Analysis of the Application of Static Load Test in Bridge Bearing Capacity Testing

This article uses real engineering projects as examples to analyze how static load test technology is applied in testing the bridge-bearing capacity.The analysis covers aspects such as testing section layout,test load and efficiency coefficient,loading plan,evaluation optimization,test result modification,and result evaluation.The aim is to support the accurate detection and evaluation of bridge-bearing capacity.

California Bearing Ratio for Cohesive Soils from Quasi Static Cone Tests

The California bearing ratio (CBR) test is the most widely spread method of determining the bearing strength of the pavement material and is fundamental to pavement design practice in most countries. This test is expensive, laborious and time consuming, and to overcome this, Quasi static cone penetrometer machine was fabricated and used to measure the consistency limits (liquid limit-LL, Plastic limit-PL and Plasticity index-PI), which were used to develop an empirical equation to determine CBR. Soil samples were collected and unsoaked CBR, PL, LL and PI were determined according to BS 1377 part 9 and BS 1377-2;1990. Quasi static penetration forces at 20 mm depth of penetration were also determined at consistency limits. It was found that the force of 1020 gf and 60 gf was achieved at a depth of 20 mm at PI and LL respectively. The correlation and regression analysis between consistency limits, and the experimental CBR obtained showed coefficient of determination, R2 = 0.907 between CBR and all the parameters using multiple linear regression analysis (MLRA). The regression equation developed was used together with the relationship developed between the Quasi static Penetration force at consistency limits and the tested consistency limits to come up with the General Empirical Equation. Verification of the formula showed that the correlation can be used accurately to determine the un soaked CBR.

Effect of Manufacturing Errors on Static Characteristics of Externally Pressurized Spherical Air Bearings

Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manufacturing errors are unavoidable, and the pursuit to enhance the manufacturing accuracy will increase the cost greatly. In order to provide some theoretical guideline for the tolerance choice in the design of the externally pressurized spherical air bearings with inherent compensation, the effects of several manufacturing errors on the static characteristics of the air bearing are studied. Due to the complex geometry of the computational domain, an unstructured meshing technology is used for mesh generation. A finite-volume method is adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations. A modified SIMPLE algorithm which is suitable for compressible flows is applied to solve the discretized governing equations. The effects of the dimension error and the roundness error of the ball head and the ball socket on the static characteristics are investigated. The investigation result shows that the positive dimension error and the oblate spheroid-type roundness error of the ball head as well as the negative dimension error and the prolate spheroid-type roundness error of the ball socket can improve the bearing capacity and static stiffness of the air bearings by reducing the mass flow. The calculation method proposed in this paper fits well for the general principle, which can be extended to the characteristics analysis of other air bearings.

Research on static bearing characteristics of magnetic-liquid double suspension bearing

Due to low viscosity of seawater,it is difficult to form a seawater-lubricated film.It is easy to cause the overload and burning phenomenon of seawater-lubrication sliding bearing,and then the operation stability and service life can be shortened seriously.Therefore,the paper introduces an electromagnetic suspension theory into the seawater lubricated sliding bearing.Then a novel magnetic-liquid double suspension bearing can be formed,which can enhance bearing capacity and stiffness greatly.Firstly,the structural characteristics,support-adjustment mechanism of magnetic-liquid double suspension bearing is analyzed.Secondly,based on force balance equation,electromagnetic equation and flow equation,the transfer functions of single DOF bearing system of magnetic-liquid double suspension bearing under constant-flow supply model are deduced.Then bearing capacity,static stiffness and total power loss are selected as static performance indexes.The influence rule of operaton and structural parameters on the static performance of single DOF bearing system will be analyzed.The results show that bearing capacity decreases with the increase of liquid film thickness and width of edge seals,bias current and coil turns decrease.Static stiffness decreases with the increase of liquid film thickness,edge seals width,bias current and coil turns.Total power loss decreases with the increase of liquid film thickness,edge seals width,bias current and coil turns decrease.And static performance indexes can not be affected by liquid viscosity.The proposed research provides some theoretical and experimental basis for the parameter design of magnetic-liquid double suspension bearing.

