Hysteretic Loops Research Articles

Seismic performance of angle-steel reinforced concrete columns confined with spiral reinforcement

Angle-steel reinforced concrete columns internally confined by spiral reinforcement (SCARC) were developed to improve the seismic ductility and energy dissipation capacity. In the present study, cyclic loading tests on nine column specimens were conducted to investigate the seismic performance. The failure process and hysteretic characteristics were examined. The bending moment, deformation capacity and energy dissipation capacity were evaluated through parametric analysis of axial load level, volumetric ratio of spiral reinforcement, transverse steel configuration and types of cross section. A hysteretic model of SCARC columns based on the experimental skeleton curves and hysteretic loops was proposed. Experimental results showed that SCARC columns exhibited more satisfactory seismic performance than angle-steel reinforced concrete columns. The hysteresis characteristics, peak strength, ductility and energy dissipation capacity of SCARC columns were improved due to the increased confinement from spiral reinforcement. The developed hysteretic model provided a reliable prediction of SCARC columns under cyclic loading.

Real-time hysteresis identification in structures based on restoring force reconstruction and Kalman filter

Identifying the local nonlinear hysteretic behaviors in structures arises as an important issue in structural health monitoring. This paper develops a new hysteresis identification framework where rather than identifying the hysteretic parameters, the restoring forces are reconstructed so as to identify the hysteretic loops. Under this new framework, there is no need to get a priori knowledge on the hysteretic models, enabling a wider range of applications, and the involved system equation is linear with unknown restoring forces, tending to be more efficient. Then, the Kalman filter is adopted for real-time restoring force reconstruction because the Kalman filter is celebrated for its efficiency, effectiveness and reliability in linear system estimation with noisy measured data. In doing so, the restoring forces are additionally augmented as state variables and such augmentation is shown to act as the role of Tikhonov regularization, by which the proper covariance of the augmentation as the regularization parameter is selected via the L-curve method. Numerical examples are presented and an experimental test is conducted to verify the effectiveness and robustness of the proposed real-time hysteresis identification method.

A simple single bounding surface model for undrained cyclic behaviours of saturated clays and its numerical implementation

A simple single bounding surface constitutive model is developed to predict the undrained behaviours of saturated clays under cyclic loads. The new model does not involve complex kinematic hardening rules, and it is only required to memorize important stress reverse events; therefore, the simplicity should be the largest advantage of the model. A new interpolation function of an elastoplastic shear modulus is proposed based on bounding surface theories. The evolution of a hardening modulus is described in the deviatoric stress space by the movement and updating of a mapping centre based on the new interpolation function, which enables the model to describe the stress-strain hysteretic responses of clays under cyclic loading. The new model can be regarded as an improvement of some classical one-dimensional soil dynamic models and a generalization in three-dimensional stress space. The model parameters can usually be determined by performing triaxial tests. The model performance has been verified by a comparative analysis on clays subjected to one-way and two-way cyclic loading at different stress levels. The developed model can capture the essential features of behaviours in saturated clay, including reverse plastic flow, evolution of hysteretic loops, accumulation of plastic deformations and soil stiffness degradation. The newly developed constitutive model has been successfully encoded into the ABAQUS software package by the secondary development interface of UMAT. The ability of the model to calculate boundary value problems, such as clay foundations subjected to seismic loads, has been verified to some extent by simulating the seismic responses of homogeneous horizontal sites.

Characterization of runoff generation in a mountainous hillslope according to multiple threshold behavior and hysteretic loop features

This study explores the rainfall and soil moisture thresholds for runoff using a classification and regression tree (CART) algorithm for a large dataset (146 events) of hydrologic variables collected from a humid hillslope. The common CART structure for the runoff coefficient successfully separated rainfall events with zero runoff generation and further identified five distinct clusters with distinct runoff generation and hysteretic loop features. The total amount of rainfall was the primary driver of runoff, with the highest relative importance in the CART model. In contrast, the antecedent soil moisture and rainfall intensity helped explain the hysteretic loop features as well as exceptional events through hysteretic loop analysis. The multinomial logistic regression model was introduced to determine the probability of different hysteretic loop variations according to the rainfall characteristics. By identifying the distinctive hysteretic loop patterns between upslope and downslope regions, these findings demonstrate the sequential development of hydrological processes from zero runoff to extreme runoff events.

