Jacket structure is a new type of offshore wind turbine foundations with advantages for its lightweight construction, high stability, and suitability for various water depths. However, jacket ...foundations are often subjected to scouring caused by tidal flows, which can significantly affect the stability of offshore wind energy systems. Limited research has been conducted on the scour characteristics around the jacket foundation under bidirectional flow actions due to the structural complexity. To address this gap, this study performs physical model tests to investigate the effects of flow properties and foundation position on the scour around the jacket foundation. This study assesses the impact of a complex upper truss structure and finite pile height on scouring, in contrast to monopile and regularly arranged pile group foundations. It also analyzes the differences in scour characteristics between a monopile foundation and a jacket foundation subjected to identical bidirectional flow conditions. The impact of flow direction on the scour evolution is evaluated by comparing the scour characteristics under unidirectional and bidirectional flow actions with the same hydrodynamic conditions. The results indicate that the equilibrium scour depth increases with the flow strength and water depth, and reaching its maximum at a foundation angle of 30°. Findings are of great significance for predicting the scour extent around the jacket foundation.
•Effect of propagation direction of incoming flow on temporal variation of scour depth is evaluated.•Examine influence of hydrodynamic parameters and foundation angle on equilibrium scour characteristics around jacket piles.•Investigate impact of truss structure and pile leg with finite height on scour extent under bidirectional flow loading.
•Soil-structure interaction of eco-sustainable reinforced concrete foundations of wind towers,•Moment-rotation capacity curve including the soil plasticization or RC structure crisis in flexure and ...shear.•Moment-rotation curve with purposes of the ultimate and operating limit state verifications of wind towers.•Direct plinth and single piers or shaft foundation in elastic and plastic phases considered as rigid bodies.•Winkler soil model for in elastic state and fully plastic model to model for non-linear behavior of soil.•Corrective coefficients to consider of type of soils (cohesive and not cohesive) and to take into account of the flexibility of foundation.
The objective of the study, concerning the soil-structure interaction of eco-sustainable reinforced concrete foundations of wind towers, was to determine the moment-rotation capacity curve including the soil plasticization or RC structure crisis in flexure and shear. The study was based on elastic and plastic analyzes of shallow and deep foundations. The moment-rotation curve of the soil-foundation complex was determined, useful for the purposes of the ultimate and operating limit state verifications of wind towers. The displacement component induced by the rotation of the foundation on the overhead displacement of the wind tower was calculated. Finally, an experimental validation of the proposed model was made with the data available from the literature.
The existing longitudinal structural model of shield tunnels usually simplify the tunnel as a Euler-Bernoulli beam on elastic foundation, which ignores the shearing dislocation between rings. To ...model the dislocation between rings, this paper proposed a soil-tunnel interaction model based on the Timoshenko beam simplified model (TBSM) of tunnel on Vlasov foundation. The governing differential equation and the closed-form solution for TBSM on Vlasov foundation subjected to any given pressure are derived with consideration of two types of boundary conditions. The proposed model was adopted to analyze the behaviors of a shield tunnel subjected to external forces transferred from surcharge load on the ground surface. Factors influencing the longitudinal behavior of shield tunnels are discussed. The factors include the equivalent of shear stiffness, location of load application, and the rotational stiffness of the joint between tunnel and station. The results indicated that Euler-Bernoulli beam model underestimates deformation and overestimates the internal forces in the tunnel structure. When the load application is close to the station, with the decrease of the distance between the load and the station will lead to a slightly decrease of the maximum settlement of the tunnel, and an increase of the maximum internal forces and the maximum joint deformation. A stiffer joint between tunnel and station will cause greater internal forces at the location of joint.
