Investigation On Spectral Characteristics Of Ground Motion And Its Effect On Dynamic Robustness Of Base-isolated Structure To Resist Collapse

Spectral characteristics,one of the three parameters of ground motion,has great influence on structural damage and progressive collapse.At present,the descri ption of spectral characteristics is not uniform.And the study on the influence regular of spectral characteristics on structural response,damage and progressive collapse is not sufficient.There is no complete theoretical system.Therefore,it is necess ary to study spectral characteristics of ground motion and effect on progressive collapse of base-isolated structures.The main study contents and conclusions are as follows:(1)To study the spectral characteristics of ground motion,single frequency simp le harmonic excitation input traditional structures and base-isolated structures are established primarily by MATLAB.And the effects of excitation frequency,self-vibration frequency and damping ratio on the response of structures are analyzed.Then,According to the concept and calculation formula of "average frequency",61 natural earthquake records are selected based on average frequency.The condition of "resonance" or "pseudo-resonance" of structures and the effect on response for structures are analyzed.Finally,the finite element analysis model of base-isolated structure is established by Perform-3D.The correlation between spectral characteristics and structural damage is discussed.The results indicate that average frequency is better to represent spectral characteristics of ground motion.(2)To study the correlation between spectral characteristics and structural damage,the concept and calculation formula are proposed for structural mode frequency influence coefficient,frequency matching degree of Fourier spectral intensity and magnification factor of pseudo-resonance.The finite element analysis model and the integral damage model of the base-isolated structure are established.The results indicate that the structural damage caused by spectral characteristics is related to the mode frequencies of the structure,and the influence of first mode frequency is significant.With the greater frequency matching degree of Fourier spectral intensity,the greater possibility of structure pseudo-resonance,and the greater the damage index of the isolation structure.Magnification factor of pseudo-resonance reflects the damage degree of the structure caused by spectral characteristics.(3)To study the effect of spectral characteristics on the progressive col lapse of the base-isolated structure,30 earthquake records are selected and divided into different working conditions according to the spectral characteristics.Surmounting probability of base-isolated under slight damage,moderate damage,severe damage a nd collapse caused with spectral characteristics and peak acceleration is calculated respectively by IDA method.By removing seismic isolator from different locations,the ability of the base-isolated structure to resist vertical collapse is analyzed by a robustness evaluation index based on bearing capacity.According to dynamic robustness evaluation index proposed by this paper,the influence of spectral characteristics on the horizontal increment collapse for the base-isolated structure is analyzed.Mean while,the relationship between frequency matching degree of Fourier spectral intensity and dynamic robustness is analyzed.The results indicate that the base-isolated structure has good resistance to vertical collapse when seismic isolator failure with di fferent location.The magnitude of spectral characteristics has great influence on the progressive collapse of the base-isolated structure.The dynamic robustness evaluation index of the base-isolated structure proposed in this paper is reasonable.