Loading Tests Research Articles

Design and Load Test of High Speed Slotless Permanent Magnet Synchronous Motor with Round-Wire Air-Core Distributed Winding

Design and Load Test of High Speed Slotless Permanent Magnet Synchronous Motor with Round-Wire Air-Core Distributed Winding

‘Robinson’ Pedestrian Bridge in Budapest, Hungary

Abstract‘Robinson’ Bridge was built as part of the National Athletic Centre project in Budapest, Hungary. The 168 m long cable‐stayed pedestrian bridge has a 65 m tall inclined pylon standing on a small island. The 12,72 m wide main girder is suspended to a monopylon with a two‐plane fan‐shaped FLC stay cable system. The landmark bridge's stunning appearance was achieved with hybrid structures. Both the pylon and parts of the slender stiffening girder were made of S460 steel tubes filled with concrete to enhance their load‐bearing and dynamic characteristics. Due to very limited construction area, a special erection process was used for the pylon involving a 200t floating crane. The stiffening girder was built with incremental launching. Cable tensioning with a curved deck proposed special design challenges. Large displacements had to be accurately predicted. To meet the strictest requirements for pedestrian comfort, TMDs were applied and dynamic load tests carried out to prove the results.

Experimental and numerical investigation of the load-bearing capacity of bolt-fastened wedge active joints for prestressed internal bracing in subway excavations

The present study develops a novel type of active joint node-bolt fasten wedge (BFW) active joints, aiming to investigate the load-bearing capacity of a BFW joint in a quantitative way and put forward precise formulas for its yield load and compression rigidity. To achieve this, indoor axial loading tests were conducted on two BFW joints, accompanied by a set of numerical simulations with the finite element approach (FEA) implemented in ABAQUS. Parametric research was then conducted to assess the impact of various factors on the yield load and initial compression rigidity of BFW joints, leading to the derivation of precise calculation formulas for accurate prediction of these parameters. The key findings indicate that enhancing the bolt strength from 10.9 to 12.9 significantly improves mechanical performance. Under axial compression, the final bearing force, yield load, and initial compression rigidity increase by 0.86, 1.06, and 0.15 times, respectively. Numerical models accurately predict joint behavior under axial force, confirming their reliability. Parameter studies reveal that increasing web and eaves thickness, bolt strength, and diameter improves bearing capacity, while splint thickness has little effect. The fitting formulas introduced can precisely estimate yield load and rigidity, providing practical value for engineering applications.

Correlations of The Dynamic Parameters on Malaysia Hemic Peat

The dynamic behaviour of Hemic peat in Johor, Malaysia is described. The index properties of three different locations in Johor were investigated. Cyclic triaxial test with different frequencies and effective stresses were applied to correlate the characteristics behaviour of Johor peat. By using the Cyclic Triaxial machine located in the Research Centre of Soft Soil, Universiti Tun Hussein Onn Malaysia, the tests conducted referred to the British Standard and ASTM. The result of cyclic shear modulus shows that hemic peat in Johor indicated less than 2MPa and damping ratio in the range of 7.70% to 24.84%. The influences for the cyclic shear modulus correlations in this research are mostly affected by the effects of fibres structures and the natural characteristics of peat. The different behaviour of fibres in peat also significantly influenced the results. These behaviours lead to a different performance of each sample used. The natural characteristics of peat results in varied and scattered behaviour. Through this assessment, the peat characteristic is significantly depending on the well-structured of hemic peat which mostly consists of fibres, water and pores that controls its behaviour during the cyclic loading test.