Real-time hybrid simulation (RTHS) divides a structural system into an analytical and experimental substructure. The former is based on a well-established analytical model while the latter consists ...of a physical model in the laboratory, for which there is not a well-established analytical model. This paper extends real-time hybrid simulation to monopile-type Offshore Wind Turbines (OWTs) to enable the investigation of their behavior considering the response of pile foundations under operational and more severe conditions. The embedded foundation and surrounding soil of the OWT are modeled physically in a soil box in the laboratory while the remaining parts of the system and loading are modeled analytically. The program OpenFAST, developed by the National Renewable Energy Laboratory (NREL), is linked to the RTHS coordinator to determine the hydrodynamic and aerodynamic loads acting on the OWT, along with modeling the dynamics of the electric power generation equipment and associated controller for the OWT. The RTHS framework along with its initial implementation and validation are described in this paper. RTHSs of a 5 MW OWT subjected to operational and more severe conditions are performed to experimentally validate the framework. The framework offers a realistic approach to investigate the behavior of OWT structures supported on monopiles. This approach accounts for the coupled response of the OWT structure with its foundation, while experimentally capturing the nonlinearities of the soil-foundation interaction in real-time.
•RTHS is extended to offshore wind turbine monopile structures.•OpenFAST software is modified and integrated into a RTHS framework.•Validated RTHS framework that incorporates the complete system into the simulation.•RTHS enables experimental assessment of offshore wind turbine foundation behavior.•RTHS computational challenges of offshore wind turbine structures are presented.
When connected piles are used as settlement reducers, the proportion of vertical load carried by the pile may come close to the allowable load of the pile. To reduce not only the vertical load, but ...also the lateral load and bending moment to which the pile is subjected, the disconnected piled raft (DPR) has been introduced as an effective design for the role of the settlement reducers. Although several DPRs have been constructed, most of the research efforts on DPRs are limited to the structural behavior such as the evaluation of the seismic acceleration of the structure on the DPR; thus, there is a need to evaluate the dynamic performance of DPRs focusing on geotechnical problems. In this study, the seismic behavior of DPRs is investigated using dynamic centrifuge tests and compared with the results obtained from connected piled rafts (CPRs). The bending moment of piles of different materials, namely aluminum and steel, is evaluated. Results show that there is a reduction in the amplitude of acceleration of the foundation horizontal motion for the DPR compared to the CPR. The edge pile of a DPR attracts the smaller dynamic bending moment of the pile compared to that of a CPR. The dynamic bending moment of piles is predominantly governed by the soil behavior rather than the pile material. Finally, the seismic behavior of DPR was evaluated comprehensively through centrifuge tests.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The problem of settlement of shallow foundations is among the most important ones in classical soil mechanics. And while for the settlement of flexible foundations elastic solutions are widely used, ...for rigid rectangular foundations where the actual contact pressure distribution is still unknown, the problem is approximated either analytically assuming a contact pressure distribution or semi‐empirically combining the theory of elasticity with experimental and/or numerical results. A third and often attractive choice is the use of simple empirical relationships or relevant tabulated values relating the elastic settlement of rigid foundations (
ρ
R
) with the settlement of the respective flexible foundations (e.g. at the center,
ρ
Ce
). Reviewing the relathionships of this third approach, the author revealed serious lack of consesous between the various sources; for example, according to the literature,
ρ
R
ranges between 68 and 125% of
ρ
Ce
, the time when it is well-known that
ρ
R
<
ρ
Ce
. In this paper, comparison of the settlement of 210 rigid foundation cases derived from 3D elastic finite element analysis, with the settlement of the respective flexible foundations derived from the theory of elasticity, led to simple empirical relationships between
ρ
R
and
ρ
Ce
as well as between
ρ
R
and
ρ
Av
(
ρ
Av
= average settlement of the flexible foundation) with coefficient of determination (R
2
) almost unity. The analysis showed that these relationships are largely independent of the aspect ratio of foundations and the thickness and Poisson’s ratio (
ν
) of the compressible medium, although separate relationships are given for
ν
= 0.5, slightly increasing R
2
. Finally, a correction factor for foundation rigidity is given exploting the known linear relationship that exists between the relative stiffness factor of foundations and settlement.
