Increase In Axial Force Research Articles

Impact of Excavation on Adjacent Elevated Bridges and Optimization Analysis of Deformation Control

Based on the deep foundation pit project of the TOD (Transit-Oriented Development) complex of the Shaoxing North High-speed Railway Station, the influence of different construction stages on the deformation and inclination rate of the adjacent elevated bridge and its variation law are studied through field measurement and numerical simulation. The construction process is optimized by the method of reinforcement outside the pit and adjustment of preloaded axial force, and the influence of distance on elevated bridges is summarized. The results show that with the excavation of the foundation pit, the deformation of the bridge pier and bridge pile foundation gradually increases, and the deformation of the bridge piers is larger than that of the bridge pile foundations. As the depth of soil reinforcement outside the pit and the preloaded axial force increases, the maximum vertical displacement of the bridge pier and bridge pile foundations gradually decreases. The deeper the depth of soil reinforcement, the better the displacement control effect on the elevated bridge. In actual construction, it is recommended that the depth of reinforcement be taken as the excavation depth of the pit. It is obvious that the preloaded axial force is subject to the pit angle effect, and the appropriate value of the preloaded axial force should be selected according to the site conditions. The deformation of the bridge pier and bridge pile foundation generally shows a decreasing trend with the increase in the distance between the elevated bridge and the foundation pit. When the elevated bridge is close to the foundation pit, it will be affected by the pit angle effect, and the fluctuation will decrease. The conclusions drawn in the article can serve as the basis and reference for design and construction, and provide reference for similar projects.

Analysis of the response of wind-induced vibrations on flexible photovoltaic mounts

Abstract This article investigates a flexible photovoltaic bracket’s response to wind vibration. A finite element model is established using SAP2000 software for time course analysis. Representative units and nodes were selected to analyze internal force response, displacement response, and acceleration response. The prestress and span change rule of the flexible photovoltaic bracket are also explored, and quantitative research is conducted on the size of prestress and span size. The magnitude of the prestress affects a structure’s responsiveness to wind vibration. As prestress grows, so do deflection and acceleration, and the rate at which axial force is increasing also increases. Conversely, when prestress increases, the rate of deflection reduction falls. Consequently, considering the prestress size, it is advised that 50-kN prestressing be used for the support and wind cables. As the span rises, so do the mid-span span and the axial force of the wind cables, while acceleration also increases. The rate of mid-span deflection increases gradually with the flexible PV mount span, but the rate of axial force increase decreases. It is recommended to limit the span to below 50 m.

Experimental investigation on the mechanical properties and failure mechanism of key joints in a new-type prefabricated pile-wall composite structure for the open-cut tunnel

To improve the failure resistance of the lining and make use of the retaining structure, this paper proposed a novel method of adding the key joints to connect the lining with the retaining structure. Usually, the joint is the weak point of the whole structure. The failure mechanism of key joints significantly influences the design and safety of the prefabricated structure. In this study, full-scale loading tests were conducted on three types of key joints: sleeve joint, spiral stirrup joint, and U-shaped rebar joint. The joint deformation, failure mechanism, concrete strain, and reinforcement strain are investigated. The results demonstrated that the deformation and failure process of the key joints can be divided into four stages. The flexural-shear failure caused by the joint opening and the sliding of lining is considered as the main failure mode of the key joints. The U-shaped rebar joint exhibited the best mechanical performance. Furthermore, the finite element modes were created to analyze the influence of axial force and the reinforcement diameter. Combining the test and numerical analysis results, the failure mechanism was revealed. In addition, the joints’ loading-carrying capacity was increased with the increase of axial force due to the axial force limiting the joint opening. The research results provide a theoretical basis and reference for the new-type prefabricated pile-wall composite structure (PPCS).

