve through connection, gluing, hammering, screwing, etc.
The material from which the hardware is made is of great importance. If it is steel of strength class 6.8 or higher, coated with an anti-corrosion coating, then the fastening will be as strong as possible. But brass will not withstand serious vertical loads.
Spacers
Expansion anchors for concrete are usually used with nuts, here the working force is the friction force. They are a small threaded pin with a cone-shaped tip and a sleeve. When the fastener is screwed into the base, it wedges and firmly holds the fastener in the monolith.
The main advantages of such anchors: the ability to perform through installation, lightness and simplicity of installation, excellent load-bearing capacity. Wedge anchors are chosen mainly for dense concrete; they sink deeply and cannot be used a second time.
If the anchor bolt has a hook (bracket) installed at the end instead of a nut, the mount is suitable for attachments. Wedge anchors come in sleeve and sleeve types. Such a bolt looks like a bushing with special cutouts; at the end it can be made with a stud with a conical extension or a wedging nut. Used for medium and high density substrates. A small contact area, even with a minimum diameter of the product, makes it possible to withstand significant loads.
The anchor bolt with nut can be electrogalvanized (KA), hot-dip galvanized (HAK), and also have acid-resistant properties (KAN). This also includes screw anchors made of stainless steel (RAR).
Drivers
Drive-in concrete anchors are chosen for dense concrete. These are short bolts with an internal cone and metric threads. The fastener wedges the base when a pin or bolt is screwed into the concrete; the fastener does not protrude onto the surface.
Installing anchors in concrete using this type of bolts is relevant when installing ducts, ceiling air ducts, and installing engineering equipment. Before hammering an anchor into a concrete wall, drill a corresponding hole. Then they hammer in the hardware, use a punch-rim to wedge it, and screw in a threaded rod of the required length.
This type of anchor includes a dowel-nail and a ceiling anchor. It is convenient to attach suspensions, slats, and Armstrong ceilings to them. Fasteners are often used as fireproof or vandal-proof, since the bolt is non-removable.
Frame
Used for fastening door and window frames. The sleeve is made with a cut along its length; a small wedging nut, during the tightening process, presses the structure well against the opening, bringing it to the desired position. To protect against displacement and rotation around its own axis, there are stops at the top of the sleeve.
Self-tapping screws for concrete
Here, the reliability of the connection is ensured by threads running along the entire length of the bolt. During the process of screwing into the concrete base, a powerful resistance to tearing or shearing of the product is created. Therefore, when using this type of fastener, a very high load-bearing capacity is observed. The self-tapping screw can easily take up to 100 kilograms of load, is very reliable in operation and easy to install.
Expanding
In everyday life, this type of anchor is called a “butterfly” (aka Molly bolt). Used for mounting cornices, shelves, lamps, paintings and other elements in hollow structures with low load-bearing capacity. The collet on the screw or bolt is made in the form of a wedging skirt, which, in the process of screwing the rod into the base, rests against the inside of the base cavity. On the outside of the collet, special spikes are embedded in the concrete, which prevent the bolt from moving or turning during installation.
Chemical anchor
The anchor bolt for concrete is made in the format of a semi-liquid mass that quickly hardens. It is with this mass that the bolt or pin is glued into the monolith. Thanks to the composition, it is possible to ensure a reliable connection between the base and the bolt without local or point stresses, but with a uniform distribution of the load along the entire length of the fastener.
Chemical anchors for concrete do not provoke internal stress at all, significantly reducing the risk of destruction and deformation.
Features of installing anchors for concrete
The strength of the fastening is affected not only by the quality of the anchor. It is necessary to observe some points that will increase the reliability of bonding surfaces:
- the quality of the material from which the base is made, where the bolt will be fixed;
- preparing the base before installing the anchor;
- length and quality of the fastening element itself.
Anchors will provide maximum strength:
- concrete walls;
- solid brick;
- concrete foundation;
- concrete slabs;
- reinforced concrete foundations.
To select a truly high-quality screw, a number of qualities that it must have are taken into account
Dimensions and characteristics of anchor bolts
Before deciding which anchor is best for concrete in performing specific tasks, it is necessary to consider not only the variety of designs, but also the sizes, because fasteners can be of different lengths and diameters.
Classification of anchors by size:
- Small – cross-section up to 8 millimeters/length up to 55
- Medium anchors – up to 12/120 millimeters
- Large - with maximum dimensions of diameter 24 and length 220 millimeters
An anchor bolt for concrete can have different sizes: the characteristics are determined by three indicators. So, if we decipher the marking M8 10/60-115, then it will be: the diameter of the thread of the anchor M8, the outer diameter 10 (this is the diameter with which the hole for fastening is drilled, this is the diameter of the drill), the length of the anchor is 115 millimeters, the approximate thickness of the element that it is planned to strengthen - 60 millimeters.
