Bidirectional Loading Research Articles

Hybrid Bidirectional Multilevel Inverter Structures for Induction Motor Drive

Multilevel inverters performance enhancement is a major topic which has attracted the attention of most of the researchers, to evolve with newer topologies and modulation strategies. In this manuscript two novel hybrid bidirectional multilevel inverter structures which are suitable for bidirectional loads are proposed. An enhancement in the voltage levels and reduction of the component count are achieved for these newly introduced structures. Modular expansion and series cascading are suggested systems for extension of the voltage levels.The prime requirement in most of the industrial drives is a controlled output. VSI fed Induction motor drive satisfies this requirement. The Multicarrier PWM technique has been applied to the basic bidirectional seven level models and nine level model and its performance with induction motor as load has been analyzed for various modulation indices. The simulated results of the proposed structures are verified using MATLAB/SIMULINK platform. The characteristics such as stator current, rotor current speed and torque plots achieved as above model affirm that its performance is good.

On dynamic behavior and failure of high lock bolted joints: Testing, analysis and predicting

A bidirectional synchronous dynamic loading technique based on electromagnetic split Hopkinson tensile bar (ESHTB) system was employed to investigate the dynamic behavior and failure of high lock bolted joints. Force-displacement curves over wide ranges of loading speed (5 × 10−6 m/s to 15 m/s) and loading state (tension, shear and three kinds of tension-shear coupling) were obtained by combining with results obtained from quasi-static tests. An obvious elevation of failure load levels when changing the loading state from shear to tension or improving the loading speed was observed. Meanwhile, such strengthening effect of loading state on failure loads presented positive correlation with the loading speed. Detailed analysis for effect of loading state on mechanical behavior of bolted joints was conducted by applying von Mises yield criterion together with failure load analysis. Moreover, on this base, the influence of loading speed on failure loads was reasonably defined by applying a relation equal to the different strain rate effect between shear and tension for bolt material. Finally, a failure criterion considering coupling effect of loading speed and loading state on failure load of bolted joint was proposed. Prediction results showed a good agreement with the experimental results, indicating the determination of failure loads for bolted joints under different loading states over a wide range of loading speeds can be achieved.

Mechanical characteristics of circular hollow section damper under bidirectional cyclic loading

During earthquake events, hysteretic dampers installed on the elevations composed of the columns and beams of structural frames can resist forces in any direction other than the in-plane direction because of the three-dimensional behavior of buildings and the interrelationship between the dampers and the adjacent members. Circular hollow section dampers (CHSDs), which form a type of steel hysteretic dampers, can be employed as seismic devices because they provide equal structural performance in any horizontal direction according to the geometrical characteristics of the cross-sectional shape. However, the cumulative hysteretic characteristics of CHSDs for multidirectional behavior remain unelucidated; therefore, an empirical review is needed. This study experimentally analyzed the cumulative hysteresis behavior of a CHSD repeatedly loaded sequentially in two horizontal directions (bidirectional cyclic loading). The results obtained were compared with previous experimental results under unidirectional cyclic loading conditions. The comparative analysis using empirical data revealed that the hysteretic curve of the CHSD under bidirectional cyclic loading maintained a relatively constant strength increase ratio and effective stiffness along with a stable spindle shape until the damper reached the ultimate state despite the continuous change in the loading direction. Further, compared with the unidirectional cyclic loading condition, the CHSD under bidirectional cyclic loading exhibited similar structural trends considering the damper aspect ratio and material influence. Moreover, the total accumulated plastic deformation in each loading direction was approximately the same as the cumulative plastic deformation caused by unidirectional cyclic loading.

Dynamic Analysis of the Seismo-Dynamic Response of Anti-Dip Bedding Rock Slopes Using a Three-Dimensional Discrete-Element Method

Earthquakes are a major external factor that induce landslides. In order to systematically study the dynamic effects and failure mechanism of anti-dip bedding rock slopes (the slope trend is the same as the joint trend, while the slope dip direction is opposite to the joint dip direction) under seismic action (as well as the spatial effects of the structural planes in the anti-dip bedding rock slopes), three-dimensional (3D) discrete-element numerical calculations were performed to analyze anti-dip bedding rock slopes with different slope angles, joint angles, and joint trends subjected to the action of natural seismic and sinusoidal waves. The results were analyzed to investigate the amplification effect, change in Fourier spectrum, failure mechanism, and permanent displacement of the slope under the applied seismic action. The permanent displacement of the slope was calculated using Newmark’s method and the results obtained were discussed and compared with those obtained from a dynamic analysis performed using the 3D discrete-element method. The results showed that the regularity of the spatial distribution of the amplification effect was less clear than that encountered in the planar problem (unidirectional or bidirectional dynamical loading), and this leads to the effect of having an overall rhythmical nature. The seismic wave decays in the high-frequency part from the bottom up of the slope, while the dominant frequency of the seismic wave decreases. The value of the permanent displacement obtained using Newmark’s method is much smaller than that obtained using the dynamic 3D discrete-element analysis approach. The angle between the joint and slope trends has a significant effect on the amplification effect, failure mode, permanent displacement, and stability of slopes subjected to seismic action.