Seismic response of braced excavation wall supporting deep sand layer using dynamic centrifuge tests

This paper presents the dynamic centrifuge model tests to investigate the seismic performance of a 24.8 m deep braced diaphragm wall supporting dry sand backfill soil at 40 g level acceleration. The model tests aim to determine the acceleration response of the backfill, seismic earth pressures acting on the wall, and the dynamic increment of the structure's inner force for sand backfills with different relative densities. Particularly, the horizontal seismic coefficient, earth pressure distribution, and dynamic thrust are analyzed in detail. Based on the experimental results, the dynamic thrust development is consistent for peak ground accelerations at bedrock less than 0.12 g and 0.10 g for relavitve densities of 78 % and 54 %, respectively. However, the dynamic thrust starts to increase when the bedrock acceleration exceeds this threshold. Moreover, the varying trend of dynamic thrusts under ground input motion employed during at the initial excitation differs from that of the succeeding input motions, likely due to the changes in relative density caused by backfill disturbance from sequential excitation. The increasing rate of increase on the dynamic thrusts among Northridge, Kobe, and artificial excitations was changed with the amplitude of the acceleration response. Lastly, the wall bending moment and strut axial force increase by up to 97.3 % and 12.9 % of the maximum value of member force on the at-rest condition due to earthquake loading.

Static performances of scissor structures

Scissor structures have very promising applications and have attracted much attention due to their novel characteristics of being deployable and foldable. However, most of the current studies have focused on its geometric and kinematic characteristics, while neglecting the analysis of their mechanical properties as load-bearing structures. In this study, general formulas for calculating the internal forces and equivalent bending stiffness of scissor structures are derived and verified using finite element method. The results show that the analytical and numerical simulation solutions are in good agreement and the expansion angle is the main factor affecting the static performances of the scissor structures. In particular, the extreme increase in axial force at expansion angles above 60°will lead to instability problems. Therefore, special attention should be paid when determining the expansion angle at or above 60°. Herein, the bending moment dominates the internal forces and the stresses generated by the bending moment exceed the axial forces by a factor of about 10–30. This study is expected to contribute greatly to scissor structure design by quantitatively evaluating preliminary design, exploring the impact of various parameters, optimizing design, and understanding limitations and potential issues.

Bearing Capacity Characteristic Analysis of Anti-floating Bolts in Unsaturated Soil Based on Mindlin Solution

AbstractBased on Mindlin solution and the theory of unsaturated soil mechanics, the theoretical solutions of shear stress and axial force distribution in the elastic stage of full-length binding-type anti-floating bolts were derived, and the bearing capacity characteristics of such bolts and the influencing factors were analyzed. In this paper, the design parameters of anti-floating anchor in a negative two-floor basement of a commercial square are substituted into the formula derived in this paper. The results show that, in unsaturated soil, the shear stress and axial force of the full-length bonded anti-floating anchor are distributed along the total length of the anchor, but neutral points appear in both of them, which is mainly due to the reduction of the axial force and shear stress of the anti-floating anchor caused by the matric suction. The formula derived in this paper is used to analyze the factors affecting the bearing capacity of anti-floating anchor bolt in unsaturated soil. The results show that: the greater the elastic modulus of soil mass, the greater the peak value of shear stress curve, the closer the peak value is to the head of anchor bolt, and the greater the axial force decline rate. With the increase of anchor solid diameter D, the peak value of shear stress decreases, the peak value moves backward, the neutral point moves forward, the negative shear stress value increases, the decline rate of axial force distribution curve decreases, but the negative axial force increases. With the increase of the additional shear stress τ0, the peak value of the shear stress curve decreases, the peak value moves to the hole of the anchor rod, the neutral point moves to the hole, the negative shear stress increases, the decline rate of the axial force distribution curve increases, and the negative axial force increases.

Unsteady effects of a winglet on the performance of horizontal-axis tidal turbine

A tip winglet can reduce the induced drag and the load fluctuation of a blade, considerably improving the hydrodynamic performance of a tidal turbine. Up to now, there are fewer studies on the unsteady effects of winglets, which limits the application of this design scheme. In this paper, a tidal turbine model is established based on computational fluid dynamics (CFD) and verified by a flume experiment. Then, unsteady effects on the turbine blade are analyzed considering different winglet lengths and cant angles. According to the study, the blade performance is optimal when the winglet cant angle is 45°, with about 11% efficiency improvement and about 8% increase in axial force; as the winglet length increases, the performance tends to further improve. In addition, this study demonstrates that the reason why a winglet can reduce blade load fluctuations is that the winglet takes the tip vortex generation position away from the blade rotation plane, instead of reducing the tip vortex intensity.

