This study proposes a steel plate retrofit method and a polyurea method to improve the structural stability and usability of a factory floor slab with a thickness of 120mm. To assess vibration changes, vibrations were measured before and after retrofit. A numerical analysis model was also developed to evaluate improvements in structural safety and usability. The natural frequency increased from 11.4Hz to 17Hz through steel plate reinforcement, confirming an increase in slab stiffness. The damping ratio increased from 2.3% to 3.2% with polyurea reinforcement, indicating improved vibration reduction. Additionally, numerical analysis modeling showed that the natural frequency increased from 13.9Hz to 16.2Hz due to the steel plate reinforcement, enhancing the dynamic characteristics of the floor slab and confirming the reliability of the analysis model.

Steel plate concrete (SC) composite structure is now being recognized as a promising technology applicable to nuclear power plants as it is faster and suitable for modular construction. It is required to identify its dynamic characteristics prior to perform the seismic design of the SC structure. Particularly, the damping ratio of the structure is one of the critical design factors to control the dynamic response of structure. This paper compares the criteria for the damping ratios of each type of structures which are prescribed in the regulatory guide for the nuclear power plant. In order to identify the damping ratio of SC shear wall, this study made SC wall specimens and conducted experiments by cyclic lateral load tests and vibration tests with impact hammer. During the lateral loading test, SC wall specimens exhibited large ductile capacities with increasing amplitude of loading due to the confinement effects by the steel plate and the damping ratios increased until failure. The experimental results show that the damping ratios increased from about 6% to about 20% by increasing the load from the safe shutdown earthquake level to the ultimate strength level.