Studies of natural frequency degradation and the nature of destruction of reinforced concrete frames in case of an earthquake

Abstract

The article presents the results of a numerical study of the impact of local damage to load-bearing structures on the degradation of natural frequencies and the integrity of the structure during an earthquake. The research was carried out using LS-DYNA software complex, which implemented Continuous Surface Cap Model (CSCM), the nonlinear model of concrete. The design model of a reinforced concrete building is modeled using volume finite elements for concrete, and rod finite elements for reinforcement. A two-storey building with a frame structural diagram was chosen as an object of modelling. Studies have shown a significant (up to 22%) decrease in the frequencies of natural oscillations during an earthquake of 8 points intensity. This suggests that damage appears in the structure and overall stiffness of the building decreases. Attempting to estimate damage using the percentage of failed items shows that structural damage exceeds 7%. Analysis of the results shows that the most intense decrease in the frequencies of natural oscillations occurs during the active phase of the earthquake. When the active phase ends, the frequencies stabilize and stop decreasing. The LS-DYNA software package allows to perform studies of the impact of local damage to load-bearing structures on the dynamic properties during an earthquake when concrete is reinforced with reinforcement bars, and can be used in calculations and design of buildings and structures.