The inerter-based systems have proven to be effective for vibration control of adjacent structures. The interaction through the soil medium between adjacent structures in urban areas is generally ...accepted. However, existing studies concerning the inerter-based adjacent structures are primarily based on the assumption of a fixed base, without considering the inevitable interaction. To address this issue, this study incorporated the soil effects into the theoretical analysis of adjacent structures interconnected by an inerter system, and correspondingly develops an optimal design framework for such system. Employing a classic discrete model for structures and soil, the interaction behavior between inerter-based adjacent structures and soil was extensively studied in a comparative analysis. Based on the revealed interaction phenomena, the need for considering the soil condition in the design of an inerter system for adjacent structures was addressed, and a performance-demand-based optimal design framework was developed. The results indicated that for inerter-based adjacent structures spaced closely, the coupled interaction effect of soil and structure requires careful consideration, especially in soft soil conditions. Owing to the soil effects, the inerter system exhibited a weakened effectiveness for displacement reduction. A larger inner deformation of the inerter system is required to meet the demand for energy dissipation. With consideration of the soil condition, the proposed design method can satisfy the pre-specified target displacement demands for adjacent structures, simultaneously optimizing the control cost as an economical solution.
Offshore wind turbines (OWTs) are dynamically loaded structures and therefore the estimation of the natural frequency is an important design calculation to avoid resonance and resonance related ...effects (such as fatigue). Monopiles are currently the most used foundation type and are also being considered in deeper waters (>30m) where a stiff transition piece will join the monopile and the tapered tall tower. While rather computationally expensive, high fidelity finite element analysis can be carried to find the Eigen solutions of the whole system considering soil–structure interaction; a quick hand calculation method is often convenient during the design optimisation stage or conceptual design stage. This paper proposes a simplified methodology to obtain the first natural frequency of the whole system using only limited data on the WTG (Wind Turbine Generator), tower dimensions, monopile dimensions and the ground. The most uncertain component is the ground and is characterised by two parameters: type of ground profile (i.e. soil stiffness variation with depth) and the soil stiffness at one monopile depth below mudline. In this framework, the fixed base natural frequency of the wind turbine is first calculated and is then multiplied by two non-dimensional factors to account for the foundation flexibility (i.e. the effect of soil–structure interaction). The theoretical background behind the model is the Euler–Bernoulli and Timoshenko beam theories where the foundation is idealised by three coupled springs (lateral, rocking and cross-coupling). 10 wind turbines founded in different ground conditions from 10 different wind farms in Europe (e.g. Walney, Gunfleet sand, Burbo Bank, Belwind, Barrow, Kentish flat, Blyth, Lely, Thanet Sand, Irene Vorrink) have been analysed and the results compared with the measured natural frequencies. The results show good accuracy (errors below 3.5%). A step by step sample calculation is also shown for practical use of the proposed methodology.
•Methodology for Eigen solution for monopile supported WTG.•Foundation flexibility and effect of deeper water installation.•Hand calculation for stiffness of foundations.•A review of damping of WTG system.
To clarify the contribution of the bridging effect from three metal cations (Ksup.+, Mnsup.2+, and Fesup.3+) on the humification of lignin-rich Tilia wood shavings and further enrich the theory of ...lignin humification, an indoor incubation method with constant temperature and humidity was adopted. Ksup.+, Mnsup.2+, and Fesup.3+ served as additives, with CK as the control for studying the differential influence of metal cations with different valences on the humus composition of dark-brown soil mixed with Tilia wood shavings. The change in the C contents of water-soluble substance (Csub.WSS), humic-extracted acid (Csub.HE) and humin (Csub.Hu), ∆logK value of HE, atomic ratio and FTIR spectra of humic acid (HA), and the ratio of C content of humic acid to fulvic acid (Csub.HA/Csub.FA) of dark-brown soil mixed with Tilia wood shavings were analyzed after 0, 30, 80, and 150 days of incubation, and the following conclusions were reached: (1) The addition of metal cations, regardless of their valence, could effectively improve the microbial utilization and consumption of WSS, and the effect was as follows: Fesup.3+ > Mnsup.2+ > Ksup.+. The addition of three metal cations could effectively inhibit mineralization and reduce the loss of TOC, and the effect could be seen as follows: Fesup.3+ > Mnsup.2+ > Ksup.+. (2) Although the Csub.HE content first decreased and then increased with incubation, the addition of Fesup.3+ and Mnsup.2+ ions increased the Csub.HE content, showing that Fesup.3+ > Mnsup.2+, and Ksup.+ ions had no significant effect. Throughout the incubation, the structure of HE molecules changed first via a complex process and then through a simple process. Comparing the change before and after the incubation, the overall structure of HE molecules tended to be simpler with the CK control, and HE became more complicated with the addition of Fesup.3+ and Mnsup.2+; however, the addition of Ksup.+ had little effect on the structure of HE molecules. (3) At the end of the incubation, the addition of Fesup.3+, Mnsup.2+, and Ksup.+ ions strengthened the molecular condensation of HA and its aromatization degree, while the CK control without any added metal cations caused HA molecules to decompose and obtain a greater aliphatic degree. In addition, the number of O-containing functional groups and N-containing compounds in HA molecules increased to varying degrees regardless of which metal cation was added. The decomposition of Tilia wood chips led to a partial entry of the decomposition products into the HA component, which was then reconsumed by continuous mineralization. After incubation, the polysaccharides in HA molecules were consumed only with the addition of Mnsup.2+ ions. Fesup.3+ and Mnsup.2+ ions had greater advantages in increasing the Csub.HA/Csub.FA ratio and improving the humus quality than Ksup.+ ions. (4) The addition of metal cations could effectively inhibit the mineralization and decomposition of the Hu component, among which Fesup.3+ ions had the most significant effect, followed by Mnsup.2+ ions. Compared to monovalent cations (Ksup.+), polyvalent cations (Fesup.3+ and Mnsup.2+) had the advantage of a bridging effect, and their addition promoted the microbial utilization of WSS, effectively reduced the loss of TOC, increased the Csub.HE content, complicated its molecular structure, improved the humus quality, and inhibited the decomposition of Hu. Regardless of which metal cation was added, the degree of molecular polycondensation and aromatization of HA was enhanced, and the number of O-functional groups and N-containing compounds in HA molecules increased.
