Relative Stiffness Research Articles

Analysis of interface mechanical properties between geotextiles and tailings during pull-out tests.

Considering the strain-softening characteristics of the pull-out interface between geotextiles and tailings; to determine the interface interaction characteristics, this paper proposes a trilinear shear stress displacement softening model of geotextile-reinforced tailings. The obtained nonlinear governing equations were dimensionless, which were expressed in finite difference form. The results indicated that an accurate numerical solution could be obtained within a reasonable calculation time by discretizing the reinforcement length into 300 units. Three new dimensionless interaction terms, namely, the relative stiffness α, relative displacement β, and relative interface shear stiffness η of the reinforcement-tailings interaction, were introduced. In addition, an estimation method based on the approximate value of the relative stiffness α of the reinforcement-soil interface in the low-tensile-force displacement range was proposed. The interface shear stress range according to parameters α, β, and η was parameterized, and the normalization relationship between the tensile force and pull-out end displacement was determined. The numerical values calculated by the model were compared with the pull-out test results, demonstrating that the proposed model can accurately predict the pull-out behavior of the extensible reinforcement.

Free Vibration Analysis of Elastically Restrained Laminated Planar Frames

Abstract A wave-based model that incorporates the effects of shear deformation, rotary inertia and elastic coupling due to structural anisotropy, is developed to analyze the free vibrations of elastically restrained laminated planar frames. In this work, a generalized frame structure is represented as an assemblage of laminated beam segments that act as one-dimensional waveguides. The segments are assumed to undergo only in-plane motion, which upon applying Hamilton's principle, is described by a system of coupled differential equations. Dispersion analysis is conducted, and the nature of the wavefields associated with the propagation matrix is discussed. Generally restrained boundaries and internal joints are considered, and the associated reflection and transmission matrices are derived. Using the principle of wave-train closure, the characteristic equation is obtained by systematically assembling the propagation, reflection, and transmission matrices. The wave-based model is inherently deterministic, and solving the characteristic equation offers the advantage of determining the exact natural frequencies using conventional root finding algorithms. Application of the proposed model is demonstrated by analyzing an elastically restrained inclined laminated portal frame. Extensive computational analysis is conducted to illustrate the influence of stacking sequence, frame angle, relative frame length, orthotropicity ratios, and spring stiffness on the exact natural frequencies (and in certain cases the mode shapes) of the frame. Independent finite element simulations conducted in ansys® APDL are consistently used to verify the validity of the analytical results.

Distributed parameter modeling for prefabricated wall-frame system assembled by horizontal and vertical connection

Distributed parameter model (also referred to as continuum model) is commonly used to analyze the behavior of conventional frame-shear wall structure. In recent decades, extensive research has been published and proved the well-controlled seismic performance of wall-frame system, beyond which some researchers applied the continuous philosophy to the analysis of specified wall-frame systems. This paper extends the distributed parameter model to a general distributed parameter model, and corresponding closed-form solutions for three typical load cases are derived, verified, and parametric analyzed. The model in this paper unifies the three nondimensional parameters into one model and parameterizes the relative stiffness between wall, frame, vertical connection, and horizontal connection. Additionally, the proposed model can analyze the system with various horizontal connection (hinged/fixed/semi-rigid) as well as vertical connection (dampers/coupling links). Further, the shear demand of frame retrofitted by resilient wall, a new retrofit has been constructed lately, is theoretically studied using the proposed model. Results shows that the shear demand of frame at upper floor levers may increase after retrofitting.

