Effective Shear Research Articles

Physical Modelling of Rainfall-Induced Sandy and Clay-Like Slope Failures

Small-scale slope modelling was performed to evaluate the failure process of a landslide triggered by artificial rainfall. The model platform 2.3 m long, 1.0 m wide, and 0.5 m deep was used to build small-scale slope models with the same geometric conditions but different soil types/materials, including sand and two sand-kaolin mixtures with the same slope angle. The hydraulic response of the slope models under simulated rainfall conditions was monitored using volumetric water content, pore water pressure, and matric suction sensors installed at different depths and along different profiles. Slope surface deformation and failure development was also monitored. This paper discusses the factors affecting landslide initiation and propagation, and their relationship to the slope material, infiltration process, and overall soil resistance in a slope related to soil strength, effective stress, and matric suction contribution in the unsaturated part of the slope. Rainfall infiltration caused increase of volumetric water content, dissipation of suction in initially partially saturated materials of the small-scale slope models, resulting in a decrease in effective stresses and shear strength, which in turn led to the occurrence of movements and initiation of slope failures. The main observations arising from the results of the conducted tests relate to initiation and development of the observed instabilities of sandy and clay-like slopes. The test results have shown that within the slopes built from clean sand failure occurs due to groundwater level rising at the slope foot and further retrogressive failure towards the top of the slope, while in the slopes built from sand-kaolin mixtures, instabilities occur in the form of cracks in unsaturated conditions and are the result of matric suction dissipation due to rainfall infiltration.

Propagation characteristics of shear horizontal waves in piezoelectric semiconductor nanoplates incorporating surface effect

Elastic wave-based devices made of piezoelectric semiconductors (PSs) find wide applications in modern scientific and technological fields. Elastic waves propagating in PS nanostructures have a rich variety of propagation characteristics due to the interaction between deformation, polarization, and charge carrier, as well as the influence of surface effect. Based on the Gurtin-Murdoch surface model, we conduct an analysis of horizontally polarized shear (SH) waves propagating in an infinite n-type PS plate with nano-thickness in this paper. For the open-circuit and electrically isolated boundary conditions, the analytical frequency and phase velocity spectrum relations and cut-off frequencies of SH waves with anti-symmetric and symmetric modes are presented. The influence of the surface effect, initial electron concentration, and thickness of the PS plate on the propagation characteristics of SH waves, such as frequency spectrum, phase velocity, and cut-off frequency, are elaborated in detail. Numerical results show that propagation characteristics of SH waves are size-dependent, and the macroscopic effective shear rigidity is softened at the nanoscale due to surface effect, which thus leads to the reduction of the frequency and phase velocity of SH waves. Moreover, the propagation characteristics of SH waves can be manipulated by changing the initial electron concentration.

Cyclic Capacity of Monopiles in Sand under Partially Drained Conditions: A Numerical Approach

Cyclic loading of saturated sand under partially drained conditions may lead to accumulated strains, pore pressure buildup, and consequently reduced effective stress, stiffness, and shear strength. This will affect the ultimate limit state capacity of monopile foundations in sand for offshore wind turbines. This paper calculates the performance of large-diameter monopile foundations, which are installed in uniform dense sand, subjected to storm loading using the partially drained cyclic accumulation model (PDCAM). The simultaneous pore pressure accumulation and dissipation is accounted for by fully coupled pore water flow and stress equilibrium (consolidation) finite element analyses. Drainage and cyclic load effects on monopile behavior are studied by comparing the PDCAM simulation results with simulation results using a hardening soil model with small strain stiffness. At the end, a simplified procedure of PDCAM, named PDCAM-S, is proposed, and the results using this approach together with PLAXIS 3D and the NGI-ADP soil model are compared with the PDCAM results.