Research on the influence of heat release from cement hydration on the mechanical properties of casing

In order to study the influence of cement hydration heat release on the mechanical properties of casing, this paper calculates the wellbore temperature and pressure field based on the mathematical model of steady-state heat conduction of casing-cement ring-formation rock, establishes a mathematical model for the mechanical evaluation of cement hydration heat release and casing interaction, and performs finite element calculation and experimental simulation of the effect of cement hydration heat release on casing loss, and the results show that the results show: Along the axial direction of the wellbore, the maximum stress on the entire cement ring occurs in the lower position of the cement ring, and the maximum deformation on the casing occurs in the middle position. The axial stress variation range of the middle part of the casing is 50MPa, and the strain is 0.12%; The axial stress variation range of the outer ring is 235MPa, and the strain is 0.09%; The circumferential stress of the middle part varies from 500MPa to 0.255%. It is found that the stress and strain in the middle part of cement sheath are large, and yield is prone to occur. Under the action of cement hydration heat release, the long-axis elliptical deformation of (7.15∼31.8) mm occurs in the casing, that is, a large ovality is produced, which weakens the collapse strength of the casing. Two repeated tests showed that under the cement hydration heat release condition at the casing loss position, the temperature change of 60°C caused the increase of axial force of casing column and the increase of annular air pressure, which caused the non-uniform deformation of casing under the composite load of external extrusion and compression axial force.

Process parameter assessment on the dissimilar deposition of AA2024-T351 on AA7475-T761 by friction surfacing

Friction surfacing as a solid-state deposition process allows the joining of materials with different chemical and physical properties at temperatures below their respective melting points. This experimental work focuses on generating sound, defect-free metallurgical joints between single friction surfacing deposits and substrate surfaces from dissimilar Al alloys of the 2xxx and 7xxx series. In this context, the influence of axial force and deposition speed on surface morphology and deposit geometry of the two heat-treatable Al alloys AA7475 as substrate and AA2024 as deposit are investigated. Process parameter variation shows that an increase in axial force from 8 to 12 kN, in conjunction with a deposition speed of 8 mm/s, leads to smooth surface morphology and consistent deposit width along its length. The AA2024 deposits consist of fine-grained microstructure with higher hardness at the top and lower hardness at the deposit-substrate interface. The joining mechanism is by interdiffusion, with a 7.5 μm thick diffusion zone across the dissimilar interface. Three-point bending tests reveal excellent bonding in the lateral surface of the advancing side due to the absence of delamination for all conditions tested. Minor delamination appears predominantly on the retreating side region for process parameter sets with low axial force. Tensile test results reveal that the AA2024 deposit on the AA7475 substrate presents an ultimate tensile strength equivalent to the AA7475-T651 base material and an increase of 37 % in ductility.

Dynamic amplification factor and interactions of a beam under compressive axial force and load travelling at varying velocity

In this article, the deflection profile and response characteristic of axially prestressed continuous beam under the actions of load travelling at non-uniform velocity is explored. To achieve this, The governing equation is transformed using weighted residual method to obtain a set of coupled second-order Ordinary Differential Equations (ODEs) governing the amplitude factors of the beam-mass system. This set of ODEs is further simplified by applying a modified asymptotic method of Struble. Impulse response function is finally employed to obtain solutions representing the responses of this structural member to accelerating masses. Dynamic time history is carried out. Deformation and responses due to the stress in the structure are evaluated for different parameters. Dynamic effects of decelerating, accelerating and uniform velocity-type of motions on the dynamic amplification factor (DAF) and response characteristics are extensively studied for various vital structural parameters such as the beam span length, foundation stiffness, prestress, rotatory inertia correction factor, load position and velocity. The values of the amplification factors (DAF) against various pertinent parameters are presented in plotted curves for the pinned-pinned beam. It is found that, for accelerating, decelerating and constant velocity-type of motion, the value of the dynamic amplification factor increases as the values of axial force, foundation subgrade, and rotatory inertia factor increase. Various useful results in perfect agreement with existing studies are presented. It is further established that variations of the various structural parameters of interest significantly alter the response characteristics of the vibrating system.

