Research on modal combination coefficients considering the spectral characteristics of strong ground motion

• Published in: Soil dynamics and earthquake engineering (1984) Vol. 183; p. 108762
• Main Authors: Shi, Luwei, Peng, Lingyun, Zhang, Ruhan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2024
• Subjects: Modal combination; Modified Kanai-Tajimi spectrum; Narrow bandwidth; Random vibration; Spectrum characteristics; Spectrum characteristics; Modal combination; Narrow bandwidth; Modified Kanai-Tajimi spectrum; Random vibration
• ISSN: 0267-7261; 1879-341X
• DOI: 10.1016/j.soildyn.2024.108762

To address the limitations of traditional complete quadratic combination (CQC) modal combination coefficients in calculating ground motions with narrow bandwidth and long periods, a revised methodology is proposed. The new CQC modal combination coefficients are formulated by considering the spectral characteristics of strong ground motion, taking the modified Kanai-Tajimi spectrum model as a prerequisite, and applying random vibration theory. Simultaneously, a random phase simple harmonic process model for a single harmonic component is established, and corresponding combination coefficients are provided. The necessity and rationality of considering the spectral characteristics of strong ground motion are demonstrated from three perspectives: differences in power spectral models, variations in combination coefficients, and the inherent combination mechanism. As an illustrative example, the layer shear model is analyzed and compared with the results of the structure's modal combination taking different combination coefficients. This comparison is conducted under the influence of long-period simple harmonic waves, four natural seismic waves in the basin, and the 50 natural ground motions suggested by ATC-63, respectively. The results indicate that the modal combination coefficients developed by considering the spectral characteristics of strong ground motions are more reasonable and can serve as a viable replacement for traditional CQC combination rules. This is especially advantageous when dealing with ground motion inputs characterized by narrow bandwidth and long periods, providing significant benefits in such scenarios. •New modal combination rule considers the spectral characteristic of the ground motion.•Derived modal combination coefficients based on random vibration theory.•New modal combination rule reflects a more reasonable combination mechanism.•New modal combination rule can obtain higher accuracy in handling narrow band inputs.•New modal combination rule is applicable to frequency inputs of any bandwidth.