Analytical and numerical evaluation of quarter-elliptic-braced steel moment frames (QEB-MFs)

Concentrically braced frames (CBFs) have an excellent performance to the lateral seismic forces at the time of the mild earthquakes, but they are weak under severe seismic loads due to the occurrence of buckling of the bracing members and the lack of proper ductility in terms of energy absorption and do not behave properly. This article introduces the new quarter-elliptic brace. Adding this brace to the moment frame improves the stiffness of this system and impedes the excess structural deformation in this system. In the present study, a precise analytical formulation is presented using the concept of strain energy and Castigliano’s theorem in order to calculate the elastic lateral stiffness of a two-dimensional single-span and single-story steel moment frame equipped with quarter-elliptic brace. In this relation, all effective factors, including axial and shear forces as well as bending moment, were considered for all frame members. The proposed formulation was controlled by the results of various examples in OpenSees software. The error percentage between the results obtained from the newly developed formulation and numerical analysis of finite elements is very insignificant so that it can be ignored. Also, the seismic performance of this system was investigated according to the FEMA P695 methodology for near-field and far-field ground motion records compared with the intermediate moment frame. The results showed that using a quarter-elliptic brace in the intermediate moment frame improves the seismic performance of this system.

The proneness assessment of a mineral deposit to tectonic rockburst: A case-study of Yuzhnoe deposit

The procedure of the proneness assessment to tectonic rockburst (with fault-slip mechanism) is insufficiently described in guidelines and regulatory documents, thus, additional investigations are required in this regard. The tectonic rockburst proneness criteria at Yuzhnoe deposit, Primorye are considered to be the location of large faults in the modern stress field and the critical stress state of rock mass. It is found that the maximum (compression) principal stress, reconstructed using the methods of tectonophysics and the data on rock mass faulting, fits the orientation of the maximum compression in the stress field, determined by instrumental measurements. In this stress field, in the plane nearby the plane of the effective maximum shear stresses, a large fault exists and is traced underground and on ground surface for more than 10 km. The analysis of geodynamics at the deposit, deformation of boundaries of underground excavations, core discing in wells far from the underground excavations, as well as rock bursts both at the study deposit and at the similar Nikolaevskoe deposit nearby shows that the level of the natural stresses at Yuzhnoe deposit is rather high and the rock mass is everywhere in the critical stress state. Yuzhnoe deposit is assumed to be to tectonic rockburst prone as both criteria are fulfilled: the rock massif is in the critical stress state and there is large fault which lies comfortably for mutual movement of rock blocks.The studies were carried out using facilities of the Center for Shared Use of Scientific Equipment at the Center for Processing and Storage of Scientific Data of the Far East Branch of the Russian Academy of Sciences, supported by the Ministry of Science and Higher Education of the Russian Federation, Project No. 075-15-2021-663.

Stiffness tailoring in sinusoidal lattice structures through passive topology morphing using contact connections

Structures with adaptive stiffness characteristics present an opportunity to meet competing design requirements, thus achieving greater efficiency by the reconfiguration of their topology. Here, the potential of using changes in the topology of planar lattice structures is explored to achieve this desired adaptivity and observe that lattice structures with rectangle-like unit-cells may undergo elastic buckling or bending of cell walls when subject to longitudinal compression. Under sufficient load intensity, cell walls can deform and contact neighbouring cells. This self-contact is harnessed to change the topology of the structure to that of a kagome-like lattice, thereby establishing new load paths, thus enabling enhancement, in a tailored manner, of the effective compressive and shear stiffness of the lattice. Whilst this phenomenon is independent of characteristic length scale, we focus on macroscopic behaviour (lattices of scale ≈ 200 mm). Experimentally observed responses of 3D-printed lattices correlate excellently with finite element analysis and analytical stiffness predictions for pre- and post-contact topologies. The role of key geometric and stiffness parameters in critical regions of the design space is explored through a parametric study. The non-linear responses demonstrated by this topology morphing lattice structure may offer designers a new route to tailor elastic characteristics.

Hydrological and erosion responses of steep spoil heaps to taproot and fibrous root grasses under simulated rainfalls

