Anchor bolts

Anchor bolts, commonly used fasteners, are widely applied in construction, machinery, electricity, and various other fields. Their primary function is to fix equipment, structures, etc., to the foundation, ensuring the stability and safety of the connection. The following is a detailed introduction from aspects including definition, classification, structural characteristics, materials and properties, application scenarios, installation key points, common problems, and maintenance:

Definition and Function

Anchor bolts, have one end embedded in the foundation concrete and the other end used to connect equipment or structural components. Their core role is to transfer various loads (such as vertical loads, horizontal loads, torque, etc.) borne by the equipment to the foundation through a firm combination with the foundation, preventing the equipment from displacement, overturning, etc., and ensuring the normal operation of the equipment and the safety and stability of the structure. For example, in industrial plants, large machinery needs to be fixed to the ground foundation via anchor bolts to avoid equipment displacement caused by vibrations during operation; in bridge construction, anchor bolts can fix the bridge bearings to the piers to ensure the load-bearing and stability of the bridge.

Classification

By Shape:

• L-shaped anchor bolts: One end is bent at 90 degrees into an L shape. After being embedded in the concrete, they are fixed by the friction and anchoring force of the bent part with the concrete. This type has a simple structure and is easy to install, often used for fixing small equipment or light structures with relatively low anchoring force requirements.
• 9-shaped anchor bolts: Shaped like the number "9", consisting of a vertical section and a horizontal section. The horizontal section is embedded in the concrete, providing good anchoring effect. Suitable for fixing medium-load equipment, such as some medium-sized machinery and steel structure supports.
• U-shaped anchor bolts: U-shaped, with threads at both ends, which can pass through the holes in the equipment base and be fixed with nuts. Mainly used for fixing steel columns of steel structures, pipeline supports, etc., featuring convenient installation and strong adaptability.
• Welded anchor bolts: Usually composed of a screw and a bottom plate welded together. The bottom plate increases the contact area with the concrete, effectively improving the anchoring force. Commonly used for fixing large equipment and heavy machinery, capable of withstanding large loads and vibrations.

By Purpose:

• Equipment anchor bolts: Specifically used to fix various mechanical equipment, such as machine tools, generators, compressors, etc., with different types and specifications selected according to the size and load requirements of the equipment.
• Structural anchor bolts: Used in building structures to connect steel structure components with concrete foundations, such as the connection between steel columns and foundations, ensuring the integrity and stability of the structure.
• Pipeline anchor bolts: Used to fix pipeline supports, preventing pipeline displacement caused by thermal expansion and contraction, medium flow, etc., ensuring the safe operation of the pipeline system.

Structural Characteristics

Anchor bolts generally consist of a screw, a threaded section, an anchoring section, etc. The screw is the main body of the anchor bolt, used to transmit loads; the threaded section is located at the upper end of the screw, used to install nuts and washers for connecting with equipment or structural components; the anchoring section is the part embedded in the foundation concrete, with various shapes (such as the above L-shaped, 9-shaped, etc.) to increase the friction and biting force with the concrete and improve the anchoring effect. For example, the anchoring section of a welded anchor bolt is tightly combined with the concrete through the bottom plate, while the anchoring section of an L-shaped anchor bolt relies on its bent shape to form anchoring force in the concrete. In addition, the length and diameter of anchor bolts are determined according to actual usage needs, usually ranging from tens of millimeters to several meters in length, and there are various specifications in diameter to meet different load and installation scenarios.

Materials and Properties

• Common Materials: The material selection of anchor bolts needs to consider factors such as strength, corrosion resistance, and toughness. Common materials include Q235 carbon steel, 45# steel, 35CrMo alloy steel, etc. Q235 carbon steel has certain strength and toughness and a relatively low price, suitable for anchor bolts in general occasions; 45# steel has higher strength and hardness after heat treatment, suitable for situations bearing large loads; 35CrMo alloy steel has good comprehensive mechanical properties, fatigue resistance, and wear resistance, often used for anchor bolts in important structures or working in harsh environments. In environments with high corrosion resistance requirements (such as coastal areas, chemical plants, etc.), stainless steel materials (such as 304 stainless steel, 316 stainless steel) are also used to make anchor bolts to prevent bolt rust and corrosion and ensure the reliability of the connection.
• Performance Requirements: Anchor bolts should have sufficient tensile and compressive strength to bear the loads transmitted by equipment or structures; they should also have a certain degree of toughness to avoid brittle fracture under impact or vibration; in addition, they need to have good corrosion resistance, especially in humid, corrosive medium environments, to ensure that the anchor bolts will not reduce strength and anchoring performance due to corrosion during long-term use.

