Load Transmission Mechanism Research Articles

Research on the clearance evolution of preloading filling spiral case and surrounding concrete

Abstract The embedment of steel spiral cases within concrete under a pressurized condition is a kind of construction approach that widely used in pump-turbines. There will be an initial preloading clearance between the spiral case and surrounding concrete after the construction. The clearance is directly determined by the preloading water head and changes with the variation in operational hydraulic pressure, which will effect the combined load transmission mechanism. This paper investigates the clearance evolution of preloading filling spiral cases and surrounding concrete under different internal pressure. The effect of the preloading water head on the initial clearance, the contact characteristics and the combined load transmission mechanism under different internal pressure are numerically studied. The results show that the initial clearance between the spiral case and concrete increases with the rise of the preloading water head. The maximum clearances are all located at the waist of the spiral case. The clearance during operation presents uneven distribution characteristics in spatial and temporal scales. Before the internal water pressure comes to the preloading water head, the inlet, outer part in the direction of 45° and the sectional area are the first to close, the outer part of the waist follows, while the outer area of the spiral case middle remains open when the pressure reaches the preloading water head. The contact pressure distribution is consistent with the contact status characteristic. The conclusion of this paper aims to improve the understanding of the effect of the clearance between the preloading filling spiral case and concrete, so as to provide theoretical reference for safe and stable operation of pump-turbine units.

Experimental study on long friction-type bolted joint combined with interference fit bolt

In recent years, high-strength bolts with friction-type joints have been lengthened to withstand increased traffic load. However, with increase in the joint length, the force able to be resisted by bolted joints has decreased owing to uneven distribution of the bolts within the joint. In addition, the proximity of secondary members to the joint has restricted the allowable size of the splice plates. It is therefore necessary to reduce the joint length while maintaining its design strength. In this study, interference fit bolts were assembled at both ends of a friction-type bolted joint to form a hybrid joint, and tensile tests were conducted to elucidate the load transmission mechanism, analyse the slip resistance, and verify whether the addition of the interference fit bolts improves the strength of the friction-type joint. It was concluded that despite a minor slip in the hybrid joint, the slip resistance was approximately 10% higher than that of the friction-type joint, and the overall load–deformation relationship maintained a quasi-linear behaviour up to 1.1 times the slip resistance of the friction-type joint. In addition, the hybrid joint had smaller data scattering than the friction-type joint, suggesting that the uneven load distribution and deformation in the joint was slightly improved by installing the interference fit bolts. The performance of hybrid joints is superior to that of the existing friction-type joints under the current slip limit specification.

Numerical and analytical models of the mechanism of torque and axial load transmission in a shock absorber for drilling oil, gas and geothermal wells

The paper proposes an improved design of a shock absorber used in drilling deep oil and gas and geothermal wells with polycrystalline diamond compact (PDC) bits. The proposed innovations successfully combat the dangerous phenomenon of self-excited vibrations, which can lead to malfunctions such as stick-slip and whirling of the drilling tool. Most conventional drill shock absorbers are designed to only absorb longitudinal vibrations, which was sufficient when using roller cutter bits for the drilling process. However, the design features of PDC bits and the phenomenon of interaction of their cutters with interlayered rocks during deep drilling impose new requirements on the properties of the drill shock absorber. To protect the downhole tool from abnormal torque values and torque oscillations, it is proposed to equip the shock absorber with a special torque transmission unit in the form of a fourteen-thread self-releasing screw pair. This unit is capable of transforming increases in external torque into increases in the force that loads the elastic element of the shock absorber. The numerical and analytical models of the mechanism of transferring external axial load and torque to the elastic element of the drill shock absorber are constructed. The distribution of contact pressures on the interacting surfaces of the screw pair and the distribution of equivalent stresses in the screw pair parts are analysed. The strength of the proposed drill shock absorber assembly was evaluated using the Huber-von Mises energy criterion. The dependence of the load transmitted to the elastic element of the shock absorber on changes in the external torque and external axial force is investigated. In general, it is determined that the external load is distributed evenly between all turns of the screw pair, and the limit state of the parts of the proposed assembly is not reached even under high-torque operating load. The obtained analytical dependencies will allow to effectively determine the required strength and stiffness of the elastic element of the drill shock absorber at the design stage. The obtained analytical results were verified using a finite element model.