Spoil heaps, resulting from excavation and backfilling activities at construction sites, are one of the most important risk sources of soil erosion, threatening local ecosystems and even leading to geological disasters. However, after revegetation, spoil heaps can be transformed into available land resources such as cultivated land and forest land. Previous studies have reported the runoff and sediment reduction benefits of different vegetation measures on spoil heaps, while little information has been documented about what differences in the taproot and fibrous root grasses were transferred into the differences in hydrological and erosion processes. This study compared the effects of taproot (Artemisia gmelinii (A. gmelinii)) and fibrous root (Cynodon dactylon (C. dactylon)) grasses on soil erosion and runoff production processes and the reduction benefits of spoil heaps with silt loam soil. A series of rainfall events at three intensities (0.8, 1.2, and 1.8 mm min−1) were simulated on runoff plots (length of 3.0 m and width of 1.0 m) under treatments of A. gmelinii, C. dactylon, and bare soil (BS, as control) (each treatment was replicated), and the initial runoff time (IRT), saturated hydraulic conductivity, runoff rate (RR), flow velocity, and soil loss rate (SLR) were measured. The results showed that grasses delayed the IRTs on spoil heaps by 0.69–12.96 min compared BS, and the delay effects were more significant for fibrous root grass than for taproot grass. The soil loss reduction benefits (91.1 %) of the two kinds of grass were approximately 2.2 times greater than those of runoff volume reduction (42.1 %), and shear stress could be used to predict the soil loss rate following power functions (R2 = 0.72–0.85) for the grass-covered plots. The taproot grass exhibited a higher erosion reduction than fibrous root grass and is thus preferred to control the soil erosion of spoil heaps. Taproot grass has a greater stem diameter and can insert deeper into spoil heaps to consolidate the soil particles, which can improve roughness and hydraulic resistance, thereby producing a lower effective hydraulic shear stress that is directly exerted on soil particles. This study enhances the understanding of different grasses on the water erosion process and mechanism of spoil heaps and provides scientific guidance for selecting erosion control practices.

Microstructural evolution in graphene nanoplatelets reinforced magnesium matrix composites fabricated through thixomolding process

The distribution characteristic of reinforcements is a critical issue for the final performance of magnesium matrix composites (MMCs). Here, the microstructural evolution of graphene nanoplatelets (GNPs) reinforced MMCs fabricated by thixomolding process was investigated. The GNPs successfully penetrated through the grain boundaries and embedded in two adjacent grains. Those intragranular GNPs/Mg interfaces not only could provide efficient barriers to pin dislocations, but also contribute to the multiplying dislocations to accumulate rather than dissipate. In addition, the finer MgO particles and elongated Mg17Al12 were anchored around the GNPs, which could effectively improve the interfacial load transfer due to the increased load-bearing capability and the effective interfacial shear strength. These special distribution characteristic of GNPs was beneficial to the significant enhancement of mechanical properties for the composites. The concept of intragranular reinforcements anchored by finer particles in this work may bring positive and directive significance for the structural design of the composites.

Rheology of a Viscous-Plastic Liquid in a Porous Medium

The hydrodynamics of the capillary flow of a viscous-plastic liquid in cylindrical rectilinear pores is considered, as a result of which the structural velocity distribution over the pore cross section is obtained. Analytical solutions are proposed for the equations of hydraulic diffusion and nonlinear filtration for a non-Newtonian fluid in a cylindrical porous medium. It is noted that when a non-Newtonian fluid flows in a porous medium, the filtration equations take a nonlinear form due to the effective viscosity, shear, and yield stresses taken into account in its structure. The proposed solutions make it possible to evaluate the state of the porous medium and its main parameters (permeability, hydraulic diffusion, and effective viscosity coefficients). The obtained solutions are compared with existing experimental data for non-Newtonian oils.

ЖЕСТКОСТЬ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ ПРИ ИЗГИБЕ С УЧЁТОМ ПОПЕРЕЧНОЙ И ПРОДОЛЬНОЙ СИЛ (ЧАСТЬ 1)

The paper provides a physical and computational model for determining the parameters of limit states of reinforced concrete structures under complex stress state such as bending with effect of axial and shear forces. The forward and backward transitions for determining the stiffness matrix coefficients of reinforced concrete bar structures with inclined and normal cracks have been constructed on the basis of the adopted cross-section discretization scheme and the duality theorem between force and deformation parameters by A.R. Rzhanitsyn. Determination of the stiffness of structures in the zone of inclined cracks was performed on the basis of the model of composite strips into which the zone with inclined cracks is divided. It is assumed a hypothesis about the character of deformation distribution in a complexly stressed reinforced concrete element with inclined cracks. For this model the effective shear modulus has been obtained. It allows to determine the average relative linear and angular strains of concrete and reinforcement at the point adjacent to the shear joint between inclined cracks. Using this model and the experimentally obtained value of the relative shear in the inclined crack, the dowel forces in the reinforcing bar crossed by the inclined crack were determined. The use of the obtained analytical dependences in the practice of designing reinforced concrete structures allows to clarify significantly the definition of displacements and width of opening of inclined and normal cracks, as well as to bring the calculation and physical model based on experimental data as close as possible.