Application Scenarios

• Construction Engineering Field: In industrial and civil buildings, anchor bolts are used to fix steel structure components such as steel columns, roof trusses, and crane beams, firmly connecting the steel structure with the concrete foundation to ensure the safety and stability of the building structure. For example, the steel columns of high-rise steel structure buildings need to be fixed to the foundation slab through a large number of anchor bolts to bear the overall weight of the building and horizontal loads such as wind and earthquakes.
• Mechanical Manufacturing Field: The installation of various mechanical equipment is inseparable from anchor bolts, such as machine tools, printing machines, textile machinery, etc. When installing a machine tool, anchor bolts fix the machine tool base to the foundation, adjusting the level and verticality of the machine tool to ensure machining accuracy.
• Power Engineering Field: In power plants and substations, large equipment such as generators and transformers are fixed to the foundation through anchor bolts to prevent the equipment from shifting due to vibrations during operation. In addition, the foundation of power transmission towers also needs anchor bolts to fix the tower feet, ensuring the stability of the tower in harsh weather such as strong winds.
• Bridge and Transportation Engineering Field: Anchor bolts are often used for fixing bridge bearings, guardrails, lighting facilities, etc. For example, bridge bearings are connected to bridge piers through anchor bolts, enabling the bridge to bear forces generated by vehicle loads and temperature changes; the columns of traffic signal poles and expressway guardrails are also fixed to the ground foundation by anchor bolts.
• Chemical and Petroleum Field: In the installation of chemical devices, petroleum storage tanks, and other equipment, anchor bolts are used to fix large equipment such as reaction kettles, towers, and storage tanks. Since the environment in these fields may be corrosive, stainless steel anchor bolts are often selected to improve the reliability and service life of equipment connections.

Installation Key Points

• Preparation Before Construction: Before installation, carefully check whether the specifications, models, and quantity of anchor bolts are consistent with the design drawings, and inspect whether the bolts are damaged, deformed, or have worn threads. At the same time, confirm whether the strength of the foundation concrete meets the design requirements, clean up debris and oil stains on the foundation surface, and ensure the installation surface is flat.
• Positioning and Fixing: According to the requirements of the design drawings, accurately measure the position of the anchor bolts on the foundation, and use a positioning template or bracket to fix the anchor bolts in the correct position, ensuring that the verticality and spacing of the bolts meet the requirements. For example, when fixing the anchor bolts of a steel column, precise control of the bolt position and elevation should be carried out through measuring instruments to avoid difficulties in steel column installation due to position deviations.
• Concrete Pouring: During the pouring of foundation concrete, pay attention to preventing the displacement of anchor bolts. Do not directly impact the anchor bolts during concrete pouring. Stratified pouring and vibration can be adopted to ensure that the concrete is closely combined with the anchoring section of the anchor bolts. After pouring, cure the concrete in a timely manner to ensure the normal growth of concrete strength.
• Equipment Installation and Tightening: After the foundation concrete strength reaches the design requirement, proceed with equipment installation. Align the holes in the equipment base with the anchor bolts, place washers and nuts, and then tighten the nuts evenly. When tightening the nuts, follow a certain sequence, such as diagonal tightening, to avoid equipment deformation or anchor bolt damage caused by uneven force.

Common Problems and Maintenance

Common Problems:

• Bolt Loosening: Factors such as vibrations during equipment operation and temperature changes may cause anchor bolts to loosen, affecting equipment stability.
• Corrosion and Rust: In humid and corrosive environments, anchor bolts are prone to corrosion and rust, reducing the strength and anchoring performance of the bolts.
• Fracture: When the load borne by the equipment exceeds the bearing capacity of the anchor bolts, or the bolts have quality defects, fracture may occur.

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Maintenance Measures:

• ​Regularly inspect anchor bolts to check whether the bolts are loose and whether there are signs of corrosion and rust. Tighten loose bolts in a timely manner; for corroded and rusted bolts, carry out rust removal treatment, and replace them with new bolts if necessary.
• In corrosive environments, anti-corrosion measures can be taken for anchor bolts, such as painting anti-rust paint or using anti-corrosion coatings, to extend the service life of the bolts.
• When the equipment experiences abnormal vibrations or load changes, promptly check the status of the anchor bolts, and deal with problems in a timely manner to avoid equipment failures or safety accidents caused by bolt problems.

In conclusion, although anchor bolts seem to be small components, they play a crucial role in the installation of engineering and equipment in various fields. Understanding knowledge about their classification, structure, materials, applications, installation, and maintenance is of great significance for ensuring project quality and equipment safety operation. In practical applications, suitable anchor bolts should be selected according to specific needs, and installation and maintenance should be carried out strictly in accordance with specifications to fully exert their due role.

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