Lateral earth pressure of granular backfills on retaining walls with expanded polystyrene geofoam inclusions under limited surcharge loading

Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.

A Multi-mode Electronic Load Sensing Control Scheme with Power Limitation and Pressure Cut-off for Mobile Machinery

In mobile machinery,hydro-mechanical pumps are increasingly replaced by electronically controlled pumps to improve the automation level,but diversified control functions(e.g.,power limitation and pressure cut-off)are integrated into the electronic controller only from the pump level,leading to the potential instability of the overall system.To solve this problem,a multi-mode electrohydraulic load sensing(MELS)control scheme is proposed especially considering the switching stability from the system level,which includes four working modes of flow control,load sensing,power limitation,and pressure control.Depending on the actual working requirements,the switching rules for the different modes and the switching direction(i.e.,the modes can be switched bilaterally or unilaterally)are defined.The priority of different modes is also defined,from high to low:pressure control,power limitation,load sensing,and flow control.When multiple switching rules are satisfied at the same time,the system switches to the control mode with the highest priority.In addition,the switching stability between flow control and pressure control modes is analyzed,and the controller parameters that guarantee the switching stability are obtained.A comparative study is carried out based on a test rig with a 2-ton hydraulic excavator.The results show that the MELS controller can achieve the control functions of proper flow supplement,power limitation,and pressure cut-off,which has good stability performance when switching between different control modes.This research proposes the MELS control method that realizes the stability of multi-mode switching of the hydraulic system of mobile machinery under different working conditions.

ELASTIC MODULUS REDUCTION METHOD FOR LIMIT LOAD EVALUATION OF FRAME STRUCTURES

A new strategy for elastic modulus adjustment is proposed based on the element bearing ratio （EBR）,and the elastic modulus reduction method （EMRM） is proposed for limit load evaluation of frame structures. The EBR is defined employing the generalized yield criterion,and the reference EBR is determined by introducing the extrema and the degree of uniformity of EBR in the structure. The elastic modulus in the element with an EBR greater than the reference one is reduced based on the linear elastic finite element analysis and the equilibrium of strain energy. The lower-bound of limit-loads of frame structures are analyzed and the numerical example demonstrates the flexibility,accuracy and effciency of the proposed method.

Fatigue Life Prediction under Service Load Considering Strengthening Effect of Loads below Fatigue Limit

Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule （PMR）, this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories： damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages： stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule （MMR）, and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are –3.78% and –1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.

Limit Load Solution for Electron Beam Welded Joints with Single Edge Weld Center Crack in Tension

Limit loads are widely studied and several limit load solutions are proposed to some typical geometry of weldments.However,there are no limit load solutions exist for the single edge crack weldments in tension（SEC（T））,which is also a typical geometry in fracture analysis.The mis-matching limit load for thick plate with SEC（T） are investigated and the special limit load solutions are proposed based on the available mis-matching limit load solutions and systematic finite element analyses.The real weld configurations are simplified as a strip,and different weld strength mis-matching ratio M,crack depth/width ratio a/W and weld width 2H are in consideration.As a result,it is found that there exists excellent agreement between the limit load solutions and the FE results for almost all the mis-matching ration M,a/W and ligament-to-weld width ratio（W-a）/H.Moreover,useful recommendations are given for evaluating the limit loads of the EBW structure with SEC（T）.For the EBW joints with SEC（T）,the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal,when M changing from 1.6 to 0.6.When M decreasing to 0.4,the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal only for large value of（W-a）/H.The recommendations may be useful for evaluating the limit loads of the EBW structures with SEC（T）.The engineering simplifications are given for assessing the limit loads of electron beam welded structure with SEC（T）.

