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Experimental Test and Finite Element Analysis on a Concrete Box Girder of a Cable-Stayed Bridge with W-Shaped Prestressed Concrete Diagonal Braces

This paper presents an experimental study on the box girder of a low-tower cable-stayed railway bridge with a W-shaped section that consists of prestressed concrete diagonal braces. A 1:6 scale test model was designed and constructed for the experiment. The mechanical behavior of the test model was investigated under two loading conditions: a double-track train symmetrical load and a single-track train unsymmetrical load. The experimental results were validated against a finite element model. Furthermore, the torsional performance of the box girder section was analyzed and discussed.

A Theoretical Method to Optimize the Control Signal Power for High-Efficiency Symmetrical Load Modulated Balanced Amplifier Designs

A Theoretical Method to Optimize the Control Signal Power for High-Efficiency Symmetrical Load Modulated Balanced Amplifier Designs

Two-speed Synchronous Generator for Special Purposes

This paper deals with basic performances of a design of a two-pole three-phase 40MVA synchronous generator. The generator is designed to test three-phase and single-phase high power transformers aimed to work within 50 Hz and 60 Hz network frequency. This means that the generator will operate at two nominal speeds, at 3000 rpm and 3600 rpm, with nominal power of 40 Mvar induction load when rating with symmetrical three-phase load. The additional requirements relate to constant operation with two-phase 25 MVA load and single-phase 13.5 MVA load, since for testing single-phase and special transformers phase connection you like will be used. In the course of designing, special attention was paid to correct dimensioning of the damper rotor winding as well as to the geometry of stator windings, rotor and air gap, which in the end will produce minimum voltage wave distortion, i.e. generator voltage wave shape with harmonious content less than 1% (as it was demanded).

Stress discontinuity and singularity around the vertex of a triangular inhomogeneity

The stress field around a vertex of angular inhomogeneity has been investigated by Eshelby’s equivalent inclusion method (EIM). Different from Eshelby’s problem for ellipsoidal inhomogeneity with a uniform or polynomial eigenstrain, a singular eigenstrain field is derived by Airy’s stress function and asymptotic analysis, in which the singular elastic fields can be expressed in terms of the distance to the vertex. The discontinuity of Eshelby’s tensor along the boundary has been analytically derived and are used in the stress equivalence condition at the vertex, which can be converted into an eigenvalue problem with the integral of the Green’s function and singular eigenstrain over the inhomogeneity. To verify the solution, when the opening angle 2β at the vertex approaches zero, the triangular void reduces to a slit-like crack, and the paper reproduces the classic solution of 1/r singularity. When β increases from 0 to π/2, the singularity parameter λ around the vertex of the triangular void reduces at different pace under the symmetric and antisymmetric loading conditions. When a triangular inhomogeneity exhibits nonzero stiffness and different angles, λ changes with the stiffness ratio, β, and loading conditions, and the dominant stress singularity around the vertex and stress discontinuity across the boundary are analytically provided. Particularly, the stress singularity for an adhesive interface with varying stiffness provides insight for structure repair and integration.

Numerical simulation of punching shear in flat slabs with spherical voids subjected to symmetric and asymmetric loadings

Numerical simulation of punching shear in flat slabs with spherical voids subjected to symmetric and asymmetric loadings

Numerical modeling and fatigue analysis of the dynamic response of main pump cable in nuclear power plant

Abstract The structural temperature rise and thermal stress caused by operation current and ambient temperature are some of the main factors affecting cable fatigue life. Combined with the operating and environmental conditions of the main cooling pump of the nuclear power plant, the thermal-structural coupling field numerical modeling and fatigue analysis of the 6kV single-core and three-core cable of the main pump is carried out. Based on obtaining the steady-state operating current, the motor start-up transient current, and the circulating ambient temperature, the thermal-structural coupling field numerical model of the main pump cable is established using the load transfer method to obtain the thermal and stress field distribution of the internal structural layer. The load history of one cycle is extracted for the fatigue numerical simulation of the main pump cable. The stress time history of the cable structure layer was constructed by the stress calculation results and the load time history of a single period, and the fatigue life of the main pump cable was obtained based on the S-N curve of the main insulation material and the Miner’s linear cumulative damage theory. The simulation results show that the force acting on the main pump cable by the operating current and ambient temperature is an approximately symmetric cyclic load of constant amplitude. The life cycle of the cable can reach 2.235*e4 times, and the overall life of the cable is about 63.97 years. This study can provide theoretical guidance for the safety and reliability design and state operation and maintenance of the main pump cable of the nuclear power plant.

