Strength Criterion Research Articles

A Study on Improving the Construction of Tunnel Steel Ribs Using High-Tensile Long Bolts

Steel ribs installed to enhance tunnel stability have consistently been criticized owing to their structural vulnerabilities and on-site construction inconvenience. Therefore, this study aims to address these issues and contribute to safer tunnel construction. To address the structural weaknesses resulting from the reduced steel section at the upper and lower junction parts of the tunnel steel ribs as well as the keystone junction parts, reinforcement was achieved by using long high-tensile bolts and steel bars. Test results on the bending strength of the junction revealed that the upper and lower junction parts exhibited a bending strength 1.38 times higher than those of the general sections of steel ribs, and the keystone junction parts showed a bending strength of 1.70 times higher, meeting or surpassing the equivalent strength criteria. Moreover, by utilizing high-tensile long bolts with adjustable heights, the constructability and construction speed were both enhanced. Consequently, it was determined that construction costs could be reduced by 2.42% and that the construction speed could be improved by approximately 333 h/km.

Stability assessment of jointed rock capturing roughness degradation under cyclic loading with special reference to railway formation

Repeated train loading on a jointed rock subgrade can cause excessive displacements of certain discontinuities leading to instability. Repeated shearing of discontinuities leads to a gradual reduction in joint roughness (i.e. wearing of asperities), which is quantified by the change in the joint roughness coefficient (JRC). This process reduces the joint shear strength over time. In this study, the classical shear strength criterion proposed by Barton and Choubey (1977) is extended to capture the influence of cyclic loading on joint degradation and the corresponding shear strength reduction, also considering the scale effect. This modified cyclic shear strength is implemented in FLAC-3D and validated with conventional cyclic triaxial data available from selected past studies. The model is applied to a simulated real-life track operating over a jointed sandstone formation commonly found towards the eastern coast of NSW. A modified limit equilibrium approach based on an Equivalent Factor of Safety (EFOS) is introduced and adopted to quantify the extent of instability, whereby an increase in the number of loading cycles affects a decrease in the EFOS of an unstable block. For a specific joint strike inclined to the track, the potential adversities are exacerbated when the joint dip angle is greater and when the initial JRC is smaller. In this paper, alternative geometrical combinations and different initial joint properties are considered to determine the worst combination of JRC and joint orientation upon cyclic train loading. As most past studies adhere to traditional static load analyses, the extended shear strength criterion described in this study is novel, and it offers significant practical benefit for railways that are subjected to prolonged cyclic loading.

Theoretical study on 3D elastic response and first layer failure strength of composite cylinders subjected to axisymmetric loadings

The traditional Lekhnitskii 3D elastic theory can obtain the exact stress and strain response of the composite cylinder under the axially symmetric loadings. However, when the cylinder contains 0° winding layers or isotropic layers, some calculation parameters corresponding to the two kinds of special layers will become singular. By analyzing the continuity of singular parameters and calculating their limits, the problem of singular parameters can be effectively solved and the Lekhnitskii theory can be extended to composite thick-walled cylinders with arbitrary winding angles. Furthermore, based on the Chang-Chang strength criterion of composite layers and the ideal elastic-plastic assumption of isotropic metal layers, the theoretical calculation method of first layer failure strength and the corresponding failure modes of the composite cylinders subjected to axisymmetric loadings was proposed. Then, the composite cylinder with metal liner was fabricated by fiber winding process. The experimental blasting pressure of the cylinder was 52.8 MPa with a major failure mode of fiber tensile fracture. Based on the proposed theoretical method, the cylinder's first layer failure strength of internal pressure was 44.1 MPa, and the initial failure mode was also fiber tensile fracture. The predicted result of the first layer failure strength was lower than the experimental results. The result proved the safety and economy of the proposed theoretical method for the initial design of the composite cylinder.

