In this study, ambient and forced vibration tests are proposed to evaluate dynamic characteristics of a caisson-type breakwater including natural frequencies and modal damping ratios, and the feasibility of numerical analysis model with fluid-structure-soil interaction effects, which plays an important role to evaluate structural performance and safety, is investigated by comparing the numerical results with experimental results. Oryukdo breakwater in Busan, Korea is utilized as a target structure, and this breakwater was once heightened by installing additional parapet structures as amount of about 4 m to improve the harbor tranquility in 2005. Two times of vibration tests were carried out in 2000 (before heightening) and in 2011 (after heightening). In the first test, most caissons were tested while one caisson was tested in 2011. It is found that natural frequencies are reduced as amount of 1.7-4.3 % after heightening, and similar results are observed from the numerical analysis. It is also found that forced vibration tests can make more reasonable results than ambient vibration tests. Even though there is some degree of discrepancy between experimental and numerical results, numerical analysis can be carried out to analyze dynamic characteristics and evaluate the structural performance and safety.
This paper presents the dynamic infinite element formulations that have been developed for soil-structure interaction analysis both in frequency domain and time domain by the present authors and our colleagues during the past 20 years. Axisymmetric, 2D and 3D layered half-space soil media were considered in the developments. The displacement shape functions of the infinite elements were established using approximate expressions of analytical solutions in frequency domain to represent the characteristics of multiple waves propagating into the unbounded outer domain of the media. The shape functions were determined in terms of the excitation frequency as well as the spatial and material characteristics of the far-field soil region. Thereby the element mass and stiffness matrices are frequency dependent. As for time domain analysis, the shape functions were further simplified to obtain closed-form frequency-dependent mass and stiffness matrices, which can analytically be transformed into time domain terms by the Fourier transform. The proposed infinite elements were verified using benchmark examples, which showed that the present formulations are very effective for the soil-structure interaction analysis either in frequency or in time domain. Example applications to actual soil-structure interaction problems are also given to demonstrate the capability and versatility of the present methodology.
In this study, we focused on a speed-up of KIESSI-3D program, which is based on FE-IE techniques, by introducing a p-version dynamic infinite element method. In order to evaluate performance of the KIESSI-3D, numerical analyses for eight real-scale SSI problems are carried out. We considered three types of KIESSI-3D numerical models whose radii of near-field soil region( )are 1.2, 1.5, and 3.0 times of basemat radius of structure(). In addition, SSI analyses using the SASSI2010 program are carried out used for comparison of accuracy and runtime against those of the KIESSI-3D. Numerical results show that the KIESSI-3D model of 1.2 is enough to give accurate solution. In view of the computing speed, the new KIESSI-3D was up to 25 times faster than the old KIESSI-3D.
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