We present the results of a large‐scale experimental campaign performed on the prototype structure of EuroProteas in Thessaloniki, Greece, to assess the effectiveness of gravel‐rubber mixture (GRM) ...layers underneath shallow foundations as a means of geotechnical seismic isolation (GSI). We found that the GSI of structures is optimized by increasing the rubber content of the soil‐rubber mixture up to 30% per mixture weight. The effectiveness of the GSI systems has been investigated numerically and in small‐scale experiments. This article seeks to fill the gap in the lack of full‐scale experimental studies on this subject. Three soil pits were excavated and backfilled with GRM of different rubber content per weight to serve as foundation soil. A large number of instruments were installed on the structure, the foundation, the soil surface, and inside the GRM layers beneath the foundation to fully monitor the GSI‐structure systems’ response in three dimensions. The experimental investigation included ambient noise, free‐ and forced‐vibration tests. Our results showed that a GSI layer composed of a GRM with 30% rubber content effectively isolates the structure. Even 0.5 m thickness (ie, B/6 of the foundation width) of the GSI system successfully cuts off practically all emitted waves at a (horizontal or vertical) distance of B/6 from the foundation. A significant reduction in the GSI‐structure system's stiffness was apparent, leading to a rocking‐dominant response. The rise in the system's damping and the substantial energy dissipation inside the GRM layer highlight its effectiveness as a GSI system.
Few studies have focused on evaluating regular surface roughness and its effect on interfacial shear behavior of the red clay – concrete interface. This paper presents the results of a series of ...laboratory large-scale direct shear tests conducted using different types of red clay – concrete interfaces. The objective is to examine the effect of surface roughness on these types of soil–concrete interfaces. In the smooth-interface tests, the measured peak and residual shear strength values are very close to each other, with no observed shear dilation. The surface roughness is found to have a remarkable effect on the interfacial shear strength and shear behavior, with the shear strength increasing with increased surface roughness level. The shear dilation is likely to occur on rougher interfaces under lower confining pressure due to the behavior of compressed clay matrices. Owing to the clay matrix’s cohesion and friction, the interfacial shear strength on rough interfaces consists of cohesive and frictional forces between the clay and concrete surfaces. The friction angle value is observed to fluctuate between the clay’s friction angle and the smooth interface’s friction angle. This can be related to the position change of the shear failure slip plane. The confining pressure and surface roughness could change the shear failure plane’s position on the interface. Furthermore, the red clay – structure interface is usually known as the weakest part in the mechanical safety assessment.
Mechanical behaviour of the soil–structure interface plays a major role in the shear characteristics and bearing capacity of foundations. In thermoactive structures, due to nonisothermal conditions, ...the interface behaviour becomes more complex. The objective of this study is to investigate the effects of temperature variations on the mechanical behaviour of soils and the soil–structure interface. Constant normal load (CNL) and constant normal stiffness (CNS) tests were performed on the soil and soil–structure interface in a direct shear device at temperatures of 5, 22, and 60 °C. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The sandy soil was prepared in a dense state and the clayey soil was prepared in a normally consolidated state. Results show that the applied thermal variations have a negligible effect on the shear strength of the sand and sand–structure interface under CNL and CNS conditions, and the soil and soil–structure interface behaviour could be considered thermally independent. In clay samples, an increase in the temperature increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The temperature rise had less impact on the shear strength in the case of the clay–structure interface than in the clay samples. The adhesion of the clay–structure interface is less than the cohesion of the clay samples.
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