Experimental investigation of innovative reinforcement method for two‐way concrete slabs using perforated steel plates

AbstractImprovement of the bonding and interaction between concrete and steel is crucial to achieving an optimal reinforced concrete member. The proposed technique in this paper is using perforated steel plates (PSPs) to reinforce two‐way concrete slabs. In this method, ordinary steel bar reinforcements in the tension region of the concrete slabs were replaced by PSPs. Concrete slabs reinforced with PSPs enhance structural characteristics with respect to concrete slabs reinforced with ordinary reinforcement (OR) due to the higher lateral stiffness of PSPs, the better confinement of concrete within the holes of PSPs, the biaxial performance of the steel in the tension region, and the efficient load transmission mechanism between the steel and concrete. In this paper, a comprehensive experimental investigation was conducted on two‐way concrete slabs reinforced with PSPs and ordinary steel bars. The behavior of PSPs slabs was evaluated in comparison with OR slabs in terms of failure types, ductility, energy absorption, stiffness, ultimate load, cracking load, and force transmission mechanism. Findings revealed that the PSPs slabs have higher ductility, energy absorption, and ultimate strength compared to the OR slabs.

Characterization and strengthening mechanism of CNT/TiB2 particulates added AZ91D composites

In the current work, magnesium (AZ91D) matrix composites reinforced with different weight fractions (5, 10, and 15%) of titanium diboride (TiB2) and 1.5 wt% carbon nanotubes (CNTs) are fabricated using stir casting. The improvements in mechanical, wear and corrosion resistance properties are evaluated as per ASTM guidelines. The synergistic strengthening effect of TiB2 and CNT is also studied. It was discovered that the AZ91D/(1.5CNT-10TiB2) composite outperformed other magnesium matrix composites in terms of strength and ductility. Experimental characterization and quantity analysis revealed that the load transfer process of CNT, thermal mismatch, and grain refinement are the primary factors leading to the composite’s increased tensile strength. Porosity tends to increase due to variance in the thermal expansion coefficient of particles and matrix material; Orowan strengthening mechanism plays a prominent role in enhancing tensile strength. Because of the influence of synergistic strengthening, microparticles TiB2 increased the proportion of load transmission mechanisms, and thermal mismatch facilitated the homogenous distribution of CNTs. Wear resistance and corrosion resistance increase with the inclusion of CNTs and TiB2 content. An abrasive-type wear mechanism is seen in the SEM image, and the wear craters are also seen in all the SEM images. Adding TiB2 significantly improves the cast composites’ resistance to corrosion because of grain refinement. Higher addition of TiB2 influences higher pitting corrosion due to poor grain refinement.

Recent advances in subgrade engineering for high-speed railway

Abstract In the last decade, the design and construction technologies of subgrade in high-speed railway (HSR) developed significantly. This article reviews corresponding development in five aspects, including mechanical properties of fill materials, dynamic performance of subgrade, foundation treatment, retaining structure, and smart construction technologies. It shows that for unbonded granular materials, it is acceptable to use static strength for subgrade design, but for clayey soil it would be more appropriate to base on shakedown theory. The mechanism for lime modified clay has been thoroughly reviewed, and the effect of lime content, curing age, and curing conditions on the behavior of lime-treated clay is discussed. The dynamic response of subgrade, especially the long-term deformation and dynamic stability analysis are important to understanding the behavior of HSR subgrade. The effect of track types, operation speed, etc. on the dynamic response of subgrade are reviewed first. Then, the prediction methods, influencing factors, and corresponding issue for long-term deformation of subgrade are presented, followed by the methods used for dynamic stability analysis. Three types of foundation treatment methods, including geosynthetic-reinforced pile-supported (GRPS) embankment, pile-raft structure, and pile-plate structure are reviewed for the corresponding load transmission mechanism, and application scenario. The static and dynamic behavior of four types of retaining structures are presented, including cantilever retaining wall, geosynthetic reinforced soil retaining wall, anchored retaining structure, and retaining wall reinforced by soil nailing. Finally, a series of new technologies correlated to smart construction are introduced, relating to the survey, design, construction, detection, and management of subgrade.