Abstract
When the fourth edition of the Brain Trauma Foundation's Guidelines for the Management of Severe Traumatic Brain Injury were finalized in late 2016, it was known that the results of the ...RESCUEicp (Trial of Decompressive Craniectomy for Traumatic Intracranial Hypertension) randomized controlled trial of decompressive craniectomy would be public after the guidelines were released. The guideline authors decided to proceed with publication but to update the decompressive craniectomy recommendations later in the spirit of “living guidelines,” whereby topics are updated more frequently, and between new editions, when important new evidence is published. The update to the decompressive craniectomy chapter presented here integrates the findings of the RESCUEicp study as well as the recently published 12-mo outcome data from the DECRA (Decompressive Craniectomy in Patients With Severe Traumatic Brain Injury) trial. Incorporation of these publications into the body of evidence led to the generation of 3 new level-IIA recommendations; a fourth previously presented level-IIA recommendation remains valid and has been restated. To increase the utility of the recommendations, we added a new section entitled Incorporating the Evidence into Practice. This summary of expert opinion provides important context and addresses key issues for practitioners, which are intended to help the clinician utilize the available evidence and these recommendations.
The full guideline can be found at: https://braintrauma.org/guidelines/guidelines-for-the-management-of-severe-tbi-4th-ed#/.
Adoption of the rocking isolation concept in foundation design is considered as an effective method in reducing seismic loads of structures. Despite much research conducted on the rocking behavior of ...foundations, concerns regarding the practical application of the rocking foundation design concept still prevail. The concerns primary stem from the lack of accurate understanding and knowledge associated with the soil‐foundation deformation mechanisms during rocking motions. Determination of deformation mechanisms and soil mass failure modes during foundation rocking helps to gain insight into the rocking behavior, recognize influential factors on foundation settlement or uplift, and propose appropriate improvement strategies to control foundation deformations. The primary objective of this study is to investigate the deformation behavior and failure modes of the soil mass beneath a rocking foundation with various initial static vertical factors of safety (F.S.v) and embedment depths. To this end, a series of reduced‐scale slow‐cyclic tests under 1g condition have been conducted using a single degree of freedom (SDOF) model. To determine soil deformation mechanisms, soil displacement fields have been measured using Particle Image Velocimetry (PIV) technique. Soil deformation mechanisms during loading and unloading paths, as well as causes leading to the foundation settlement or uplift have been evaluated and discussed. Additionally, changes in the effective soil‐foundation contact area in different loading cycles have been examined based on the PIV results. Based on the results, soil deformation mechanisms in the loading portions include soil densification, wedge deformation and scoop deformation. As the footing embedment depth increases, wedge deformation mechanism becomes limited, while scoop deformation mechanism becomes stronger. Additionally, as the foundation F.S.v increases, the depth of influenced zone of the rocking foundation decreases and the soil displacement occurs to a more limited depth.
This article tries to investigate the dynamic deflection response of exponentially functionally graded material (E-FGM) nanoplate considering the role of porosities when embedded in a visco-elastic ...foundation and subjected to moving load, for the first time. The effective material properties are found using an exponential model of the rule of mixture. Next, the governing equations for the nanoplates while resting on a visco-Winkler foundation are found based on the third-order shear deformation theory in conjunction with Eringen nonlocal elasticity by developing Hamilton's principle. To solve the time-dependent governing motion equations, a state-space method is developed to find the response of the structure including simply-supported edges under moving load. Through some examples, the validation of the approach is provided before investigating the roles of nonlocality, volume fraction index (exponential parameter), porosity index, visco-elastic foundation coefficients, and velocity and time span of moving load on the forced vibration of embedded E-FGM nano-size plate under moving load.
•An exponential function including porosity is developed for moving load analysis.•The embedded FGM nanoplate in the visco-Winkler foundation is modeled analytically.•A time-dependent system is solved by implementing Navier's solving procedure.•Viscoelastic foundation reduces the deformations of imperfect inhomogeneous nanoplates.
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