Laboratory and Physical Prototype Tests for the Investigation of Hydraulic Hysteresis of Pyroclastic Soils

Proper soil water retention curves (SWRCs) are necessary for a fair analysis of groundwater flow in unsaturated slopes. The question is whether hydraulic parameters operating in situ can be reliably determined from laboratory tests or physical prototype models in order to interpret and predict soil water distributions in the field. In this paper, some results obtained by tests at different scales (testing on laboratory specimens and a physical prototype) are presented to explore the hydraulic behavior of pyroclastic soils. A theoretical interpretation of the observed behavior in the laboratory and using a physical prototype is proposed by adopting the hysteretic model of Lenhard and Parker. For each tested soil, the main hysteretic loop determined by interpreting experimental tests (at laboratory and prototype scales) overlaps with paths detected by coupling the field measurements of matric suction and water content collected at the site at the same depth. From these results, the physical prototype (medium scale) and the soil specimen (small scale) seem to be acceptable for determinations of SWRC, provided that the air entrapment value is well known.

The modified cyclic multi-surface plastic model of sandy soil based on damping ratio

Traditional multi-surface plastic model always overestimates the accumulated plastic strain when it is applied into sandy soil under cyclic loading. Considering this overestimation can be reflected through equivalent damping ratio of the hysteretic loop and the damping ratio can also include the real anisotropic plastic hardening which is simply considered in kinematic hardening rule and isotropic hardening rule, series of strain-controlled cyclic simple shear tests were conducted to obtain the relationship between correction coefficient of hardening rule and initial state including initial effective, then a modified cyclic multi-surface plastic model was established by regarding the subsequent hysteretic loop as the new first loop with a new initial state which is the state at the start of the fourth quarter of the previous loop, thus, the plastic hardening formula can be upgraded in the process of loading.

Explosive synchronization induced by traffic processes in complex networks

An abundance of studies on synchronization focus on the characteristics of synchronization itself, but ignore the guiding role of information transfer between dynamic units on the synchronization process. In reality, continuous interactions between dynamic units are costly and sometimes unnecessary. Here we perform both traffic and synchronization processes in the same network and propose a model based on a constant-density traffic. Each node delivers packets with preference according to frequency mismatch and degree, and its synchronization behavior is only determined by the received packets. Explosive synchronization (ES) can be induced in both heterogeneous and homogeneous networks, as well as in both symmetric and asymmetric frequency distributions. We have concluded that the correlation between the average reception degree and the natural frequency is a key feature for the emergence of ES. Furthermore, at different packet densities, the forward and backward critical couplings and the width of the hysteretic loop in ES all exhibit nonmonotonic behavior and have minimum values. ES can still appear even if the packet density is very low.

Experimental and numerical investigation on seismic behaviours of beam-column joints of precast prestressed concrete frame under given corrosion levels

Corrosion as a major threat to civil infrastructures has been extensively investigated for decades. For precast concrete structures, corrosion medium are easier to penetrate into structural joints where precast components are connected or post-casting is applied. The corrosion process and structural deterioration, however, highly depend on structural configuration and construction procedure. Taking the frame structure comprised of precast prestressed concrete components (SCOPE) for example, this paper presents an experimental study on the seismic behaviors of corroded beam-column joints of the SCOPE system. Five specimens with different levels of corrosion were tested under cyclic loading, and crack propagation, hysteretic loops, envelope curves, bearing capacity, ductility and energy dissipation were compared and analyzed. It is observed that the cracking in concrete and the cross-sectional loss of corroded bars had a more obvious influence on the yielding load but had a relatively smaller influence on the ultimate load. The asymmetrical structural configuration of the beam-column joint resulted in non-uniform corrosion of the reinforcing steel bars in the top and bottom of the beams; accordingly, the post-peak behaviors of the specimens in positive and negative loading were different. The difference was found to be more significant with the increase of the corrosion ratio. A numerical method is proposed for simulating the behaviors of corroded beam-column joints through the constitutive models for concrete and steel reinforcements, and agreement is observed between simulated and experimental results.

Insights of Hysteresis Behaviors in Perovskite Solar Cells from a Mixed Drift-Diffusion Model Coupled with Recombination

Hysteresis in perovskite solar cells is a notorious issue limiting its development in stability, reproducibility and efficiency. Ions’ migration coupled with charges’ recombination are indispensable factors to generate the hysteretic curves on the basis of experimental and theoretical calculation studies, however, the underlying physical characteristics are rarely clarified. Here, a mixed electronic-ionic drift-diffusion model combined with bulk and interfacial recombination is investigated. Positive and negative ion species could drift to and accumulate at interfaces between the perovskite/transport layers, influencing internal electric potential profiles and delaying the charges’ ejection to the transport layers. The charges might recombine spontaneously or trap-assisted, reducing the total amount of electrons and holes collected in the external circuit, leading to a diminished photocurrent. Moreover, our calculations indicate that an appropriate measurement protocol is really essential to evaluate the device performance precisely and to suppress J–V hysteresis. Meanwhile, a negligible hysteretic loop could be obtained by balancing the material properties of the transport layers and restraining the ions mobility in the perovskite layer.