Experimental Study on the Shear Strength of Different Interfaces of Fine-Grained-Tailing-Filled Geotextile Tubes

As damming material, fine-grained tailings present challenges such as low dam strength and poor stability. To address these issues, this study employs geotextile tube technology to mix water with fine-grained tailings, forming a tailing slurry with a concentration of 60%, which is filled into a geotextile bag to form a geotextile tube, so as to improve the stability of fine-grained tailings. The shear strength characteristics of each interface under different consolidation times and different filling degrees were studied via an indoor shear experiment, including the shear strength of tailing particles, that between tailings and geotextiles, and that within geotextile tubes themselves. The results show that the shear strength of each interface conforms to the Mohr–Coulomb strength criterion, and that the interface cohesion is greatly affected by the consolidation time, while the interface friction angle is mainly affected by the filling degree. Moreover, the shear strength comparison, based on the comprehensive friction angle concept, indicates a substantial increase in shear strength at the interfaces between geotextile tubes compared to both that of the tailings themselves and the interface between tailings and geotextiles, highlighting the reinforcing effect of the geotextile tube filling technology on tailings’ shear strength.

The relationship between asymmetrical grip strength criteria and fall incidence among middle-aged and older Chinese adults.

Current handgrip strength (HGS) protocols employ a variety of criteria, affecting the assessment of asymmetric HGS. The impact of these different criteria on fall prediction is understudied. This study was devised to compare the relative performance of average and maximum HGS asymmetry criteria as tools to predict fall incidence among middle-aged or older adults in China. 9627 Chinese adults 50 + years of age who were participants in the China Health and Retirement Longitudinal Study (2013-2015 waves) were evaluated. The measurement of HGS was achieved based on either the maximum recorded value (HGSmax) or the average (HGSave), and these values were employed for the calculation of HGS asymmetry. Fall incidence over a 2-year period was evaluated based on self-reported data. Logistic regression analyses were utilized to determine the predictive performance of HGSmax asymmetry or HGSave asymmetry when gaging 2-year fall risk. Significant differences in overall rates of HGS asymmetry and the rates of subdivisions thereof were observed when comparing the HGSmax and HGSave criteria, with moderate consistency (kappa = 0.599, p < 0.001). Over the 2-year follow-up period, 1743 fall incidents were recorded. Adjusted logistic regression models indicated that only HGSmax asymmetry > 30.0% was significantly related to fall risk (p = 0.034, odds ratio = 1.36, 95% confidence interval: 1.02-1.81). These findings highlight the importance of HGS criteria in detecting HGS asymmetry, and suggest that HGSmax is a more robust criterion for predicting fall risk among Chinese adults 50 + years of age.

Theoretical study on the water-induced weakening of rock based on microstructural mechanics approach

For rock structures exposed in the natural condition, water-induced weakening (including water softening and chemical weathering) is thought to be the main reason for its’ stiffness and strength degradation, thus it is of great significance to study the mechanical properties of rocks under the influence of water. In this study, a hexagonal close-packed particle assembly (2D) composed of bonded circular particles with same diameter is considered to approximate a typical soft rock, where the composite contact model for rock materials considering the water-induced wakening is adopted to define the microscopic mechanical reactions between particles. Based on homogenisation theory and lattice model, the stress-strain relationship and strength criteria for rock considering water-induced weakening, as well as the quantitative correlation between macroscopic elastic and strength parameters with microscopic parameters are obtained. The effects of water softening and chemical weathering respectively characterised by saturation and mass loss ratio on macroscopic mechanical behaviours of rock are analysed in detail. The long-term ageing effects of water-induced weakening are also analysed. All results are in good agreement with the laboratory test results, verifying the applicability of the theoretical solution for analysing the effect of water-induced weakening on mechanical behaviours of rock.

Design for early-age structural performance of 3D printed concrete structures: A parametric numerical modeling approach

This paper presents a design framework based on structural performance of 3D concrete printing (3DCP) that considers three strength criteria for early-age failure modes: plastic collapse, elastic buckling, and flexural collapse. A simulator of structural behavior during printing was developed to take any shell or linear model, slice it into layers, perform incremental structural analysis layer by layer, and assign the respective material properties by adjusting the age of each layer when a new one is added. Then, finite element analysis for each printing stage indicates whether collapse might occur based on rheological and mechanical material properties over time. Printing experiments validated the criteria based on collapse layer estimation for a solid cylinder (plastic collapse), a thin-wall structure (elastic buckling), and an overhang structure (flexural collapse). Plastic collapse was most accurately predicted by a Drucker-Prager yield criterion for an unrestrained base and by a Modified Lade and Mohr-Coulomb criterion for a partially restrained base, while elastic buckling was predicted by linear elastic analysis. Additionally, this paper introduces flexural collapse as a distinct failure mode in early age 3DCP, proposing design criteria for overhang structures based on printing experiments. Experimental lessons learned were used to establish design constraints to aid the design of 3DCP structures, which were tested in the design of a hollow column and a cantilever structure. This study advances computational design for 3DPC structures with a new design methodology that combines constrained design and parametric numerical modeling.