Numerical simulations of the sliding impact between an ice floe and a ship hull structure in ABAQUS

This paper studies the hull structural responses of a steel grillage subjected to sliding ice loads, which have been rarely investigated in the literature. Sliding ice loads are modelled using nonlinear finite element analysis (NLFEA) method; and Abaqus Explicit is adopted as the numerical solver. Deformations and damages of ice and steel are both considered. A rigid ice model is also simulated for comparison purposes. The hull’s local structural responses under different load cases, including deformation, contact forces, and energy distribution, have been analysed. The effects of static structure-to-structure friction coefficient and the relative stiffness between ice and structure are studied. It is found that the deformation of structures will increase the total friction coefficient, which is defined as the ratio of the friction force (the tangential contact force) to the normal contact force. When the ice floe is considered rigid, the static friction coefficient has little effect on the local structural responses of the hull. If using a higher-strength steel material for hull structures in the ice-classed ship design, the hull’s deflection and total friction decrease, and the hull dissipates less energy as expected. Moreover, stationary load cases with the same loading condition in the normal direction as sliding load cases are also simulated. When using the deformable ice material model, the simulation results show that the hull’s final contact forces and deflection in stationary load cases are larger than those in sliding load cases. Besides, the effect of steel material is more significant in stationary load cases than in sliding load cases.

Sigmoid isostiffness-lines: An in-vitro model for the assessment of aortic stenosis severity.

IntroductionThe aortic valve opening area (AVA), used to quantify aortic stenosis severity, depends on the transvalvular flow rate (Q). The currently accepted clinical echocardiographic method assumes a linear relation between AVA and Q. We studied whether a sigmoid model better describes this relation and determined “isostiffness-lines” across a wide flow spectrum, thus allowing building a nomogram for the non-invasive estimation of valve stiffness.MethodsBoth AVA and instantaneous Q (Qinst) were measured at 10 different mean cardiac outputs of porcine aortic valves mounted in a pulsatile flow loop. The valves' cusps were chemically stiffened to obtain three stiffness grades and the procedure was repeated for each grade. The relative stiffness was defined as the ratio between LV work at grade with the added stiffness and at native stiffness grade. corresponding to the selected of the highest 3 and 5 cardiac output values was predicted in K-fold cross-validation using sequentially a linear and a sigmoid model. The accuracy of each model was assessed with the Akaike information criterion (AIC).ResultsThe sigmoid model predicted more accurately (AIC for prediction of AVA with of the 3 highest cardiac output values: –1,743 vs. –1,048; 5 highest cardiac output values: –1,471 vs. –878) than the linear model.ConclusionThis study suggests that the relation between AVA and Q can be better described by a sigmoid than a linear model. This construction of “isostiffness-lines” may be a useful method for the assessment of aortic stenosis in clinical echocardiography.

Transfer Matrix Method for Calculating the Transverse Load Distribution of Articulated Slab Bridges

Articulated slab bridges have been widely used by transportation administration for short-to-medium span bridges because of their good economy, convenient construction, and environmental advantages, while the presence of shear keys increases the complexity of structural behavior. Developing more reasonable analysis approaches of quick assessment, pre-design, and hand calculations for the articulated slab bridges is a challenge because of the peculiar shear key mechanism. This paper is devoted to presenting a recursive algorithm, based on the force equilibrium conditions of each individual slab, thus resulting in simultaneous equations of the transfer matrix method (TMM). In this procedure, the state vector is an array composed of vertical displacement, shear force, unit constant; and the transfer matrix contains the bending and torsional stiffness parameters of simply supported slabs. Then, the influence line of transverse load distribution (TLD) is calculated for each slab by introducing boundary conditions. To validate and verify the efficiency of the TMM algorithm, a transversely prefabricated void slab bridge with a span of 20 m is considered as a case study. The traditional force (FM) and finite element (FEM) methods are used for comparison and validation. It is demonstrated that the TMM can provide good results with higher algorithm efficiency by exempting the modeling tasks in FM and FEM and capture variations in TLD along the bridge’s span. In addition, the influence of the span length and relative stiffness coefficient of slabs on the TLD of articulated slab bridges are analyzed from the parametric analysis.