All technical characteristics of anchors are indicated in the table, these can be weight, maximum torque and permissible bending moment, minimum pull-out force, optimal loads, distance between axes and to the edge, etc. In accordance with all these parameters, suitable products are selected and high-quality fastening to concrete with anchors is performed.
Wedge anchor
This type of anchorage is most widespread in the construction industry. This hardware is made in the form of a threaded rod with a cone-shaped shank. A spacer coupling is placed on the last element. To install a wedge anchor, a hole with a certain diameter and depth is pre-drilled. The conical shank exerts an impact on the coupling while screwing the nut. And due to the thrust force, it reliably holds the entire fastener in the hole.
Wedge anchors are available in six standard sizes of metric threads. Important technical characteristics corresponding to each position of this parameter are given below in tabular form. Dimensions are indicated in millimeters.
| Thread diameter | Min. pullout force, kN, limits | Anchor hole diameter | Thickness of the object to be pinned | Anchoring depth | Anchor length | Nominal weight 1000 pieces, kg |
| M6 | 1,4…3,2 | 6,0 | 5,0…60,0 | 35,0 | 40…95 | 10,19…19,32 |
| M8 | 1,6…3,3 | 8,0 | 10,0…80,0 | 40,0 | 50…120 | 22,38…42,6 |
| M10 | 4,0…5,0 | 10,0 | 20,0…75,0 | 45,0 | 65…120 | 46…73,4 |
| M12 | 6,0 | 12,0 | 45,0…95,0 | 55,0 | 100…150 | 93,85…128,9 |
| M16 | 7,5…9,4 | 16,0 | 45,0…160,0 | 60,0 | 105…220 | 202…340,25 |
| M20 | 12,3 | 20,0 | 50,0…225,0 | 75,0 | 125…300 | 336…718,75 |
Standardization of the operating parameters of wedge anchors has not been carried out even on the international market. Therefore, their physical properties are largely determined by the technology used by each specific manufacturing enterprise. This also applies to pullout and shear loads. For specifics, we will give an example of these characteristics inherent in wedge anchors from the Finnish company SORMAT, installed in the compressed zone of C20/C25 concrete. The unit of measurement is kilonewtons.
| Thread diameter | Shear load | Pull-out load |
| M6 | 2,0…2,5 | 1,0…1,7 |
| M8 | 3,4…5,7 | 3,3…3,6 |
| M10 | 3,8…10,3 | 3,5…6,3 |
| M12 | 6,4…9,6…13,1 | 6,4…7,9 |
| M16 | 10,0…21,8…25,1 | 9,9…16,7 |
| M20 | 27,7 | 19,8 |
These products are installed using the through-mounting method.
Installation instructions
Before fixing the anchor bolt in concrete, you need to prepare the tools. To complete the work you will need: a wrench, a construction vacuum cleaner, a drill with a hammer function or a rotary hammer, a concrete drill, a hammer.
Drilling
First, the base is carefully marked for future drilling locations. Here you need to do everything as accurately as possible, since after installation it is not possible to remove the anchor bolt from the concrete - the fixation is very strong. Next, according to the markings, holes of the required length are drilled in the concrete (measured along the spacer part of the bolt), installing a limiter on the drill.
The distance from the edge of the wall should be at least 2.5 times the depth of the hole. Next, the holes need to be cleaned with a vacuum cleaner, compressed air from a can, or a rubber blower. If you cannot remove the crumbs without leaving a residue, you can deepen the hole by 1-2 centimeters.
Installation of anchor with nut
The spacer part of the bolt is inserted into the base and driven in with a hammer until it is completely immersed in the concrete (so that the edges are flush with the wall). Then a threaded rod or bolt is inserted, the nut is tightened, twisting as much as necessary so that further turning is impossible.
It is advisable to learn in advance how to use a specific type of fastener. Manufacturers may set the maximum torque, in which case a torque wrench will be needed. Tightening all the way when working with some substrates (aerated concrete, foam concrete) can cause deformation and destruction of the material.
Chemical anchor installation
To install chemical fasteners in concrete, you need a slightly modified set of tools: you will need a hammer drill, a wrench, a construction vacuum cleaner, as well as threaded rods, glue or capsules, and a mounting gun. For a large number of fasteners, glue is chosen; the choice of capsules (ampoules) is relevant where small volumes of work are planned.
First, mark the base, drill and clean the holes. Before pouring the adhesive solution into the concrete, it is advisable to screw in a mesh sleeve, thanks to which the chemical substance will be retained inside. Then you need to fill the holes 2/3 with glue (using a mounting gun) or install the capsules, insert the pin, gradually screwing it in to evenly distribute the adhesive. Now you need to wait until the glue dries and only then tighten the nut with a wrench.
Pros and cons of use
The main advantages of using anchor bolts for concrete are maximum reliability and strength of structures. Anchors can withstand enormous loads and guarantee high-quality fastening in concrete with characteristics that cannot be achieved using other types of fasteners.
