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The square concrete deck is being used as an elevated transition piece in offshore structure but has a large exposure area to extreme waves. This study focused on the horizontal wave-in-deck loads on the square concrete deck. Wave flume tests were carried out to investigate the wave-in-deck loads on a specimen of a square concrete deck. Horizontal wave-in-deck loads on the specimen with ten different structural orientations were measured under three nonlinear regular wave trains. A novel analytical model of the horizontal wave-in-deck loads on the square thick deck was proposed by including both impact maxima and pulse shape function. The temporal development of the resultant horizontal wave-in-deck loads was studied from the measured forces through data post-processing. The effects of structural orientation, inundation depth, and the correlation between the rise and decay time were considered based on the experimental data. The marginal distributions of the impact maxima and rise time for the horizontal wave-in-deck loads on the square deck were investigated, and the joint probability model of impact maxima and rise time was finally developed using Plackett copula. The research provides a useful stochastic model in assessing the wave-in-deck loads on the square concrete deck.

Grounding grids are widely used in substations to maintain the safe operation of operators and power apparatus. In this paper, an electromagnetic ultrasonic technique is proposed to diagnose the degradation of grounding grids. Firstly, the propagation of guided waves in an infinite plate is studied. It is shown that the lower shear horizontal wave (SH0) has several unique features that are attractive for long-range non-destructive testing (NDT). Secondly, the propagation of guided waves in a rectangular section bar is investigated experimentally. It is found that the SH0 wave excited by an electromagnetic acoustic transducer (EMAT), compared to a Lamb wave excited by a piezoelectric transducer, has a more powerful transmission capability in a rectangular section bar. Thirdly, SH0 wave experiments are conducted on plates with different widths; it is found that the variation in width has little influence on the propagation of the SH0 wave when the width of the plates is greater than the width of the EMAT transducers. Fourthly, experiments are conducted on a rectangular section bar in the laboratory to investigate the sensitivity of the SH0 wave to defects and the surrounding environment. It is found that SH0 wave testing offers an effective way to evaluate the health condition of a rectangular section bar. Finally, the proposed technique is applied to the NDT of a grounding grid in the field.

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