Effect of Damage on Natural Vibration Characteristics of Large Semi-cushion Spiral Case Structure

Abstract

A spiral case structure presents various natural vibration characteristics with damage in different degrees in peripheral concrete. The natural vibration characteristics and resonance safety of a large semi-cushion spiral case structure with damage in varying degrees in peripheral concrete are compared and analyzed. For this purpose, a finite element analysis method of vibration characteristics, a four-parameter damage constitutive model of concrete, and spiral case structure of the Ahai Hydropower Station are utilized. Results show that each mode of natural frequency of the spiral case structure declines after the damage in concrete. The extent of the reduction in natural frequency is large when the damage is serious. The mode shapes of the spiral structure are all complex and twisted before and after the damage in concrete. Afterward, however, amplitude increases. After considering the damage, a new possible source of resonance cannot be identified. Resonance checking shows that the damage in concrete cannot seriously harm the Ahai spiral case structure. Therefore, this study provides new reference and support for the production design and safe operation of large semi-cushion spiral case structure.