Experimental and analytical investigation of bracket moment connection for precast concrete beam-to-composite column joints

In large industrial buildings, precast prestressed concrete beams and composite columns are appealing to achieve longer span and higher story height, with temporary supporting and scaffolding minimized. To facilitate field erection of moment connection between precast beams and composite columns, a bracket connection transferring beam loads to the column by connecting the beam to a composite bracket attached to the column has been developed. Since precast beams are lap-spliced and integrated with the bracket by concrete engagement at the interfaces, the connection performance depends on beam lap length and load transfer details (i.e., concrete shear keys). In this study, the seismic performance of precast prestressed concrete beam-to-composite column joints with the bracket connection was experimentally and analytically investigated. Cyclic loading tests were conducted on four full-scale specimens with different beam lap lengths and load transfer details. For the specimens with a longer beam lap length, the bracket connection successfully transferred the beam flexural strength to the column with the connection barely damaged. The governing failure mode was beam flexural yield occurring at the bracket end. However, for the specimen with a shorter beam lap length, relative slips at the interfaces of the beam and bracket occurred and thus the strength was governed by the bracket connection. Excellent ductility satisfying the acceptance limit of special moment frame in AISC 341 was achieved in all specimens. The load transfer at the bracket connection through concrete shear keys and other details were further investigated through finite element analysis. Design models to predict the connection strength were proposed and the validity of the models was verified through comparisons with the tests and analyses.

Novel strengthening method of signal tower using prestressed CFRP plates: Concept and behavior

A novel prestressed carbon fiber reinforced polymer (CFRP) plate strengthening method for signal towers was proposed. The proposed strengthening system incorporates a circumferential anchorage system, a support system, a column system, and CFRP plates. These elements synergistically interact with the tower, forming a self-balancing system. This integrated system can provide exceptional flexural capacity and reduce the lateral displacement of the tower under wind load. To validate this novel method, a series of four static load tests were conducted. The results showed that the initial stiffness of the strengthened tower with CFRP plate prestresses of 0, 200, and 400 MPa increased by 71.0 %, 113.8 %, and 113.8 % compared with the unstrengthened tower, respectively. Moreover, the CFRP plate slacking occurred later for the strengthened tower with higher CFRP plate prestress, and the stiffness of the tower after the CFRP plate slacking kept increasing as CFRP plate prestress increases. The results indicate that the prestressed CFRP plate strengthening method effectively improved the behavior of the tower under wind load. Moreover, the finite element method (FEM) was utilized to analyze the influence of the ratio of the circumferential anchorage system height to tower height, the ratio of the support system height to tower height, the ratio of the column height to tower height, the ratio of steel support length to tower diameter, the elastic modulus of the CFRP plate and CFRP plate prestress on the strengthening effect. Finally, a strengthening procedure was proposed according to FEM results and sensitivity analysis. The analysis findings can serve as a guide for designing the strengthening system.

Experimental behavior and fracture prediction of a novel high-strength and high-toughness steel subjected to tension and shear loading tests

In this study, laboratory testing and numerical simulation methods are used to investigate the mechanical behavior and perform fracture prediction of a novel high-strength and high-toughness steel with a negative Poisson's ratio (NPR) effect under combined tensile-shear loading conditions. A test device capable of meeting different tensile-shear combination test angles is designed and manufactured, wherein the mechanical experiments on the NPR (Negative Poisson's Ratio) steel specimens are carried out at various testing angles. Q235 steel and MG400 steel are used as experimental control groups. The results show that the mechanical deformation of NPR steel is significantly better than that of Q235 steel and MG400 steel. Its tensile-shear test curve has no yield plateau and it has quasi-ideal elastic-plastic mechanical properties. The loading direction gradually changes from tension-dominated to shear-dominated as the tension-shear angle increases, and the strength and deformation of the specimens show a decreasing trend. Based on the laboratory test results, a finite element numerical model of NPR steel is established. A series of numerical simulations are carried out under the conditions of different tension and shear angles and the average stress triaxiality and fracture strain data are obtained. The fracture data of NPR steel are fitted using the Johnson-Cook fracture criterion, and the Johnson-Cook fracture parameters under the tensile-shear test conditions of NPR steel are thus obtained. The numerical simulation verifies that the fracture model can accurately predict the tensile-shear fracture behavior of NPR steel.