Novel uniaxial concrete constitutive model considering bond-slip effect

A uniaxial concrete constitutive model considering the bond-slip effect is proposed and its finite element analysis (FEA) implementation on a fiber section of a beam-column element is presented. The tension-stiffening, crack-closing, crack-opening, cyclic degradation of the tensile capacity of reinforced concrete are modeled, which reveals the significance of energy dissipation resulting from bond slip during crack opening and closing under cyclic loading. The model is based on a simplified mechanical concept in a smeared manner and verified through quasi-static test results of X-type slender RC columns. The FEA results using a common concrete model with no consideration of bond slip present significant pinching when predicting the hysteretic loop of slender columns, which is not consistent with the test results and underestimates the capacity of energy dissipation of cracking during cyclic load. The results obtained with the proposed model show good agreement with the test results, which can reflect the degradation of stiffness and strength as well as the energy dissipation of the crack opening and closing due to the bond slip effect. Considering its simplicity and computational efficiency, it is more applicable for analyzing large-scale structures than other methods that consider the bond-slip effect, especially for slender columns, such as those used in cooling towers and subjected to seismic excitation.

Cupper doping effect on the electrical characteristics of TiO2 based Memristor

Nanostructures as a starting point to solve the scaling problems of the CMOS technologies, have been concerned the attention of numerous researchers. By strong demanding for nonvolatile memory technology, resistive memories based on metal oxide has been common due to several advantages, such as low-power consumption, good scalability and fast switching speed. Even though high-temperature fabrication process has a large area limitation by their material characteristics. Metal oxide thin films are respectable candidate to fabricate at nano scale solid state electronic device. Metal/Metal-Oxide/Metal structure is employed to several devices such as Non-volatile able memories, RRAMs, resistance switching based devices and memristor. The foundation of the primary TiO2 based memristor served a number of consequences for understanding the conduction mechanisms during the formation of hysteresis loop. Also, the current-voltage characteristics (hysteretic loop) which is formed by mobile anions or oxygen vacancies motion in the set and reset process, is clarified the resistive switching behavior by swapping the resistance of TiO2 thin film. Here, the effect of Cu doping into TiO2 based memristor by focused on the hysteresis loop characteristics is considered. Similarities of hysteresis loop form in Cu doped devices are explored. Hysteresis loop is symmetric for structures having pure TiO2; however, asymmetric character appears after Cu doping. After the formation process hysteresis loop of the Cu doped devices shown higher conductance path on (I-V) characteristic than the initial forming process loop in positive cycle loop as the un-doped TiO2. Also, in spite of un-doped TiO2, this (I-V) hysteresis loop character shown lower path conductance than primary forming process in the negative cycle loop. Surface roughness of 30nm thick TiO2 is increased from 0.3nm to 0.77nm as Cu doping increased from %10 to %30. Unfortunately, XRD results cleared that there is no exchange in crystallinity but optical band gap decreased as Cu doping increased.

Matlab® Algorithm to Simulate the Dynamic Behavior of an NiTi Alloy through Ansys® APDLTM Models

In recent years, technological advances related with the so-called intelligent materials have been exploited for problem solving in many engineering fields. In this regard, shape memory alloys (SMA) seem suitable for medical and engineering applications and many others. These alloys have the ability to return to the original form after an apparently plastic deformation by applying heat and the also ability to perform phase changes with voltage variations under a specific temperature. These properties allow the development of a hysteretic loop with energy dissipation, which can be used as a damping element in a vibratory system. In this paper, a MATLAB algorithm was developed to create an interface with the Ansys® APDLTM software that simulate the dynamic behavior of a SMA. The software is capable to obtain the cyclical behavior of a vibratory mechanical system based on the energy dissipation properties of the SMA. The results show that the free vibration of a mass-damper (alloy) system presents the energy dissipation related in magnitude with the area of the hysteresis loop until the deformation caused by the motion which does not correspond to a voltage required to initiate the (direct) phase transformation of the material, thus reducing the displacement to a constant level.
 Keywords: SMA, ANSYS APDLTM, Matlab

Seismic behaviour of concrete-filled steel tubular columns with internal H-section steel under pure torsion and compression–torsion loads