Limit equilibrium stability analysis of slopes under external loads

Two calculation modes for the effect of external load on slope stability, i.e., mode I in which the external load is thought to act on slope surface, and mode II in which the external load is thought to act on slip surface along the force action line, were considered. Meanwhile, four basic distribution patterns of external load were used, of which complex external loads could be composed. In analysis process, several limit equilibrium methods, such as Swedish method, simplified Bishop method, simplified Janbu method, Spencer method, Morgenstern-Price(M-P) method, Sarma method, and unbalanced thrust method, were also adopted to contrast their differences in slope stability under the external load. According to parametric analysis, some conclusions can be obtained as follows:(1) The external load, with the large magnitude, small inclination angle, and acting position close to the slope toe,has more positive effect on slope stability;(2) The results calculated using modes I and II of external load are similar, indicating that the calculation mode of external load has little influence on slope stability;(3) If different patterns of external loads are equivalent to each other, their slope stability under these external loads are the same, and if not, the external load leads to the better slope stability,as action position of the resultant force for external load is closer to the lower sliding point of slip surface.

PLASTIC LIMIT LOAD ANALYSIS OF DEFECTIVE PIPELINES

The integrity assessment of defective pipelines represents a practically important task of structural analysis and design in various technological areas,such as oil and gas indus- try,power plant engineering and chemical factories.An iterative algorithm is presented for the kinematic limit analysis of 3-D rigid-perfectly plastic bodies.A numerical path scheme for radial loading is adopted to deal with complex multi-loading systems.The numerical procedure has been applied to carry out the plastic collapse analysis of pipelines with part-through slot under internal pressure,bending moment and axial force.The effects of various shapes and sizes of part-through slots on the collapse loads of pipelines are systematically investigated and evaluated.Some typical failure modes corresponding to different configurations of slots and loading forms are studied.

FRACTURE LIMIT LOAD OF CONE SHAPE PART IN DRAWING PROCESS

The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instability theory, the formula for calculating fracture limit load of cone shape part in drawing process is derived. Also, the formula is analyzed and verified by experiment.

Limit Load Analysis of Pipes with Local Wall-thinning

The loss of metal in a pipe due to corrosion usually results in localized thinned areas with various depths and an irregular shape on its surface. In this paper, a number of numerical models of pipes with different size defects are established. The limit loads of these pipes are researched using the nonlinear finite element method. The effect of defect parameters of the local wall-thinning pipes on the limit load is discussed. The results show that limit loads decrease obviously when the depths and lengths of the defect increase. However, when the defect length reaches a certain value, the effect of defect length on limit loads is not significant. These results are compared with the results of the method of API 579. When the defect length is adequately small, the results of FEM are in good agreement with the ones of APl 579, but when the defect depth and length is adequately large, the API 579 is not suitable.

An Analysis on Limit Load for Corroded Submarine Pipelines

By means of elastic-plastic finite element analysis, a systematic nonlinear analysis of material and geometry has been carried out for submarine pipelines. A criterion for deriving limit load is studied. Based on this criterion, the limit load for corroded submarine pipelines is calculated. The corrosion length, corrosion depth and corrosion width affect the limit load. A solution to limit load is proposed and proved valid through comparison of the solution with burst test results and ASME B31G solutions.

A new calculation method for axial load capacity of separated concrete-filled steel tubes based on limit equilibrium theory

A new calculation method for axial load capacity of separated concrete-filled steel tubes based on limit equilibrium theory was proposed,which took into account the decrease of confinement effect by steel tube and the non-uniform distribution of ultimate stress in cored concrete.The accuracy of the analytical result is validated through running the numerical result by finite element method (FEM) and experimental data as well.The influences of the key parameters on the load capacity of the concrete-filled steel tube (CFST) was studied,including the separation ratio,concrete compressive strength,and steel strength.The results indicate that the load capacity of the tube increases with concrete strength and steel strength under the separation ratio less than 4%,while decreases with a higher separation ratio improved.

