This article describes a new method for the design of rectangular foundations in cohesionless soil subject to a combination of vertical and horizontal loads, overturning moments, and torsional moments. It can be seen as a supplement to the general bearing capacity equation in which possible torsional effects of horizontal loads are not included. Torsional effects have had an increasing interest and are common in the design of offshore structures, but onshore structures, such as wind turbines and masts, may also be subject to torsional loads, which can have a substantial effect on the design. The method, which is suitable for hand calculations, applies an equation proposed by Finnie and Morgan for a Tresca material and it is shown that this equation can be used for cohesionless soil for the design of rectangular footings subject to vertical and horizontal forces, overturning moments, and torsional moments. The new method has been compared with those of DNV (DNV: global quality assurance and risk management company in the maritime industry) "Recommendations on offshore soil mechanics and geotechnical engineering" and it is shown that it produces results that are considerably more advantageous than the DNV method. In addition, comparisons have been made with results produced by OptumG3 software, and it is shown that the method leads to safe design. Charts and equations suitable for practical design have been prepared and the equations have been implemented into a computer program, which can be obtained at no cost by contacting the first author.

Søvind Marl, a high plasticity overconsolidated Danish Paleogene clay, is a stiff clay known to exhibit swelling potential. The dependency of its swelling pressure on time is investigated by performing constant volume (CV) tests. Long periods of swelling are applied to the samples. Two samples are allowed to swell for 19 weeks, the other two only for 24 hours. The long-lasting tests show that the swelling pressure reaches the maximum value (σ’ cv ) after 13 weeks of testing, and the change between the σ’ cv and the swelling pressure after 24 hours reaches 38%. In order to correct the underestimation of σ’ cv due to the sampling, a graphical correction of the consolidation curve is made. Due to the characteristic smooth yielding of the Søvind Marl, the graphical correction can be affected by personal interpretation.

While the direct displacement-based design (DDBD) method is commonly developed in seismic design of the single frame and is extensively discussed in the technical literature devoted to this subject, the proper evaluation of this method for dual frames system has received relatively little attention. Considering excellent hysteretic behavior, buckling-restrained braces (BRBs) have been increasingly configured in reinforced concrete (RC) frame to develop the reinforced concrete buckling‐restrained braced (RC-BRB) dual system. The RC-BRB dual frame system is a new lateral-load resisting dual system aimed to minimize the time and costs of repairs after an earthquake. The one of main parameters of the DDBD method is equivalent viscous damping (EVD) proposed to represent the energy dissipation of the system due to its inelastic behavior assumption. Since in the literature no damping equation has been given for the RC-BRB dual frame, the present study aims to provide a reliable EVD equation for the RC-BRB dual system, as well as in the values of the equation verified against real earthquakes, by conducting the nonlinear time-history analysis (NTHA). To this end, first, the numerical model was proposed and validated using the results of the available cyclic test in the literature. Then, the EVD equation of the RC-BRB frames was acquired based on a new method which calibrates the obtained EVDs through nonlinear time-history dynamic analysis of the structures under real earthquake records. The comparison between the calculated results and the corresponding ones acquired from previous equations illustrates that the proposed EVD equation is appropriate for estimating the energy dissipation of the RC-BRB dual frames. Furthermore, the results show that the EVD equations presented so far can conservatively estimate the damping level for the RC-BRB dual frame structures.

Modifications in aged process plants may subject piping systems to fluid transient scenarios, which are not considered in the primary design calculations. Due to lack of strict requirements in ASME B31.3 the effect of this phenomenon is often excluded from piping structural integrity reassessments. Therefore, the consequences, such as severe pipe motion or even rupture failure, are discovered after modifications are completed and the system starts to function under new operational conditions. The motivation for this study emanated from several observations in offshore oil and gas piping systems, yet the results could be utilized in structural integrity assessments of any piping system subjected to pressure waves. This paper describes how to provide an approximate solution to determine maximum bending stresses in piping structures subjected to wave impulse loads without using rigorous approaches to calculate the dynamic response. This paper proposes to consider the effect of load duration in quasi-static analysis to achieve more credible results. The proposed method recommends application of lower dynamic load factors than commonly practiced values advised by design codes, for short duration loads such as shock waves. By presenting a real-life example, the results of improved and commonly practiced quasi-static analysis are compared with the site observations as well as dynamic analysis results. It is illustrated that modified quasi-static solution shows agreement with both dynamic analysis and physical behavior of the system. The contents of this study are particularly useful in structural strength re-assessments where the practicing engineer is interested in an approximated solution indicating if the design criteria is satisfied.

