Introduction
In the analysis of riveted joints, various assumptions are made to simplify the calculations and determine the behavior of the joint. However, it is important to identify which assumptions are valid and which are not in order to ensure accurate analysis and design.

A) Centroid of rivet group is at a distance of t mm from the axis of loading
This assumption is true in the analysis of riveted joints. The centroid of the rivet group is generally considered to be at a distance of t mm from the axis of loading, where t is the thickness of the plate being joined. This assumption simplifies the calculations by assuming that the entire load is applied at a single point, making it easier to determine the distribution of forces and moments within the joint.

B) Bending of the rivets is neglected
This assumption is generally true in the analysis of riveted joints. Rivets are designed to resist shear forces, and their bending stiffness is usually much higher than the bending forces they experience. Therefore, the bending of rivets is often neglected in the analysis. However, in certain cases where the bending forces are significant or the joint is subjected to cyclic loading, the bending of rivets may need to be considered.

C) Rivets completely fill the holes
This assumption is generally true in the analysis of riveted joints. Rivets are designed to fit snugly into the holes and create a tight connection between the plates. This assumption simplifies the calculations by assuming that there is no gap between the rivet and the hole, allowing for a more accurate determination of the forces and moments within the joint. However, in reality, there may be some clearance between the rivet and the hole, which can affect the behavior of the joint.

D) Applied load is resisted equally by all the rivets
This assumption is not true in the analysis of riveted joints. The load distribution among the rivets in a joint is not equal due to variations in the contact conditions, material properties, and manufacturing tolerances. Therefore, the load is not resisted equally by all the rivets. The distribution of forces and moments among the rivets needs to be determined based on the joint configuration, geometry, and loading conditions.

Conclusion
In the analysis of riveted joints, it is important to understand the assumptions made and their validity. While the centroid of the rivet group is generally assumed to be at a distance of t mm from the axis of loading and the bending of rivets is often neglected, the assumption that rivets completely fill the holes and that the applied load is resisted equally by all the rivets is not true. These assumptions need to be carefully considered and their impact on the behavior of the joint should be evaluated for accurate analysis and design.