Calculation of pre-stressed cable-stayed steel bridge with intersecting cable stays/Berechnung einer vorgespannten Schrägseilbrücke aus Stahl mit sich kreuzenden Schrägseilen

Compared to other structural systems, cable-stayed bridges are marked by their exceptional architectural appeal. However, these bridges have several disadvantages – their deformability under asymmetrical or local loads the relatively significant mass of stiffening girder and the pylons. A successful way of stabilizing the bridge’s initial form could be using additional stay cables and additional pylons. The article discusses the calculation method of an innovative cable-stayed steel bridge system consisting of intersecting cables and additional intermediate pylons. The system’s behavior is analyzed under symmetrical and asymmetrical loading. The calculation method results are compared to the numerical analysis using the FEM software.

Uticaj solarnih panela i skladišta električne energije na gubitke u niskonaponskoj mreži

The largest part of technical losses of electricity in electricity distribution are technical losses in low-voltage lines. Technical losses of electricity are losses that occur in the distribution of electricity from transformers to consumers in electrical distribution equipment. Commercial losses include unauthorized use of electricity and losses due to errors in metering equipment. The main source of technical losses of electricity is caused by the flow of electric current through conductors. Solar panels installed by consumers can affect the reduction of losses by reducing the flow of electric current, i.e. of electricity through low-voltage lines. The introduction of electricity storage (batteries) can have an additional impact on the reduction of electricity losses by using the stored electricity in batteries at times of peak loads. The paper presents the assumed daily diagram of the symmetrical load of the low-voltage line with the calculation of hourly losses without the influence of solar panels and with the influence of solar panels without electricity storage and with electricity storage. The impacts of solar panels without and with electricity storage are also shown in a daily diagram, as well as the voltage values at the end of the low-voltage line. In the calculation, an equivalent line with half the length and full hourly load is used for the low-voltage line.

Static performance of multi-planar CFST chord-CHS brace KK joints

This paper investigates the static performance of jacket joints to promote the application of CFST jacket foundations for offshore wind power. An experimental and numerical study of the influence of loading patterns, concrete filling in the chord, geometric parameters, and material strength is examined. In total, five 1:6 scale tests and twenty-eight FEAs are described. The novelty is that a limit device is introduced to consider the interaction among the braces by connecting four braces. The experimental results indicate that, compared to symmetrical loading joints, the bearing capacity of CHS-KK joints decreased by 14% under anti-symmetric loading. Concrete filling in the chord alters the failure mode, enhancing the ultimate bearing capacity of the KK joint. However, its effect on the punching shear failure strength of the joint is limited. An FEA model incorporating the modified Mohr-Coulomb criterion (MMC) was established to explore the ultimate strength of CFST-KK joints, following validation through experiments. Through parameter analysis, it was found that the punching shear capacity of CFST-KK joints is significantly influenced by the diameter ratio of the brace to chord (β), the chord diameter to thickness ratio (2γ), the angle between the brace and chord axis (θ), and the chord steel strength. In addition, the recommended formula in GB50017–2017 for CHS-KK joint punching shear capacity conservatively predicted CFST-KK joint performance.

Experimental and Analytical Studies of String Steel Structure for Bridges

Due to their efficiency, suspension structures are widely used in both roof slabs and different kinds of bridges, from which stress ribbon pedestrian bridges can be distinguished. The main disadvantage of the latter is high deformability, especially under asymmetrical loads. Recently, string structures or their systems have been introduced into bridge building. Numerical and experimental analysis of string behaviour under symmetrical and asymmetrical loads is carried out in the article. Analytical expressions for the calculation of string displacements and tensile forces are presented. The impact of the string pre-stress on the state of its stresses and deformations was evaluated. The assessment of the accuracy of analytical expressions by applying the results of numerical and experimental research is presented. A methodology is proposed for calculating the pre-stressing force taking into account the operational requirements. Three main loading options at different string pre-stress values are analysed. It is worth mentioning that the difference (error) between the analytical and numerical results is not extensive, it does not exceed 3%. It is necessary to notice that in all cases, the analytically obtained results are somewhat higher than FEM (numerically) obtained results.

