An analytical solution of the dynamic response of offshore wind turbines under wave load with nonlinear Stokes’s wave theory and wave–structure and soil–foundation interactions is developed. Natural frequencies and the corresponding modes are obtained. The effect of the wave–structure interaction, the added mass, the foundation stiffness, and the nacelle translational and rotational inertia on the motion of the structure is investigated. The nonlinear loading provided by the drag term of Morison’s equation is successfully handled. A parametric study to examine the effect of the structural parameters on the dynamic response is conducted, and the results of the proposed analytical solution are compared to numerical ones. The proposed method has the following advantages: (a) it is accurate and straightforward because of its analytical nature, (b) it does not ignore the drag term in the wave loading by keeping its nonlinearity nature, (c) the structure of the wind turbine is modeled as a continuous system, (d) it takes into account the effect of the rotational and translational inertia of the nacelle on the dynamic response, and (e) it provides an interpretation of the effect of the sea level variation in changing the natural frequencies.

(C) 2015 The Author. Published by Elsevier Ltd in Case Studies in Engineering Failure Analysis, vol. 4. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).The bridges experience increasing traffic volume and weight, deteriorating of components and large number of stress cycles. Therefore, assessment of the current condition of steel railway bridges becomes necessary. Most of the commonly available approaches for structural health monitoring are based on visual inspection and non-destructive testing methods. The visual inspection is unreliable as those depend on uncertainty behind inspectors and their experience. Also, the non-destructive testing methods are found to be expensive. Therefore, recent researches have noticed that dynamic modal parameters or vibration measurement-based structural health monitoring methods are economical and may also provide more realistic predictions to damage state of civil infrastructure. Therefore this paper proposes a simple technique to locate the damage region of railway truss bridges based on measured modal parameters. The technique is discussed with a case study. Initially paper describes the details of considered railway bridge. Then observations of visual inspection, material testing and in situ load testing are discussed under separate sections. Development of validated finite element model of the considered bridge is comprehensively discussed. Hence, variations of modal parameters versus position of the damage are plotted. These plots are considered as the main reference for locating the damage of the railway bridge in future periodical inspection by comparing the measured corresponding modal parameters. Finally the procedure of periodical vibration measure- ment and damage locating technique are clearly illustrated

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.