Mesh-free SPH modelling of sediment scouring and flushing considering grains transport and transformation

Sediment scour numerical simulation plays a critical role in the design of water-resistant foundation engineering, and this paper addresses a significant gap in most related studies, which often overlook the transformation of sediment and struggle to identify the actual riverbed obscured by yielding bed and suspended load. To tackle this challenge, a comprehensive sediment model based on the meshless Smoothed Particle Hydrodynamics (SPH) method was developed. Firstly, to enhance computational efficiency and mitigate the high cost of Fluid-Solid Interaction (FSI) between water and sediments, cohesionless sediment grains were modelled as non-Newtonian fluids, with yield strength determined according to a combined strength criterion. Subsequently, sediment transformation and identification were determined based on sediment particle velocity and shear stress, with the seepage force driving yield sediment particle motion at the interface. The effectiveness of this comprehensive sediment model was validated through comparison with three scour experiments. The results show better agreement between the model and experimental data, with a root-mean-square error of less than 2.17% in scour morphology simulation and successful identification of the actual post-scouring bed surface in each case. However, the free surface simulation in this model still exhibits slight error, with a root-mean-square error of less than 8.35%.

Bipolar coordinate solution of pillar stability for salt cavern energy storage

As one of the crucial carriers for large-scale deep underground energy storage, salt caverns have great prospects for development. Pillar in salt cavern energy storage (SCES) refers to the preserved rock mass between adjacent salt caverns, which plays a crucial role in maintaining the stability of the SCES. Given the limited research on the analytical solutions for assessing the pillar stability of SCES, this study proposes a stability analysis method that includes horizontal and vertical profiles. In the analysis of the horizontal profile, elasticity theory and the Mohr-Coulomb strength criterion are comprehensively utilized to determine the critical operating pressure of the cavern, the range of plastic zones, and the stress distribution within the pillar. In the analysis of the vertical profile, the shear stresses and additional axial stress caused by uncoordinated deformation at the interfaces are analyzed. Through case analyses involving different operating modes and pillar widths and by comparing the results with the results of numerical simulations, the following conclusions are drawn: 1) Damage is most likely to occur on one side of the pillar adjacent to the cavern, which is crucial for cavern stability; 2) Maintaining an alternating pattern of high and low pressure (asynchronous injection-production) in two adjacent caverns rather than maintaining equal pressure in two caverns (synchronous injection-production) can reduce the critical operating pressure of the SCES to some extent, thereby improving energy storage efficiency; and 3) When the width of the pillar is low, the radial stress may decrease at the center of the pillar, potentially leading to plastic failure. 4) Uncoordinated deformation causes an increase in the range of the plastic zone around the cavern and increases the likelihood of damage within the interlayer. These findings provide important theoretical methods and guidance for the stability assessment of pillars in SCES.

Plastic zone characteristics and rapid stability evaluation indexes of circular tunnels subjected to non-hydrostatic stress: A novel complex variable solution incorporating 3D rock mass strength

The morphological characteristics and distribution range of the plastic zone around tunnels, influenced by the true three-dimensional high geostress environment in deep engineering, constitute fundamental reference data for both tunnel design and the control of surrounding rock stability. Based on the GZZ three-dimensional rock mass strength criteria and the complex variable method, a novel semi-analytical method for solving the plastic zone of a circular tunnel subjected to non-hydrostatic stress is presented. The conformal mapping is employed to intricately transform the complex boundaries of plastic zones characterized by diverse shapes onto the unit circle boundary within the image plane. This framework proves invaluable for the precise analytical process of the complex plastic zone morphology and the plastic influence range within the surrounding rock under complex stress conditions. In contrast to traditional analytical methods, the efficacy and versatility of our proposed approach are substantiated. Notably, it demonstrates unique advantages, particularly in the context of non-hydrostatic stress fields and varied rock mass parameters, with respect to predicting both surrounding rock stability and plastic zone morphology. Through the analysis of numerous cases, the study reveals the systematic patterns of influence that in-situ stress and surrounding rock characteristic parameters have on the shape and maximum depth of the plastic zone. The results indicate that (1) there are notable disparities in the morphology and extent of the plastic zone between the GZZ and GHB criteria; (2) the transition of the plastic zone in surrounding rock from U-shaped to V-shaped is significantly influenced by the geostress-to-strength ratio Kσ; (3) there is a notable linear correlation observed between the maximum plastic zone thickness rmax and both Kσ and the stress concentration factor KSCF, importantly, this correlation is independent of far-field stress and the brittleness characteristics of the surrounding rock. These findings provide a novel discriminative method for the rapid analysis of surrounding rock stability in deep circular tunnels.