Constitutive modelling and damage prediction of AlSi10Mg alloy manufactured by SLM technology with emphasis on ratcheting in LCF regime

The present work has been aimed at developing an improved cyclic plasticity model in the framework of Ohno-Wang kinematic hardening formulation and evaluating the performance of the model with reference to the critical experimental investigation. LCF test specimens of the AlSi10Mg aluminium alloy have been fabricated through selective laser melting technology. The material shows strain-range dependent variation of modulus of elasticity under symmetric strain-controlled loading. The modulus of elasticity decreases with increasing strain amplitude. Stress–strain responses have been critically examined under multistep uniaxial ratcheting in the LCF regime with incremental mean stress and stress amplitude. Damage calculation considering ratcheting and LCF mechanisms as independent gives unconservative predictions. The linear damage accumulation rule taking the largest contribution of both is bringing much more accurate estimates. The proposed model incorporates effects of mean stress and stress amplitude under uniaxial multistep ratcheting in the LCF regime. All fatigue tests in the LCF regime have been simulated using the proposed improved model. Evolution of strain-range dependent elastic modulus has been incorporated in the formulation of the improved model through the memory history dependent parameter. The ratcheting parameter is newly formulated in this present work to account for the effects of accumulated mean plastic strain on the opening of stress strain hysteresis loops that results in a better prediction of the behaviour of cyclic plastic deformation. The proposed model has been validated by comparing simulated results with experimental observations and reference published simulation results.

Experimental and Analytical Studies of String Steel Structure for Bridges

Due to their efficiency, suspension structures are widely used in both roof slabs and different kinds of bridges, from which stress ribbon pedestrian bridges can be distinguished. The main disadvantage of the latter is high deformability, especially under asymmetrical loads. Recently, string structures or their systems have been introduced into bridge building. Numerical and experimental analysis of string behaviour under symmetrical and asymmetrical loads is carried out in the article. Analytical expressions for the calculation of string displacements and tensile forces are presented. The impact of the string pre-stress on the state of its stresses and deformations was evaluated. The assessment of the accuracy of analytical expressions by applying the results of numerical and experimental research is presented. A methodology is proposed for calculating the pre-stressing force taking into account the operational requirements. Three main loading options at different string pre-stress values are analysed. It is worth mentioning that the difference (error) between the analytical and numerical results is not extensive, it does not exceed 3%. It is necessary to notice that in all cases, the analytically obtained results are somewhat higher than FEM (numerically) obtained results.

Studies of the effect of preset square pores on the mechanical properties of Ag nanopsheets under biaxial stretching

This study investigated the mechanical properties of silver nanosheets with preset square pores regarding energy, natural strain, and stress properties. Additionally, the effect of different pore positions on dislocations under symmetrical and asymmetrical loading was analyzed using a model of silver nanosheets with square pores preset under biaxial stretching and molecular dynamics methods. The results revealed that the interaction between shear stress and dislocation can cause fractures, with greater shear stress observed when the pore is closer to the model boundaries. Moreover, the symmetrically positioned pores displayed different mechanical properties under asymmetric loading.

Shear cracking behavior of pre-damaged PVA-aggregate mixed ECC beams: Direct observation using DIC

Normal polyvinyl alcohol-engineered cementitious composites (PVA-ECC) exhibit high mechanical performance but are susceptible to shear cracking. It has been recently found that the shear resistance can be largely improved by including coarse aggregates. However, under complex stress conditions, the mechanism of shear movement and the contribution from coarse aggregate remain unclear. This paper presents an experimental investigation of the shear cracking behavior in pre-damaged PVA-ECC beams with a mixture that includes coarse aggregate. Symmetric and antisymmetric loading tests were carried out to examine the effects of coarse aggregate under different stress rotation fields. To clarify the shear cracking mechanism, digital image correlation (DIC) was applied to observe crack development and strain localization in the shear span of the PVA-ECC beams. The results obtained from DIC and conventional measurements showed good agreement, confirming the reliability of monitoring complex fracture processes using the DIC technique. The shear cracking mechanism of the PVA-ECC beam under complex stress conditions was analyzed. The collaboration of coarse aggregate was observed from the orientation of secondary cracks, which showed less dependence on the presence of precracks. Crack opening and sliding were significantly limited due to the reduced anisotropic effect of the predamage. Therefore, using the DIC technique, the positive effect of coarse aggregates was verified, and the shear cracking mechanism of pre-damaged PVA-ECC beams was revealed through direct observations.