In this paper, we present the ongoing developments of a novel computational model for non-linear water waves that aims to provide a suitable framework for wave-structure interaction. The proposed model is based on radial basis function-generated finite differences, which allow for arbitrary and moving boundaries without the use of ghost nodes. In order to take advantage of the mesh-free setting, we propose a node generation strategy, suitable for moving boundaries. Numerical properties of the proposed model are investigated and finally the model is benchmarked. The proposed model is expected to provide a suitable computational framework for wave-structure interaction problems, due to its geometric flexibility and high-order nature.

The constructive dimension of structures becomes more important today as its inclusion within the digital design process is enabled in novel and disruptive manners, and the question of sustainability encompasses a broader meaning in regards to the material resources. The question of "building light" has fascinated several generation of architects and engineers, and it captures new meaning through sustainability concepts related to material usage, carbon footprint, and embodied energy of a building. Form-finding is one operational approach aiming to determine the (optimal) structural shape from an inverse formulation of equilibrium. However, in the context of built architectural structures, one cannot separate the shape design from the construction design, one being strongly interlinked to the other. The construction process and method have an equally strong impact on the sustainability of a structure. Therefore the authors propose that the determination of the optimality of a built structure should be evaluated globally including material usage, construction efficiency, detailing and construction time. Novel approaches to structural optimization, that encompass material use, construction methods and structural performance are discussed through two case studies: a greenhouse designed to maximize the reuse of a stock of available material, and a reciprocal form finding tool suitable for multi-dimensional search.

Harmonic excitation of structures caused by rotating equipment is a problem faced by many engineers in the field of Operational Modal Analysis (OMA). Several methods to discard the influence of harmonic inputs over systems natural responses has been proposed in the literature and implemented in various software solutions. This paper recalls some of the most used techniques and uses a new time domain method for removing harmonics from measurements. Deployed method does not rely on filtering, statistical detection nor on non-linear fitting. Instead, it predicts the harmonic part of the time series and deploys an orthogonal projection of the latter onto the raw measurements to remove the harmonic part of the signal. The new technique is a part of an semi-automated framework for OMA of structures contaminated with harmonics, whose flow is presented in this paper. The merit of the framework is discussed in the context of OMA of a full scale operating ship with rotating machinery on-board.

In the context of detecting changes in structural systems, multiple vibration-based damage detection methods have been proposed and successfully applied to both mechanical and civil structures over the past years. One of the popular schemes is based on a robust subspace-based residual and enjoys favorable statistical and computational properties, like invariance to changes in the excitation covariance and numerical stability. This paper presents an alternative Gaussian residual that is based on the difference of normalized Hankel matrices between reference and damaged states, which can be easily computed. The statistical properties of the residual are reported and used for efficient hypothesis testing. Its robustness to excitation changes is shown. The proposed scheme is evaluated in numerical simulations, validating its robustness, and tested on real data sets from a full scale bridge.

Environmental and operational variabilities (EOVs) are known to pose an issue in structural health monitoring (SHM) systems, as these variabilities can mask the effect of structural damage. Numerous approaches to remove, or, at least, mitigate, the effect of EOVs in SHM applications have been proposed and tested through numerical simulations and in experimental studies. One of the approaches that has exhibited promising potential is cointegration, which, in this particular SHM context, is a technique for singling out and removing common signal trends stemming from the EOVs. In the present paper, the cointegration technique is employed to mitigate the effect of certain EOVs in an experimental, vibration-based damage detection analysis of a wind turbine blade under operating conditions. In the experimental campaign, the installed SHM system was recording blade accelerations and different environmental and operational conditions over a 3.5-month period. In the period, one of the blades was treated in its reference state and in damaged states with a trailing edge opening of increasing size. Based on the available data from these different structural states, it is demonstrated how cointegration can be used to successfully detect the introduced damages under conditions not allowing for direct discrimination between damage and EOVs.

