Short Answer:

Riveted joints are subjected to shear when the external forces acting on the plates tend to make one plate slide over the other. The load is transferred from one plate to another through the rivets, which experience a shearing action along their cross-sectional area.

In simple terms, when two or more plates joined by rivets are pulled or pushed in opposite directions, the rivets resist the motion by developing shear stress. Depending on how the plates are arranged, the rivets may be subjected to single shear or double shear conditions.

Detailed Explanation :

Riveted Joints Subjected to Shear

A riveted joint is a type of permanent mechanical joint used to connect two or more metal plates by inserting a rivet through aligned holes and deforming its ends. These joints are widely used in structures like bridges, boilers, and pressure vessels.

When forces are applied on the connected plates, the rivets must transfer the load from one plate to another. In many cases, this load acts parallel to the plates, trying to make one plate slide over the other. This sliding tendency creates a shearing action on the rivets, which is known as shear stress in the rivets.

Thus, a riveted joint is said to be subjected to shear when the external load acts tangentially to the rivet cross-section.

Shear Action in Riveted Joints

When two plates are joined by a rivet and a load is applied, the load is transmitted from one plate to the other through the rivet. The rivet experiences a tangential force along its cross-sectional area that tries to cut it into parts. This cutting tendency is called shear.

The strength of a riveted joint under shear depends on:

• The number of rivets,
• The diameter of the rivets, and
• The shear strength of the rivet material.

The total shear force on a single rivet can be determined by dividing the total load on the joint by the number of rivets sharing the load.

The shear stress (τ) in a rivet is given by:

Where,
τ = Shear stress in the rivet (N/mm²)
P = Force acting on the rivet (N)
A = Cross-sectional area of the rivet (mm²)

The rivet will fail in shear if the applied stress exceeds the shear strength of the material.

Types of Shear in Riveted Joints

Depending on the arrangement of the plates and rivets, rivets in a joint may be subjected to either single shear or double shear.

1. Single Shear:
   • Occurs when two plates are joined by a rivet.
   • The rivet is sheared across one plane only.
   • Example: Single lap joint.
   • In this case, the shear area is equal to the cross-sectional area of one plane of the rivet.

Mathematically,

Where d is the diameter of the rivet.

1. Double Shear:
   • Occurs when three plates are joined together by rivets, where the middle plate is sandwiched between two outer plates.
   • The rivet is sheared across two planes.
   • Example: Double lap joint.
   • In this case, the total shear area is twice the area of one plane, hence the rivet can resist nearly twice the load compared to single shear.

Mathematically,

Example Explanation

Imagine two metal plates joined by a single rivet. When a pulling force acts on the plates in opposite directions, the rivet resists this motion. The upper plate tends to move one way, while the lower plate tends to move the opposite way. The rivet in between experiences a cutting force at the contact plane of the plates — this is single shear.

If an additional plate is placed between two outer plates and riveted, then there will be two such planes where the rivet is likely to shear — this is double shear.

Thus, depending on how the plates are arranged, the rivets carry load in one or two shear planes.

Calculation of Shear Stress in Rivets

The formula used to calculate shear stress is:

Where,

• τ = shear stress in the rivet,
• P = load on the joint,
• n = number of rivets sharing the load,
• A = area of one shear plane per rivet.

In single shear, .
In double shear, .

This relation helps to check whether the rivet can safely resist the applied load without failure.

Failure Due to Shear in Riveted Joints

A rivet may fail in shear when the shear stress exceeds the material’s shear strength. Common reasons include:

• Improper rivet material or diameter,
• Excessive external loading,
• Poor workmanship during riveting,
• Incorrect arrangement of plates.

Shear failure causes the rivet to split into two or more parts along the shear planes. To prevent this, designers ensure that the calculated shear stress remains below the allowable limit for the rivet material.

Design Considerations

To ensure safe operation under shear:

1. Rivet diameter should be selected according to the load and material strength.
2. The number of rivets must be sufficient to distribute the load evenly.
3. Proper alignment of holes and plates is necessary to avoid uneven load distribution.
4. The shear stress must be checked using both theoretical and empirical formulas to avoid overloading.

Design codes usually provide allowable shear stresses for different materials, which must not be exceeded.

Applications of Riveted Joints in Shear

• Bridges: Rivets are used to connect plates and girders under shear forces.
• Boilers: In lap and butt joints of boiler shells, rivets experience shear while holding plates together.
• Aircraft and Ship Structures: Rivets resist shear in lightweight but strong joints.
• Trusses and Frames: Rivets transfer shear loads between members efficiently.

Conclusion

In conclusion, riveted joints are subjected to shear when the applied load acts tangentially to the rivet cross-section, trying to make one plate slide over another. The rivets resist this motion by developing shear stress. Depending on the joint type, the rivets may experience either single shear or double shear. Proper design ensures that the rivets have sufficient strength to resist these shear forces without failure, ensuring the safety and durability of the joint.