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MindMap Gallery Steel structure connection-1

Steel structure connection-1

This is a mind map about the connection of steel structures-1, including the basic knowledge of welding connections, the design of fillet weld connections, the design of butt weld connections, etc.

Edited at 2023-11-15 22:36:27

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Steel structure connection-1

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Outline

steel structure connection

3.1 Basic knowledge of welding connections

3.1.1 Characteristics of welded connections: Advantages: simple structure, economical use of materials, convenient production and processing, and good link sealing. Disadvantages: The bearing capacity of the pressure-bearing structure is reduced, and the welded structure is very sensitive to cracks.

3.1.2 Form of welding connection:

Fillet welds: according to different cross-sectional forms: divided into right-angle fillet welds and bevel fillet welds

Butt weld: According to the force and weld position of the butt weld, it is divided into right angle weld and bevel angle weld.

3.1.3 Representation of weld symbols: generally consists of basic symbols and guide lines, and supplementary symbols and weld dimensions if necessary.

3.1.4 Welding position: According to the welding position, it can be divided into flat welding, horizontal welding, vertical welding and overhead welding.

3.1.5 Welding method: arc welding is often used for steel structures

Advantages of arc welding: simple equipment and easy operation. Disadvantages: low production efficiency, high labor intensity, unstable weld quality

Commonly used welding rod models in steel structures are E43, E50, and E55, and E represents the welding rod, and the two subsequent letters represent the minimum tensile strength.

3.1.6 Weld defects and inspection:

Weld defects: For example, the chemical composition of the steel is inappropriate, the welding process conditions are unreasonable, and the surface stains are not cleaned

Weld inspection: The existence of weld defects will weaken the stress area of the weld, cause stress concentration at the defect, and affect its impact toughness and cold bending.

3.2 Design of fillet weld connection

3.2.1 Working performance of fillet welds

Side fillet welds: mainly bear shear stress, low strength, but good plasticity

Front fillet weld: complex stresses, both normal stress and shear stress

Oblique weld: The mechanical performance and strength value are between the front fillet weld and the side fillet weld.

3.2.2 Basic formula for calculating the strength of right-angle fillet welds

Use page 34 (3.1) (3.2) (3.3) in the book to calculate its tensile strength and design value, as well as the stress on a right-angled side.

The basic formula for calculating the strength of right-angle welds is in the book p35 (3.7), and the right-angle welds and side fillet welds are calculated using (3.8) (3.9) of the book p35, and the fixed-value strength increase coefficient of the front angle is 1.22.

3.2.3 Calculation of bevel fillet welds: Use the formula on page p35 (3.10) of the book

3.2.4 The grade of the fillet weld should be changed: the specified quality is generally grade three, and only the grade two that meets the appearance of the fillet weld is used.

3.2.5 The structure of the fillet weld needs to be improved: In order to avoid basic over-burning of the weld and reduce the welding residual stress and weld deformation of the weldment, when the thickness of the plate is >6mm, it is not easy to weld to the full thickness according to welding experience. Of course, hf < t minus (1-2) mm, when t ≤ 6mm, use a small electrode for welding, and it is easy to weld to the full thickness, then hf is less than or equal to t.

3.2.6 Application example of right angle fillet weld connection calculation:

Three-sided surround welding: Use (3.13 calculation) on page 39 of the book. To find the balance conditions for the fillet welds on the back of the angle steel limb and the side of the limb tip, use (3.14) (3.15) to calculate

Side welding on both sides: Use (3.14-3.17) on page p40 to calculate the calculated length of side welding on both sides.

3.3 Design of butt weld connection

3.3.1 Connection design of penetrating butt welds: For tensile grade three welds, use page p45 (3.37) for strength verification, and subtract the thickness of one arc strike plate from one defect, and subtract n lengths from n defects.

3.3.2 Examples of butt weld connection applications:

Butt welds of steel plates subjected to bending and shear: To meet its strength, use (3.39) and (3.40) on page p46 to check

Butt welds subjected to the combined effects of bending, shear and axis are still calculated using (3.40)

3.3.3 Partial penetration butt weld connection design: For butt welds with small stress, it is not necessary to fully penetrate. In this case, partial penetration butt welds can be used. The butt weld opening is divided into V-shape. , U-shaped, J, K-shaped.

3.4 Weld residual stress and welding deformation

3.4.1 Classification of welding residual stress:

Longitudinal welding residual stress

Transverse welding residual stress

Welding residual stress in thickness direction

3.4.2 Effect of welding residual stress on structural performance:

Effect on the static strength of the structure: Under the action of static load, the welding residual stress will not affect the structural strength, and the welding residual stress will not affect the static strength of the structure.

