Dynamic parameters and seismic response of reinforced concrete shell roofs of unique buildings during long-term operation

This paper investigates changes in the dynamic parameters and seismic response of reinforced concrete shell roofs of unique large-span buildings during long-term operation. The aim of the study is to evaluate how long-term loading, stiffness degradation, support rigidity, and boundary conditions affect the vibration characteristics and structural safety of shell systems subjected to high-intensity seismic actions. The research combines experimental modeling and theoretical analysis. Shell models and full-scale spatial structures were tested under long-term static loading and forced dynamic actions corresponding to design seismic intensities of 7, 8, and 9 points. The study considers free-standing and coupled conical domes, as well as shells of various geometric forms, with attention to oscillation modes, vibration periods, amplitudes, deflections, residual deformations, and crack development. The results show that long-term operation significantly reduces the dynamic rigidity of reinforced concrete shell systems and increases their deflections and residual deformations. A 5.86-fold increase in column rigidity increased the frequency of horizontal oscillations by 74.3 %, while the influence on vertical vibration frequencies remained limited. Long-term loading increased ultimate deflections by 1.5-2 times, fiber deformations by 2.4-2.75 times, and crack development by up to 2 times. A resolving system of equations for shell deformation under nonlinear creep conditions is proposed for assessing the stress-strain state of structures at the operational stage. The obtained results can be used to improve the seismic safety assessment and rational design of reinforced concrete shell roofs in seismic regions.