Analysis on Mechanical Characteristics of Substation Wall under Flood

The safety and stable operation of substation facilities during a flood depends on the dependability of substation flood walls. The finite-element (FE) model of the prefabricated flood wall is established based on the actual project, and the mechanical characteristics of the wall are analyzed, along with the load transmission mechanism of the wall, in order to study the bearing capacity of the prefabricated flood wall under the flood. The critical parameter study is completed, and its impact on the wall’s force characteristics is made clear. The findings demonstrate that the load transfer mechanism of the prefabricated flood wall is clear, and that crucial joints, such as those connecting the wall panel to the column and the column to the base, are under increased stress. The performance of the wall is significantly influenced by both flood depth and flood velocity. The safety of the prefabricated flood wall is obviously decreased when the flood velocity is greater than 2 m/s or the flood depth is greater than 1.0 m.

Large-Scale Wind Turbine’s Load Characteristics Excited by the Wind and Grid in Complex Terrain: A Review

With the development of wind resources under flat terrain, wind farms in extreme wind conditions are developed, and the size of the WT’s rigid-flexible coupling components increases. Therefore, accurately understanding the load characteristics and transmission mechanism of each component plays an important scientific role in improving the reliability of WT (WT) design and operation. Through the collation and analysis of the literature, this review summarizes the research results of large-scale WT load under source–grid coupling. According to the classification of sources, the variation characteristics of different loads are analyzed, and different research methods for different loads are summarized. In addition, the relative merits of the existing improvement schemes are analyzed, and the existing problems are pointed out. Finally, a new research idea of ‘comprehensively considering the coupling effects of source and network factors, revealing WT load characteristics and transmission mechanism’ is summarized. This paper provides important implications for the safety design and reliable operation research of large WTs with complex terrain.

Analysis of electromagnetic properties of Ce–Zn substituted barium hexaferrite for electronic circuit applications

Electromagnetic properties of Ce–Zn substituted barium hexaferrite (Ba0.5Ce0.5ZnFe11O19 ferrite) synthesized using ceramic technique were analyzed in detail in the X band frequencies to describe its response to microwave absorber and microwave electronic device applications. The phase formations, structural morphology, polarization mechanisms and magnetic properties for Ba0.5Ce0.5ZnFe11O19 ferrite, which provide important information about electrical load transmission mechanism were analyzed using X-ray diffraction, scanning electron microscopy, two-port vector network analyser and vibrating sample magnetometer techniques, respectively. The experimental complex dielectric plane plots (Cole-Cole plots) of the Ba0.5Ce0.5ZnFe11O19 ferrite represent an equivalent RC circuit corresponding to the impedance circuit in the Smith Chart. The reflection loss increased to the highest value (−17.04 dB) depending on the amount of Ce in the structure of the Ba0.5Ce0.5ZnFe11O19 ferrite and the bandwidth, which is important for microwave absorbers, increases.

Seismic Behavior of Extended End-Plate Connections Subjected to Cyclic Loading on the Top-Side of the Column.

