Investigation Of Rotary Inertia Effect For The High-rise Structures Under Seismic Loads

This paper focuses on investigating the effects of rotary inertia on the seismic response of the high-rise structures. The calculation formulas for inter-storey(or inter-segment) shear force and bending moment are established by considering the bending, shear and axial deformation of the high-rise structures. The calculation model, investigated lump and its kinetic equilibrium equations are established. By using the formulas and the equilibrium equations recursively in the time domain, the numerical methods are presented respectively for the elastic and elastoplastic analysis of the high-rise structures with or without the rotary inertia being considered. The accuracy and applicability of the present approach are verified by comparing the results with the finite element method.According to the division standard of the soil type by USGS (United States Geological Survey), the main earthquake records retrieved from the PEER web site are used as seismic loads for inputting. For elastic analysis, according to the Chinese Seismic Code (GB50011-2001), the PGA of the horizontal excitation is scaled to 0.2g, and the PGA of the vertical excitation is 0.65 times of the horizontal PGA. For the elastoplastic analysis, the peaks of horizontal and vertical seismic accelerations are all taken the real recording.The seismic responses of three typical high-rise structures are analyzed under the horizontal and vertical earthquake. The spatial distribution of maximum inter-segment shear force, bending moment and seismic normal stress are respectively investigated by the elastic analysis of the 210m RC chimney and the Nanjing TV tower when the rotary inertia is considered and ignored. By the elastoplastic analysis of the 24-storey frame, the absolute maximum inter-storey shear forces are compared and the spatial distribution of yield-storey is respectively investigated for the cases of with and without rotary inertia.The influences of plastic stiffness coefficient on yield-storey are discussed. The vertical seismic load and the forces of the columns are also analyzed.In addition, the influences of the vertical force in the structural geometry stiffness on the horizontal responses are studied respectively for three structures.The numerical results demonstrated that the rotary inertia had significant effect on the seismic responses of high-rise structures. For the tall chimney and TV tower, the rotary inertia can increase the inter-segment shear force, bending moment and seismic normal stress. For the high-rise frame structures, the number of yield storey obtained by considering rotary inertia is less than it obtained by ignoring. The vertical seismic load and the structural dead load possess a little influence on the inter-storey shear force caused by horizontal seismic load. The columns of high-rise frame structure can be in the state of tension when the structure is subjected to severe vertical seismic load. The effects of rotary inertia in the anti-seismic calculation of high-rise structures should be considered.