Quasi-static Analysis of Thrust-loaded Angular Contact Ball Bearings Part Ⅰ:Theoretical Formulation

Ball bearings play an important role in various rotating machineries,but the complicated kinematic and tribological features of ball bearings make many aspects of their operating behaviors still inconclusive.Most theoretical analyses of ball bearings up to date are based on either the hypothesis of race control or other empirical models to determine the ball motion of ball bearings,but none of these strategies can reveal and consequently employ the intrinsic coupling mechanism between the spin and the tangential traction of contacting bodies rolling upon one another.To remedy the deficiency of current analytical models for ball bearing analysis,the rolling contact theory is employed to establish an explicit link between motions and interactions within ball bearings.A differential slip model is established to precisely define the slip component due to the significant curvature of the common contact patches between the ball and inner/outer raceways.The creepage and the spin ratio are formulated to accurately define the relative rigid motion between the ball and the inner/outer raceway.Then a quasi-static analytical model is established that can accurately determine the motions of the balls and races of the ball bearing.It can also give a vivid description of the slip and traction distributions within the contact area.The analytical model can be effectively used to analyze the operational conditions and tribological features of solid-lubricated ball bearings.It can also be used optimize the construction of ball bearings for specific applications.

Quasi-static Analysis of Thrust-loaded Angular Contact Ball Bearings Part Ⅱ:Results and Discussion

Ball bearings are widely employed mechanical components characterized by high precision and quality,and usually play important roles in various rotary machines and mechanisms.Many advanced applications require a deep understanding of their various kinematic and tribological characteristics that are essential to predict the fatigue endurance,relieve the vibration and minimize the power dissipation of ball bearings in particular applications.An angular contact ball bearing under a specified operating condition is simulated with the quasi-static/creepage analytical model proposed in the preceding article.The results demonstrate that the ball bearing is a statically determinate system.That the balls spin on both inner and outer races means the ball is controlled by neither the inner nor the outer raceway.The friction between the ball and raceway renders the inner and outer contact angles unequal.The larger the coefficient of friction is,the larger the angle deviation.The tangential traction perpendicular to the rolling direction due to the spin induces a gyro-like rotation of the ball with respect to the raceway even if no inertial effects are considered.The tangential elastic compliance of contacting surfaces gives rise to locked areas within the contact patch and transforms the sliding lines from circles into spirals.The differential slip due to the close conformity of the ball and raceway makes the sliding and traction distributions asymmetric,which will influence the location of the spinning center of the ball with respect to the raceway.The quasi-static/creepage model can be used to reveal the operating behaviors of ball bearings running under steady conditions and to optimize the design of ball bearings for specific applications.

Contact Force Distribution and Static Load-carrying Capacity of Large Size Double Row Four-point Contact Ball Bearing

Clearance not only affects the startup torque,rotation precision and stiffness of bearing,but also affects the load distribution,load-carrying capacity and life of bearing.A computational model in which the clearance of bearing is first included is presented for determining the contact force distribution and static load-carrying capacity of a double row four-point contact ball bearing which is subjected to the combined radial,axial and overturning moment loadings.The relation between the negative axial clearance and the contact force distribution is analyzed.The static load-carrying capacity curves are established,and the effects of the changes in negative axial clearance,curvature radius coefficient of raceway groove and initial contact angle on the static load-carrying capacity are analyzed.The results show that,with the increase in the absolute value of negative clearance,the maximum contact load decreases first and then increases.The clearance values in the range of 0.2 mme0 mm have little effect on the static load-carrying capacity of bearing.With the increase in the curvature radius coefficient of raceway groove and the decrease in the initial contact angle,the static load capacity of bearing decreases.

MODELING OF STATIC RECRYSTALLIZATION KINETICS OF Nb-BEARING STEELS

By using isothermal double hit compression tests and applying the 2% offset method, a new model was developed to predict the microstructural evolution of Nb-bearing steels at temperatures above and below the start temperature of strain-induced precipitation （Tp）. The Tp was developed as a function of true strain, initial austenite grain size and the Nb content. The activation energy of static recrystallization （Qrex） was expressed as a function of the content of different alloy elements. It was found that Nb played the most important role in increasing the value of Qrex, The microstructural observations and measurements confirmed the validity of the model developed in the present investigation.

Static characteristics of new type externally pressurized spherical air bearings

In order to provide some theoretical guideline for the structure design of the new type externally pressurized spherical air bearings,the static characteristics and the factors affecting the static characteristics of the air bearings were analyzed.A finite volume method was adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations,and a modified SIMPLE algorithm for compressible fluid was applied to solve the discretized governing equations.The pressure field and velocity field of the air bearings were obtained,and the factors and rules affecting the static characteristics were analyzed.The results show that the pressure of near air intakes can reach above 80% of air supply pressure,and there is a pressure steep fall around the air intakes.When the film thickness is greater than 20 μm,the bearing capacity rapidly decreases as film thickness increases.As the air supply pressure increases from 0.2 to 0.6 MPa,the maximum static stiffness increases by more than three times.The calculation method proposed well fits the general principle,which can be extended to the characteristic analysis of other air bearings.

