Probability-based uncertainty evaluation through Markov Chain Monte Carlo sampling and response surface technologies

Inspection of a pre-stressed concrete variable cross-section box girder bridge discovered the phenomenon of padding in expansion joint, corrosion of steel plate and local edge failure in pot type rubber bearing, and cracks of box girder. They are the main sources of structural uncertainty for structural performance evaluation, and how to quantificationally evaluate their influences on bridge performance is important. In this article, an approach using the Markov Chain Monte Carlo sampling technology and the Response Surface Method is proposed to deal with the uncertainty problem. First, a population of finite element (FE) models will be established by sampling the main uncertainty sources through the Markov Chain Monte Carlo technology. Then, the posterior probability of each FE model will be evaluated by using the measured static responses and identified structural dynamic characteristics. Especially, the second order response surface method will be used in this step to improve the computation efficiency. Through the above procedures, probability features of the defined key parameters representing structural uncertainty, including the stiffness of expansion joint, the stiffness of pot type rubber bearing and the elasticity modulus of the box girder will be estimated, which will provide valuable information for reliable structural performance evaluation

Analysis of window structures for super and megayachts

In the last years, after the economic crisis that modified the super and megayacht market and construction, the project focus of shipyards and owners has been moved from the research of higher performances and whimsical exteriors to more classic aesthetics and higher level of onboard comfort. This first aspect has led to the use of larger openings on superstructures\u2019 sides in order to enlarge windows and bring more natural light onboard vessels. The request of more comfortable units has granted a strong effort to find new solutions in order to reduce the noise and vibration level, dealing in particular to the structural elements that with higher noise radiations, such as dampers, pillars and windows. The aforementioned trends is reflected on a more intensive use of glazed windows onboard, that have led to non-trivial problem of both structural response (since the structural component are reduced in order to enlarge opening) and NVH assessment, considering that glued glass panes act as an harmonic speakers, having natural frequencies closed to ones of the main superyacht excitations. In this PhD thesis, the use of glass onboard superyacht has been focused with particular attention to finding new, simpler numerical and experimental procedure to take into account the vibroacustic properties of glass, that are actually ignored by Classification Societies, during their structural scantling and mounting. The proposed simplified methods has been tested also in two different global models, for the assessment of the vertical hull girder vibration at low frequency and for the NVH assessment in the mid-high frequency respectively. Moreover, the role of openings has also been tested from a structural point of view, as a first step of a wider research that should verify the stress transfer mechanisms between metallic structures and glazed windows