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This paper investigated bond behaviour of concrete-filled steel tube (CFST) columns at the Arctic low temperatures. A testing program with ten square and ten circular CFSTs were tested under different low temperatures ranging from 30 °C to −80 °C. The influences of different low temperature levels, diameter to thickness ratio (D/t), grades of concrete, length to diameter ratio (L/D), and cross-section type were checked through these 20 tests. The test results showed that the Arctic low temperatures significantly improved the bond behaviour of CFST columns; lower grade concrete exhibited larger ultimate bond strength (τu); increasing D/t ratio reduces the ultimate bond strength; L/D ratio has marginal influences on τu values; and circular CFST columns exhibited higher ultimate bond strength than those of square ones. Different from the CFST column at ambient temperature, the frozen-ice bond for the CFST columns at low temperature improves its ultimate bond strength. A prediction equation was proposed for ultimate bond strength of CFST columns at low temperatures. The validations against the reported 20 tests show that the proposed equation offered conservative predictions but more accurate predictions than the design codes, e.g., Eurocode 4 and ANSI/AISC.

Twisted two-dimensional bilayer materials exhibit many exotic physical phenomena. Manipulating the twist angle between the two layers enables fine control of the physical structure, resulting in development of many novel physics, such as the magic-angle flat-band superconductivity, the formation of moire exciton and interlayer magnetism. Here, combined with analogous principles, we study theoretically the near-field radiative heat transfer (NFRHT) between two twisted hyperbolic systems. This two twisted hyperbolic systems are mirror images of each other. Each twisted hyperbolic system is composed of two graphene gratings, where there is an angle {\phi} between this two graphene gratings. By analyzing the photonic transmission coefficient as well as the plasmon dispersion relation of twisted hyperbolic system, we prove that the topological transitions of the surface state at a special angle (from open (hyperbolic) to closed (elliptical) contours) can modulate efficiently the radiative heat transfer. Meanwhile the role of the thickness of dielectric spacer and vacuum gap on the manipulating the topological transitions of the surface state and the NFRHT are also discussed. We predict the hysteresis effect of topological transitions at a larger vacuum gap, and demonstrate that as thickness of dielectric spacer increase, the transition from the enhancement effect of heat transfer caused by the twisted hyperbolic system to a suppression. This technology could novel mechanism and control method for NFRHT, and may open a promising pathway for highly efficient thermal management, energy harvesting, and subwavelength thermal imaging.

This paper mainly focused on the behaviours of circular concrete-filled steel tubular (CFST) stub columns (CCFST-SCs) subjected to axial compression at different cold-region low temperatures. A test-program consisting of 14 CCFST-SCs was firstly carried out at four low temperature levels, i.e., 20, −30, −60, and −80 °C. The investigated parameters included low temperature levels and wall thickness of tube in CCFST-SC. These test results reported that under compression the CCFST-SC at low temperatures failed in shear mode, concrete crushing, outward local buckling and tensile fracture in steel tube. The axial compressive load versus shortening behaviour was reported. This paper discussed and analysed influences of different parameters on compressive behaviour of CCFST-SCs. This paper also developed theoretical models to describe the axial shortening versus compressive load behaviour of CCFST-SCs at low temperatures. Moreover, different modified code equations were proposed for determinations of ultimate compressive resistances of CCFST-SCs at low temperatures. Finally, the accuracies of these theoretical models and modified code equations were confirmed by the validations of their predictions against 25 test results. Conclusions were also given at the end based on these tests and analysis results.

International audience; In this Letter, active control of near-field radiative heat transfer (NFRHT) between two isotropic materials is realized by a coating-twisting method. The two slabs are coated with graphene gratings, and then the NFRHT can be not only enhanced but also weakened, by tuning the twisted angle between the two gratings. The physical mechanism is attributed to the modes coupled by the graphene gratings and the isotropic material, which can vary with the twisted angle. The proposed method is also applicable for other kinds of anisotropic films and may provide a way to realize high-precision nanoscale thermal management, nimble thermal communications, and thermal switch.