Analytical method for calculation of the strength of cylindrical rock specimens during their longitudinal stress

The goal of this research is to develop a method for calculating the strength of cylindrical rock specimens under axial failure. This will allow for the management of the stress-strain state of rock masses, which is an important issue for many mining companies. To achieve this goal, analytical modeling of the process of failure of cylindrical rock specimens under axial failure was carried out. This was done using experimental values of four indicators of rock properties: shear strength, coefficients of internal and external friction, and elasticity modulus. The results of this research allow for the determination of the ultimate strength and residual strength of cylindrical rock specimens using the four property indicators. These indicators can be experimentally determined using simple methods in laboratory conditions of mining companies. The scientific novelty of this research lies in the fact that analytical modeling of the process of failure of cylindrical rock specimens under axial failure was conducted for the first time, taking into account internal and external friction. This allowed for new results to be obtained and provided a basis for the development of new methods for managing the state of rock masses. The practical significance of this research lies in the fact that the proposed method allows for the determination of the ultimate and residual strength of rock specimens using four property indicators. These indicators can be experimentally determined in mining company laboratories, making the calculation results applicable for the management of the state of rock masses and the efficient destruction of rocks during disintegration. Thus, this method has significant practical significance for the mining industry. A method for calculating the strength of cylindrical specimens under longitudinal failure mode has been developed. The average convergence of calculated strength values with fс = 0.5 to experimental data is 83.4%, which corresponds to a good level of reliability for rock materials. It has been shown that the self-organization of longitudinal failure mode in cylindrical rock specimens occurs in accordance with Coulomb's criterion of maximum effective shear stress, which has been improved to account for contact friction.

The effective shear modulus of a random isotropic suspension of monodisperse liquid n-spheres: from the dilute limit to the percolation threshold.

A numerical and analytical study is made of the macroscopic or homogenized mechanical response of a random isotropic suspension of liquid n-spherical inclusions (n = 2, 3), each having identical initial radius A, in an elastomer subjected to small quasistatic deformations. Attention is restricted to the basic case when the elastomer is an isotropic incompressible linear elastic solid, the liquid making up the inclusions is an incompressible linear elastic fluid, and the interfaces separating the solid elastomer from the liquid inclusions feature a constant initial surface tension γ. For such a class of suspensions, it has been recently established that the homogenized mechanical response is that of a standard linear elastic solid and hence, for the specific type of isotropic incompressible suspension of interest here, one that can be characterized solely by an effective shear modulus n in terms of the shear modulus μ of the elastomer, the initial elasto-capillary number eCa = γ/2μA, the volume fraction c of inclusions, and the space dimension n. This paper presents numerical solutions-generated by means of a recently introduced finite-element scheme-for n over a wide range of elasto-capillary numbers eCa and volume fractions of inclusions c. Complementary to these, a formula is also introduced for n that is in quantitative agreement with all the numerical solutions, as well as with the asymptotic results for n in the limit of dilute volume fraction of inclusions and at percolation . The proposed formula has the added theoretical merit of being an iterated-homogenization solution.

Recomendações para avaliação da resistência à força cortante e punção de lajes unidirecionais sob cargas concentradas de acordo com a ABNT NBR 6118:2014

Abstract This study describes a set of recommendations to improve the precision of shear and punching shear capacity predictions for one-way slabs under concentrated loads, regardless of the governing failure mechanism, using the ABNT NBR 6118:2014 code provisions. For this purpose, a database of 143 test results was developed, including one-way slabs with different support conditions and loading layouts and that failed by different shear failure mechanisms: one-way shear, punching shear or a mixed mode. The key parameters influencing the load capacity and failure mechanism of these slabs were considered for the proposed recommendations: load position and slab width. Adjustments to the effective shear width definition and shear resisting control perimeter were described. Arching action for loads close to the support was also considered in both one-way shear and punching shear predictions. Considering the whole database and without separation by the failure mechanism, the ratio between tested and predicted resistances with the one-way shear expressions shows an average value of 1.22 and a coefficient of variation of 18.3%. The respective ratio between tested and predicted resistances with the punching shear expressions reached an average ratio of 1.23 with a coefficient of variation of 21.3%. Therefore, the proposed recommendations allow for reaching enhanced levels of precision in assessing the shear and punching shear capacity of one-way slabs under concentrated loads, regardless of the governing failure mechanism of the slabs.