Cumulative deformation and non-coaxial characteristics of fiber and cement-modified iron tailings under the rotation of principal stress

In order to study the deformation characteristics of fiber and cement-modified iron tailings (FCIT) under traffic loads, the cumulative deformation, stress–strain paths, cyclic stiffness, and non-coaxial characteristics of FCIT under the coupling of different cyclic stress ratios (CSR) and torsional shear stress ratios (η) were analyzed by using a heart-shaped stress path. The results indicate that: 1) The cumulative strain and torsional shear strain of FCIT under the rotation of the principal stress vary with CSR and η. The established empirical formula for the cumulative strain can be used to calculate the cumulative deformation of FCIT under different principal stress rotations based on the results of cyclic triaxial tests. 2) The difference between shear stiffness and positive deviation stiffness is the inherent mechanism that induces the non-coaxial characteristics of FCIT, that is, shear stiffness is subjected to torsional shear stress more than positive deviation stiffness is subjected to axial stress. 3) The non-coaxial characteristics of FCIT gradually weaken with the increase of axial force and torsional shear force, while the non-coaxial angle between the direction of strain increment and the direction of stress decreases.

Computational assessment of leg response to extreme loadings using a detailed finite element model.

This study focuses on evaluating the response of the Total Human Model for Safety™ lower extremity finite element model under blast loading. Biofidelity of the lower extremity model was evaluated against experiments with impact loading equivalent to underbody blast. The model response was found to match well with the experimental data for the average impactor speeds of 7 and 9.3 m/s resulting in an overall correlation and analysis rating of 0.86 and 0.82, respectively. The model response was then used to investigate response for antipersonnel mine explosion where the numerical setup consists of a charge mass of 40 g trinitrotoluene placed at a depth of 50 mm below the heel. The explosion was modeled using Multi Material-Arbitrary Lagrangian Eulerian method. The model was subjected to the graded input in terms of variation in standoff distance and mass of explosive to investigate the sensitivity of the model. The model found sensitive to the threat definition and predicted an increase of 110% in peak fluid-structure interaction force with 20% reduction in its time to peak and 29% increase in peak calcaneus axial force with a reduction of 33% in its time to peak when explosive mass varied from 40 g to 100 g. The location of the explosive below the foot was discovered to have significant effect on the injury pattern in near-field explosion. A comparative study suggested that the model predicted similar response and damage pattern compared to experimental data.

Experimental study on the compression-shear performance of a new-type circumferential joint of shield tunnel

To investigate the compression-shear behavior of a new circumferential joint based on the sleeve-straight bolt combination type connection of large-diameter shield tunnels, a series of full-scale joint experiments was carried out. In the process of the experiment, more attention was paid to the specimen displacement, bolt stress and joint damage mode. On the basis of these experiment phenomena, this study discussed the compression-shear bearing process of the new connector, analyzed the damage mode of the joint structure, and finally evaluated the performance of the new connector. It is found that the bearing process of the joint can be divided into four stages: the transitional stage for overcoming the friction of the concrete, the sleeve bearing stage for the sleeve bearing shear loads alone, the combined bearing stage for bearing shear loads by the connector system, and the structural damage stage for structural instability and damage. Generally speaking, affected by connector position and hand hole, the positive compression-shear stiffness of the joint is less than the negative compression-shear stiffness, and the positive shear strength of the joint is greater than the negative shear strength. The increase of longitudinal axial force will improve the compression-shear performance of the joint. The relationship between longitudinal axial force and joint stiffness is a logarithmic function. The use of new type of connector can effectively improve the compression-shear stiffness of joints under low shear loads, but the application of straight bolts will lose part of the strength performance.

Numerical evaluations on the effects of different factors on thermo- mechanical behaviour of an energy pile group

