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Sinkholes are a severe problem in urban areas located in karstic regions, especially where evaporitic rocks such as gypsum exist. Identification and proposal of mitigation measures are needed to reduce this geo-hazard effect on buildings and social urban living. This paper presents a case study of the town of Alcalá de Ebro (Spain), which is located in the highest sinkhole risk region of Europe. The identification and mitigation of a series of sinkholes that appeared are analyzed. The former involves a geological investigation, including boreholes, field tests and geophysics. The latter is addressed by the use of geogrids, mortar injections and polyurethane injections. A complementary finite element analysis is carried out to set the ground behavior associated with the sinking process and assess its future evolution. The Ebro River appears to be the main cause of sinkholes, and results show that ground treatments applied were successful in their purpose, as there are no apparent deformations indicating that the subsidence or sinking process is still active in the area. The use of different techniques depending on the size of the sinkhole, the objectives pursued and the element affected is discussed. [ABSTRACT FROM AUTHOR]

Ageing infrastructure has been a significant concern for different industrial sectors across Europe. Fatigue cracking is one of the most important damage mechanisms that affect structural health of welded steel structures. Fatigue assessment of welded details in large, complex structures is a difficult and time consuming task. In this paper a numerical framework for fatigue assessment of welded details is presented. In view of industrial applications, automated hot spot stress algorithms for plate and tubular joints were developed and integrated in the framework. The framework provides practicing engineers with an effective tool for fatigue assessment of different components in conformity with leading design codes. Furthermore, apart from Miner’s rule the framework allows easy implementation of different nonlinear damage accumulation models in order to account for load interaction and load sequence effects. [ABSTRACT FROM AUTHOR]

Abstract: Background: Vascular support structures are important devices for treating valve stenosis. Large population of patients are treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved technology in minimal invasive cardiac surgery. This technology now accounts for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and short duration of hospitalization. Methods: This paper discusses the design and finite element analysis (FEA) of a percutaneous aortic valve stent. The stent design was modeled and subjected to FEA. The improved model design was carried out to meet the functional and surgical requirements. Analysis was done with different materials with loads ranging from 50 to 73 kgf/mm2. These forces were selected because these values are far greater than the normal human blood pressure which ranges from 10 to 16 kPa. It was also to understand the mechanical behavior of different stent materials under such high pressures. Results: A stent model was generated and its physical, mechanical, and behavioral properties were studied. Finite element analysis and simulation of the model help the designer to optimize the geometry suitable for performance during and after implantation. The design objective for the stent is to have long-term durability, low thrombogenicity, and resistance to migration and paravalvular leak. Conclusion: The analysis performed in this paper may aid in understanding the stent''s tolerable pressure ranges in comparison with the physiological pressures exerted by the heart and cardiac blood flow during abnormal cardiovascular conditions. It may also help in finding the material that will best suit the stent. [Copyright &y& Elsevier]

• The impact of a pendulum hitting five obstacles with a similar mass is studied. • The studied system models the crash of a vehicle into various anti-terror barriers. • The combination of experiments and FEA highlights the properties the barrier needs. • A powerful mobile barrier should be deformable and use water to dissipate energy. • A ballast made of metals positioned in the lower part reduces the displacement. The most important recent terrorist attacks in Europe consist of vehicles rammed into crowds. The current response to this phenomenon is the adoption of concrete barriers, whose effectiveness is still not clear. The authors of this paper have already designed an innovative mobile anti-terror barrier which combines high performance and good look. This paper explains the most significant concepts which have been used for the design of this new barrier with the help of simple models. In detail, the impact of a pendulum hitting some obstacles with a similar total mass is investigated by means of experimental tests and finite element analysis. The purpose of this study is to identify the best solution which most efficiently stops the impacting object. The results show that a powerful mobile system should be extremely deformable and use water to dissipate energy. A ballast made of metals positioned in the lower part of the anti-terror system helps to reduce the total displacement of the barrier itself. [ABSTRACT FROM AUTHOR]

Multiple scattering of parallel cylinders with arbitrary cross section is computed using the T-matrix of each single scatterer and the general translational matrix for cylindrical waves. Usually, the recommended golden rule to compute the translational matrix is Graf’s addition theorem. However, this approach cannot be properly implemented for some geometries, such as in a two-cylinder case when the center of one of them falls within the minimum circular cylinder that circumscribes the other one. In order to overcome this limitation, a transformation between cylindrical waves and plane waves, followed by propagation of the latter, is proposed. The new approach succeeds due to an adequate truncation of the evanescent plane wave spectrum. This strategy is demonstrated by studying the scattering of three infinite elliptic metallic cylinders for different electrical sizes and observing the convergence of the results as a function of the truncated spectrum. Finally, to conclusively show the interest and applicability of the approach, two more complex problems are treated: a group of infinite elliptic metallic cylinders where two different sizes are combined and a practical real-life filter in substrate integrated waveguide (SIW) technology, including several groups of rectangular dielectric cylinders. [ABSTRACT FROM AUTHOR]