2.5D FE-BE modelling of dynamic responses of segmented tunnels subjected to obliquely incident seismic waves

Segmented tunnels are widely used nowadays. However, most existing studies on the seismic response of underground tunnels are based on the model of continuous linings, without considering the segment joints. This paper presents a numerical study aiming to investigate the factors that affect the seismic response of segmented tunnels, with a step further than previously, considering obliquely incident seismic waves. The numerical simulation is carried out by a 2.5D coupled finite element-boundary element (FE-BE) model, which can properly simulate the soil-tunnel interaction for obliquely incident seismic waves and predicts both the transverse and longitudinal seismic responses of the tunnel. It is shown that the joint distribution is one of the critical factors that determine the seismic responses of the segmented tunnel, and the influence of the segment joints tends to be more pronounced when they are located near the positions of large transverse bending moments in the tunnel lining. Compared with the homogeneous tunnel, the reduction in the transverse bending moment and axial force of the segmented tunnel is significant, while it is minor in the longitudinal bending moment and axial force, and the effect of the segment joints highly depends on the soil-tunnel relative stiffness. In addition, the influence of the spectral characteristics of the input motions on the tunnel responses is highlighted.

Optimal Design of Mixed Structures under Time-history Loading Using Metaheuristic Algorithm

In this paper, an optimum design of concrete-steel mixed frames under time-history loadings was formulated as an optimization problem. The behavior of a mixed structure is different from the steel and reinforced concrete structures because of vertically irregular in their mass, stiffness and damping of each part. Moreover, current codes and available commercial software packages do not present solutions for such structures. Researches have indicated that the structures exhibit higher-mode effects and responses that are sensitive to the relative stiffness and mass of the two parts of the structures. Thus, the equivalent static analysis is not applicable, a dynamic analysis has to be performed to analyze and design such structures. Therefore, the optimum design of mixed structures under an earthquake can be relatively complicated and time-consuming. Because the design methods for these structures are iterative and dynamic. The main objective is to find the minimum cost of the structure under time-history loadings while satisfying all design constraints. The results show that the proposed optimization procedure is ideal to obtain the optimum design for a mixed structure subjected to time-history loadings. Also, for comparison, the optimal design of reinforced concrete (RC) frames and steel frame are presented using the algorithm.

Maturity status influences perceived training load and neuromuscular performance during an academy soccer season

ABSTRACT Commonly we see large within-age-group variations in physique, including body mass, stature, and percentages of predicted adult height, which suggests that age-specified training loads are flawed. Aims were to investigate how maturation impacts training load and neuromuscular response within academy soccer and to provide recommendations for practitioners. Fifty-five male soccer players (age 14.5 ± 1.2 years; stature 172 ± 10 cm; body mass 59.8 ± 10 kg; 94.1 ± 1.8% predicted adult height) reported differential ratings of perceived exertion (AU) across a season. Neuromuscular performance (countermovement jump, reactive strength index, absolute and relative leg stiffness) was measured at three time points across the season. Perceived exertion and neuromuscular performance were examined using linear mixed modelling, supplemented with non-clinical magnitude-based decisions. Analysis indicates every 5% increase in maturity status results in players perceiving overall session intensity 6.9 AU lower and 13.9 AU lower for a 10% maturity shift. Both 5% and 10% changes in maturity most likely resulted in higher countermovement jump, with likely to very likely differences observed for RSI and ABS. Maturity substantially influences neuromuscular performance over the season. Therefore, maturity-specific load prescription may prevent significant within age-group differences in accumulated load, possibly reducing injury risk and/or burnout.

Folding-angle framework for structural modeling of rigid triangulated Miura-ori lattices

Abstract Origami is rapidly gaining prominence in the research of metamaterials as it allows for tuning the properties of interest by change in the folded state. Origami-based lattices that allow low-frequency wave-propagation can potentially find use as acoustic metamaterials. Rigid panel origami tessellations have lattice modes which are exclusively due to the low-energy folding deformations at creases and hence will be suitable for low-frequency wave-propagation applications. Modeling frameworks like bar-and-hinge that are typically used to study origami lattice mechanics allow for panel stretching behavior which is forbidden and redundant in rigid panel origami lattices. This drives the necessity for an efficient analysis framework dealing exclusively with folding-angles for study of origami lattices with rigid panels. As a first step in this direction, in this paper, we propose a folding-angle-based analytical framework for structural modeling of infinite lattices of triangulated Miura-ori with rigid panels. We assign rotational stiffness to the creases and analytically derive the stiffness matrix for the lattices based on a minimal number of folding-angle degrees of freedom. Finally, we study the influence of the equilibrium folded state and the relative crease stiffness on the modal energies, to demonstrate the tunable and programmable nature of the structure. The framework proposed in our work could enable the study of wave dynamics in rigid panel Miura-ori-based lattices and our findings show significant promise for the future use of 1D origami with rigid panels as acoustic metamaterials.