Impact on structural strength: The presence of welding residual stress in components will reduce the strength of the structure.

Impact on low-temperature work: Reducing welding residual stress in the weld is one of the measures to improve low-temperature cold brittleness performance

Effect on fatigue strength: Welding residual stress has obvious adverse factors on the fatigue strength of the structure.

3.4.3 Forms of welding deformation: shrinkage deformation, lateral shrinkage deformation, bending deformation, angular deformation, and twisting deformation.

3.4.4 Methods to reduce welding stress and welding deformation:

Reasonable arrangement of welding positions

Proper weld size

Welds should not be too concentrated

Steel plate butt joints adopt segmented de-welding

Steel plate splicing adopts block splicing

Use anti-deformation

3.5 Basic knowledge of bolted connections

3.5.1 Forms and characteristics of bolted connections:

Ordinary bolt connections: Commonly used 4.6 grade C grade ordinary bolts are taken as an example) 4 indicates that the minimum tensile strength of the bolt is 300Mpa, 6 indicates the yield ratio, and the ratio of yield strength to tensile strength is 0.6.

High-strength bolt connection: Advantages: simple construction, convenient disassembly and assembly, high-strength bolt friction type connection performance is good, fatigue resistance, disadvantages: scrap, weakened opening section, high bolt hole processing accuracy and high requirements.

3.5.2 Arrangement requirements for bolts: the principles of neat order, unified planning, and compact arrangement.

3.5.3 Structural requirements for bolted connections: The number of permanent bolts for each rod should not be less than two, and high-strength bolts should be connected and tightly fitted. The connecting plates should be made of steel plates with weak stiffness.

3.5.4 Symbol representation of bolts: Bolt symbols are represented in Table 3.8 on page p55.

3.6 Design of ordinary bolt connections

3.6.1 The working performance of bolts in shear resistance: shown in Figure 3.48 on page p55 of the book.

3.6.2 Shear-resistant connection of ordinary bolts: Its damages include:

Screw rod damaged by shear

Hole wall pressure damage

The board may be pulled apart

Screw punching and shear damage

The calculation formula for the design value of bolt rod shear bearing capacity is as shown on page p56 (3.42) (3.43) of the book.

3.6.3 Tensile connection of ordinary bolts:

The design value of the bearing capacity of a single tensile bolt is: (3.44) on page 57

And ftb=0.8f

3.6.4 Ordinary bolts act together in tension and shear:

Calculation of bolt rod failure in both shear and tension: Use (3.46) on page p57 of the book.

Calculation of hole wall pressure: Calculation using (3.47) on page p58 of the book

3.6.5 Application examples of ordinary bolt connection calculations: In the case of eccentric shear force of the bolt group, the bolt group is simultaneously affected by the combined action of axial shear force F and torque T = fe

Decompose N1t into horizontal component and vertical component, and calculate it using (3.50) (3.51) on page p59 of the book. Finally, when the bolt group is in shear, its resultant force is calculated using (3.52).

3.6.5.3

Ordinary bolt group axial tension: calculated using (3.57) on p60 in the book

3.6.5.5: Ordinary bolt group eccentric tension:

Small eccentric tension: calculated from (3.57) (3.58) on p61 in the book

Large eccentric tension: calculated from p62 in the book.

3.7 Design of high-strength bolted connections

3.7.1 Pretension and anti-slip system of high-strength bolts:

The prestressing force of high-strength bolts is expressed and calculated by (3.60) of p64 in the book

Anti-slip coefficient of high-strength bolts: expressed by (3.10) on page p65

3.7.2 Shear connection of high-strength bolts:

High-strength bolt friction type connection: Calculation using (3.61) of book p65,

Calculation of pressure-bearing type of high-strength bolts

3.7.3 Tensile connection of high-strength bolts:

High strength bolt friction type connection

High-strength bolt pressure-bearing connection

3.7.4 High-strength bolts act together in tension and shear:

High strength bolt friction type connection

The calculation method for high-strength bolt pressure-bearing connections is the same as that for high-strength bolts that bear shear force and tension in the direction of the rod axis: calculation on p67 (3.65) in the book.

3.7.5 Summary of the formulas for the design value of the bearing capacity of a single bolt connection: it can be obtained by looking up the table in the continued table (3.11) on page p68 of the book

3.76 Application examples of high-strength bolt connection calculations:

When using friction type connection

Use pressure-bearing connections