Characteristics of sandstone unloading creep and modelling for safe tunnel construction under high perimeter pressure and high pore water pressure condition

Research on the properties of sandstone in the tunnel environment has been conducted due to the building industry’s rapid development, which is gradually involving underground water. Sandstone used in tunnel construction is susceptible to high perimeter and water pressures as a result of the abundance of sand and gravel close to groundwater, which might result in mishaps resembling collapses. The modified Burgers Model for the Malm dataset is the foundation of this study, which aims to reduce the internal crack extension caused by sandstone’s unloading creep. First, the study increased the material’s Poisson’s ratio in accordance with the Mohr–Coulomb strength criterion and builds a triaxial loading model on its foundation. Next, it analyzed the extension of the fracture surface of sandstone while taking high peripheral pressure and high hydraulic pressure into account. Finally, it discretized the unloading creep of sandstone using the improved Burgers model. On the basis of the model put forward in the study, experimental validation was then done on the Malm dataset. The sandstone would reach the final rupture area without any protection measures in just 10 days, but the model suggested in the study can delay this time to 200 days, while the effects of the other three models would delay this time by 75, 60, and 41 days, respectively. The model’s breadth was indicated by the linear fit value of 0.9827 for 36 experiments. The experimental findings demonstrated that the model suggested in the study can successfully lower the rate of sandstone unloading creep and increase worker safety.

Риск-ориентированный анализ безопасности и защищенности промышленных объектов на основе характеристик прочности и ресурса

The concept of computation and experimental determination of safety and protectability of industrial facilities on parameters of risk of initiation of refusals, accidents and disasters taking into account possibility of regular and emergency situations is considered. The scientifically substantiated, normalized and controlled parameters of risks estimated by criteria of strength, life-time and survivability are its basis. Risks at the same time are estimated on probabilities of initiation of emergency situations and losses accompanying them at their interdependence. It is shown that generally safety is defined by ability of installations not to pass into emergency and catastrophic states with drawing significant damages to the person, a technosphere and environment; the risk is defined by probability of initiation on installation of adverse situations and possible losses from these situations; protectability is defined by ability of installation to resist to initiation and an evolution of adverse situations (refusals, accidents, disasters) in regular and emergency conditions. The new perspective direction for maintenance of conditions of safe service of industrial facilities is that which initially forms the level of their protectability, and this protectability is defined by the formed and acceptable risks. In this case the solution of basic problems of protectability, safety and risk has to be guided surely by the solution of problems of strength, a life-time, survivability in their direct interaction This circumstance is based on a quantitative estimation of conditions of service damages accumulation and on the analysis of conditions of transition from regular to the damaged and limit states of installation taking into account criteria of strength, fatigue life and survivability. The solution of practical problems of maintenance of strength, life-time and safety within of strength, life-time and risk-focused design assumes determination of nominal and local stresses from service loadings in the most loaded zones with use of characteristics of mechanical properties of constructional materials. In the paper it is put and solved the new scientific and almost important problem about risk-focused definition, maintenance, increase and a standartization of complex safety and protectability of technosphere installations by criteria of the acceptable and controlled risks.