Kinematic seismic response of end-bearing piles to S-waves

In this paper we revisit the problem of modelling analytically the kinematic interaction between a single pile and its surrounding soil under the action of seismic shear waves, by means of a Tajimi-type continuum elastodynamic model in three dimensions. The model provides the steady-state kinematic response of a cylindrical end-bearing pile embedded in a homogeneous viscoelastic soil layer, subjected to vertically propagating harmonic S-waves. Results of the model are first validated against the results of numerical simulations, and the results of an existing, approximate solution. Accordingly, we employ the model in a parametric study, where we investigate the sensitivity of the seismic response of piles to certain key problem parameters, including pile slenderness, soil-pile relative stiffness, excitation frequency and fixity conditions at the pile head. The solution yields closed-form expressions for pile deformations and for the soil resistance developing on the pile, that do not require introducing fitting coefficients.

Shear buckling coefficients of web panels for composite girders considering flange-web stiffness ratio

Designing a web panel for composite girders necessitates an accurate evaluation of the shear buckling strength. However, the current design specifications calculate the strength of web panels for composite girders conservatively. Additionally, its rational determination is missing in existing studies. This study investigates the shear buckling coefficients of composite girders through numerical analysis. The numerical analysis model assumes that the concrete slab fully restrains the web panel. In addition, the concrete slab of the composite girders in the numerical analysis model is replaced by equivalent top flange sections using a transformed thickness according to the modular ratio (n) of the concrete and steel. Additionally, the stiffness of the bottom flange and web panel is parameterized to evaluate the effect of their relative stiffness on the critical shear buckling strength of the web panel. The results show that the relative stiffness of the flange and web panel significantly affects the shear buckling coefficient. To determine the shear buckling coefficient by reflecting these structural characteristics, the relative stiffness is defined as the ratio of the torsional stiffness of the flange to the flexural stiffness of the web panel. The proposed formulas for the shear buckling coefficient of web panels for composite girders correlate well with the numerical analysis results. Since the accurate shear buckling strength can be derived from these formulas, the web panel for composite girders can be designed more accurately and economically.

Assessment of knee collateral ligament stiffness by strain ultrasound elastography.

BACKGROUND:Knowledge of the biomechanics of the normal collateral ligaments is important to secure optimal stability of the knee following injury. Various in vitro methods have been described in evaluating the biomechanics of these ligaments. However, a method of direct evaluation has not been reported.OBJECTIVE:To determine the stiffness characteristics of the collateral ligaments of the knee using strain ultrasound elastography.METHODS:Strain ultrasound elastography was performed on different components of the collateral ligaments in various angles of knee flexion in 18 healthy males (36 ligaments). We measured relative stiffness of the ligaments using strain ratio (SR = target tissue strain/reference strain). A lower strain ratio indicates higher relative stiffness.RESULTS:There was moderate to excellent intra- and inter-rater agreement for strain ratio measurements in all ligament portions. Strain ratios were lowest at 0° in all three ligaments, indicating high relative stiffness. In the superficial and deep medial collateral ligaments, the strain ratio increased with increasing knee flexion, whereas in the lateral collateral ligament, stiffness showed a tendency to fluctuate.CONCLUSION:Strain ultrasound elastography is a reliable tool for monitoring relative stiffness of the collateral ligaments of the knee and is easily applied to the routine clinical setting.