Anti-progressive collapse performance and design method of novel T-stub connections

To address the insufficient anti-collapse capacity of T-stub connections due to premature failure, this study proposes a novel T-stub connection (NTC) by adding four V-shaped laminated plates. Monotonic loading tests are conducted on the T-stub web and V-shaped laminated plate to analyze the influence of geometric parameters on their deformation and load-bearing capacity. The working mechanism of NTC is investigated through the validated numerical models by analyzing the failure mode, impact force history, deformation pattern, internal force development, and energy dissipation. The research results indicate that, compared to the T-stub connection, the NTC exhibits two-phase failure characteristics, which begin with the fracture of the bolt-hole in the T-stub web, followed by the gradual straightening and eventual fracture of the V-shaped laminated plates. NTC undergoes three stages under impact loads: peak, oscillation, and platform stages. The addition of V-shaped laminated plates enhances the ductility of NTC by 93 %−130 % and its energy dissipation capacity by 189 %−235 %. This significant enhancement in deformation and energy dissipation capabilities can be attributed to the addition of the V-shaped laminated plates. The deformation and bearing capacity calculation formulas for both the T-stub web and V-shaped laminated plate are provided. Additionally, a design method for NTC is proposed based on theoretical analysis, and its rationality is verified through numerical examples involving three different sets of beam and column sections.

Test methods for determination of shear properties of sandwich panels

This paper presents analysis and comparison of test methods for determining transverse shear strength and shear modulus of steel-faced sandwich panels commonly used in construction. The test methods are taken from the governing European standard EN 14509:2013. Two-point loading and four-point loading test methods as well as a full-scale test method are examined. Based on extensive experimental work on sandwich panels with varying core thickness, comprising mineral wool (MW) and polyisocyanurate (PIR) and encompassing both roof and wall panels, this study provides details of the test setup for the four-point loading and vacuum box methods with which a pure shear failure is obtained. Such details are missing from EN 14509. This paper highlights that the two-point loading method fails to consistently produce shear failure, especially in thicker panels, indicating it does not accurately measure transverse shear strength. The results of the experiments conducted in this study indicate that the four-point loading and full-scale test methods provide consistent shear failure for thicker panels while yielding greater transverse shear strength than the two-point loading test in general.

Strain amplitude dependency of cyclic hardening/softening behavior of 490 N/mm2 class steel

Existing studies on the strain amplitude dependency of cyclic softening behavior in structural steels often involve limited cycles or strain amplitudes below 2.5%, failing to provide a comprehensive understanding of stabilized cyclic behavior. This study performed uniaxial tension–compression cyclic loading tests using SN490B structural steel under three loading patterns: constant, variable, and offset constant strain amplitudes. The cyclic hardening and softening behaviors and stress–strain hysteresis loops were compared. Under variable strain amplitude loading, the specimens were subjected to increasing and decreasing strain amplitudes to investigate the strain amplitude dependency of the cyclic hardening and softening behaviors. Under offset constant strain amplitude loading, mean strains were initially introduced in either the tension or compression strain range, followed by cyclic loading with a constant strain amplitude centered around the mean strains. The test results revealed the following: (1) Under constant strain amplitude cyclic loading, the material exhibited cyclic softening and hardening behaviors at strain amplitudes smaller than and larger than 0.5%, respectively; (2) Under variable strain amplitude cyclic loading, increased and reduced strain amplitudes resulted in cyclic hardening and softening behaviors, respectively. The cyclic hardening/softening behavior strongly depended on the strain amplitude. Applying a significant number of cycles after strain amplitude reduction resulted in the stress–strain curves closely resembling those under constant strain amplitude conditions; (3) Even under offset constant strain amplitude cyclic loading conditions with nonzero mean strain, the peak stresses and shapes of the hysteresis loops approached those under constant strain amplitude conditions without mean strain.