True triaxial unloading test on the mechanical behaviors of sandstone: Effects of the intermediate principal stress and structural plane

A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states. The experimental results indicate that the dip angle of structural plane (θ) and the intermediate principal stress (σ2) have an important influence on the peak strength, cracking mode, and rockburst severity. The peak strength exhibits a first increase and then decrease as a function of σ2 for a constant θ. However, when σ2 is constant, the maximum peak strength is obtained at θ of 90°, and the minimum peak strength is obtained at θ of 30° or 45°. For the case of an inclined structural plane, the crack type at the tips of structural plane transforms from a mix of wing and anti-wing cracks to wing cracks with an increase in σ2, while the crack type around the tips of structural plane is always anti-wing cracks for the vertical structural plane, accompanied by a series of tensile cracks besides. The specimens with structural plane do not undergo slabbing failure regardless of θ, and always exhibit composite tensile-shear failure whatever the σ2 value is. With an increase in σ2 and θ, the intensity of the rockburst is consistent with the tendency of the peak strength. By analyzing the relationship between the cohesion (c), internal friction angle (φ), and θ in sandstone specimens, we incorporate θ into the true triaxial unloading strength criterion, and propose a modified linear Mogi-Coulomb criterion. Moreover, the crack propagation mechanism at the tips of structural plane, and closure degree of the structural plane under true triaxial unloading conditions are also discussed and summarized. This study provides theoretical guidance for stability assessment of surrounding rocks containing geological structures in deep complex stress environments.

Probabilistic assessment of the durability of metallurgical equipment based on microstructural modeling of the stressed state of the material

A methodic is developed for the probabilistic assessment of durability indicators of metallurgical equipment according to strength criteria based on microstructural modeling of the stressed state of the material, the distinctive feature of which is the ability to take into account its anisotropy and structural defects in the form of non-metallic inclusions or the consequences of poor-quality heat treatment. This methodic can be used to make a reasonable choice of material for parts when designing of the equipment or developing of the structure of repair cycles at the renovation stage for objects entered to service. Keywords:metallurgical equipment, durability, life, material, structure, modeling, stressed state m.slobodianskii@gmail.com

Considerations for the structural design of wind turbine towers: A practical application

AbstractAiming to achieve efficient structural performance, this article presents a methodology for the design of the shell structure and dimensioning of the connections of an S355J2 tubular steel tower with a height of 80 m, compatible with a SWT‐2.3‐93 wind turbine. The tower is made up of three segments, interconnected by flanged connections made of high‐strength steel. The analysis considers various load cases, taking into account stress and resistance in different directions, as well as designing connections using Petersen's theory, according to maximum strength and fatigue criteria. The results indicate that the circumferential stresses are nearly negligible compared with the resistant stresses, while the shear stress is significantly higher at the base due to the torsional moment. Meridional stress determines the stability of the structure, requiring consideration of internal pressure for safety. Maximum stress values range from 135.00 to 168.47 MPa, depending on the location along the tower height. Flanged connections meet the strength and fatigue criteria, with the first flange enduring 63.0% of the fatigue effect and the second, 39.7%. Therefore, the results provide reliable information and methodologies for tower design, contributing to the practical and efficient development of these structures.

Understanding past rules of the art in columna-capreoli wood trusses

A transversely isotropic structural model for wood, based on a polytope strength criterion, is proposed and deployed in the analysis of solid wood columna-capreoli A-trusses reproducing the geometry and connection details of those currently erected in the Aula Magna of the Monastery San Lorenzo ad Septimum in Aversa. The predictivity of the polytope strength criterion is assessed verifying its capability of identifying the closest crisis mode against experimental evidence from a simple flexural test, with minimal wood sacrifice. The model is employed in parametric optimization analyses to infer a design provision for the columna-capreoli connection which appears to be in reasonable agreement with the rule of the art empirically inferable from the observation of many samples of open-node King Post A-trusses belonging to the architectural heritage in Campania of historical and artistic value. A final discussion examines a perspective of extending these optimization analyses to the sustainability of the built environment.