Energy pile is a kind of economical and efficient underground energy structure. Obtaining the effects of different factors on the performance of energy pile help to improve the working efficiency of the energy pile. However, the thermo-mechanical behaviour of energy pile groups are more complex than that in single energy pile due to the mutual interference of energy pile groups. In this paper, the energy pile group with the layout of 3 × 3 was simulated by a 3-D numerical model. The influences of soil type, pile spacing, pile material performance and pile arrangement form on the thermo-mechanical behaviour of the energy pile group were investigated. The results show that increasing pile spacing can not only improve the thermal performance of energy pile group but also reduce the pile displacement, but it will lead to the increase of pile axial force because of the weakening of pile group effect. The thermal performance of energy pile group is the highest under the rock-soil condition, followed by sand and clay. However, the pile displacement is the largest when the soil type is sand, followed by clay, and the rock-soil is the smallest, and the influence of soil type on pile axial force is just opposite to pile displacement. At the same time, the increase of thermal conductivity of pile material benefits to heat transfer performance of energy pile group, but it also aggravates the heat accumulation and results in a larger top displacement and axial force of pile. As for concrete compression modulus, increasing the concrete compression modulus can increase the axial force of pile, but the change of concrete compression modulus has no effect on the pile displacement. In terms of layout of energy pile group, the per unit soil volume heat exchange rate of energy pile group in the cross arrangement form is larger than that in sequential arrangement form. However, the variation range of soil temperature in the cross arrangement form is larger than that in the sequential arrangement form, thus increasing pile displacement and reducing pile axial force.

Eccentric Rotor Drop Dynamics Study of Vertical Maglev Bearing System

When considering the problem of a vertical magnetic levitation bearing system, the rotor eccentric fall is more likely to cause the failure of the protective bearing. In this paper, a rotor drop collision model and a protective bearing dynamics model are constructed. It compares and analyzes the evolution of collision force values of the rotor eccentric drop as well as the non-eccentric drop. Further, this paper discusses the law of influence of three factors, rotor quality, rotational speed, and axial protection clearance, on the collision characteristics of the protected bearing in eccentric and non-eccentric cases. It has also experimentally verified this characteristic of rotor speed. The results show that compared with the non-eccentric condition, the axial impact force and radial impact forces of the rotor in the eccentric condition increase by 14% and 114%, respectively. Compared with the non-eccentric condition, with the increase in rotor quality, the axial and radial impact force increase by 68% on average, and the axial depth amplitude of the rotor increases by 350%. With the increase of rotor speed, the axial impact force without an eccentric drop is basically unchanged; the axial impact force of an eccentric drop increases slightly, and the radial impact force increases by 110%. With the increase of axial protection clearance, the radial displacement vibration of the rotor axis increases; the average increase of the maximum axial force is 120 N, and the average increase of the maximum radial force is 100%.

Performance evaluation of light-weighted cement-stabilized-clay columns for soft ground improvement using the centrifuge model test

The thick soft clay (>20 m) is difficult to be treated by the deep mixing method for financial reasons; accordingly, the light-weighted cement-stabilized soil (LWCS, 1.0 Mg/m3) columns produced by casting are proposed as an alternative. To investigate the performance of the LWCS columns, a centrifuge model test with an acceleration of 100 g was conducted on a composite ground with LWCS columns and traditional deep mixing columns (1.7 Mg/m3). The results indicate that the ground with traditional columns exhibits a significantly larger deformation than that with LWCS columns. The axial force increases and then decreases with respect to the traditional column depth, and decreases with respect to the LWCS column depth. The stress concentration ratio and column efficacy of LWCS columns is significantly lower than that of traditional columns, suggesting that the LWCS columns and soil could share the loading together, thus realizing a better coordination between the column and soil.

Numerical studies on rock breaking of single axe-shaped PDC cutter

For a drill bit, the cutter is the most important part to break the rock. In oilwell drilling, polycrystalline diamond compact (PDC) bit is widely used to shear the rock formation. In this paper, a finite element model with including the axe-shaped PDC cutter and rock formation is developed to study the rock breaking behaviours. Results show that the effect of axe-shaped PDC cutter on rock breaking is better than that of the planar PDC cutter. The front rake angle and face angel play significant role on the axial force but have little influence on the tangential force. In addition, both the tangential force and axial force increase rapidly with increasing the depth of cut.