Parametric resonance of bi-directional axial loads shallow arch microresonators

In this work, we investigate analytically and experimentally parametric resonances of an in-plane clamped-guided shallow arch microresonator. The arch is connected to a T-shaped moveable mass, which is sandwiched between two electrodes to electrostatically activate the device and to offer bi-directional axial loads option. The device is tested under primary and secondary parametric resonances. In addition, an analytical model is presented taking into account the initial rise of the microbeam and the sliding motion at the guided side. The static and free vibration problems are solved using the Differential Quadrature Method, and the dynamic response is simulated using an assumed mode Galerkin approximation. The theoretical results of the static and dynamic behavior of the device are compared to experimental data showing good agreement. Moreover, we demonstrate the use of parametric excitation to significantly amplify the axial motion. It is found that the second parametric resonance, corresponding to the fundamental mode of the arched microbeam, has a higher amplitude than the principal parametric case, due to the initial curvature of the beam. Thus, the proposed device can be a promising candidate for variety of sensing applications.

Behavior of stiffened and multi-cell L-shaped CFST columns under eccentric compression

The mechanical behavior of the traditional special-shaped concrete-filled steel tubular (CFST) columns can be improved by employing longitudinal stiffeners or using multi-cell cross-section. In practical application, the stiffened and multi-cell L-shaped CFSTs are often subjected to bi-directional loading. However, there are only few research studies on their performance as loaded eccentrically with different orientations of the loading and there is no relevant design guideline. This paper reports tests on 16 L-shaped CFST columns (nine stiffened, six multi-cell specimens and one reference specimen) loaded in eccentric compression. The main variables were the angle indicating the orientation of the load action line (0°, 45°, 135°, 180° and 225°), load eccentricity ratio (0, 0.25 and 0.5) and slenderness ratio (31.5 and 41.9). Finite element models for the eccentrically loaded stiffened and multi-cell L-shaped CFST columns were developed. Based on the parametric analysis, practical design methods were proposed for predicting the bearing capacity based on the stability loss and the axial force vs. bending moment interaction diagrams for the members considering the influence of the load orientation at the end face of the column.

HSS steel corner column to H-beam joints under cyclic bidirectional loadings: Experiment, numerical modeling, and calculation

The paper investigates the flexural performance of hollow structural section (HSS) steel corner column to H-beam joints, varying beam depth to width ratio, cyclic load paths, and weld leg size. Finite element analysis (FEA) models were successfully validated in the failure mode, hysteresis behavior, stress distribution, and shear deformation. Parametric analysis of 27 FEA models extended the test variables to the column width to thickness ratio (D/t), beam depth to width ratio (h/b), axial load ratio (n), loading ratio (Mw/Ms), and loading paths at beam ends. The analysis results indicated that the bending capacity of the corner column connections decreased with D/t and n increase but increased with h/b increase. In addition, the coupling effect degraded the bearing capacity of corner column joints, which was most significant at a loading ratio of 1:1. Finally, calculation formulae for the flexural capacity of corner joints were proposed for comparison with the FEA results.

Effects of design parameters on the static responses of two-way beam string structure

A two-way beam string structure is composed of upper beam and two different cables, namely, sagging and arch-shaped cables. It is designed for structural members under bi-directional loads because the maximum stress and displacement can dramatically reduced. In this study, a parametric study for this structure is presented to provide optimal design parameters, which include number of struts and curvature of cable. Numerical examples are implemented in the ABAQUS finite element package to validate and then study the effects of the number of struts, deflections and stresses as well relationships of ultimate loads for various cable curvatures. Besides, the stress sharing ratio of top/bottom of the beam and the sagging cable under positive and negative pressure are investigated.