The extended end-plate connections provide excellent performance in resisting seismic loads in high-risk areas. Most scholars’ experiments and finite element studies on this type of joint are focused on the method of applying displacement loads on the beam tip, while the method of applying displacement on the column side has not been the subject of further study. However, the load transmission mechanism of this type of connection is not completely consistent in actual engineering, as the design concept of “strong column weak beam” does not apply to all joints. Therefore, in this paper, the lateral displacement of the applied column is used to simulate the seismic horizontal force to study the mechanical properties of the connection joints of the “weak column and strong beam” under the limit state of earthquake action. Based on the two internal columns (IC-EP1/2) and two edge columns (EC-EP1/2), the failure modes, strength, stiffness, moment–rotation curve, skeleton curve, ductility, and energy dissipation of this type of connection were studied. Experiment results indicated that this type of connection features semi-rigid and partial strength joints. The connection rotation angle of all specimens in the test exceeds 0.05 rad, which suggests it is an ideal seismic joints. Besides, the relationship between the thickness of the end-plate and the diameter of the bolt has a greater impact on the failure mode of the joint. The finite element (FE) analysis models were established for the above connection. The numerical model was validated against experimental results and showed acceptable consistency.

Comparative Evaluation of Stress Distribution around Various Threaded Implants with and without Platform Switch: A 3-D Finite Element Analysis

The purpose of this study was to compare the stress distribution around various thread design implants with or without platform switching in the maxillary posterior region. Stress-based performances of four different thread design implants (single, double, triple, and asymmetric thread design each with or without platform switching) were analyzed by the three-dimensional finite element method under a static load of 100 N at 15° oblique direction buccolingually at the central portion of the abutment. A geometric model of the posterior maxillary segment (first molar region) with an implant and abutment was modeled using the CATIA V5R19 software. Type IV bone quality was approximated and complete osseous integration was assumed. The von Mises stresses recorded around the neck of the fourthread design implants without platform switching were greater than the platform switching variety. The single-threaded implant with platform switching showed the lowest amount of von Mises stress. Additionally, total displacement or micromovement of single, triple, and asymmetric thread implants with platform switching was found to be greater than the without platform switching variety. Further, the total displacement of the single-threaded implant without platform switching was lowest. Implant surface design, platform switching, and site of placement affect load transmission mechanisms. Due to low crestal resorption, single thread design with platform switching is preferred. The success of an implant in the maxillary molar region is more challenging in terms of the density of bone and the worst load transfer mechanism. With the right kind of implant surface design selection, this can be reduced to a great extent by the preservation of crest of the ridge. Crestal bone resorption following implant placement is an important issue. An optimum implant design with a single thread having a platform switch could compensate for this issue to a great extent.

Single-leg weight limit of fixation model of simple supracondylar fracture of femur

Early postoperative rehabilitation training for supracondylar fracture of femur aids in accelerating healing with shorter recovery periods. Presently, clinical studies on early postoperative weight training are still in the nascent stage. The weight-bearing capacity at different healing stages typically depends on clinical experience, and there is a lack of standards to quantify the weight that is conducive to healing of fractures. In this paper, a three-dimensional (3D) geometric model of the femur is obtained using imaging data, a locking plate fixation model of a simple supracondylar fracture of the femur, considering the angle and spatial direction of the fracture surface, is established, the stress distribution and load transmission mechanism of the fracture fixation model in a single-leg standing posture are studied, and the weight-bearing capacity of a standing single leg at the early stage of fracture is given. This provides the basis for objective quantification of early postoperative weight-bearing capacity.

Cyclic Behavior of Steel Beam to CFT Column Connections with Gusset Plates

Beam‐brace‐CFT (concrete‐filled tubular) column connections provide excellent performance in resisting seismic loads in high‐risk areas. However, the load transmission mechanism of this type of connection still remains unclear, and there is a lack of study on it. Therefore, in this paper, the mechanical behavior of beam‐brace‐CFT column (BBC) connections penetrated by gusset plates was evaluated through experiments and finite element analysis to resolve this issue. The failure modes, strength, stiffness, ductility, and energy dissipation of this type of connection were studied. Experiment results indicated that the gusset plates in BBC (beam‐brace‐CFT) connections could effectively move the plastic hinge on beam away from the column face, reduce the strain concentration between the beam end and column face, and notably improve the hysteretic behavior; the plastic rotation was able to achieve at least 4% story drift angle before 20% strength degradation. Numerical studies were carried out and validated by experiment results, and then the influence of the weld length and strengthening methods were investigated; some improvement of design suggestions was proposed.

