查看更多>>摘要：? 2022 Elsevier LtdIn this study, we aiming at the problems of severe surrounding rock deformation and support failure during the reuse of gob side entry retaining, we conducted field observations, theoretical analyses, numerical simulations and engineering projects to analyze the surrounding rock deformation mechanism, and we proposed a corresponding combined support technology. The results show that: (1) the surrounding rock failure is mainly affected by the advance abutment pressure, followed by the lateral abutment pressure, and the lateral abutment pressure has a certain lag. (2) According to borehole detection and theoretical analyses, multiple dynamic pressures influence the relationship between roadway support system and surrounding rock state. (3) The high proportion of inelastic zone volume is the main cause of severe surrounding rock deformation. Consequently, we developed a combined support technology, and applied it to an engineering project, realizing roadway stability; thus, the study provides a reference for similar engineering projects.
查看更多>>摘要：? 2022 Elsevier LtdAdditive manufacturing enables fast manufacturing of polymer gears directly from a 3D model. Failed polymer gears can be replaced easily and quickly using many different materials. Mechanical and thermal characteristic of gears manufactured using additive manufacturing are mostly dependent on selected manufacturing parameters and material. In this research, the influence of the most important manufacturing parameter (infill percentage) on failure types and service life of additive manufactured nylon gears is experimentally investigated. The experimental tests were carried out using a custom-made gear testing device. Samples with 20, 40, 60, 80 and 100% of infill volume were tested. Infill type, shell thickness, and manufacturing speed were the same for all samples. Service life of gears was tested and failure types were characterized.
查看更多>>摘要：? 2022 Elsevier LtdDifferent proportions of coral aggregate, coral sand and basic magnesium sulfate cement (BMSC) were used to prepare the basic magnesium sulfate cement-coral aggregate concrete (BMSC-CAC), which was applied in the island and marine engineering as a brand new type of concrete. The specimens of BMSC-CAC exposed to elevated temperature (100°C, 300°C, 500°C, 700°C, and 900°C) were tested by the non-destructive method to obtain the surface characteristics at different temperatures. A new parameter, elevated temperature damage (D), derived from continuous damage mechanics (CDM) was applied to indicate the degree of concrete damage after being exposed to elevated temperature. The surface characteristics of the specimen were changed significantly at different temperatures, especially the aggregate colours. The fitting relationship between ultrasonic velocity and temperature was established, which can be well used to fit different types of concrete. The elevated temperature damage degree (D) was defined by damage mechanics, and the mathematical relationship between D and the residual compressive strength was discussed.
查看更多>>摘要：? 2022 Elsevier LtdThe effect of damping rate on the failure tendency of a truck cab suspension swing arm was numerically investigated. Firstly, the mechanical design of the swing arm was carried out using topology optimisation by taking the standard load cases into account. Displacement differences which occurred in the front cab suspension springs, as a result of the cab roll, were obtained for an uneven road surface by using the Multibody Dynamics (MBD) model of the truck. Using these data, full transient Finite Element (FE) analyses and arm fatigue analysis were conducted for various damping characteristics of the shock absorber. Results showed that, reducing the damping ratio of the shock absorbers by, e.g., 50% in comparison with the reference value, may result in swing arm damage under dynamic loading conditions. Therefore, it was concluded that, damping rate should be considered in the design stage of cab suspension components which can be categorised as a safety system.
查看更多>>摘要：? 2022 Elsevier LtdOn October 30th 2020, offshores of Samos Island, Greece was hit by a shallow earthquake of Mw = 6.9 moment magnitude. Located 76 km away from the earthquake's epicenter, the mid-rise reinforced concrete (RC) building stock of the densely populated Izmir Bayrakli district experienced the most severe structural damage. Although the horizontal peak ground acceleration recorded at the site (PGA = 0.11 g) was well below design values recommended by the past and the present Turkish seismic codes, many buildings suffered heavy damage and 12 buildings collapsed, resulting in a death toll of 117. This paper aims to identify the seismic performance of mid-rise infilled RC frame buildings in Bayrakli by investigating the ground motion recordings, local soil conditions, characteristics of the building stock and the observed damages. The structural performance of 140 RC buildings between 7 and 12 stories that have exhibited poor performance during the earthquake was inspected in detail based on the field surveys conducted right after the earthquake. A database was created documenting the number of stories, major seismic deficiencies, date of construction, geographic coordinates, damage state of structural members and masonry infill walls of the inspected buildings. The localization of structural damage could be partially attributed to the amplified long-distance seismic waves for 0.5–1.5 s periods range due to local soil conditions and basin effects. Seismic vulnerabilities, structural deficiencies and construction quality of the buildings played a significant role in the experienced damage intensity. The influence of infill walls on the seismic performance of RC frame buildings is also clearly observed for code-compliant as well as aseismic buildings.