Concrete-filled steel tube (CFST) columns have been widely used in the construction industry because of their excellent compression capacity and torsion resistance. Regarding traditional CFST columns, the H-CFST column with an additional H-section steel member embedded in the core concrete provides improved fire and compression resistance. In this study, the seismic performance of nine H-CFST columns under cyclic torsional and compression–cyclic torsional loads was experimentally analysed. In the experiments, the failure mode, torque versus torsional angle hysteresis, torque versus torsional angle skeleton, torsional stiffness degradation, and energy dissipation capacity were determined. The hysteretic curves of the H-CFST columns under torsion were relatively plump in shape and exhibited no ‘pinching’ phenomenon, and the torsional stiffness of the H-CFST columns under unloading and reverse loading was approximately equal to the initial torsional stiffness. In addition, the applied compression had remarkable effects on the torsional capacity, torsional ductility, torsional stiffness, and hysteretic loop energy dissipation of the H-CFST columns. The shear capacities of the steel and concrete under normal stress or combined normal and shear stress were determined based on the latest theories and test results. Moreover, design method for the determination of the torsional capacity of H-CFST columns under compressive torsion is proposed based on the test results, and the theoretical contribution ratio of the H-section steel, steel tube, and concrete in the H-CFST columns to the torsional capacity was determined.

Development and validation of a new code for longitudinal train dynamics simulation

Longitudinal train dynamics have a significant impact on both safety and performance of railway systems. Numerical simulation of long heavy haul trains can thus provide essential information for the development of diagnostic and signaling systems as well as coupling elements and braking systems. Long trains are usually modeled by considering only the longitudinal degree of freedom and by adding extra resistant forces to represent the track curvature and gradients. The prediction of in-train forces represents the most critical aspect in modeling the longitudinal dynamics of long trains made up of several vehicles. In fact, coupling elements have non-linear force–deflection characteristics, with different behavior in loading and unloading states, thus featuring a hysteretic loop. Look-up tables storing data from experimental tests are generally used to model these elements; however, other strategies, such as fitting curves and white-box models are witnessed in the literature. Recently, an international benchmarking of longitudinal train dynamics simulator was established in order to compare the output results obtained by different models with the same input data. The research group from Politecnico di Torino performed the simulations using the multibody software Simpack, but computational inefficiencies and numerical divergences occurred. To overcome these issues, a new dedicated in-house code was developed in the MATLAB environment. The paper focuses on the description of this new code and its validation, which was carried out by performing the simulations according to the benchmark inputs and comparing the results with the outputs from the other participants.

Method for estimating vibration responses of belt drive systems with a nonlinear tensioner

A friction-type tensioner is widely used in a belt drive system for maintaining belt tension constantly and reducing vibration. Owing to friction dampings, the curve of the reaction torque and the imposed angle of tensioner arm is a hysteretic loop. Here, the hysteretic behavior of tensioner is considered in dynamic analysis of a belt drive system. A hysteretic model for describing the applied torque versus the imposed angle of tensioner arm is established. And an iterative algorithm is proposed for estimating the nonlinear equivalent viscous damping of tensioner under a varying excitation frequency. A timing belt drive system is taken as an example. Based on the existing research, the dynamic models for a belt, an automatic tensioner and rotational pulleys of system are also given. The vibration responses of a belt system, such as the oscillation angle of tensioner arm, the transmission error between pulleys and the hub load applied on pulley, are calculated and compared with the measurements, which are validated the presented method. The influence of damping ratio of tensioner on dynamic responses of system is investigated, and the influence of iteration parameters on the iterative efficiency is discussed. The presented method is beneficial to modifying the existing method for calculating the vibration responses of a belt drive system.

Identification of viscoelastic properties of Dacron aortic grafts subjected to physiological pulsatile flow

In vascular surgery, most synthetic vascular grafts currently used for large vessels replacements are made of Dacron (polyethylene terephthalate; PET). In this study, the dynamic response of these synthetic arterial substitutes to physiological pulsatile conditions is investigated in depth. Experiments were performed on a mock circulatory loop developed to replicate physiological pulsatile pressure and flow. Two different models of Dacron grafts (branched and straight) were tested at various heart rate conditions. Results are presented in terms of cyclic axisymmetric diameter changes, hysteretic loops of the pressure-diameter change, and viscoelastic parameters, such as loss factor and storage modulus that are identified from the hysteresis loop. The amplitude of cyclic diameter change of the Dacron graft was found to be always below 0.2% for all the heart rates considered (from 57 to 187 bpm). The loss factor of the Dacron graft slightly increased with the heart rate; almost no effect of the pulse rate was observed on the storage modulus, which was identified to be around 100 MPa. Both glycerol-water mixture (i.e. the blood analogue fluid) and saline solution were used in the circulatory loop and results did not present significant differences between the two cases. This shows that the effect of the shear load on the dynamic response of Dacron grafts is negligible. A comparison between Dacron vascular implants and human thoracic aortas shows a large mismatch in their viscoelastic mechanical properties.