Behavior of wire arc additively manufactured 316L austenitic stainless steel single shear bolted connections

This paper aims to investigate the behavior of single shear bolted connections made of wire arc additively manufactured 316L austenitic stainless steel. A set of 44 wire arc additive manufacturing (WAAM) 316L austenitic stainless steel single shear bolted connections were included with consideration of various bolt positions, surface conditions and loading orientations respective to the printing layer direction. The geometric dimensions of the WAAM austenitic stainless steel plates were measured with the assistance of non-contact 3D laser scanning prior to tensile testing. Monotonic tensile tests were carried out to investigate the load-deformation responses, failure patterns and resistances determined by both the deformation and strength criteria of the single shear bolted connections. The effects of geometric and printing parameters on the single shear bolted connections were analyzed. Due to the absence of codified design provisions for WAAM austenitic stainless steel bolted connections, the suitability of the existing design rules originally developed for traditionally manufactured carbon steel and stainless steel bolted connections was examined. Design resistances calculated by the Eurocode 3 (prEN 1993-1-8 and prEN 1993-1-4), the American Specification (ANSI/AISC 370-21) as well as the prevalent design recommendations proposed in existing literature were compared with the obtained experimental results. It is shown that the abovementioned design methods offer conservative predictions for the resistances of WAAM 316L austenitic stainless steel single shear bolted connections. Further study is needed to improve the accuracy of design resistance predictions.

Determination of mine fault activation degree and the division of tectonic stress hazard zones

This article conducts a comprehensive study on the activation characteristics of faults in the mine and analyzes the distribution patterns of the original rock stress field. Through quantitative research and analysis, we determine the partitioning characteristics of tectonic stress in the mine field under the dual effects of fault activation and original rock stress. The study also reveals the significant impact of different fault activation characteristics and different tectonic stress partitions on the stability of roadway surrounding rock. Using the Mohr–Coulomb strength criterion as a foundation, we investigate the mechanisms of fault activation and establish a mathematical model for fuzzy comprehensive evaluation. This model enables us to determine the strength level of fault activation in coal seam 9 of the Limin coal mine and construct a geological structure model. It has realized the transformation of fault activation degree from qualitative evaluation to quantitative evaluation. The stress state analysis software is used to draw the division of tectonic stress dangerous areas under the synergistic effect of fault activation and original rock stress. We then analyze the impact on the stability of roadway surrounding rock in these different hazardous areas. Utilizing the fuzzy comprehensive evaluation method, we take into account the impact of faults on the distribution characteristics of stress fields and the stability of roadway surrounding rock. This approach enables us to more accurately and comprehensively determine the hazardous areas of tectonic stress in the mine field under the dual effects of faults and original rock stress.

Limitations of composite strength theory for predicting the ultimate strengths of layered 3D printing polymers

Composite laminates and 3D printing materials both have layered structures. Although the Tsai–Hill composite strength criterion is useful for predicting the strengths of some 3D printing polymers made with fused filament fabrication (FFF), our experimental and theoretical studies showed that this criterion has some limitations in predicting the strengths of other 3D printing polymers. In this study, a new quadratic strength criterion was employed to predict a conservative lower bound for the strengths of polymers made with FFF and selective laser sintering (SLS). The printing surface angles of the printing specimens ranged from 0° to 90°. Interestingly, the scope of this study unexpectedly widened from strength research to fracture mechanics research because dynamic crack branching was observed in some SLS specimens (printing surface angles ranged from 0° to 75°) under static tension—a novel phenomenon among 3D printing materials. Crack branching not only followed previous crack branching rules, such as rules on the crack speed and energy release but also presented new challenges for dynamic fracture mechanics theory.

Enhancing Load-Bearing Capacity of Calcareous Sands through Gel Stabilization: A Mechanical and Material Characterization Study.

Calcareous sands often display wide ring grain configurations, high intragranular porosity, a complex structure, and low grain hardness. These attributes typically do not meet the strength criteria necessary to sustain overlying infrastructure in civil engineering applications. This study investigates gel stabilization techniques, blending gel material with calcareous sand at concentrations ranging from 5% to 22%, followed by curing periods of 3 to 28 days to evaluate the load-bearing capacity. Subsequently, an unconfined compressive test is performed to determine the gel material content in stabilized specimens and investigate the influence of gel material types. The gel material-to-sand ratios employed are set at 5%, 10%, and 16% for Portland cement and 13%, 16%, and 22% for gypsum. After that, a triaxial consolidated undrained test is conducted to assess mechanical behavior, pore water pressure, and mechanical properties. The findings reveal increased dilation, stress-strain hardening, and softening post-yield, regardless of gel material type. Principal stress ratios, secant modulus, and cohesion show a positive correlation with maintenance duration and binder content, with implications for improved load-bearing capacity. The study also elucidates the qualitative relationship between secant modulus E50 and confining pressure.