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SiC/multi-walled carbon nanotube (MWCNT) composites are considered to be promising materials for high-temperature electromagnetic wave (EMW) absorption due to their strong thermal stability and tunable dielectric properties. However, the EMW absorption performance of these composites is limited by poor impedance matching. This study proposes a novel multiscale structure synergistic regulation approach to enhance EMW absorption performance, which involves constructing a heterointerface structure and a triple periodic minimal surface (TPMS) meta-structure. The addition of a SiO 2 shell as an impedance layer to the SiC/MWCNT core to improve the intrinsic impedance. Meanwhile, the heterointerface between the core-shell structure leads to multiple interface polarization, significantly enhancing EMW energy dissipation. Consequently, the effective absorption bandwidth (EAB) of SiO 2 –SiC/MWCNT composites increased from 0.88 to 4.56 GHz. Furthermore, a TPMS meta-structure, fabricated by three-dimensional (3D) printing and sol infiltration technology, is developed to further improve impedance matching with the equivalent electromagnetic effect. Simulation and experimental results demonstrate that the SiO 2 –SiC/MWCNT TPMS meta-structure exhibits broadband EMW absorption performance, with the EAB reaching 7.2 GHz. This improvement is attributed to the synergistic regulation of the heterointerface structure and TPMS meta-structure, which provides a good balance between the requirements of electromagnetic loss and impedance matching. Additionally, the composites exhibit excellent oxidation resistance, as their EAB remains almost unchanged after exposure to 1000 °C for 6 h. This research offers a new design paradigm for ultrabroadband design of the nonmagnetic high-temperature absorbing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, precast segmental concrete bridge columns became prevalent because of the benefits of accelerated construction, low environmental impact, high quality and low life cycle costs. The lack of a detailed configuration and appropriate design procedure to ensure a comparable performance with monolithic construction has impeded this structural system from being widely used in areas of high seismicity. In this study, precast segmental bridge column cyclic loading tests were conducted to investigate the performance of unbonded post-tensioned segmental bridge columns. One monolithic and two precast segmental columns were tested. The precast segmental column exhibited minor damage and small residual displacement after the maximum 7% cyclic drift; energy dissipation (ED) can be enhanced byadding ED bars. The experimental results were modeled by a simplified pushover method (SPOM), as well as a fiber model (FIBM) finite element method. Forty-five cases of columns with different aspect ratios, axial load ratios and ED bar ratios were analyzed with the SPOM and FIBM, respectively. Using these parametric results, a simplified design method was suggested by regressive analysis. Satisfactory correlation was found between the experimental results and the simplified design method for precast segmental columns with different design parameters. [ABSTRACT FROM AUTHOR]

In this study, we carried out a series of physical experiments using a submersed flume model to investigate how sand/clay content influences the depositional mechanism of submarine debris flows. A three-dimensional biphasic numerical model, with a Herschel-Bulkley rheology, was used to back-analyze the physical experiments. The calibrated numerical model was then used in a back-calculation to investigate the effects of viscosity on the deposition process. The results show that as submarine debris flows mix with water during the deposition process, shear stress at the slurry-water interface generates a vortex that leads to a swirl-wedge front head. High-viscosity slurry flows with a swirl-wedge front head travel at a higher aspect ratio and with a greater radius of rotation. Hydroplaning was observed when the front head was lifted by water during flow. The lifting height increased with flow depth fluctuation. Higher viscosity slurry was found to lift more rapidly due to its larger vortex and the decrease in density at the front head over time, both of which promote fluctuation. Although a high-density slurry has a greater lifting height, the ratio of lifting height to front head height is lower, indicating a smaller lifting force influence. Lower density flows have higher kinetic energy as the transfer of potential energy into kinetic energy is more efficient. Kinetic energy dissipation comprises three stages: (1) gravity-dominated coherent flow and hydroplaning lead to a rapid increase in kinetic energy; (2) sharp reduction in kinetic energy as slurry mixes with water, coherence and hydroplaning are reduced, and the influence of the shear stress increases; (3) slurry mixed very well with water, turbidity current dominates the kinetic energy dissipation. High-density slurry dissipates quicker in the last two stages. In stage 3, which dominates the temporal evolution of the debris flow, the Froude number is lower than 1, the flow thins and elongates, and the deposition process of submarine debris flows is dominated by gravity, and the difference of morphology of the different cases become clear. [ABSTRACT FROM AUTHOR]

In order to investigate the seismic behavior of steel beam to steel-reinforced concrete filled square steel tubular column connections, five specimens were tested by quasi-static tests. The influences of end-plate thickness, bolt diameter, concrete strength and axial compression ratio on the load-carrying capacity, moment-rotation curve, energy dissipation capacity, load degradation, rigidity degradation, ductility and ultimate failure modes of end-plate connections were analyzed. The experimental results show that these new type of composite connections belong to the category of semi-rigid connections, and the initial rotational stiffness of connections increase with end-plate thickness and bolt diameter, but the utmost rotational capacity of connections decrease with end-plate thickness. The connection shows excellent behavior in terms of ductility and energy dissipation when the strength of connection is controlled by end-plate or steel beam. The load degradation coefficients of all specimens are between 0. 8 and 1.0, varying within a narrow range. Compared with load degradation, the rigidity of specimens degrades seriously. Moreover, the high strength bolt should avoid brittle failure in the design procedure. [ABSTRACT FROM AUTHOR]

The results of an experimental research involving the testing of six bolted moment-resisting connections under simulated seismic loading conditions were presented. The test specimens modeled the interior joint of a moment-resisting frame consisting of concrete-filled double skin tubular column and H-shape steel beams with reinforced concrete slab using high-strength bolts and T-stub connectors. To investigate the seismic behavior of the composite joints, the failure modes, hysteretic performance, shear strength, bearing capacity degradation, rigidity degradation, energy dissipation and strain were evaluated in detail. The test parameters varied including the axial load level on the column, the stiffener, the size of T-stub, the thickness of slab and the reinforcement ratio in slab. The experimental results indicate that the compressive capacity in column and the shearing capacity in joint are improved by the inserted tube. In some extent, the increase of reinforcement ratio in slab (1% ≤ ρ ≤ ρmax) and the decrease of the loading level on the column (n ≤ 0.3) will improve the total energy dissipation and reduce the ductility of joint, without obvious influence on the joint the bearing capacity. The seismic behavior of joint will be affected by the thickness of T-stub flange and the stiffener. [ABSTRACT FROM AUTHOR]