The Effect of Thumb Metacarpophalangeal Hyperextension on Thumb Axial Load and Lateral Pinch Force in a Cadaver Model of Thumb Trapeziectomy and Flexor Carpi Radialis Suspensionplasty

The purpose of our study was to investigate, in a cadaver model, the effect of increasing thumb metacarpophalangeal (MCP) joint hyperextension on thumb axial load and key pinch forceafter thumb trapeziectomy and flexor carpi radialis suspensionplasty. We developed a cadaveric model to test whether thumb MCP joint hyperextension after trapeziectomy would have a negative effect on key pinch force and increase loads across a reconstructed thumb carpometacarpal (CMC)joint. We created a cadaveric biomechanical model that varied thumb MCP joint hyperextension while measuring thumb CMC axial and key pinch force under standardized loads. Direct observations were made of how key pinch and axial thumb CMC force change with increasing thumb MCP joint hyperextension. We measured the thumb key pinch force and axial thumb CMC joint load with the thumb MCP joint in 0°, 10°, 20°, 30°, 40°, 50°, and 60° of hyperextension. There was a 0.88 N (2.4%) increase in axial force across the thumb CMC per every 10° of increasing thumb MCP joint hyperextension. We found a 0.53 N (4.4%) reduction in key pinch force for every 10° of increasing thumb MCP joint hyperextension. Therefore, at 60° of thumb MCP joint hyperextension, the axial force across the thumb CMC increased by 5.3 N (14.6%) and the key pinch force was weakened by 3.2 N (26.6%). With progressive thumb MCP joint hyperextension after thumb CMC arthroplasty, we found a decrease in key pinch force and an increase in axial thumb CMC joint force. The decrease in key pinch force was larger than the relatively small increase in thumb CMC force. This study helps elucidate the biomechanics of the thumb CMC joint after resection arthroplasty with thumb MCP joint hyperextension and helps understand the interplay between these 2 conditions.

Numerical study of blockage and arching behavior of particle with different shapes in packed bed

Blockage has a significant impact on the flow and heat transfer characteristics of particles in discharging process and can affect the system security seriously. In this study, the discrete element method (DEM) was adopted to analyze the discharge flow of pebbles, ellipsoids, and cubes. The mechanism of blockage formation is the mechanical interaction between particles. With the increase of axial force, the frequency of the blockage increases. High probability of blockage formation arises when the local axial velocity difference dvzl is less than 0.075, while a large local difference in axial velocity (dvzl≥ 0.075) can efficiently avoid blockage. With the increase of the bottom cone angle α of the geometric of the packed bed, blockage during particle flow can be avoided. When α increased to 60°, the particles of Rd less than 0.248 can be discharged smoothly. In addition, the coefficient of friction μ between particles, the ratio of particle diameter to discharge orifice diameter Rd and the aspect ratio Ra of non-spherical particles are all factors influencing the formation of blockages. The critical conditions for particle blockage formation were proposed. For actual working condition of engineering, the application of Rd less than 0.24 and μ less than 0.4 can effectively avoid blockage formation and ensure relatively safe operation for spherical particle systems. For ellipsoidal particles, low aspect ratio (Ra≤4) can effectively avoid blockage.

Effect of oblique bolt arrangement on flexural behavior of segmental joint for shield tunnel

As the width of segments increases, segmental joints containing three oblique bolts are increasingly used while their flexural behavior is still not clear. Therefore, this paper presents a comprehensive investigation on the flexural behavior of such joints; and the effects of bolt arrangement are also highlighted. A series of full-scale experiments and numerical simulations are first performed to reveal the typical flexural behavior and failure characteristics of the joint with one single oblique bolt. Then, the verified numerical model is extended to investigate the influence of different oblique bolt arrangements (i.e. number and direction) on the joint flexural behavior under different axial forces. Five bearing stages can be identified during the whole loading process of joints, and they are separated by the bolts tension, concrete severe damage, contact of the segment top, and joint failure. Under small axial force, the joint failure under the positive moment is dominated by the tensile damage of concrete around bolt holes; while the compressive damage of concrete at the same position controls the joint failure under the negative moment. The concrete damage area changes to the compression zone as the axial force increases. The oblique bolt arrangement has little effect on the identification of five-stage bearing process of such segmental joints, but increasing the number of bolts can improve the flexural stiffness and ultimate bearing capacity of joints. Moreover, the joint containing three cross oblique bolts has a stronger flexural capacity than that containing three parallel bolts under small axial forces, which is because the change of the bolt direction avoids the connection of tensile damage zones around the bolt holes. However, these effects of bolt arrangement fade away as the axial force increases.