Electrically conductive roller-compacted concrete (ERCC) is a novel functional construction material with self-heating ability, which can be applied to solve problems of low efficiency of crushed ...snow removal and deicing on expressway and airport runway, and difficult temperature control of dam structures. Natural aggregates with high sphericity and crushed aggregates with low sphericity are the sources of ERCC construction. However, the impact of aggregate sphericity on ERCC is currently unclear. This study performed the macro and micro experiments of the core samples from a large-scale ERCC specimen with rolling construction technology. Based on the experimental results, the mechanical properties of ERCC with different aggregate sphericities are analyzed with the highly detailed simulation method by coupling continuous medium method and discontinuous medium method. The results show that increased sphericity of the aggregate can lead to a decrease in the number of aggregates generated, and the simplified spherical model adopted in the traditional mesoscale simulation method will underestimate the strength of concrete. Furthermore, When the sphericity of aggregate is 0.645, the compressive strength and splitting tensile strength of ERCC are increased by 25.34% and 35.04% compared with that of spherical aggregate respectively. In engineering, the crushed aggregate is suggested for rolling construction of ERCC. The results are in accordance with the statistical laws of the field statistical data in engineering practice.
Composite bucket foundation (CBF) is an environmentally friendly form of offshore wind power foundation. By virtue of the air-floating subdivision structure in the bucket, the foundation has a ...self-floating characteristic and can allow for long-distance air-floating towing and transport. In this study, first, a numerical analysis was performed on the towing motion characteristics of CBF, and the formula for foundation stability was deduced; then, we probed into the variation rules of the natural period of the foundation with draft and analyzed the response amplitude operator (RAO) responses, added mass coefficients, radiation damping coefficients, and exciting forces (moments) of the composite bucket foundation under different drafts and different wave directions. Finally, we clarified the basic hydrodynamic characteristics of the composite bucket foundation in the frequency domain and adopted multiple random wave models to investigate the effects of different wave heights, periods, and spectral peak factors on the towing motion characteristics of composite bucket foundation.
The velocity pulse contained in near-fault ground motions have a tremendous impact on dam safety. Previous studies have mainly focused on the response of dams under near-fault seismic records without ...considering the obliquely incident seismic waves. In this study, the structure–soil interaction (SSI) is taken into consideration, and the nonlinear behavior of a conventional concrete roller-compacted concrete (CC-RCC) gravity dam under near-fault pulse records and non-pulse records is investigated with consideration of the obliquely incident P waves. On the basis of the dam site conditions, three groups of near-fault pulse records are chosen, and three corresponding non-pulse records are fitted by their acceleration response spectra. Combining with the viscous-spring artificial boundary, the wave input method is proposed to transform the near-fault seismic records into the equivalent nodal forces at the boundary of the foundation. The concrete damaged plasticity model is used for the nonlinear analysis. The results show that the pulse ground motions are more destructive than the non-pulse motions. The nonlinear behavior of the dam varies with the incidence angle of P waves and generally reaches a maximum at 60° and 75°, the worst damage occurs at the interface between different materials of the dam, and the spatial variation of its damage is very obvious under near-fault seismic records with various incidence angles. Therefore, the effect of the angle of obliquely incident seismic waves and near-fault pulse effect should be considered comprehensively in the seismic analysis of dams.
•Sliding support with large sliding displacement and high tensile strength for metal roof system is proposed.•Experimental test and numerical analysis results of the novel wind resistant sliding ...support were presented.•Large displacement and high tensile strength capacity was illustrated and compared with original designed support.•Wind loading capacity of a metal roof system using new support is calculated and illustrated for demonstration.
The metal roof is widely used in large-span spatial structures for its lightweight. However, the traditional rivet connection cannot effectively handle the large deformation caused by the temperature effect. In traditional sliding supports, the metal roof tears and the roof lifts due to insufficient sliding displacement or low tensile strength, which reduces the service life of the metal roof system. To solve this problem, a new sliding support was proposed by changing the structure of the traditional sliding supports. The model experiments were performed to attain the tensile strength and eccentric mechanical properties. Afterward, a numerical simulation was adopted to investigate the corresponding performance of the proposed sliding support. A quantitative model of the relationship between the eccentric distance and the ultimate tensile strength was established to attain the true strength when the supports are installed at different positions of the roof. For structures, the wind load capacity and failure modes of metal roof systems with different sliding supports were simulated and investigated. The results showed the preference of the proposed sliding support over the traditional one. Compared to the traditional sliding support, the sliding displacement of the proposed sliding support was increased by 2.0–3.24 times and the ultimate tensile strength was increased by 3.14–3.87 times. Therefore, choosing the proposed sliding support instead of traditional rivet connections provides a more flexible and suitable way for large-span structures. Thus, the proposed sliding support is a promising connection in civil engineering.
Excellent electro-thermal performance ensures that electrically conductive roller-compacted concrete (ERCC) has the potential to solve infrastructure safety problems caused by low temperature ...environment. Vibration rolling is an effective way to improve the construction quality of ERCC. However, quantitative evaluation of vibration induced non-uniform distribution of aggregates in concrete is challenging due to the lack of monitoring method. Against this background, two kinds of continuous-discontinuous coupling methods are proposed to simulate the rolling construction and analyze the uneven stratification of aggregate after rolling respectively. The result shows that the simulation method of rolling construction developed in this study can simulate the actual rolling construction process well. Although higher frequency, exciting force and lower speed can improve the compaction effect, it is also easier to cause aggregate uneven stratification (AUS). The compressive strength reduction caused by AUS can reach 17.04%. Therefore, in the actual construction process, the selection of parameters in these ranges should be more careful. The results can provide guidance and important reference for rolling construction of ERCC.
