Seismic incident directionality effect of a bi-degree-of-freedom damped system

The incident direction of multi-dimensional ground motion on the structure is uncertain, which is easy to lead to the incident directional earthquake damage of structures. Existing seismic design methods still cannot ensure the seismic safety of structures in any incident direction. Therefore, the recombination relationship of horizontal ground motion components with respect to the incident direction was studied. The results show that the two orthogonal horizontal components have a complex recombination mechanism after the incident direction changes. This mechanism will be used as the basis for the classification and selection of ground motion. Taking a bi-degree-of-freedom damped system (BDOF-DS) as the object, the spectral response amplification factor (SRAF) prediction model is generated by using a statistical method. This SRAF prediction model is based on the traditional excitation method, considers the uncertainty of the incident direction, and holds an owner-defined confidence level. A large number of parameter analyses are performed on the BDOF-DS using the SRAF prediction model, and the parameters include structural period, biaxial period ratio, damping, and site type. It is indicated that for the influence of incident direction on the structural response (quantitatively characterized by the SRAF), the larger the fundamental period of the structure, the smaller the biaxial period ratio, and the greater the influence degree. The greater the damping ratios of the two axes are, or the closer the two ratios are, the smaller the influence degree is. The influence is basically stable under different site conditions. The SRAF prediction model will be applicable for the multi-dimensional seismic design of structures. © 2024 Science Press. All rights reserved.