THE STATIC PERFORMANOE AND PARAMETER STUDY OF FLOATING-RING HYDRODYNAMIC THRUST BEARINGS

In this paper, floating--ring thrust bearings are investigated. A mathematical model is established to analyze the static performance of this kind of bearings, such as the load capacity, frictional power loss, temperature rise as well as the angular speed ratio between the floating ring and runner.Meanwhile, a parameter study is also conducted on the characteristics of floating-ring thrust bearings.Finally, the theoretical calculation results are verified by experiments.

Analysis on Static Pressure Bearing Seal Characteristics of Guide Sleeve of Electro-hydraulic Servo Cylinder

As a typical bionic walking robot, hydraulic quadruped robot has attracted much attention because of its high mobility, strong load capacity and steady motion. The electro-hydraulic servo cylinder, as its power actuator, requires low friction, good lateral load resistance and high speed motion. The electro-hydraulic servo cylinder hydrostatic bearing seal guide sleeve is taken as the research object in this paper. By using Fluent software to analyze and contrast the film characteristics of rectangular and I-shaped oil chamber of hydrostatic bearing seal guide sleeve, the relationship between piston rod moving speed, eccentricity, oil film carrying capacity, friction force and leakage volume, as well as the relationship between oil feed flow and oil film bearing capacity, friction force, inlet pressure and leakage volume were analyzed. This study provides a theoretical basis for optimizing the static pressure bearing seal parameters.

Computer Aided Analysis of the Performances of a Tilting Pad Gas Journal Bearing

Tilting pad gas journal bearing is one of the most widely used types of aerodynamic bearings due to its inherent excellent stability in high speed applications.A practical method for analyzing and calculating the per- formances of such bearings is presented as well as its rotordynamics based on the computer aided technique.The method of calculation and the philosophy of programming with a microcomputer for the computer aided analysis are highlighted.

Theoretical and experimental research on static stiffness,performance,and lift-off characteristics of multi-layer gas foil thrust bearings

In this study,a new comprehensive fully coupled elastic–hydrodynamic model is developed for a multi-layer gas foil thrust bearing(GFTB).The interaction effects among the top foil,back board,middle foil,and bottom foil,as well as the Coulomb friction effect,are considered.The stiffness and static characteristics obtained by the experimental and theoretical approaches are in good agreement,which verifies the accuracy of the model.The contribution of each foil layer to the overall stiffness and the load-carrying mechanism are analyzed.Interaction effects of the load,preload,and rotational speed on the static performance are investigated comprehensively.Furthermore,start–stop tests are performed to achieve the lift-off speed,start-up torque,and shut-down torque under various operating conditions.

Pit Bearing Capacity Effect on Status of Soil Plug During Pile Driving in Ocean Engineering

Foundation piles of the offshore oil platforms in the Bohai Bay are usually longer than 100 m with a diameter larger than 2 m. Driving such long and large-sized piles into the ground is a difficult task. It needs a comprehensive consider ation of the pile dimensions, soil properties and the hammer energy. Thoughtful drivability analysis has to be performed in the design stage. It has been shown that judging whether the soil column inside the pile is fully plugged, which makes the pile behave as close-ended, strongly influences the accuracy of drivability analysis. Engineering practice repeatedly indicates that the current methods widely used for soil plug judgment often give incorrect results, leading the designers to make a wrong decision. It has been found that this problem is caused by the ignorance of the bearing capacity provided by the soil surrounding the pile. Based on the Terzaghi＇s bearing capacity calculation method for deep foundation, a new approach for judging soil plug status is put forward, in which the surcharge effect has been considered and the dynamic effect coefficient is included. This approach has been applied to some practical engineering projects successfully, which may give more reasonable results than the currently used method does.

Experimental and numerical study on hysteretic performance of SMA spring-friction bearings

This paper presents an experimental and numerical study to investigate the hysteretic performance of a new type of isolator consisting of shape memory alloy springs and friction bearing called an SMA spring-friction bearing （SFB）. The SFB is a sliding-type isolator with SMA devices used for the seismic protection of engineering structures. The principle of operation of the isolation bearing is introduced. In order to explore the possibility of applying SMA elements in passive seismic control devices, large diameter superelastic tension/compression NiTi SMA helical springs used in the SFB isolator were developed. Mechanical experiments of the SMA helical spring were carried out to understand its superelastic characteristics. After that, a series of quasi-static tests on a single SFB isolator prototype were conducted to measure its force-displacement relationships for different loading conditions and study the corresponding variation law of its mechanical performance. The experimental results demonstrate that the SFB exhibits full hysteretic curves, excellent energy dissipation capacity, and moderate recentering ability. Finally, a theoretical model capable of emulating the hysteretic behavior of the SMA-based isolator was then established and implemented in MATLAB software. The comparison of the numerical results with the experimental results shows the efficacy of the proposed model for simulating the response of the SFB.

