How to Calculate Bolt Shear Strength? | MachineMFG

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How to Calculate Bolt Shear Strength?

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Key takeaways:

1. The article outlines the principles of calculating the shear strength of bolted connections, emphasizing that the load on each bolt is determined by the working shear force, and the bolt's ability to withstand this force is contingent on factors such as the bolt's diameter, the permissible shear strength of the material, and the number of shear faces.

2. It provides a detailed methodology for ensuring the structural integrity of bolted connections, including the minimum height of engagement between the bolt and the hole wall (Lmin), and introduces a safety factor to account for uncertainties, thereby ensuring a conservative design approach.

3. The article also serves as a reference for the stress cross-sectional areas of bolts of various sizes (M1 to M39), which are crucial for engineers to calculate the shear stress and design bolted connections that are both safe and cost-effective, as these values directly influence the selection of appropriate bolt sizes for a given application.

Bolted connection under working shear force

As shown in Figure 1-8, this connection uses a bolt to resist the working load F through a punched hole. Assuming each bolt receives an equal working load, the shear force received by each bolt is F.

Therefore, the compressive strength condition between the bolt rod and the hole wall is:

The conditions for the shear strength of bolts are:

In the formula:

F represents the operating shear force exerted on the bolt, in Newtons;

d0 represents the diameter of the shear face of the bolt, which can be taken as the bolt hole diameter, in millimeters;

[τ] represents the permissible shear strength of the thread, in MPa, for steel

, where [S]τ is the safety factor as per Table 1-9;

Lmin represents the minimum height of the bolt rod squeezed by the hole wall, in millimeters.

During design, Lmin should be greater than or equal to 1.25d; i represents the number of shear faces on the bolt rod. In Figure 1-1b, i=2, and in Figure 1-8, i=1.

Figure 1-8: Tight Bolt Connection Undergoing Shearing Stress in Operation

The required shear stress for bolts is typically selected as 60Mpa.

The stress cross-sectional area of M1 bolt: 0.46mm2

The stress cross-sectional area of M2 bolt: 2.07mm2

The stress cross-sectional area of M3 bolt: 5.03mm2

The stress cross-sectional area of M4 bolt: 8.78mm2

The stress cross-sectional area of M5 bolt: 14.2mm2

The stress cross-sectional area of M6 bolt: 20.1mm2

The stress cross-sectional area of M8 bolt: 36.6mm2

The stress cross-sectional area of M10 bolt: 58mm2

The stress cross-sectional area of M12 bolt: 84.3mm2

The stress cross-sectional area of M14 bolt: 115mm2

The stress cross-sectional area of M16 bolt: 157mm2

The stress cross-sectional area of M18 bolt: 192mm2

The stress cross-sectional area of M20 bolt: 245mm2

The stress cross-sectional area of M22 bolt: 303mm2

The stress cross-sectional area of M24 bolt: 353mm2

The stress cross-sectional area of M27 bolt: 459mm2

The stress cross-sectional area of M30 bolt: 561mm2

The stress cross-sectional area of M33 bolt: 694mm2

The stress cross-sectional area of M36 bolt: 817mm2

The stress cross-sectional area of M39 bolt: 976mm2

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