Synergistically program thermal expansional and mechanical performances in 3D metamaterials: Design-Architecture-Performance

Metamaterials, incorporating specific micro-architectures, could be purposely customized to export the programmability in both thermal expansional and mechanical performances, which are beneficial to obtain the thermal and structural stabilities in engineering devices. Here, by focusing on developing an original design strategy, multiple classes of metamaterials were devised and analyzed to integrate the programmable coefficient of thermal expansion (CTE) and mechanical performances (relative density, stiffness and strength). In detail, firstly, a series of the bi-material metaunits was devised, and a vector analysis method was proposed to analytically identify the CTE tensors. Then, an original design strategy, i.e., matrix transformation method, was developed to systematically devise multiple classes of 3D metamaterials with the unidirectional, transversal isotropic and isotropic CTEs. Besides, the mechanical performances, including the relative density, stiffness and strength, were theoretically established. It was identified that these metamaterials well balanced the directionality and programmability of the CTEs. Most importantly, by modulating the geometrical parameters, the desirable CTEs, light weight, high stiffness and strength could be synergistically achieved in these metamaterials. Eventually, a principle was established to guide the development of metamaterials. That was the original design strategy acted as the underlying foundation to map the specific architectures in metamaterials, correspondingly, to build the ability to synergistically program or customize the thermal expansional and mechanical performances.

Quantifying the uncertainties in modeling soft composites via a multiscale approach

The goal of this paper is to evaluate the uncertainties in soft composites composed of a soft solid as the matrix filled by incompressible liquid inclusions. The surface stresses at the liquid–solid interfaces can significantly impact the elastic deformation of the bulk composite at the macroscale. Depending on the characteristic dimension, a stiffening or softening can happen. We model the elastic behavior employing a stochastic multiscale approach and counting on well established rules for composites. Insights on the mechanics of elasto-capillary coupling are provided considering the heterogeneity at different length scales. Global sensitivity analysis is performed to quantify the effect of variation in the material properties, surface tension, the size, and the random dispersion and agglomerations of the inclusions. The influence of the model choice at the mesoscale on the uncertainty of the response is also taken into account as an additional source of uncertainty. The results show that the relative stiffness is mainly influenced by the uncertainties in the size of liquid inclusions and the surface tension, while the remaining parameters show a significant interaction effects.

Peeling of finite-length elastica on Winkler foundation until complete detachment

Quasi-static peeling of a finite-length, flexible, horizontal beam (strip, thin film) from a horizontal substrate is considered. The displaced end of the beam is subjected to an upward deflection or to a rotation. The action of the adhesive is modeled as a Winkler foundation, and debonding is based on the common fracture mechanics approach. The behavior is examined from the application of loading to the initiation of peeling and then to complete detachment of the beam from the substrate. During at least a portion of the debonding process, the model corresponds to what traditionally has been considered a short beam on an elastic foundation. In the analysis, the beam is modeled as an elastica, so that bending is paramount and large displacements are allowed. The effects of the relative foundation stiffness to the beam bending stiffness, the work of adhesion, and the length, self-weight, extensibility, and initial unbonded length of the beam are investigated. In addition, experiments are conducted to complement the analysis.

Integrated reed valves applicable to miniature high pressure compressor and investigation on their dynamic characteristics based on equivalent model

Miniature high pressure compressor (MHPC) is key component of continuous gas supply system in aircraft for missile launching and infrared cooling. Valve design makes a crucial role in reciprocating compressors and traditional valves in high-pressure reciprocating compressors usually occupy a large space, have relative larger clearance volume and spring stiffness, which are incompetent to be applied to MHPC. In this study, integrated reed valves with four cantilevers on a steel plate are proposed to serve as the suction valves and discharge valves in MHPC. By this method, the number of valve parts and the axial dimension can be greatly reduced. Theoretical research has been carried out to reveal the dynamic characteristics of the proposed integrated valves. Numerical methods based on equivalent model of cantilever valve are proposed to improve the calculating efficiency compared to traditional CFD method. The equivalent stiffness and equivalent mass for valve motion equations have been calculated and plugged into the whole mathematical models. Based on the optimized valve parameters, experimental investigation on MHPC has been carried out.