Load-dependent stiffness model and experimental validation of four-station rotary tool holder

The four-station rotary tool holder is used to clamp multiple turning tools and realize automatic tool change on a lathe. For the accurate estimation of structural stiffness, a deeper understanding of mechanical behavior within locking tool holder is needed. This paper is the first attempt to introduce a theoretical vertical stiffness model of tool holder. The rough surface joint effect is characterized by fractal geometry theory, including lower-upper tool holder plane joint, gear plate joint with trapezoidal tooth, screw spiral surface joint. The interface base bulk stiffness and the support bearing deformation are also unified in the stiffness modeling. Through the force interaction, the nonlinear relationship of load–displacement is established. The bidirectional static loading test under various locking forces is conducted using a commercial tool holder. The different intercepts of load-dependent displacement curve for various preloads are experimentally captured. The vertical stiffness under compression load is higher than that under tensile load. The predicted values agree well with experimental results by the micro-topography characterization of surface joints. The numerical simulation shows that vertical stiffness increases with the increase of compression load, locking force, fractal parameter D, nominal area of surface joints, and the decrease of dragged load, fractal parameter G.

Experimental study on the dynamic modulus of compacted loess under bidirectional dynamic load

The dynamic characteristics of compacted loess are of great significance to the seismic construction of the Loess Plateau area in Northwest China, where earthquakes frequently occur. To study the change in the dynamic modulus of the foundation soil under the combined action of vertical and horizontal earthquakes, a hollow cylindrical torsion shear instrument capable of vibrating in four directions was used to perform two-way coupling of compression and torsion of Xi'an compacted loess under different dry density and deviator stress ratios. The results show that increasing the dry density can improve the initial dynamic compression modulus and initial dynamic shear modulus of compacted loess. With an increase in the deviator stress ratio, the initial dynamic compression modulus increases, to a certain extent, but the initial dynamic shear modulus decreases slightly. The dynamic modulus gradually decreases with the development of dynamic strain and tends to be stable, and the dynamic modulus that reaches the same strain increases with an increasing dry density. At the initial stage of dynamic loading, the attenuation of the dynamic shear modulus with the strain development is faster than that of the dynamic compression modulus. Compared with previous research results, it is determined that the dynamic modulus of loess under bidirectional dynamic loading is lower and the attenuation rate is faster than that under single-direction dynamic loading. The deviator stress ratio has a more obvious effect on the dynamic compression modulus. The increase in the deviator stress ratio can increase the dynamic compression modulus, to a certain extent. However, the deviator stress ratio has almost no effect on the dynamic shear modulus, and can therefore be ignored.

Kinematic response of single vertical and batter piles to bidirectional ground motions in liquefiable soil

Kinematic responses of single fixed head vertical and batter piles in liquefiable soil under bidirectional ground motions have been studied with fully-coupled three-dimensional nonlinear dynamic analyses. Pressure dependent multi-yield constitutive model has been adopted for modeling the liquefiable sand behavior. The variable permeability of saturated sand during the process of liquefaction process has also been considered. The analyses are carried out for combinations of bidirectional earthquake loading conditions. For this, combination of longitudinal and transverse ground motions as well as combination of longitudinal and vertical motions are considered. The responses of the soil-pile systems under liquefying ground conditions, subjected to these bidirectional ground motions, are compared with the unidirectional loading conditions. Further, the effect of sloping ground on the response of the piles under bidirectional ground motions is also investigated. The developed sectional forces in both vertical and batter piles are lesser under bidirectional motions in comparison to unidirectional ground motion in both level and sloping grounds. However, the pile displacement is more in case of sloping ground under bidirectional ground motions comparing to unidirectional motion.

Research on Integrated Electrical and Mechanical Response of Piezoelectric Asphalt Pavement Material Under Bidirectional Cyclic Loads

Research on Integrated Electrical and Mechanical Response of Piezoelectric Asphalt Pavement Material Under Bidirectional Cyclic Loads

Investigations on Dynamic Mechanical Analysis and Crystalline Effect of Neem/Banyan Fiber–Reinforced Hybrid Polymer Composite

Abstract Natural fiber is often considered to be deficient for high-performance reinforcement of polymer matrix composites. However, the environmental aspects of natural fiber are attractive to many researchers in the area of natural composites because of the specific strength and eco-friendly properties of natural fibers. In this research, alkali-treated natural fibers are chopped neem fibers, and bidirectional woven mat was used as reinforcement and blended with epoxy matrix. Also, sawdust cellulose was used as a filler material to fabricate composite laminates by the conservative hand layup method. The composite laminates are varied by different weight fractions of reinforcement (25 %), epoxy matrix (70 %), and filler (5 %). Then, to quantify the effect of storage modulus, loss modulus and the damping factor of the hybrid composites are taken by conducting dynamic mechanical analysis. Maximum storage modulus is 1,343 MPa. The results show that increasing the bidirectional woven fiber loading will give 61 % more stiffness in the elastomeric region when compared to chopped neem fiber loading in the hybrid composites, and analyses of the crystallinity effects by x-ray diffraction also identify the adhesion quality between the fibers, fillers, and matrix by using the surface morphology test scanning electron microscopy of the hybrid composites.