Working Mechanism of Pile Group with Different Pile Spacing in Dense Sand

Complex interaction mechanism exists between the pile group and soil. To realize the pile‐soil load transmission mechanism in detail, the failure pattern of pile groups installed in dense sand considering different pile spacing was investigated by means of laboratory experimental model test and three‐dimensional discrete element method. The results suggested that the narrow pile spacing was beneficial to the development of the pile tip resistance, and it enhanced the bearing performance of the pile group at the initial stage of settlement. The pile spacing changed the shaft resistance pattern with modification of the strain energy mechanism released within the subsoil. The pile group with 6b pile spacing had higher composite group efficiency. A joint fan‐shaped displacement zone was formed beneath the pile tip for the pile group with 3b pile spacing; this pile foundation presented the block failure mechanism. The sand displacement beneath the cap for the pile group with 6b pile spacing mainly located on the upper part of the piles, the sand displacement around both sides of the piles presented asymmetric, and a relatively independent fan‐shaped displacement zone was formed beneath the pile tip.

Elastic response of a light-weight floating support structure of FOWT with guywire supported tower

To obtain fundamental knowledge on the elastic response characteristics of a light-weight floating support structure of a FOWT (floating offshore wind turbine) with guywire supported tower, basic load transmission mechanism was investigated. Static analysis with elastic frame model, numerical analysis and wave tank experiment with elastically and dynamically similar segmented backbone model were conducted to clarify the dynamic elastic response characteristics of the structure. In the numerical analysis, analysis code of a rotor-floater-mooring-control coupled response NK-UTWind developed in University of Tokyo is used. It is clarified that when the rigidity of the frame structural part is low compared with guywire, the load is mainly borne by guywire under pitch motion. It was found that the tension fluctuation of guywire becomes large at wave period of 6 s when the inertial force due to pitch motion is large, and at wave period of 18–20 s when inclination of tower is larger the tension fluctuation also becomes large due to the overturning moment.

Experimental investigation of special-shaped concrete-filled steel tubular column to steel beam connections under cyclic loading

This paper presents experimental investigation and numerical investigation on seismic behavior of special-shaped concrete-filled steel tubular (CFST) column to steel beam joints. Exterior diaphragm and vertical rib are respectively introduced as joint stiffeners. A pseudo static experiment was conducted to investigate load transmission mechanism, failure mode and seismic performance index based on load-deformation curves and strain curves. The seismic behavior of the two kinds of joints were compared and evaluated. The classification of the joints by stiffness is conducted according to Eurocode. Inter-story drift of the specimens was calculated with data from laboratory apparatus and verified with test results. A design formula of joint shear resistance based on internal load transmission was proposed for engineering application. A finite element model of special-shaped CFST to steel beam connections was established as a supplement to analyze load transmission mechanism.

Anisotropy in the viscoelastic response of knee meniscus cartilage.

The knee meniscus is instrumental to stability, shock absorption, load transmission and stress distribution within the knee joint. Such functions are mechanically demanding, and replacement constructs used in meniscus repair often fail because of a poor match with the surrounding tissue. This study focused on the native structure-mechanics relationships and on their anisotropic behavior in meniscus, to define the target biomechanical viscoelastic properties required by scaffolds upon loading. To show regional orientation of the collagen fibers and their viscoelastic behavior, bovine lateral menisci were characterized by second harmonic generation microscopy and through time-dependent mechanical tests. Furthermore, their dynamic viscoelastic response was analyzed over a wide range of frequencies. Multilevel characterization aims to expand the biomimetic approach from the structure itself, to include the mechanical characteristics that give the meniscus its peculiar properties, thus providing tools for the design of novel, effective scaffolds. An example of modeling of anisotropic open-cell porous material tailored to fulfill the measured requirements is presented, leading to a definition of additional parameters for a better understanding of the load transmission mechanism and for better scaffold functionality.