In this paper, magnetoplasmonic manipulation of near-field radiative heat transfer (NFRHT) is realized using two twisted graphene gratings. As a result of the quantum Hall regime of magneto-optical graphene and the grating effect, three types of graphene surface plasmon polaritons (SPPs) modes are observed in the system: near-zero modes, high-frequency hyperbolic modes, and elliptic modes. The elliptic SPPs modes, which are caused by the combined effect of magnetic field and grating, are observed in the graphene grating system for the first time. In addition, the near-zero modes can be greatly enhanced by the combined effect grating and magnetic field, rendering graphene devices promising for thermal communication at ultra-low frequency. In particular, the near-zero modes result in a unique enhancement region of heat transfer, no matter for any twisted angle between gratings. The combined effect of grating and magnetic field is investigated simultaneously. By changing the strength of magnetic field, the positions and intensities of the modes can be modulated, and hence the NFRHT can be tuned accordingly, no matter for parallel or twisted graphene gratings. The magnetic field endows the grating action (graphene filling factors and twisted angles) with a higher modulation ability to modulate the NFRHT compared with zero-field. Moreover, the modulation ability of twist can be tuned by the magnetic field at different twisted angles. In sum, the combined effect of magnetic field and grating provides a tunable way to realize the energy modulation or multi-frequency thermal communications related to graphene devices.

Recently, gravity base offshore platforms consisting of novel steel-concrete-steel (SCS) sandwich ice-resistant walls with J-hook connectors have been developed for the Arctic oil & gas production. This paper made pioneer studies on compressive behaviours of SCS sandwich composite walls with J-hook connectors (SCSSWJ) at the Arctic low temperatures through a nine-specimen testing program. The low temperatures ranging from 20 to −80 °C, thickness of steel faceplate, spacing of connectors, and concrete strength were selected as key parameters in this experimental study. The test results revealed the failure modes and load versus shortening/strain behaviours of the SCSSWJ at low temperatures. These studied parameters were found to have significant influences on the compressive behaviours of this novel SCSSWJ. Including experimental studies, this paper also developed theoretical models to predict the ultimate compressive resistance of SCSSWJ at the low temperature environment. The validations of predictions against results of nine reported tests confirmed that the theoretical models were capable of provide reasonable but conservative estimations on the compressive resistance of such novel SCSSWJ.

Black phosphorus (BP), as a two-dimensional material, has exhibited unique optoelectronic properties due to its anisotropic plasmons. In the present work, we theoretically propose a radiative thermal switch (RTS) composed of BP gratings in the context of near-field radiative heat transfer. The simply mechanical rotation between the gratings enables considerable modulation of radiative heat flux, especially when combined with the use of non-identical parameters, i.e., filling factors and electron densities of BP. Among all the cases including asymmetric BP gratings, symmetric BP gratings, and BP films, we find that the asymmetric BP gratings possess the most excellent switching performance. The optimized switching factors can be as high as 90% with the vacuum separation d=50 nm and higher than 70% even in the far-field regime d=1 µm. The high-performance switching is basically attributed to the rotatable-tunable anisotropic BP plasmons between the asymmetric gratings. Moreover, due to the twisting principle, the RTS can work at a wide range of temperature, which has great advantage over the phase change materials-based RTS. The proposed switching scheme has great significance for the applications in optoelectronic devices and thermal circuits.

Firstly, this paper proposed a type of steel-concrete-steel (SCS) sandwich composite shear wall with J-hook connectors (SCSSWJ) and boundary concrete-filled-steel-tube (CFST) columns. Five full-scale cyclic tests were performed to study seismic performances of SCSSWJs. The studied parameters were connectors’ spacing and axial force ratio. Test results showed that flexure failure occurred to these five SCSSWJs with boundary CFST columns, which is characterized by tensile fracture of boundary steel tube, local buckling in the edge tube and faceplates, and concrete crushing. The test results revealed that increasing the spacing of J-hook connectors from 100 mm to 160 mm and 200 mm firstly slightly improves but then compromised the seismic behaviour of SCSSWJ due to early buckling of steel faceplate; increasing the axial force ratio significantly compromised the seismic behaviours of SCSSWJ. This paper also developed theoretical models to evaluate lateral peak shear resistance of SCSSWJ. The validations proved that the developed models predicted well lateral peak shear resistance of SCSSWJ with boundary CFST columns.