Stator current signal crossing for fault diagnosis of self-excited induction generators

This paper presents a novel method for modelling and diagnosis of electrical and mechanical faults in fixed-Speed Self-Excited Induction Generators (SEIGs) operating in autonomous mode in a small-scale wind energy system. The proposed method is validated using the finite element method. After the selection of the magnetising capacitors, the self-excitation process is performed under no-load conditions. Once the stator voltage is established, a symmetrical three-phase load is connected. The fault detection method introduced here is called Stator Current Signal Crossing (SCSC). The SCSC extracts a new signal from the stator currents, that enables the detection of stator inter turn shortcircuits, broken rotor bars, and dynamic eccentricity faults in SEIGs. A spectral analysis of SCSC using the Fast Fourier Transform (FFT) algorithm is used to precisely locate the induced fault components. What sets this fault-tracking method apart from its predecessors is its exceptional ability to detect faults of any magnitude by analysing the modulation of the SCSC signal. These faults are directly identified by the presence of distinct harmonics, each indicative of a specific type of fault. This study also focuses on the SEIG in a wind energy system, whereas previous works have mainly addressed the induction machine in motor mode. In contrast, previous methods involved analysing a single current signal and isolating specific harmonics from a wide frequency range. The effectiveness of the proposed fault detection method and the self-excitation process are illustrated by simulation results and spectral analysis.

A constitutive model for the gravelly soil-structure interface considering particle breakage and fabric change

The isolated foundation with cushions is gaining popularity as a viable option for building bridges in active seismic zones due to its exceptional seismic isolation performance. However, the efficacy of this foundation relies heavily on the interactions within the cushion layer and between the caisson foundation and the cushion layer. The cushion layer, composed of 0.5 m thick crushed aggregate layer and 2.5 m thick pebble gravel, is susceptible to particle breakage and fabric change, which can significantly impact the overall behavior of the foundation. To better characterize the mechanical behavior of the cushion layer and the interface between aggregates and the structure, a new elastoplastic constitutive model is proposed in this study. The current model is built based on an existing constitutive model, Saberi’s model (Model-S). Two parameters are introduced, including a particle breakage coefficient, B10, calculated by total plastic work, and a fabric-dilatancy variable, z, to determine the interfacial dilatancy variation. The current model consists of 13 parameters in total. Comparison evident that the current interfacial constitutive model can better simulate the change of the physical state and asymmetrical response in the stress-displacement relationship due to symmetrical loading in different directions.

Effect of Purposely Induced Asymmetric Walking Perturbations on Limb Loading After Anterior Cruciate Ligament Reconstruction.

Patients often sustain prolonged neuromuscular dysfunction after anterior cruciate ligament reconstruction (ACLR). This dysfunction can present as interlimb loading rate asymmetries linked to reinjury and knee osteoarthritis progression. To evaluate how asymmetric walking protocols can reduce interlimb loading rate asymmetry in patients after ACLR. It was hypothesized that asymmetric walking perturbations would (1) produce a short-term adaptation of interlimb gait symmetry and (2) induce the temporary storage of these new gait patterns after the perturbations were removed. Descriptive laboratory study. Fifteen patients who had undergone ACLR were asked to perform an asymmetric walking protocol during the study period (2022-2023). First, to classify each limb as overloaded or underloaded based on the vertical ground-reaction force loading rate for each limb, participants were asked to perform baseline symmetric walking trials. Participants then performed an asymmetric walking trial for 10 minutes, where one limb was moving 0.5 m/s faster than the other limb (1 vs 1.5 m/s), followed by a 2-minute 1 m/s symmetric deadaptation walking trial. This process was repeated with the limb speeds switched for a second asymmetric trial. Participants adopted a new, symmetric interlimb loading rate gait pattern over time in response to the asymmetric trial, where the overloaded limb was set at 1 m/s. A linear mixed-effects model detected a significant change in gait dynamics (P < .001). The participants exhibited negative aftereffects after this asymmetric perturbation, indicating the temporary storage of the new gait pattern. No positive short-term gait adaptation or storage was observed when the overloaded limb was set to a faster speed. Asymmetric walking successfully produced the short-term adaptation of interlimb loading rate symmetry in patients after ACLR and induced the temporary storage of these gait patterns in the initial period when the perturbation was removed. These findings are promising, as they suggest that asymmetric walking could serve as an effective gait retraining protocol that has the potential to improve long-term outcomes in patients after ACLR.