The constructive dimension of structures becomes more important today as the question of sustainability encompasses a broader scope in regards to material use. The inclusion of construction constraints within the digital design process enable novel design approaches, such as design and construction based on reuse of reclaimed material. Reciprocal structures were used in the past for different purposes, but in this context, it is worth noting their use for solving the practical issue of spanning distances especiallly in slabs when the available elements were shorter than the span. The use of reciprocally connected elements allows defining a set of variables that allows adapting to design constraints and goals related to structure and construction. Computational strategies are investigated to generate layouts that are able to span planar configurations with non-standard reclaimed elements. This work presents an optimization study for the design of standardized structural layouts for floors and/or walls, using the SPEA-II Multi Objective method. A set of geometrical and material parameters are defined for modelling the panel architecture, while competing objective functions are defined related primarily to aspects such as structural lightness and efficiency in construction. The results are presented in the form of Pareto optimal sets, from which conclusions can be drawn for the design of cost effective panels from reclaimed elements.

A presence of a high amplitude periodic signals in the output responses from operating structures often pose a challenge for output-only system identification and, in case of health monitoring, damage detection/localization methods. This paper introduces a pre-processing approach that removes the harmonic part from the output signals directly in the time domain. The new method uses orthogonal projections of the harmonic realization of the signal onto the raw time series within the stochastic subspace framework. Proposed algorithm is tested on two experimental examples. First, an aluminum plate excited with both random white and periodic excitations. Second, a full-scale industrial case of a ferry excited by a random environmental load with harmonic interference from a rotating machinery on-board. In both cases the proposed method removes the harmonics from the structural responses while leaving the random part of the output signal.

Lower bound calculations based on the finite element method are used to determine the bearing capacity of circular and strip foundation on cohesionless soil with varying surcharges and with relative densities in the range 0.30-0.90. Bearing capacities are found without the conservative premise of superposition of the contributions due to selfweight and surcharge. The soil is presupposed perfectly plastic following a failure criterion dependent on the relative density and stress level and the authors see this as an improvement compared to the assumption of a constant friction angle as currently used in Eurocode 7. The results are reported as equations suitable for practical design, giving the bearing capacity as a function of the relative density of the soil, the surcharge ratio and the dimensions of the footing. The bearing capacity of rectangular footings can be determined by interpolation.The results are in good and better accordance with test results than the Eurocode values.

The stability and the dynamic response of the offshore wind turbines can be affected by the erosion of the foundation, referred to as scour. As an alternative to applying costly scour protection, monitoring of scour development is often performed based on a shift in the fundamental natural frequency of the structure. This paper considers scour detection as an outlier detection problem using features that do not require system identification. A state of the structure is classified as healthy or damaged based on three damage sensitive features extracted from the response signals: auto-regressive model coefficients, unique entries of the response covariance matrix and transmissibility functions. The examination is performed using a numerical monopile model supported by Winkler springs and loaded by random excitation. The results show that, among the presented features, the auto-regressive model coefficients display the highest sensitivity to scour, as the use of this feature allows for detection of scour corresponding to 3% of the embedded monopile depth even in the presence of noise.

To protect a pressurized system from overpressure, one of the most established strategies is to install a Pressure Safety Valve (PSV). Therefore, the excess pressure of the system is relieved through a vent pipe when PSV opens. The vent pipe is also called "PSV Outlet Header". After the process starts, a transient two-phase flow is formed inside the outlet header consisting of high speed pressurized gas interacting with existing static air. The high-speed jet compresses the static air towards the end tail of the pipe until it is discharged to the ambiance and eventually, the steady state is achieved. Here, this transient process is investigated both analytically and numerically using the method of characteristics. Riemann's solvers and Godunov's method are utilized to establish the solution. Propagation of shock waves and flow property alterations are clearly demonstrated throughout the simulations. The results show strong shock waves as well as high transient pressure take place inside the outlet header. This is particularly important since it indicates the significance of accounting for shock waves and transient pressure, in contrast to commonly accepted steady state calculations. More precisely, shock waves and transient pressure could lead to failure, if the pipe thickness is chosen only based on conventional steady state calculations.