Nonlinear Fe Model for Shear Strengthening of Simply Supported RC Beams with FRP DE Bars

Deep embedment (DE) is emerging as a potential and effective shear strengthening approach for existing reinforced concrete (RC) structures. A two-dimensional nonlinear finite element (NLFE) model for simply supported RC T-beams strengthened in shear with embedded carbon fibre reinforced polymer (CFRP) and steel bars is presented in this study. VecTor2, version 4.2, was used to create a two-dimensional NLFE model. To validate the nonlinear FE models, three sets of six simply supported RC T-beams from Breveglieri et al. (2015) are employedEach set consists of two beams with vertical and inclined (45) DE bars. Set one strengthens the beams with steel DE bars without vertical steel stirrups in the shear span. In the shear span, the beams of Sets two and three are reinforced with CFRP DE bars with vertical steel stirrups @180 mm c/c and @300 mm c/c, respectively. The above-mentioned NLFE model is validated by comparing experimental and predicted results for failure load, deflection, and failure mode. For both experimental and simulated beams, the fracture pattern is diagonal, and the failure mode is shear failure. The overall mean predicted/experimental loads at failure and deflection at failure ratios are 1.09 and 1.00, respectively, with corresponding standard deviations of 0.03 and 0.04. Following the validation of the proposed NLFE model's correctness, numerical parametric tests are conducted to determine the influence of concrete compressive strength and effective depth of RC T-beams on shear capacity of simply supported RC T-beams. The parametric analysis findings reveal that enhancing the cylinder compressive strength increases the predicted failure load while increasing the effective beam depth decreases it

The effect of process parameters on the mechanical properties of additively manufactured parts using a hierarchical multiscale model

Purpose This paper aims to present a hierarchical multiscale model to evaluate the effect of fused deposition modeling (FDM) process parameters on mechanical properties. Asymptotic homogenization mathematical theory is developed into two scales (micro and macro scales) to compute the effective elastic and shear modulus of the printed parts. Four parameters, namely, raster orientation, layer height, build orientation and porosity are studied. Design/methodology/approach The representative volume elements (RVEs) are generated by mimicking the microstructure of the printed parts. The RVEs subjected to periodic boundary conditions were solved using finite element. The experimental characterization according to ASTM D638 was conducted to validate the computational modeling results. Findings The computational model reports reduction (E1, ∼>38%) and (G12, ∼>50%) when porosity increased. The elastic modulus increases (1.31%–47.68%) increasing the orthotropic behavior in parts. Quasi-solids parts (100% infill) possess 10.71% voids. A reduction of 11.5% and 16.5% in elastic modulus with layer height is reported. In total, 45–450 oriented parts were highly orthotropic, and 0–00 parts were strongest. The order of parameters affecting the mechanical properties is porosity > layer height > raster orientation > build orientation. Originality/value This study adds value to the state-of-the-art terms of construction of RVEs using slicing software, discarding the necessity of image processing and study of porosity in FDM parts, reporting that the infill density is not the only measure of porosity in these parts.

Constitutive model of elastic response for Fe-TiB2 composites

The constitutive model of Fe-based matrix composites to the macroscopic stress was established for revealing the elastic response at multiscale. The effective elastic constants (EECs) of the Fe-TiB 2 composites were predicted by the constitutive model in this study, including the effective elastic modulus E ̅ , effective bulk modulus K ̅ , effective shear modulus G ̅ , and effective Poisson's ratio ν ̅ . And then, the diffraction elastic constants (DECs) related to the crystal planes ( hkl ), ν hkl and E hkl of the constituents of the composites, were also evaluated based on the multiscale correlation constitutive equations. Compared with experimental values, there was excellent agreement for the EECs of the Fe-TiB 2 composites and reasonable errors in DECs of the Fe-based matrixes and TiB 2 reinforcements. Furthermore, the multiscale coupling between the EECs and DECs related to elastic response and residual stress was also concerned in this micromechanical model. The internal stress in the TiB 2 reinforcements is higher than the Fe-based matrixes at the same applied stress of the composites, which means the desired load transfer has occurred.