This paper evaluates the low-temperature compressive behaviours of square CFST stub columns (SCFST-SCs) in steel-concrete composite structures. 21 compressive tests were firstly performed on 14 SCFST-SCs and seven rectangular CFST stub columns (RCFST-SCs) at low temperatures of 20, -30, −60, and −80 °C. The key parameters in this testing program are low temperatures, wall-thickness of steel tube, and shape of the cross section. Concrete crushing, outward local buckling of steel tube, and tensile fracture at the corner of steel tube were three observed failure modes in the compressive tests. The SCFST-SCs and RCFST-SCs exhibited linear, elasto-plastic, and recession working stages. The test results showed that the ultimate compressive resistance and initial stiffness were increased, but the ductility was decreased for the square CFST stub columns as the temperature decreases from 20 to −80 °C. The wall-thickness of steel tube showed equivalent contributions on the improvements of ultimate compressive resistance due to different low temperature, but its influences on ductility tends to be weakened as temperature decreases. Modified Eurocode 4 code equations have been proposed for the predictions on ultimate compressive resistances of SCFST-SCs at low temperatures, and their accuracies were checked by 21 reported test results.

This paper firstly proposed steel-concretes-steel sandwich walls with J-hook connectors (SCSWJs) as protective structures in the Arctic offshore platforms. Followed, six large scale SCSWJs were tested under lateral cyclic loading to investigate their lateral seismic behaviours. The investigated parameters in the testing program included spacing of J-hook, concrete core strength, thickness of steel faceplate, and aspect ratio. Seismic behaviours of SCSWJs were reported in details, and the effects of these parameters on their seismic behaviours were reported and discussed. The test results showed that the SCSWJ failed in flexure mode with characteristics of tensile yielding of side plate and steel faceplate, concrete crushing at the bottom toe, and outward local buckling of steel faceplates. Pinching effect was observed in the load versus lateral drift curves after the peak load due to premature local buckling of side plates and faceplates locating between the first and second row of J-hook from the bottom. This paper developed analytical models to predict the peak lateral resistance of SCSWJ. The validations against 12 results from six cyclic tests confirmed that the developed models offered reasonable but conservative predictions on the peak lateral resistance of SCSWJ. This study promotes the applications of the SCSWJ in the earthquake-prone Arctic regions.

International audience; In the published paper [1], an error has been made in the formulation of the capacity function C (Sw). In Equation (21) of that paper, the capacity function C (Sw) should be given as,C(SW)=θdSWdϕc(SW)in which θ denotes the capillary porosity for cement-based material. In accordance, after adopting the Zhou model Equation (24) to quantify the water retention characteristics, the capacity function C (Sw) in Equation (25) should be formulated as,C(SW)=βθSW[1+(α−1)SW],C(SW=1)=αβθThese above modifications have no further implications for the remaining part of the published paper [1]. The authors apologize for the naive errors they have made.Reference [1] C. Zhou, W. Chen, W. Wang, F. Skoczylas, Unified determina tion of relative molecular diffusivity and fluid permeability for partially saturated cement-based materials, Cem. Concr. Res., 67 (2015), pp. 300–309

International audience; The hydraulic diffusivity, water permeability and relative gas permeability for cement-based materials are indirectly evaluated from measured sorptivity and water vapor sorption isotherms (WVSIs). The dependence of sorptivity on initial saturation degree is first established to help calculate hydraulic diffusivity and other transport properties. An experimental program with a self-scaled preconditioning strategy is also carefully designed and conducted on three concretes to measure their sorptivity, WVSIs as well as permeability to various fluids. It's found that hydraulic diffusivity of ambiguous physical significance may be not a good durability indicator. The predicted water permeability is larger than measured value but at the same order of magnitude. This overestimation is attributed to the required drying preconditioning. The predicted relative water permeability agrees well with reported data. However, the predicted relative gas permeability agrees with the measured data from classical CEMBUREAU method better than that from tri-axial permeameter with higher inlet gas pressure.

