Bolt Arrangement In Steel Structure

Bolt structure in steel structure

Bolts in steel structures have four main components, including bolt body, bolt cap, nut , and gasketEach component plays an important role in creating a strong connection between steel parts, and these components can be manufactured in a variety of sizes to suit the specific requirements of the project.

1.1. Bolt body

The bolt body is the most important part of the bolt, usually has a circular cross-section and is made of steel. The diameter of the bolt body (symbol: d) range from 12 to 48 mm, with the most common bolt diameter being 20 to 30 mm.

• Internal thread diameter (symbol: do) is the diameter of the threaded part inside the bolt body, and according to the formula due = 0,85d. This means that the threaded portion diameter will be slightly smaller than the overall diameter of the bolt body.
• For bolts half lace (according to DIN 931 standard), the thread length is usually denoted as lo, with the formula for thread length being lo ≈ 2,5d. For this type of bolt, the length of the unthreaded part must be 2-3 mm less than the thickness of the steel plate when performing through-bolt connection.
• For bolts thread (according to DIN 933 standard), the thread length is the length of the bolt, symbol is l. This type of bolt has a common length from 35 to 300 mm.

The exact structure and size of the bolt body is very important because it affects the load-bearing capacity and durability of the steel structure when assembled.

1.2. Bolt Cap

Bolt caps are usually manufactured in the form of a hexagon with beveled corners for easy handling during assembly. The main parameters of the bolt cap include:

• Diameter of circumscribed circle of the bolt head, symbol is D, has the formula D = 1,7d. This means that the diameter of the bolt head is 1,7 times larger than the bolt body diameter (d).
• Bolt head thickness symbol is h, is calculated by the formula h = 0,6d. This means that the thickness of the bolt head is 60% of the diameter of the bolt body.
• Diameter of inscribed circle of the bolt head, symbol is S, is a common size in bolt heads with even numbers, for example S = 12, 14, 16, 18,….

1.3. Nut

Nuts, like bolt heads, are typically hexagonal in shape and are drilled and threaded so that the thread pitch of the nut and bolt body are the same. Important nut specifications include:

• Nut thickness, the symbol is h, conditional h ≥ 0,6d, that is, the thickness of the nut must be greater than or equal to 60% of the diameter of the bolt body.

1.4. Washer

The washer is manufactured in a circular shape and has the function of distributing the pressure of the nut evenly to the surface of the basic steel structure. The dimensions of the washer, including the parameters D, do, lo, and h, is specified based on the diameter of the bolt body (d).When the diameter d The larger the size, the larger the upper dimensions of the gasket also need to be.

The components of steel structure bolts including bolt body, bolt head, nut and washer all have certain sizes and proportions, helping them work effectively in creating strong connections between parts of the steel structure. The selection and arrangement of these components must comply with technical standards to ensure the safety and stability of the project.

2. Types of Bolts in Steel Structures

2.1. Rough Bolt, Normal Bolt

Raw bolts and bolts are usually made from carbon steel through forging and stamping methods. The main characteristic of this type of bolt is that the bolt body diameter is 2÷3mm smaller than the hole of the steel plate, so the accuracy is low. The production process is fast and low cost but the quality is not high. Therefore, when using this type of bolt, the contact between the bolt and the hole is not tight, leading to high deformation during operation, especially when subjected to sliding force.

Application: Coarse thread bolts and bolts are suitable for locating components during assembly or in cases where they are mainly tensile, not subjected to excessive loads.

2.2. Fine Bolts

Fine bolts are made from carbon steel or low alloy steel by turning method, ensuring high precision. The diameter of this bolt does not differ more than 0,3mm from the hole. There are two types of fine bolts: one type is installed in a hole without clearance and the other type is installed in a hole with clearance. The type of fine bolt without clearance helps to create a strong connection, has high load-bearing capacity and little initial deformation.

Application: Fine bolts are used in constructions that require high precision and good load-bearing capacity.

2.3. High Strength Bolts

High strength bolts are made from alloy steel and undergo a heating process to increase tensile strength and tightening ability. These bolts can create large frictional forces between steel plates, helping to transfer force from one structure to another mainly through frictional forces. High strength bolts have very good load bearing capacity, high durability and little deformation.

Application: This type of bolt is very popular in heavy load-bearing structures, especially in structures requiring high mechanical strength such as steel structures subject to dynamic or static loads.

These types of bolts all have their own characteristics and applications, depending on the technical requirements and loads of the project. Rough bolts are suitable for simple assembly work, while fine bolts and high-strength bolts are suitable for projects requiring high precision and strong load-bearing capacity.

3. Ways to Arrange Bolts in Steel Structures

The arrangement of bolts in steel structures must ensure a reasonable distance to both save materials and ensure the durability of the connection. Arranging bolts too close together can make the steel plate easily torn, while if too far apart, the connection will be loose and increase costs. Therefore, it is necessary to have a reasonable calculation of the distance between bolts to ensure the load-bearing capacity and stability of the structure.

There are three main bolt arrangements in steel structures:

1. Parallel layout
   The bolts are arranged parallel to each other in straight rows. This method is often used in structures that require uniform load-bearing capacity over a large area.
2. Staggered layout
   Bolts are arranged in a cross- or staggered pattern between rows, which helps to increase the distribution of force more evenly and reduce the risk of connection failure under load.
3. Bolt arrangement for steel profiles
   The arrangement of bolts in steel profiles will depend on the size of each type of steel profile. Specifically, for angle steel:
   • If the width (symbol b) of the angle steel is less than 100 mm, only 1 row of bolts needs to be arranged.
   • If the angle steel width is greater than 100 mm, 2 rows of bolts will be required to ensure the stability of the connection.