Determination of Optimal Load-Resistance Factors for Gravitaional Loads-Governed Limit State of Korean Bridge Design Code

Hae Sung Lee, Sang Won Song, Ji Hyeon Kim

ABSTRACT

  This paper proposes a new concept for the estimation of modal damping ratios. This new concept is based on an operational modal analysis (OMA) technique that uses dynamic displacement reconstructed from measured acceleration. The reconstructed displacement physically suppresses the high-mode components in measured acceleration data and leads to modal participant factors that are sequentially arranged from low- to high-frequency modes. Thus, compared with the conventional approach that utilizes acceleration data, the proposed procedure provides a more reliable and robust damping estimate regardless of the model order selection. Furthermore, the use of reconstructed displacement guarantees the equilibrium of the system all the time. The OMA adopts a natural excitation technique (NExT) combined with an eigensystem realization algorithm (ERA). A finite element method (FEM)-based finite impulse response filter is adopted to reconstruct the dynamic displacement. The effectiveness and accuracy of the proposed approach is demonstrated for low-frequency dominant structures by using the numerical simulation study of a 9-story shear building and an actual field test of a cable-stayed bridge under operation in Korea. These examples allow a comparison of modal damping ratio estimates using reconstructed displacement and accelerations.

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