Aspect Ratio and Relative Beam-Slab Stiffness Effects on the Long-term Deflection of Flat Plates and Beam Supported One-Way Slabs

This study investigates the ACI 318-19 two-way slab provisions for the long-term deflection control in flat plate slabs with an aspect ratio ranging between 1 to 3 at different panel locations (interior, edge, and corner) with a large span of 5.0 m, 7.5 m, and 10.0 m. Further, the study examines the effects of the relative beam-slab stiffness of the beams provided at the two long sides of flat plat slabs of aspect ratio greater than two using ACI318-19 recommended one-way slab thickness. The paper uses the Finite Element SAFE software to calculate the long-term deflection (LTD) by using nonlinear analysis (long-term cracked analysis) that considers concrete creep and shrinkage of two-way slabs and one-way slabs for different beam-slab stiffnesses and aspect ratios. The aspect ratio of a flat plate slab had a considerable effect on the LTD, where for slab panels of the same long span length and variable aspect ratio, as the aspect ratio gets smaller (square slab), the LTD increases, a behavior that ACI318-19 two-way slab deflection control procedures overlook. So, the deflection under the beams is within the ACI318-19 long-term deflection limits for different panel locations (interior, interior, exterior, and exterior edge). In addition, this part has been conducted to recommend a minimum relative beam-slab stiffness for the supporting beams.

Density functional theory studies of the structural, optoelectronic, bond stiffness and lattice dynamical properties of double perovskite oxides M2YVO6 (M= Mg, Sr): Promising candidates for optoelectronic applications

The double perovskite type oxides are deemed to be an eloquent materials to be used for applications in efficient optoelectronic devices/transducers. In order to explore physical properties of M2YVO6; (M = Mg, Sr) perovskites Full potential Linearly Augmented Plane Wave (FPLAPW) method is used in the frame work of WIEN2K code. LDA + U functional has been preferred here for getting an accurate and systematic results associated to the electronic and optical response of these compounds. These compounds fall into semiconductor category showing direct energy band gap of 1.45 eV (Mg2YVO6) and 0.82 eV (Sr2YVO6). Appearance of the energy states of different level in the conduction regions of both compounds fortify the view point that the valence electrons may jump to these states while enhancing conductivity of such devices (i.e., solar cells) whichever are fabricated for producing eternal energy. Projected density of states (PDOS) confirm the presence of Mg2+/Sr2+, Y3+, V5+, O2− in the M2YVO6 where M = Mg, Sr. In addition to it, optical analysis shows that these materials reflect very little electromagnetic radiations when fall on their surfaces. Sr2YVO6 holds relative bond stiffness greater than its standard value of ½ while it is less than half for Mg2YVO6. Phonons analysis shows few soft modes of frequency in case of Mg2YVO6 which might be due to particular orientation of monoclinic phase of the crystal structure, whereas no imaginary modes of vibrations are observed for Sr2YVO6. It looks very fabulous to claim that these compounds might be an appealing ones for optoelectronic applications due to their huge absorption rate/optical conduction ability, which also declares them very suitable materials for devising transducers.

Hierarchical and fractal structured materials: Design, additive manufacturing and mechanical properties

Novel rationally designed structured materials (SMs) exhibit unconventional mechanical properties that cannot be found in common materials. Although most microarchitectures of the developed SMs are based on regular unit cell tessellation design, few studies have explored the potential of fractal geometry as a design tool for creating new SMs. A novel strategy for creating fractal-like aperiodic SMs based on Hilbert self-filling fractal curves synthetization is presented here. Families of continuous Hilbert structured cubes derived from two separate Hilbert curve iterations at three different matching relative densities were obtained, additionally, a method to decompose the Hilbert curve to obtain non-continuous Hilbert structured cubes is proposed. To obtain a broad overview of their mechanical response, samples were manufactured out of thermoplastic polyurethane via fused filament fabrication and tested under compression. An apparent model of elasticity has been proposed to classify their mechanical performance under low and high strain. Results showed that relative stiffness, energy absorption and deformation could be tuned by adjusting parameters of the Hilbert structured cubes. By iterating the Hilbert curve from n = 4 to n = 5, a 51% increase in stiffness was obtained. A significant increment of 82% and 148% on stiffness was observed on non-continuous Hilbert structured cubes for the first and second orders, respectively; besides, energy absorption capabilities and great shape recovery were observed.