Potential triggers for large earthquakes in open‐pit mines: A case study from Kuzbass, Siberia

AbstractThe extraction and movement of rock during mining operations is considered a possible trigger for slip along the fault. In this study, possible anthropogenic causes were analyzed for triggering the earthquake with the local magnitude of ML = 6.1 (at a depth of 4 km just beneath the quarry), in the vicinity of the large coal open‐pit mine in Russia. This event was the largest earthquake associated with a quarry (an open pit). A sufficiently deep occurrence of the source testified that seismic vibrations were produced in a dynamic slip along a preexisting and prestressed tectonic fault. Analytical calculations were conducted of increments of normal and shear stresses at fault planes with several dip angles at depths corresponding to the probable location of the hypocenter of the Bachat earthquake. As the results show, long‐term rock excavations bring a prestressed thrust fault closer to the ultimate Coulomb strength, and stress variations at those depths may suffice to initiate a movement along the fault. By measuring seismic vibrations at different quarries and mines in Russia, the dynamic effect at the supposed depth of the source occurrence could be reliably estimated. As is shown, the ultimate anticipated dynamic deformations are noticeably lower than corresponding values produced by seismic waves of distant earthquakes in the case when the effects of dynamic triggering were observed. Accordingly, the seismic effect of explosions cannot trigger a large earthquake with deep source occurrence. Operations in open‐pit mines can only bring forward the moment of an earthquake at a potentially seismogenic fault. At the same time, the numerical calculations reveal that a branching network of underground tunnels located at several horizons can noticeably reduce the effective shear modulus of the host rock. This effect can even provoke a dynamic movement at a previously aseismic fault.

Advanced monitoring of tailings dam performance using seismic noise and stress models

Tailings dams retain the waste by-products of mining operations and are among the world’s largest engineered structures. Recent tailings dam failures highlight important gaps in current monitoring methods. Here we demonstrate how ambient noise interferometry can be applied to monitor dam performance at an active tailings dam using a geophone array. Seismic velocity changes of less than 1% correlate strongly with water level changes at the adjacent tailings pond. We implement a power-law relationship between effective stress and shear wave velocity, using the pond level recordings with shear wave velocity profiles obtained from cone penetration tests to model changes in shear wave velocities. The resulting one-dimensional model shows good agreement with the seismic velocity changes. As shear wave velocity provides a direct measure of soil stiffness and can be used to infer numerous other geotechnical design parameters, this method provides important advances in understanding changes in dam performance over time.

A new concept and algorithm to transfer brittle and arbitrary load-slip curves into an effective shear resistance suitable for Eurocode 4

A new concept and algorithm to transfer brittle and arbitrary load-slip curves into an effective shear resistance suitable for Eurocode 4

Influence of periodic flow field on synthesis of perovskite nanocrystals: Synthetic pathway and productivity

Here it was demonstrated that series–parallel reaction pathway for CsPbBr3 and Cs4PbBr6 perovskite nanocrystals (PNCs) were selective by the periodic flow fields as well as precursor ratio. The periodic Taylor vortex flows (PTVFs) in a Couette-Taylor batch reactor (BR) were applied for controlling the synthetic pathway of PNCs and the random turbulent eddy flow (RTEF) in a stirred tank BR was also used for comparison. The PTVFs in the Couette-Taylor BR promoted not only the formation reaction of CsBr from the reaction between Cs-oleate (Cs-OA) and PbBr2 but also the reaction between CsBr and the remained PbBr2. As a result, the CsPbBr3 and Cs4PbBr6 PNCs could be selectively formed according to the ratio of Cs-OA:PbBr2 under the PTVFs in the Couette-Taylor BR, whereas they couldn’t under the RTEF in the stirred tank BR. In addition, the production yield of CsPbBr3 and Cs4PbBr6 PNCs in Couette-Taylor BR increased up to 30 % and 57 %, respectively, compared to their yield in the stirred tank BR due to the effective micro-mixing and shear dispersion of PNCs.