Edge effect and indentation depth-dependent contact behavior in contact of an elastic quarter-space

The edge effect in contact of an elastic quarter-space is numerically studied in this work. The extension of Hetényi’s approach of overlapping two elastic half-spaces is implemented in the boundary element method to obtain the solution of an elastic quarter-space whose top and side surfaces could be both loaded. In the study on the indentation test of a rigid sphere on an elastic quarter-space, the dependencies of the normal force, mean contact radius, and pressure distribution in contact area as well as the internal von Mises stress in relation to the position of the sphere from the side edge are obtained numerically and expressed by fitting the numerical results. These equations can be also used to interpret the indentation depth-dependent contact behavior: from Hertzian contact at the beginning of the indentation to the non-circular contact at large indentation depth.In addition, the results are compared with a contact case of a quarter-space in which the side surface of the quarter-space is not completely free: shear stresses on the side surface vanish but normal stress exists. The latter case generates very similar results, especially the contact area, but its solutions are much easier to achieve by applying a symmetrical loading on an elastic half-space, offering an effective way to approximate the solution of a quarter-space.

Devising procedures for design and verification calculations of the beam-wall with edge breaks under static and cyclic loads

This paper considers a thin-walled steel beam-wall with broken edges, which is part of many structures. The wall of this beam consists of two prismatic parts with a straight transition from a lower wall height to a higher one, forming a broken upper edge together with the edges of the prismatic parts. The bottom straight edge of the wall is attached to the cladding. The beam-wall is affected by static and cyclic nominal loads, which can cause the appearance of elastic-plastic deformations in the stress concentrator. This causes non-fulfillment of static strength and the appearance and growth of fatigue cracks. In the current work, procedures of design and verification calculation of a steel beam-wall with fractured edges at elastic static and cyclic elastic-plastic deformation in the stress concentrator are proposed. The material of the beam is ideal elastic-plastic. Features of the procedures are the possibility of optimal design under conditions of elastic and elastic-plastic deformation, using dependences only for optimal elastic design. A distinctive signature of the procedures is that, through Neiber's formula, elastic-plastic characteristics are not determined by known elastic ones, as usual, but vice versa. According to the established dependences for cyclic elastic-plastic deformations in the concentrator, the theoretical concentration coefficient is determined, which, in turn, is involved in determining the optimal geometric parameters. The procedures give reliable results with nominal symmetrical cyclic loads up to 0.6 of the yield strength. This is because Naber's formula always yields conservative results, causing excess strength. The procedures can be applied separately for stretching-compression and bending, and with their combined action

Vertical Monotonic and Cyclic Responses of a Bucket in Over-Consolidated Clay

Bucket foundations, especially multi-bucket foundations, have become an alternative for large offshore wind turbines. Vertical responses of a single bucket are critical for the serviceability design of tripod or tetrapod bucket foundations. Centrifuge tests are conducted to investigate the responses of a single bucket under monotonic and symmetric cyclic loading in over-consolidated clay. The strength of clay is obtained by cone penetration tests. The monotonic vertical capacity measured in the centrifuge tests are compared with the finite element results, with errors less than 6%. The effects of the ratio of cyclic loading amplitude to vertical capacity (ranging between 0.37 and 0.64) and the number of cycles on the accumulation of vertical displacement and evolution of stiffness are explored. Simplified functions are proposed to predict the evolutions of dimensional and dimensionless stiffness.