查看更多>>摘要：? 2022 Elsevier LtdThe deterioration of concrete caused by sodium sulfate attack (SSA) is a process of volume expansion and cracking layer by layer, causing the external solution to flow directly into concrete. Taking ettringite type of SSA as an example, this paper studies the SSA-induced deterioration of concrete. Based on Fick's law and reaction kinetic theory, the diffusion-reaction model of sulfate ion in concrete is proposed. Introducing the crack density coefficient, the chemical damage of concrete is characterized by expansion strain caused by sulfate products, and then the condition of boundary movement is further established. Using the finite element method, the Crank-Nicolson-Galerkin scheme governing equation of diffusion-reaction model is developed. On the basis of model validation, a numerical simulation is performed to analyze the temporal-spatial variation of sulfate ion and damage degree in concrete. The result show that, the SSA-induced cracking of concrete obviously lags behind the ion diffusion and chemical reaction.
查看更多>>摘要：? 2022 Elsevier LtdA flood protection structure was built around the industrial area of Nava Nakorn in Pathum Thani Province, Thailand to ensure the safety of the industrial estate. Three types of flood protection walls were constructed and completed in 2012, which were prestress corrugated concrete sheet pile and reinforced concrete retaining wall. A large-scale experiment using a large navy watercraft for generating the water pressure on the flood protection structure was performed. Finite element analysis for simulation the flooding over 4 months was also performed. Factor of safety (FS) against external and internal failures decreased with increasing the flooding levels; however, all FS values were higher than the typical requirement for geotechnical design. All bending moments and shear stress in the flood protection walls were found to be lower than the required design values. The knowledge gained from this research can be applied to other flood walls, in similar soft clay deposits.
查看更多>>摘要：? 2022 Elsevier LtdAiming at the karst-induced collapse of overlying sandy stratum, an equivalent numerical simulation method of karst-induced collapse is proposed in combination with the causation mechanism and physical model test result and applied in a project. The research results showed that: 1) The mechanism of karst-induced collapse of overlying sand layer is that the sand particles above fall into the karst cave and form a “funnel-shaped loose sand mass”. 2) The equivalent numerical simulation method can calculate the volume of the loose sand mass by introducing sand loose coefficient and the physical model test of collapse angle in sandy stratum, which provides a new method for evaluating the disturbance analysis of karst-induced collapse of overlying sand layer. 3) For the applied project, the calculation results indicate that the karst-induced collapse of overlying sandy stratum has a greater impact on surrounding strata and segment lining structure when the tunnel is completely constructed.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, a three-dimensional non-linear finite element model of aluminium drill pipe body and tool joint assemblies is established to analyze the effect of interference on ultimate strength and failure modes. Johnson-Cook model is selected to describe the plastic behavior and failure phenomena. For quickly meshing thread connection into hexahedron grids, grid parametric modeling program is written by Matlab software. The interference assembly is carried out by coupling the temperature field with the stress field. The accuracy of the model is verified by experiments, and the error is less than 6%. The ultimate torsional strength, ultimate tensile strength, ultimate torque under different tension, failure modes and anti-loosing ability are obtained for different interference values. The result shows that interference values have little impact on ultimate tensile strength but have positive effect on torsional strength. For the coupling action of tension and torque, the ultimate strength for larger interference value is greater than smaller interference value. Besides, critical values for failure mode transition are found under different interference values. When tension exceeds the critical value, the failure modes changes from thread body fracture to thread teeth failure. The anti-loosing ability increases with the increase of the interference, however, for the interference being greater than a critical value, the influence of the interference will be almost unchanged. The present results can help to determine the safe range of working parameters for aluminium drill pipe in practical engineering, and provide theoretical support for the optimization of interference in the production of aluminium drill pipe.
查看更多>>摘要：? 2022 Elsevier LtdStored solids loads on silo vertical walls are composed of two orthogonal components: the horizontal component that internally pressurizes the silo and the vertical wall frictional component that causes axial compression. For an imperfect cylinder, the elastic axial buckling resistance may be considerably raised by a uniform internal pressure as it alleviates the detrimental effect of the geometrical imperfections. However, at high internal pressures, the combination of axial compression and circumferential tension may result into a plastic instability that is commonly termed elephant's foot buckling. Both stabilizing and destabilizing effects of internal pressure are taken into account by EN 1993–4-1 in the buckling stress design of steel silos with isotropic walls under axial compression. In this paper, using non-linear Finite Element (FE) analyses, the effects of internal pressure on axial buckling of steel silos have been fully investigated and the Eurocode provisions on this issue have been thoroughly examined.
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