The main advantages of concrete anchors:
- Resistance to deformation and corrosion
- Lightness, simplicity and high speed of installation
- Resistance to dynamic and static loads of various types
- Large selection of anchors by length, diameter, type of fastening, load, function, shape, material, etc.
Selecting an anchor bolt for a particular task is not difficult. There are no obvious disadvantages to this type of fastener. Unless you need to remember some features: the importance of accurate markings, the correct selection of drills for concrete and determining the depth of the hole, the need to use a certain set of tools.
general characteristics
Anchors (anchor-type fasteners) are designed for permanent installation in solid, dense, porous and fragile foundations. They are used for hanging heavy equipment or furniture, fixing massive structures to the floor, walls and ceilings with a mineral composition (concrete, brick, foam blocks, etc.). In essence, this is a fastener that is a more durable and reliable alternative to nails with self-tapping screws.
The material for the manufacture of anchors can be adhesive mass, hard plastic or polyamide, metal alloy:
- Aluminum with zinc or brass for use in the domestic sector;
- Structural or carbon steel for increased loads and to ensure a safety margin for the connection;
- Corrosion-resistant or alloy steel with high moisture resistance is also able to withstand heavy loads.
The operating principle of various anchors is based on one of the physical phenomena:
- friction force;
- resistance to fracture and crushing;
- voltage compensation.
Concrete anchor with a ring Source cook.minemshop.ru
The consequences of incorrect installation of the fastener or exceeding the permissible load on the fastener can be of different nature:
- tearing out an anchor or a section of the base used for its immersion;
- violation of the shape, integrity of the bolt or body;
- destruction of fasteners due to corrosion or overheating (melting, burnout).
In order for the “anchor” to work according to the stated scheme, the fastening element must have an internal thread for screwing in the bolt. As a result of its advancement, the functional body expands in the middle or at the end. The chemical group of products works a little differently. Let's look at the types of anchors in more detail.
For foam concrete
Foam concrete is used today in many areas due to its poor flammability, low density, excellent thermal insulation properties and resistance to temperature changes of the material. The structure of the foam block consists of a large number of frozen bubbles. Screws, dowels, and self-tapping screws can be used to fasten the material. The highest level of reliability of foam block fastening is provided by plastic and chemical anchors.
How to install an anchor bolt in concrete
The whole process is quite simple, the main thing is to take the measurements correctly and implement everything as accurately as possible. But there are several nuances that need to be taken into account.
Practical tips for installing anchors in concrete:
- The strength of the fastener is influenced not only by the anchor, but also by the quality of the base material (concrete in this case), proper preparation for installation, taking into account the material of the attached structure and the design of the bolt itself.
- If a layer of finish is applied to the wall, the hole must be deeper because the finish is usually less durable than concrete.
- It is advisable to take a drill 0.5 millimeters thinner than the diameter of the future hole.
- When working with a hammer drill, it is best to use a tip made of a special carbide material.
- Read the instructions carefully - the packaging with anchors should indicate the permissible force and the maximum number of revolutions.
- When screwing the anchor into foam concrete or aerated concrete, under no circumstances twist it all the way, as the material may collapse.
Eternal fastener: concrete dowel
A dowel is a spacer element made of polypropylene or nylon, which is similar in function and performance to an anchor. It cannot be used independently; it is fixed in concrete with special nails or self-tapping screws. To strengthen the fixation, it is often performed with spikes or antennae.
This type of fastening is used where there are not too large loads on the concrete - fastening shelves, TV hooks, lighting fixtures. The dowels are driven into the concrete wall with a hammer, and the screws are screwed in with a screwdriver or screwdriver. You will also need a regular hammer to drive in nails.
You can also find dowel nails designed for use with a mechanical gun. The fasteners in concrete are made of metal; in appearance, they somewhat resemble a bullet. Relevant where you need to hang a large number of small items.
Concrete dowel: fast but durable
Pins are concrete screws that are most often used to install fasteners near the edges of a concrete wall. The fastener does not require additional fixation; it is screwed into the hole, where a little epoxy glue is first poured. There is no need to drill holes - the dowel can be screwed directly into the concrete wall. If you still need to make a hole in concrete, then it is better to choose a drill (a hammer drill can damage the wall).
They screw it in with a screwdriver - and after that it is no longer possible to unscrew the dowel back. Therefore, preliminary marking must be done especially carefully.
What is a concrete anchor: general concept
Previously, only nails and screws were used in construction to secure structures. However, the strength of walls in residential and industrial premises does not always allow working with them. Concrete anchors are often used in fastening furniture and equipment to the walls of rooms. Most often, anchor bolts are used in the installation of windows, doors and heavy equipment.
The anchor is a special fastening element that looks like a regular bolt. It has the shape of a cylinder with a cone-like extension at the end of the attachment. This spacer part opens after installing the anchor in concrete and allows you to create maximum density between the elements and reliability of fastening.
Fasteners such as concrete anchors can ensure reliable fixation of various objects and structures on concrete surfaces