Stress and stability of plate-screw fixation and screw fixation in the treatment of Schatzker type IV medial tibial plateau fracture: a comparative finite element study.

PurposeThe purpose of this study is to compare the stress and stability of plate-screw fixation and screw fixation in the treatment of Schatzker type IV medial tibial plateau fracture.MethodsA three-dimensional (3D) finite element model of the medial tibial plateau fracture (Schatzker type IV fracture) was created. An axial force of 2500 N with a distribution of 60 % to the medial compartment was applied to simulate the axial compressive load on an adult knee during single-limb stance. The equivalent von Mises stress, displacement of the model relative to the distal tibia, and displacement of the implants were used as the output measures.ResultsThe mean stress value of the plate-screw fixation system was 18.78 MPa, which was significantly (P < 0.001) smaller than that of the screw fixation system. The maximal value of displacement (sum) in the plate-screw fixation system was 2.46 mm, which was lower than that in the screw fixation system (3.91 mm). The peak stress value of the triangular fragment in the plate-screw fixation system model was 42.04 MPa, which was higher than that in the screw fixation model (24.18 MPa). But the mean stress of the triangular fractured fragment in the screw fixation model was significantly higher in terms of equivalent von Mises stress (EVMS), x-axis, and z-axis (P < 0.001).ConclusionsThis study demonstrated that the load transmission mechanism between plate-screw fixation system and screw fixation system was different and the stability provided by the plate-screw fixation system was superior to the screw fixation system.

Dynamic Responses of Intact Post Mortem Human Surrogates from Inferior-to-Superior Loading at the Pelvis.

During certain events such as underbody blasts due to improvised explosive devices, occupants in military vehicles are exposed to inferior-to-superior loading from the pelvis. Injuries to the pelvis-sacrum-lumbar spine complex have been reported from these events. The mechanism of load transmission and potential variables defining the migration of injuries between pelvis and or spinal structures are not defined. This study applied inferior-to-superior impacts to the tuberosities of the ischium of supine-positioned five post mortem human subjects (PMHS) using different acceleration profiles, defined using shape, magnitude and duration parameters. Seventeen tests were conducted. Overlay temporal plots were presented for normalized (impulse momentum approach) forces and accelerations of the sacrum and spine. Scatter plots showing injury and non-injury data as a function of peak normalized forces, pulse characteristics, impulse and power, loading rate and sacrum and spine accelerations were evaluated as potential metrics related to pathological outcomes with the focus of examining the role of the pulse characteristics from inferior-to-superior loading of the pelvis-sacrum-lumbar spine complex. Interrelationships were explored between non-fracture and fracture outcomes, and fracture patterns with a focus on migration of injuries from the hip-only to hip and spine to spine-only regions. Observations indicate that injury to the pelvis and or spine from inferior-to-superior loading is associated with pulse and not just peak velocity. The role of the effect of mass recruitment and injury migration parallel knee-thigh-hip complex studies, suggest a wider application of the recruitment concept and the role of the pulse characteristics.

Experimental investigations of reinforced concrete columns in the edge connection zone with a reinforced concrete slab

In this paper the results of the experimental investigations of edge column – slab connections are presented and commented on. The load transmission mechanism between high strength concrete columns and slab made of normal, five times lower strength concrete was considered. The variable parameter of presented study was the overhang of slab cantilever. The performed study showed important effect of slab cantilever on effective concrete strength of column in the connection zone.