Experimental study on seismic performance of replaceable shear links with low-yield-point steel

Based on the design concept of controllable seismic damage during earthquakes and rapid functional recovery after earthquakes, a replaceable shear link with low-yield-point steel was proposed. Quasi-static cyclic loading tests and numerical analysis were conducted on six specimens. The failure mode, seismic performance, energy dissipation behavior, and shear distribution of each specimen were carefully considered to investigate the effects of web steel, web stiffening configuration and stiffener-plate stiffness ratio. The results showed that the stiffened specimens showed full-sectional shear yielding behavior, while the non-stiffened specimens exhibited coupling behavior of web yielding and buckling. Specimens with reasonable design parameters had excellent ductility and energy dissipation capacity, with the plastic shear angle exceeding 0.157 rad and the maximum equivalent viscous damping coefficients greater than 0.51 (80% of the theoretical maximum value). Owing to the cyclic strengthening of the low-yield-point steel web and the contributions of stiffeners and flanges, the specimens showed obvious overstrength behavior, with the overstrength factor ranging from 1.99 to 2.39. The cross-stiffening configuration was conducive to enhancing the seismic performance of shear links. Smaller web width-to-thickness ratios were recommended to match with smaller stiffener-plate stiffness ratios. Extended cross stiffeners and diagonal stiffeners resulted in earlier cracking of the web welds, which adversely affected the ductility of the specimens.

Poor Adherence and Limited Treatment Support are Risk Factors for Second Line Treatment Failure among HIV Children Under 15 Years, 2022: A Case Control Study

Title: Poor adherence and limited treatment support are risk factors associated with second line treatment failure among children under 15 years at Victoria Chitepo provincial hospital, 2022: a case control study. Background: New HIV resistance mutations have been emerging and frequently changing. HIV positive people switching to third line have been increasing in Manicaland Province. Third line anti-retroviral therapy (ART) combinations are not always available. We sort to determine the factors associated with second line treatment failure among HIV positive patients. Methods: We conducted a 1:1 unmatched case-control study among 107 case-control pairs. A case was any HIV positive individual with treatment failure confirmed by 2 viral load of ≥1000 copies/ml while a control was any HIV positive individual with a viral load of <1000/ml copies; on second line therapy at Victoria Chitepo Provincial Hospital (VCPH), in 2022. Systematic random sampling was used to select cases and controls from the line-list. Administered questionnaires were used to ascertain risk factors to second line treatment failure. Patient booklets were reviewed for demographic and clinical characteristics. Frequencies, means, medians and odds ratios were generated. Multivariate analysis and stratified analysis was performed to identify independent risk factors. Permission to proceed was sought from relevant authorities and all ethical considerations were observed. Results: Defaulting treatment (aOR=2.42, 95% CI: 1.03-5.93), missing a viral load test (aOR=5.52, 95% CI: 2.30-13.26) and being under 15 years of age (aOR=6.18, 95% CI: 1.46-26.20) were independent risk factors associated with second line treatment failure. Having a treatment support was an independent protective factor (aOR=0.30, 95% CI: 0.10-0.86). Conclusion: Poor adherence is the key drive to second line treatment failure. Good adherence is critical in children under 15 years. Treatment support promotes viral load suppression.

Optimizing resistance training intensity in supportive care for survivors of breast cancer: velocity-based approach in the row exercise.

Resistance training mitigates side effects during and after cancer treatment. To provide a new approach for precisely and safely assessing and prescribing the intensity of resistance training in supportive cancer care, the purpose of this study was to evaluate the load-velocity relationship during the row exercise in women survivors of breast cancer. Twenty women survivors of breast cancer who had undergone surgery and had completed core breast cancer treatment within the previous 10years completed an incremental loading test until the one repetition maximum (1RM) in the row exercise. The velocity was measured during the concentric phase of each repetition with a linear velocity transducer, and their relationship with the relative load was analyzed by linear and polynomial regression models. A strong relationship was observed between movement velocity and relative load for all measured velocity variables using linear and polynomial regression models (R2 > 0.90; SEE < 6.00%1RM). The mean velocity and mean propulsive velocity of 1RM was 0.40 ± 0.03m·s-1, whereas the peak velocity at 1RM was 0.64 ± 0.07m·s1. In women survivors of breast cancer, monitoring movement velocity during the row exercise can facilitate precise assessment and prescription of resistance training intensity in supportive cancer care.