•Proposed the rolling motion control method for roller entity.•The rolling resistance constitutive model meso-parameters of ERCC were calibrated.•Highly refined continuous medium models, including aggregate, ITZ and mortar.•The effects of rolling parameters on AUS were analyzed.•The effects of AUS on concrete performance were studied.
•SCGF is developed to promote the utilization of industrial solid waste.•Attention-based tree models are adopted to predict the mechanical properties of SCGF.•An intelligent design method of SCGF is ...proposed and verified.
To promote the utilization of industrial solid waste, a new green binder system namely SCGF for sustainable concrete is developed, in which slag-fly ash is activated by soda residue-carbide slag. However, the mix design of the SCGF is challenging due to heavy workload and the lack of theoretical basis. The relationship between mix proportion and mechanical properties of SCGF needs to be accurately expressed. In this paper, an intelligent design method of SCGF is proposed by coupling the attention mechanism, machine learning and multi-objective heuristic optimization algorithm. After training with experimental data, the prediction performance of attention-based tree model is evaluated. Multiple Pareto optimal solutions can be obtained by the proposed intelligent mix proportion design method. The results show that attention-based tree models perform higher accuracy (accuracy > 95 %) and better measures than that of classical tree models. Compared the strength and cost of SCGF to cement mortar, the mix proportion designed in this study has obvious advantages in environmental protection and economy (>50 % cost saving). Therefore, the proposed method can provide a theoretical basis for the recycling and utilization of industrial solid wastes.
Concrete dams are prone to cracks during construction and operation process. Cracks on the upstream surface may induce the risk of hydraulic fracturing, thereby significantly reducing the safety of ...dam structure. Nevertheless, image processing technology, non-destructive testing technology and structural performance analysis technology with cracks are in a relatively independent state, leading to difficulties in analysis of actual cracks combined with numerical simulations. This paper proposes a novel approach for combination of intelligent identification technology and refined finite element method (FEM) for modeling and simulating the hydraulic fracturing resistance of the actual crack in concrete dams. With image processing technology and non-destructive testing technology, direction and depth of actual cracks are identified and extracted, then the 3D geometric model of actual cracks is generated. The refined model with the identified actual crack is constructed by the node projection strategy. This approach is used to assess the hydraulic fracturing resistance of the concrete dam with actual cracks in the alpine region. The results demonstrate that the critical crack depth of hydraulic fracturing is 12.93 m, and the opening width is 1.01 mm, which is 2.53 times the limit value for Class D cracks in the code (DL/T5251–2010). The refined modelling method based on actual crack detected on site can accurately evaluate the crack state compared to the conservative code.
•A novel approach for generation and simulation of the 3D actual crack is proposed.•Refined FEM model with the identified actual crack is established by node projection strategy.•Hydraulic fracturing resistance of the actual crack in the concrete dam is evaluated.•Refined simulation method based on actual crack can accurately evaluate crack state compared to the conservative code.
•A novel simulation method for massive concrete structures with cracks is proposed.•Refined simulation model with irregular cracks is established based on the method.•The method reduces meshing ...difficulty in complex 3D models with cross-scale cracks.•Crack propagation during dam construction and under an earthquake is examined.
The irregular cross-scale cracks in massive concrete structures threat the safety. Due to huge difference in scale between structures and cracks, the stability of the irregular cross-scale cracks (millimeter level) cannot be accurately analyzed in the massive concrete structures (hundred-meter level). The imprecision of the mesh model is incompatible with existing advanced cracking methods. To address the problem, this paper presents a novel numerical simulation method for irregular cross-scale cracks in massive concrete structures with node projection strategy. The elements that the crack passes through are identified on the original mesh model without cracks, and the numerical simulation model with irregular cracks is generated by projecting the corresponding nodes of elements that the crack passes through onto the crack point cloud. The primary advantage of this method is that it does not require modifying the original element types or meshing the geometric model with cracks. To verify the present method, the three-point bending beams of concrete with regular cracks and irregular cracks are examined with experiment and numerical simulation. It demonstrates that the shape characteristics of an irregular crack can result in distinct tension damage patterns compared to a regular crack. In addition, the crack propagation during dam construction and earthquake loading is investigated to demonstrate the applicability of the present method for simulating crack propagation in massive concrete structures.
We used resting-state fMRI to evaluate longitu- dinal alterations in local spontaneous brain activity in Parkinson＇s disease （PD） over a 2-year period. Data were acquired from 23 PD patients at ...baseline and follow-up, and 27 age- and sex-matched normal controls. Regional homogeneity （ReHo） and voxel-based-morphometry （VBM） were used to identify differences in local sponta- neous brain activity and grey matter volume. With disease progression, we observed a progressive decrease in ReHo in the sensorimotor cortex, default-mode network, and left cerebellum, but increased ReHo in the supplementary motor area, bilateral temporal gyrus, and hippocampus. Moreover, there was a significant positive correlation between the rates of ReHo change in the left cerebellum and the rates of change in the Unified Parkinson＇s Disease Rating Scale-III scores. VBM revealed no significant differences in the grey matter volume among the three sets of acquisitions. We conclude that ReHo may be a suitable non-invasive marker of progression in PD.
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