To meet the basic requirements of long spans, steel footbridges are generally lightweight structures with low stiffness. Moreover, current trends in innovative structural design have led to more vibration problems related to resonance or quasi-resonance of footbridge structures at typical pedestrian walking frequencies. The present authors apply a feasible methodology to assess the vibration performance of footbridges based on an equivalent beam model developed from a detailed finite-element model and experimental measurements. Free- and induced-vibration tests are performed on a long-span inverted-queen-post-truss steel footbridge located in Rio de Janeiro, which exhibits vibration problems. Pedestrian walking simulations are performed with the simplified footbridge model using a typical dynamic load given from a Fourier series, as well as with a biodynamical formulation that considers human–structure interactions. The equivalent beam model provides a practical means of investigating corrective intervention strategies for the problem of excessive footbridge vibration using tuned mass dampers, and allows the in-service footbridge performance to be assessed based on current standards and design guidelines.

Footbridges are generally slender and lightweight structures with low stiffness, designed to support dynamic loads generated by crowds. Therefore, these structures are exposed to vibration problems related to the resonance of human walking step frequencies and the lower vibration modes. To mitigate these problems, one of the most applied corrective strategies is the installation of tuned mass damper (TMD) systems that aim at the vibration reduction of the footbridge’s dominant mode. A fundamental matter in both the footbridge and the TMD design is the pedestrian load modelling, generally considered as a deterministically moving force or a biodynamic model. However, as human gait is a random process, the deterministic models can lead to non-realistic results, directly affecting the TMD system efficiency. In contrast, the use of probabilistic distributions to simulate the human walk randomness can lead to more reliable time series predictions. In this paper, a random walk (RW) algorithm is developed and applied to simulate different crowd scenarios using a simplified plane model of a coupled human-structure-TMD system. In each scenario, the TMD efficiency in reducing the vibration amplitudes is assessed. Results highlight the importance of considering the walking randomness and pedestrians’ dynamic properties in the TMD design.

During drilling operations, the wellhead system and top hole casings shall be designed to support dynamic loads from the connected riser through the BOP stack/LMRP. As dynamic motions are associated to stress variations, fatigue becomes a major concern for designers. The accumulation of damage at the wellhead and close regions is dependent on several aspects, such as the riser components, the interactions soil-conductor and conductor-surface casing, and of course the environmental conditions. Consequently, fatigue analysis involves complex numerical models and requires the simulation of a huge number of loading cases. The present paper aims to estimate the fatigue damage at critical components of the top hole casings and at the wellhead. Two different approaches were investigated. In the first, a global model is analyzed in the time domain (TD), and the Rainflow cycle counting method is used to calculate fatigue damage. The global model includes the drilling riser, wellhead, casings, and interactions between components and with soil. In the second, the same model is analyzed in the frequency domain (FD), and the Dirlik method is used to calculate fatigue damage. Additionally, to allow a better evaluation of stresses at complex geometry regions, forces and moments obtained using the TD methodology were combined with load-to-stress transfer functions, defined by means of a local model and symbolic regression (SR) analysis. The local model includes a detailed 3D model of the pressure housings, and soil-to-casing interaction. The obtained results indicate that the pressure housings are not sensitive to fatigue, and also that the analyses performed are feasible, contributing to reduce computational costs in wellhead fatigue assessments.

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Mooring systems play an important role in the safety of floating production units and must comply with ultimate, accidental, and fatigue limit states criteria defined by design standards and classification societies. However, in the last few decades, many mooring lines failures have been reported in the literature. Most of these were related to fatigue and corrosion degradation in the top chain links, becoming a major concern. Since then, a great effort has been made to improve fatigue assessment methodologies of these elements and to model the effects that are not properly considered in the current design practice, such as the mean tension effect and the chain-link surface roughness due to localized corrosion. The design practice of mooring lines usually assumes a uniform corrosion model with a constant corrosion rate. That way, corrosion degradation is considered only by reducing the net area of the chain-link. As a consequence, effects of stress concentration due to localized pitting are not directly addressed, and this may lead to an unconservative design. The present work aims at assessing the stress concentration associated to chain links with pitting corrosion employing finite element analyses and by comparing the localized pitting against the uniform corrosion stresses conditions in the chain link hotspots. Results highlight that, even for small pits, fatigue damages are higher than considering a uniform area reduction, showing one feasible way of improving the current fatigue design methodologies.