Effect of joint-slippage on transmission tower performance with a simplified model of bolted joints

ABSTRACT Bolted joint behaviour is a key parameter in predicting transmission tower performance. Various types of joints are based on the number of bolts and their configuration. However, a few types of these joints were tested or modelled. In the present study, the load-deformation response of transmission tower joints as a joint behaviour was predicted using a simplified numerical model. Then, available experimental load-deformation responses of joints were used to verify the results of the proposed model. In the last step, the joint behaviours of a 400 kV transmission tower were predicted with the proposed numerical model. Then, the evaluation of the tower’s response was done with a numerical model in ABAQUS under testing loading conditions. Lastly, the deformation of a full-scale tested tower was compared with the numerical results. The numerical model results show a good agreement with the experimental results. The ultimate strength and its corresponding displacement at the full-scale model are predicted with an error of about 4%. Moreover, the failure mode of the transmission tower was not affected by the behaviour of the joints.

Effect of Load Cycling on High Temperature Creep of 316L Stainless Steel

For components in concentrating solar thermal plants, the creep mechanism will cause a significant portion of material damage to receivers, storage tanks, turbines and pipework. These components will undergo conditions where loads, temperature, or both load and temperature are not constatnly applied. This creep damage process will not resemble the constant load creep tests used to characterise creep of materials. Therefore, creep tests incorporating a load cycle were undertaken to obtain a better understanding of how high temperature materials respond to these cyclic conditions. These tests showed that when time under load was considered, creep undertaken under load cycling conditions were accelerated relative to constant load conditions. A modified Larson-Miller approach was used to assess this effect and determine an equivalent stress where constant load test data agrees with the cycled test data. This found that cycling the load was equivalent to if the system were under 3 and 7 MPa higher stress, for tests which were loaded for 12 hrs and 6 hrs per 24 hrs respectively. This could be a potential approach to simply and easily consider these load cycling effects for design and life analysis.

Experimental analysis of the cyclic behavior of rammed earth walls reinforced with arundo donax natural fiber

This experimental study analyzes the seismic behavior of rammed earth walls with Arundo donax natural fiber inclusions, also called "caña brava” (REWC), and without inclusions (REW). The experimental program consists of two stages: physical and mechanical characterization of materials, where properties such as particle size, density, Atterberg limits, and compressive and flexural strength were determined; and dynamic tests, which included compressive and cyclic load tests on REW and REWC walls. The walls were subjected to cyclic loading with derivatives between 0.2 % and 1.4 % in-plane combined with a constant vertical compressive stress of 13 kPa to simulate seismic forces in the presence of gravity loads. The results regarding loading, hysteretic response, energy dissipation, stiffness degradation, and failure mode are compared. In addition, the envelope curves of the load-displacement hysteretic responses are analyzed using a capacity spectrum approach. It is observed that the inclusion of Arundo donax natural fiber negatively affects the mechanical properties of the walls and their hysteretic response. It is also observed that the energy dissipation is affected by the inclusion of Arundo donax natural fiber. However, the stiffness behavior is similar in all the walls. Rigid body failure modes are identified in all the walls, but the walls, including Arundo donax natural fiber, form failure planes that divide the wall into two bodies.