EX draconis: using eclipses to separate outside-in and inside-out outbursts

ABSTRACT We present a study of the eclipses in the accreting white dwarf EX draconis (EX Dra) during TESS Cycles 14 and 15. During both of the two outbursts present in this data set, the eclipses undergo a hysteretic loop in eclipse-depth/out-of-eclipse-flux space. In each case, the direction in which the loops are executed strongly suggests an outburst that is triggered near the inner edge of the accretion disc and propagates outwards. This in turn suggests that the outbursts in EX Dra are ‘inside out’ outbursts; events predicted by previous hydrodynamic studies of dwarf nova accretion discs and confirmed spectroscopically in a number of other accreting white dwarf systems. We therefore propose that the direction of the loop executed in eclipse-depth/out-of-eclipse flux space be used as a test to phenomenologically distinguish between ‘inside out’ and ‘outside in’ outbursts in other eclipsing dwarf novae; a reliable and purely photometric test to differentiate between these phenomena.

Experimental study of a steel damper with X-shaped welded pipe halves

In this paper, a new steel damper named X-shaped pipe damper (XPD), is proposed and examined. The proposed damper is made through welding two oppositely positioned pipe halves to form a X-shaped core, and connecting the X-shaped core to side plates with fillet welds or circumferential welds. The XPD damper provides the lateral resistance and energy dissipation behaviors initially through flexural bending of pipe plates, and latter through the tensile stretching at composite pipe halves. Theoretical derivations of initial stiffness and yielding properties were conducted, and the nonlinear working mechanisms and seismic performance were investigated through cyclic quasi-static tests. Effect of welding methods and pipe configurations on the stiffness, strength, ductility and energy absorption efficiency of the XPDs were studied. The XPDs can presented similar lateral load resistance with only half pipe usage than dual pipe dampers. The XPD specimens all presented stable and pump hysteretic loops, and had a steady strength increase after yielding until fracture failure. The circumferential weld XPDs displayed higher initial stiffness, strength and better deformation ability than the fillet welded ones, but also possessed fatigue fracture potential at the heat affecting zones under fatigue cyclic protocols. Based on the obtained results, the application field and improving suggestions for the XPDs are discussed.

Experimental study of seismic performance of full-scale basalt FRP-recycled aggregate concrete-steel tubular columns

Abstract Hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) have received extensive attention in the research community over the past decade. Generally, a DSTC consists of an inner steel tube and an outer FRP tube, with the space between them filled with natural aggregate concrete (NAC). This paper studied a new form of hybrid FRP-recycled aggregate concrete (RAC)-steel tubular column (FRSTC) in which the outer FRP tube was made of environmental-friendly basalt fibers and the concrete was made of recycled coarse aggregates (RCAs). Quasi-static tests of five full-scale basalt FRSTCs were conducted to gain an improved understanding of the behavior of FRSTCs, and to enable further application potentiality of FRSTCs in earthquake-prone areas. Three key column parameters, including RCA replacement percentages, axial load ratios, and steel reinforcement ratios were carefully designed to clarify their influence on the performance of FRSTCs under combined axial compression and cyclic lateral loading. The test results, including the hysteretic loops, skeleton curves, curvature and strain distributions, ductility characterization, energy dissipation capacity, stiffness and strength degradation, and cumulative damage, are presented and discussed. The experimental results show that the RCA replacement percentage has little impact on the seismic performance of FRSTCs, while the effect of the axial load ratio is significant. The bearing capacity and energy dissipation of FRSTCs can be superior to those of DSTCs with NAC.

Optical nonlinearity, saturation in absorption and optical bistability of AZO films synthesized in presence of sodium hydroxide

In this paper, the aluminum-zinc oxides composite (AZO) films are prepared through the sol-gel method which is a proposed material for fabrication the transparent conductive oxides (TCOs). Sodium hydroxide is used during synthesis process in order to change surface and optical properties of AZO films. The absorption spectrum, band gap and saturable intensity values are presented as functions of sodium atomic percent. As the ratio of Na to Zn atoms is 0.153, the best surface quality is obtained which has side effects on the optical properties of the films. The results confirm that by increasing the sodium atomic ratio, the optical band gap reduces and saturation intensity decrease. These films are used as optical bistable devices and show different threshold values for the hysteretic loops.