This paper presents the development of efficient design equations for high strength steel (HSS) welded I-section beam–columns under the framework of the Continuous Strength Method (CSM). The present work includes a collection of available experimental data on HSS S690 and S960 welded I-section beam–columns and a comprehensive numerical modelling programme considering a wider spectrum of parameters that influence the structural behaviour of the HSS welded I-section beam–columns. The developed FE models were first validated against test results collected from the literature, after which parametric studies were performed to generate further results to assess the accuracy of the codified design methods as used in Europe and the US, as well as to underpin new design proposals for HSS non-slender welded I-section beam–columns. It has been shown that the proposed CSM-based design approach is able to provide reliable design predictions with improved accuracy and reduced scatter over the existing design methods, and its reliability has been confirmed by means of statistical analyses. • Numerical models validated against test results for HSS beam–columns. • Validated numerical models used to perform parametric studies considering key parameters. • Current European and American design provisions assessed using the experimental and numerical data. • The Continuous Strength Method extended to cover the design of HSS beam–columns with welded I-sections. • Reliability of the CSM evaluated by means of statistical analyses according to EN 1990. [ABSTRACT FROM AUTHOR]

The suction bucket foundation is considered as an effective option for offshore wind turbines because of its advantages in rapid installation and recyclability. However, the depth of the suction bucket inserted into the seabed is shallower compared to the monopile. Earthquakes and liquefaction threaten the safety and stability of suction bucket foundations in the North Sea of Europe and the Chinese offshore where earthquakes are active and the seabed is prone to liquefaction. This paper investigated the behavior of the suction bucket foundation located in the liquefiable sand under earthquakes using an advanced liquefaction model. The FE-FD method with the cyclic mobility constitutive model for soil was used to carry out the nonlinear dynamic analyses. Responses of the excess pore water pressure ratio, acceleration, displacement, and rotation were studied under different earthquake magnitudes and sand density. The distribution of excess pore water pressure of the suction bucket foundation from the results show strong space-time characteristics. The failure mechanism of the suction bucket foundation after liquefaction was revealed. The numerical results indicate that offshore wind turbines will be subjected to permanent displacements and tilt to reach 40% of the safety threshold due to earthquakes and liquefaction. Thus, seismic load and liquefaction of the foundation must be considered in the design. • Suction bucket foundation response under earthquakes was investigated using an advanced liquefaction model. • The excess pore water pressure ratio, acceleration, displacement, and rotation were studied. • The failure mechanism of the suction bucket foundation after liquefaction was revealed. • Seismic load and liquefaction of foundation are important items in the design. [ABSTRACT FROM AUTHOR]

When computational modeling is used to evaluate the true strength of an imperfect elastic-plastic shell structure, the current European standard on shell structures requires that two reference strengths are always determined: the linear bifurcation load and the plastic limit (plastic collapse) load. These two loads are used in more than one way to characterize the strength of all imperfect elastic-plastic systems. Where parametric studies of a problem are being undertaken, it is particularly important that these two loads are accurately defined, since all other strengths will be related to them. For complex problems in shell structures, it is not possible to develop analytical solutions for the plastic collapse strength, and finite element analysis must be used. Unfortunately, because a collapse mechanism often requires the development of very extensive plasticity involving large local strains, and the collapse load is simply at the end of a slowly rising loaddeflection curve, it is sometimes difficult for the analyst to accurately determine this plastic collapse strength. This paper describes two methods, based on modifications of the Southwell plot, of obtaining very accurate evaluations of the plastic limit load, irrespective of whether a fairly complete plastic strain field has developed or not. These two methods allow plastic collapse limit loads to be reported with great precision. [ABSTRACT FROM AUTHOR]

The present paper investigates structural response and buckling of long unstiffened thin-walled cylindrical steel shells, subjected to bending moments, with particular emphasis on stability design. The cylinder response is characterized by cross-sectional ovalization, followed by buckling (bifurcation instability), which occurs on the compression side of the cylinder wall. Using a nonlinear finite element technique, the bifurcation moment is calculated, the post-buckling response is determined, and the imperfection sensitivity with respect to the governing buckling mode is examined. The results show that the buckling moment capacity is affected by cross-sectional ovalization. It is also shown that buckling of bent elastic long cylinders can be described quite accurately through a simple analytical model that considers the ovalized prebuckling configuration and results in very useful closed-form expressions. Using this analytical solution, the incorporation of the ovalization effects in the design of thin-walled cylinders under bending is thoroughly examined and discussed, considering the framework of the provisions of the new European Standard EN1993-1-6. [ABSTRACT FROM AUTHOR]