Effect of material variability on the seismic response of reinforced concrete box-girder bridges for different pier heights

RC bridges situated in regions prone to seismic activity are susceptible to undesirable pier column movements and deck displacements. The component-level nonlinear response evaluation can give a better picture of the seismic safety of the existing bridge structures. Many times, the material strength variability also affects the inelastic response of the structures significantly. The present study looks into the effects of column heights and material strength variability on the seismic performance of reinforced concrete bridge models adopted from past investigations, subjected to bi-directional loading. Chosen suite of 40 far-field ground excitations are employed to simulate the seismic response of chosen models in OpenSees and their non-linear response is evaluated. The seismic response of the structure is evaluated as curvature ductility of piers (primary component), and deck displacements (secondary component). Fragility curves so obtained across the damage states considered depict the difference in seismic performance of the model considering only record variability and considering record and material strength uncertainties. The results showed that for the primary component, damage probability for different states is found to be increased under material variability irrespective of the column pier height, while secondary components showed an increase in the damage state due to material strength variability for the shorter pier.

Multi-axial cyclic loading tests for RC shear walls of nuclear power plant structures

Reinforced concrete (RC) walls have been widely studied through experimental testing. A great number of these existing studies considered only the in-plane loading cases, ignoring the out-of-plane loading effect on the in-plane structural response, although earthquake ground motions have multi-axis loading components. Some recent studies addressed the bidirectional loading effect on RC walls, and reported that the out-of-plane loading lowers the displacement capacity of RC walls. However, these studies are for flexural response of RC walls, and little experimental data for shear response of RC walls under bidirectional lateral loading is available. In this study, a series of cyclic loading tests were conducted to investigate the effect of multi-axial loading on the in-plane shear response of RC walls. A prototype nuclear power plant structure was selected, and a part of the prototype RC wall was manufactured as a test specimen, which was designed to have shear failure. Out of the five wall specimens manufactured for this study, two specimens were subjected to the same unidirectional lateral loading with different axial forces to investigate the effect of axial force on the wall response. Remaining three specimens were subjected to bidirectional lateral loading with different loading protocols. It was found that both out-of-plane loading and axial force can substantially impact on the in-plane shear strength and displacement capacity of RC walls.

Deformation simulations of sand under Bi-directional shear loading

A well-developed sand plasticity model is further revised and validated based on bi-directional simple shear test data on medium to high relative density sands, which includes circular, oval and figure-8 type stress paths at different cyclic stress ratio (CSR) levels. The sand properties revealed from non-proportional loading tests, such as extended contractive behavior for medium to dense sands, flow rule dependency on plastic strain increment direction, stress increment direction dependency of plastic moduli, as well as the so-called non-coaxial property are incorporated into the new model development. Specifically, the recently proposed strain increment direction dependent flow rule is formulated and validated using bi-directional simple shear test results; and the relatively simple plastic moduli revised for the non-proportional loading are validated.After the model parameters are calibrated using a circular stress path, predictions are made for oval and figure-8 type stress paths at two cyclic stress levels. The modeling results show that the computed deformations up to a large strain state (i.e., 6% double amplitude strain) match fairly well with the test results; and the predicted pore-water pressure generation (or the effective stress change) followed the trend of test measurements including the repeating contractive and dilative cycles near the failure surface. A fabric dilatancy concept-based stiffness reduction approach is adopted that is active for the simulations of oval and figure-8 type stress paths.By comparing with test results, the model predictions demonstrate the capability of the present model in simulating the complex deformation magnitudes and patterns for sands under bi-directional loadings.

Cyclic behavior of high-performance fiber-reinforced cementitious composite corner joints

In moment frames, beam-column joints are critical elements that ensure the structural integrity of the frames. During earthquakes, beam-column joints can withstand large shear forces transmitted from nearby columns and beams. In old reinforced-concrete (RC) moment frame buildings, beam-column joints had little joint transverse reinforcement, which are susceptible to significant damage during large earthquakes. Their corner joints could experience a more severe seismic loading environment than other joints because they are subjected to bidirectional lateral loadings during earthquakes. The objective of this study was to improve the cyclic behavior of corner joints by using high-performance fiber-reinforced cementitious composite (HPFRCC). For this purpose, seven corner joint specimens were made and tested under unidirectional and bidirectional cyclic loadings. The application of HPFRCC improved the cyclic behavior of corner joint specimens. The contribution of HPFRCC outweighed that of the minimum joint transverse reinforcement. The minimum joint transverse reinforcement moderately affected the cyclic behavior of the specimens. The shear strength and drift capacity of unidirectional HPFRCC specimen without the joint transverse reinforcement had 13% and 24% larger than those of unidirectional RC specimens with the joint transverse reinforcement, respectively. Similar observations were made for bidirectional specimens. Particularly, the failure mode of the specimens was changed by using HPFRCC from brittle joint shear failure and axial failure to beam flexural failure followed by joint shear failure.