Prediction method for re-damage behavior of the repaired CFRP bolted joint

Composite materials are widely used in various aircraft due to their high specific strength, stiffness, corrosion resistance, and robust design flexibility. However, when subjected to complex loading conditions, composite structures are susceptible to damage, necessitating prompt repair upon aircraft return. Analyzing the re-damage process of repaired structures is crucial for assessing aircraft structural reliability, lifespan, and determining whether a repeat flight is warranted. In this study, a prediction method was proposed for re-damage behavior through meso-modeling and energy analysis of the repaired composite bolted joint. First, this article established a meso-mechanical model for composite laminates, analyzed force transfer characteristics at the fiber − matrix interface, and derived equations for stress field. Additionally, a strain energy distribution model was developed for composite bolted repaired joint near fibers and repaired area, proposing a damage prediction method based on the strain energy criterion. This method could anticipate the location, type, sequence, and magnitude of damage. Finally, simulation calculations yielded mechanical characteristics of the repaired area under typical load conditions, while loading tests verified the feasibility of the prediction method. This study offered an effective means of predicting performance degradation in composite structures and provided a vital direction for optimal spacecraft structure repairing methods and parameters.

Factors affecting the tensile strength of bituminous geomembrane seams

The tensile shear strength, break location, and constant tensile load failure times are examined for seams made from one 4 mm-thick bituminous geomembrane (BGM) product, with corresponding observations specific to that material. In short-term tests, failure is observed within the sheet material once the seam strength exceeded 0.8 times that of the sheet material. The effects of seam thickness reduction and overlap width on seam strength are examined for two methods of seaming. Seams with a short-term strength meeting or exceeding 80% of the sheet strength are subjected to constant tensile loads between 18 and 55% of sheet ultimate strength and the time to failure is reported. The relationship between short-term seam strength and time to failure under sustained load and thickness reduction and squeeze-out is investigated. Constant tensile load testing is proposed as a construction quality assurance procedure to assess the degree of geotextile engagement of field seams.

In-Plane Cyclic Behaviour Comparison of Adobe Wall Retrofitted by Mortar Enhanced by Physical and Chemical Methods

ABSTRACT A mortar overlay on damaged adobe masonry is employed for its load carrying capacity improvement and low skill requirement. Nevertheless, delamination between the adobe wall and mortar has been commonly observed due to bonding failure. Physical enhancement (groove, shear dowel, and wire mesh) and chemical enhancement (a novel biological and traditional Chinese binder, sticky rice pulp, SRP) are carried out to enhance the bonding between mortar and adobe. The high-moisture adsorption mortar is also utilized to alleviate water accumulation resulting from the application of mortar on earthen buildings. Four adobe walls with different retrofitting methods are subjected to in-plane lateral cyclic loading tests to analyse the failure mode, hysteretic load-displacement response, skeleton curve, ductility behaviour, energy dissipation and stiffness degradation. It indicates that the retrofitting effectiveness of adobe walls coated only with mortars is limited, as their peak load increases are comparatively modest compared to other retrofit wall systems. However, employing additional bonding enhancement methods significantly enhances the peak load capacity. Specifically, a combination of physical and chemical enhancements results in a remarkable 114% increase on the positive side and an astonishing 500.1% increase on the negative side.

Study on static performance and dynamic characteristics of a spoke cable-truss suspen-dome system

The proposed spoke cable-truss suspen-dome structure is a new structure system based on the traditional chord-supported dome structure. In this structure, the upper lattice shell is modified to a radial cable-truss structure. The lower part of the structure is a cable network structure composed of radial cables, ring cables and radial cables. There are few research results on the mechanical properties of the new structure, so a 1:10 scale model is established, multi-condition static loading test, local cable force failure test and natural vibration characteristic test are carried out, and the measured results are compared with the finite element results. The changes of axial force and joint displacement under different loads, the changes of static properties under cable damage and the dynamic characteristics of the structure are obtained. The results show that the loading method adopted meets the test accuracy requirements. Under the action of uniform load, the upper chord, the lower chord end and the inner ring truss of the main truss are in a pure compression state. The middle bar of the lower chord span and the outer ring truss change from the compression state to the tension state with the increase of load. The structure is still in the elastic stage when part of the cable fails, and the coordinated deformation ability is strong. The base frequency of the measured structure is 7.97 Hz, and the stiffness distribution is uniform.