Strategies for the Seismic Protection of Power Plant Equipment

The present paper shall give some ideas to protect power plant machinery against seismic demands. The elastic support of turbine foundations, fans, boiler feed pumps and coal mills is a well-accepted strategy for the dynamic uncoupling from their substructures and for the vibration isolation. If the corresponding bearing systems are combined with certain strategies an efficient earthquake protection for the important machinery can be achieved. Seismic control may be obtained by increasing the fundamental period or increasing the damping or changing the shape of the fundamental mode of a structure. A combination of these measures could lead to an optimum seismic protection system as described in this contribution. Here, the first step consists of the choice of the required stiffness properties of the flexible support. Helical steel springs possess the possibility of providing a three-dimensional flexibility. Thus, it is possible to obtain a vertically and horizontally acting protection system. Depending on the seismic input the spring properties could be chosen in a specific range. The system frequency can be decreased and simultaneously, the damping ratio can be increased by incorporating viscous dampers at different locations of the spring supported structure. Internal stresses of important members, acceleration amplification as well as deformations due to seismic excitation can be decreased compared to a structure without any precautions. The possible damage after a severe earthquake can be reduced significantly, and the behaviour of the structural members could remain in the elastic range. Details of executed projects and corresponding results of numerical analyses document the effectiveness of the presented seismic protection strategies. Selected pictures demonstrate the general applicability of the applied systems.