Finite element modeling and behavior of dissipative embedded column base connections under cyclic loading

This paper explores, by means of continuum finite element (CFE) analysis, a recently developed concept that promotes controlled inelastic energy dissipation within the embedded portion of column base connections rather than in steel columns of conventional embedded column bases. As such, dissipative embedded column base connections become resilient to local buckling. Several loading and geometric parameters are interrogated through parametric simulations with a high-fidelity CFE model, which is thoroughly validated with available experimental data. The simulation results suggest that steel columns in conventional embedded bases are prone to local buckling even at modest lateral drift demands (i.e., 2% rad), thereby exhibiting 10 to 30 mm of axial shortening in the presence of constant compressive axial load. On the other hand, dissipative bases are resilient to local buckling till at least 4% rad lateral drift demands regardless of the column cross-sectional characteristics and loading parameters. At larger lateral drift demands, the use of horizontal stiffeners in dissipative bases alleviates localized flange deformations attributable to bearing of the embedded column flange with the reinforced concrete foundation. Axial shortening in dissipative base connections is only attributable to inelastic cyclic straining within the dissipative zone and is up to 60% less than that of steel columns in conventional bases at lateral drift demands of 2% rad. The CFE simulations reveal that the hysteretic response of dissipative bases is insensitive to bidirectional loading.

The effect of vertical near-field ground motions on the collapse risk of high-rise reinforced concrete frame-core wall structures

According to the observations of past earthquakes, the vertical ground motions have had a striking influence on the engineering structures, especially reinforced concrete ones. Nevertheless, the number of studies on their aftermath is insufficient, and despite some endeavors done by researchers, there is still a shortage of knowledge about the inclusion of vertical excitation on the seismic performance and the collapse probability of RC buildings. Hence, the variation in the collapse risk of three high-rise RC frame-core wall structures when they undergo bi-directional ground motions is discussed. In this paper, incremental dynamic analyses are carried out under two circumstances, including the horizontal (H) and the combined horizontal and vertical (H+V) earthquakes, and the seismic fragility curves are derived. The inter-story drift ratio corresponding to the onset of collapse has also been defined. The buildings collapse risk under the two circumstances is obtained from the risk integral. Results indicate that in the H+V state, structures meet the collapse criteria for lower intensity measures. Thus, the collapse risk increases as the structures are subjected to bi-directional seismic loads, and the consideration of this effect leads to a more accurate evaluation of buildings seismic performance.

Bi-directional loading of unbonded rectangular fiber-reinforced elastomeric isolators

Elastomers are ideal for application as base isolators due to their ability to accommodate large recoverable strains. The formation of a composite with reinforcement, either steel or fibers, takes advantage of the near incompressibility of the elastomer to enhance the vertical and bending properties of the bearing. Although the conceptual design of a fiber-reinforced and steel-reinforced elastomeric bearing is similar, the lack of flexural rigidity of the fiber reinforcement results in unique performance characteristics, especially in the lateral direction. In this paper, an experimental program is conducted to evaluate the effect of lateral coupling in rectangular unbonded fiber-reinforced elastomeric isolators (UFREIs). An apparatus with six degrees of freedom was used to apply a vertical load with simultaneous displacement in both primary lateral directions, whereas previous experimental programs are mostly based on a two degree of freedom analysis (vertical and lateral). The UFREI specimen was subjected to cyclic lateral displacements including tests with initial lateral offsets in the secondary lateral direction, in directions angled off the principal lateral axis, and in a circular motion. This experimental program is the first to investigate lateral coupling in rectangular UFREIs. A comparison was conducted based on the effective lateral stiffness, equivalent viscous damping, and energy dissipation characteristics. The considered rectangular UFREIs were found to exhibit lateral coupling but the degree of coupling and the impact on the structural performance under bidirectional loading require further investigation. Residual displacement was observed in the experimental program and is discussed in depth. Also, a theoretical equation is derived to calculate the lateral stiffness based on the angle of loading and lateral displacement. Theoretical values are compared with experimental results to verify the equation.