Smart energy storage materials, which not only store electrochemical energy but also exhibit sensitivity to environmental stimuli, can provide novel multi-functionalities. Here, we report a smart shape memory fiber supercapacitor constituted with a highly stretchable shape memory polymer nanocomposite fiber substrate, multi-walled carbon nanotubes (MWCNT) conductive layer and pesudocapacitive polyaniline layer. Using layer by layer (LBL) technology, we first produce a densely packed MWCNT layer that serves as a well-developed conductive current collector network. Then polyaniline, as an active material, was deposited on the surface of the MWCNT layer to further promote the energy storage capability of the fibers. After the infiltration of a polyvinyl alchohol (PVA) based polymer electrolyte into the porous MWCNT and PANI layer, conductivity of ∼50 S/cm and stretchability of more than 400% are obtained. The resultant shape memory polymer supercapacitors (SMPFSCs) not only possess shape memory properties, but also exhibit outstanding energy storage performance, with the best pseudo-capacitance exceeding ∼427 F/cm3. Such design strategies can also be extended to other polymer substrates, and could open the door to smart (multi-functional) supercapacitor technologies.

International audience; This paper deals with actuator fault estimation for a class of discrete-time Linear Parameter-Varying (LPV) descriptor systems. By considering the fault as an auxiliary state vector, an augmented system is established. Then, a fault estimation observer is designed based on the augmented system. In this paper, the fault estimation observer design is formulated as a Linear Matrix Inequality (LMI) feasibility problem. Therefore, all parameters of the observer can be simultaneously designed by solving a set of strict LMIs. In order to attenuate the effect of the unknown disturbance, fault variation, and measurement noise, we further propose a robust fault estimation observer design method, which is the main contribution of this paper. Finally, performance of the proposed robust fault estimation observer is shown through the application to a trucktrailer model.

International audience; From conductivity theory, general models for relative molecular diffusivity and fluid permeability are first derived with unknown tortuosity function and modification coefficient, which can be respectively deduced from hydraulic diffusivity and water retention curve (WRC). Based on empirical laws for hydraulic diffusivity and WRC of cement-based material, unified models for relative molecular diffusivity and fluid permeability are further formulated with only two measurable parameters. Because of practical difficulty for measuring water permeability and pure gaseous molecular diffusivity, only relative gas permeability and relative chloride diffusivity models are verified by the reported data. It is found that the predicted relative gas permeability agrees with measured values and exponential law is a little more preferable than power law for quantifying hydraulic diffusivity. Moreover, relative chloride diffusivity from the unified model also agrees well with experimental data derived via Nernst–Einstein Equation. However, the unified model doesn't capture the possibly overestimated relative chloride diffusivity from Fick's law.

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International audience; In order to understand the effects of the coupling between smooth and nonsmooth nonlinearities in dynamical systems, we introduce a simple mechanical model containing the exact expression of nonlinear strains together with non-regularized unilateral contact and Coulomb friction conditions. This model is suggested both by previous work dealing with unilateral contact conditions and by work closer to classical dynamical systems which has recently led to the introduction of a new attractor. The main part of the paper concerns the investigation of the set of equilibrium states which turns out to be much more intricate than when the strains were linearized. Then the paper ends by suggesting some possible paths towards the study of the stability of these equilibria and of the qualitative dynamics.

Demand of composite fuel tank for space vehicles keeps increasing globally in the aerospace industry, and requires of a mean to detect the structural damage or predict its service life. As important and valid tools, in the past years, lots of nondestructive evaluation techniques have been developed, and they are carried out according to a regular time schedule. The structure has to be taken out of service during each inspection, causing serious financial implications for the user. That is why much research effort is now focused on real-time monitoring techniques. Optical grating fiber attracts more and more attention due to its excellent sensing and mechanical performances and ability of monitoring online. But it still can only measure the local deformation, but not the damage that is far away from the location of optical fiber sensors. Statistical model-based vibration-based monitoring methods have proved to be useful for the detection and localization of structural damages which might occur far from the location of the sensors. An experimental investigation on the modal properties and dynamic response of composite fuel tank filled with fluid under external excitation in the transverse direction are reported, and a vibration signal, which was obtained when the composite fuel tank filled with water was under impulsion until it failed. Proposed in this study is a method to detect the damage of the composite fuel tank with the scarce gradual damaged vibration signal. The experiment setup is also described in detail with inclusion of modeling a damaged situation of a structure. The damage detection algorithm is developed by applying a residually generated form of a subspace-based covariance-driven identification method and the vibration signal analysis. Results of the modal identification and the damage detection are reported in this article.

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