Bearing capacity and mechanical behavior of CFG pile composite foundation

CFG pile (i.e., pile constructed by granular materials of cement, fly-ash and gravel) composite foundation is applied in subsoil treatment widely and successfully. In order to have a further study of this kind of subsoil treatment technology, the influencing factors and calculation methods of the vertical bearing capacity of single CFG pile and the CFG pile composite foundation were discussed respectively. And based on the obtained solutions, effects by the cushion and measurements to reduce negative friction area were analyzed. Moreover, the developing law of settlement and bearing capacity eigenvalue controlled by the material strength with the increase of load were given for the CFG composite foundation. The in-situ static load test was tested for CFG pile. The results of test show that the maximum test load or half of the ultimate load is used from all the points of test, the average bearing capacity eigenvalue of single pile is 390 kN, and slightly greater than the design value of bearing capacity. The bearing capacity eigenvalues of composite foundation for 3 piles are greater than 300 kPa, and the mechanical properties of CFG pile composite foundation are almost identical in the case of the same load and cushion thickness. The pile-soil stress ratio and the load-sharing ratio can be adjusted through setting up cushion thickness.

Evaluation of ultimate bearing capacity of Y-shaped vibro-pile

Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.

Numerical study on the influences of preload factor on the properties of three-lobe journal bearing

The influences of preload factor on the characteristics of three-lobe journal bearing, such as dimensionless load capacity, attitude angle, stiffness coefficients and damping coefficients, were studied by using the numerical calculation. And the influences of eccentricity ratio and wide-to-diameter ratio on the characteristics of journal bearing were investigated as well. The results show that with the increasing of preload factor, eccentricity ratio and wide-to-diameter ratio, the dimensionless load capacity and damping coefficients increase; meanwhile, the absolute value of stiffness coefficients increases; and with the increasing of preload factor and eccentricity ratio and the decreasing of wide-to-diameter ratio, the attitude angle decreases. The study offers theoretical base for engineering application of three-lobe journal bearing.

多孔质静压轴承静态特性预测研究

在多孔质静压轴承设计中,轴承设计参数是影响其静动态特性的关键因素之一,通常情况下,要得到合适的轴承设计参数,需要多次重复建模和仿真,且由于轴承结构复杂,建模难度大,仿真时间长,严重影响了轴承的设计效率。本文构建了一种基于遗传算法(Genetic algorithm,GA)优化反向传播(Back propagation, BP)神经网络的轴承静态特性预测模型,采用拉丁超立方抽样方法在轴承参数设计空间内采样,并进行Fluent流体仿真,将仿真数据用于GA-BP神经网络模型的训练与测试,实现了对设计空间内任意设计参数下的多孔质静压轴承静态特性的预测。研究结果表明,训练出的GA-BP神经网络模型能够准确预测多孔质静压轴承的静态特性,预测精度在95%以上,对多孔质静压轴承的快速设计和参数优化具有重要意义。

部分充填式窄幅钢箱-UHPC组合梁抗剪试验研究

目的为研究部分充填式窄幅钢箱-UHPC组合梁的抗剪性能,方法对4根倒置组合梁试件通过三点加载方式进行了静载试验,通过研究其负弯矩作用下的破坏形态及变形特征,得到了组合梁的荷载-挠度曲线、应变分布、荷载-滑移曲线、最终破坏形态等。结果试验研究结果表明:UHPC翼板显著提升了组合梁的变形能力和极限承载力;相较于试件SUCB-3(NC翼板),试件SUCB-1(1/2UHPC翼板和SUCB-4(全UHPC翼板))的承载力分别提高了18.2%和27.3%,变形能力则分别增强了38.02%和41.2%;钢纤维的添加能有效地抑制翼板裂缝的开展,钢纤维掺量从0提高到2%,试件的最大裂缝宽度从1.06 mm降低到0.92 mm,变形能力增强了23.61%,承载力则提高了4%。结论提出了考虑钢箱、UHPC翼板和充填混凝土贡献的组合梁抗剪承载力计算公式。