Causes of insufficient axial dynamic stiffness or asymmetric stiffness on both sides of split bearing pedestals. Due to poor installation, operation, and structure, the bearing stiffness between the split bearing pedestal and the foundation plate, as well as between the foundation plate and the foundation, is uneven. In the axial direction, some parts have large stiffness, while others have small stiffness or different vertical stiffness between the middle and both ends, which can lead to insufficient axial dynamic stiffness or asymmetric stiffness on both sides, poor stability, and axial deflection (vibration) under the action of rotor disturbance (excitation) forces. Sometimes even when the excitation force is small, large axial vibrations can occur, depending on the degree of insufficient axial dynamic stiffness or asymmetric stiffness on both sides of the split bearing pedestal. The main reasons for insufficient axial dynamic stiffness or asymmetric stiffness on both sides of the split bearing pedestal are:

1. Part of the connecting bolts of the split bearing pedestal or foundation bedplate are loose or the sizing block is loose;

2. Poor contact between the split bearing pedestal base and the foundation platen, such as a small contact area between the base and the foundation platen (not meeting the requirement of more than 75% of the contact area), or only partial point or line contact, or uneven contact parts (Figure 2);

3. The thickness of the cushion between the split bearing pedestal and the foundation platen is uneven or the number of layers is different, and there are problems with the installation process;

4. Some of them are normal and their connections are normal, but they are installed together with a complex structure of the base plate, forming a system with weak axial stiffness. For example, the base plate welded to the exciter of some small units is itself a component with uneven stiffness, with weak axial stiffness.