Prediction and Verifcation of Forming Limit Diagrams Based on a Modifed Shear Failure Criterion

The forming limit diagram plays an important role in predicting the forming limit of sheet metals.Previous studies have shown that,the method to construct the forming limit diagram based on instability theory of the original shear failure criterion is efective and simple.The original shear instability criterion can accurately predict the left area of the forming limit diagram but not the right area.In this study,in order to improve the accuracy of the original shear failure criterion,a modifed shear failure criterion was proposed based on in-depth analysis of the original shear failure criterion.The detailed improvement strategies of the shear failure criterion and the complete calculation process are given.Based on the modifed shear failure criterion and diferent constitutive equations,the theoretical forming limit of TRIP780 steel and 5754O aluminum alloy sheet metals are calculated.By comparing the theoretical and experimental results,it is shown that proposed modifed shear failure criterion can predict the right area of forming limit more reasonably than the original shear failure criterion.The efect of the pre-strain and constitutive equation on the forming limits are also analyzed in depth.The modifed shear failure criterion proposed in this study provides an alternative and reliable method to predict forming limit of sheet metals.

A Discusion on Limited Load-Carrying Capacity of Rectangular Plates

The elastic-plastic method is often used in designing the inner flat bulkhead plates of submarines, and the upper structure of ships and drilling platforms. Such bulkhead plates can bear the load only once. For the improvement of the load-carrying capacity or the reduction of the weight of plates, the yield line analytical method is employed in this paper to design the bulkhead plate to improve economy and increase the effiective load. Besides, a further sutdy of this method has been made theoretically and experimentally, and the data of the limited load-carrying capacity of the plate have been obtained. Furthermore, the safety coefficients for such a method are presented, which can be used as reference for related departments and staffs.

含椭球腐蚀缺陷对油气管道极限载荷分析

借助Solidworks和ANSYS Workbench有限元分析软件,以单、双椭球腐蚀缺陷为研究对象,考察不同类型缺陷几何因素对管道极限载荷的影响。首先,对于单椭球缺陷,考察缺陷深度、缺陷长度、轴向夹角、长短轴比例变化对极限载荷的影响;其次,对于双椭球缺陷,考察轴向水平距离、环向相距角度变化对极限载荷的影响;最后,利用响应曲面法分析研究单腐蚀缺陷3种缺陷参数对极限载荷的影响。结果表明,对于单椭球腐蚀缺陷,由于缺陷深度、缺陷长度的增大,极限载荷逐渐降低;由于缺陷长短轴比例的减小,极限载荷逐渐降低;由于轴向角度的增大,极限载荷先减小后增大,出现极值;对于双椭球腐蚀缺陷,随着两缺陷轴向水平距离和环向角度的逐渐增大,极限载荷先减小后增大,出现极值;在单一参数中,缺陷深度对极限载荷的影响最为突出;在多参数交互作用中,缺陷长度和缺陷深度的交互作用对管道极限载荷影响最为突出。

超深井套管卡瓦效应的拉伸极限载荷理论计算

针对新疆某油田超深井井口套管悬重过大,造成卡瓦牙对套管外壁齿入损伤,且累计损伤导致卡瓦悬挂器套管断裂失效的事故频繁,提出了“卡瓦效应的拉伸极限载荷”来评价井口卡瓦悬挂器夹持部分套管的强度设计,具体为基于第三强度理论和第四强度理论,分别建立了井口卡瓦悬挂器夹持套管的“卡瓦效应拉伸极限载荷”计算模型。计算结果表明,从安全角度评价套管强度,采用第三强度理论计算卡瓦悬挂器套管的卡瓦效应拉伸极限载荷更合理,但为更充分利用材料的力学性能,应采用第四强度理论进行评价,还得到在四通有限空间内,可以保证有较大的卡瓦效应拉伸极限载荷的最佳卡瓦半锥角为23°~25°,最佳卡瓦有效接触长度为135~145 mm。研究方法和结果将为卡瓦悬挂器井口套管的强度设计、各种安全施工作业等提供理论依据。

基于移动荷载谱的高速铁路简支梁桥基频限值分析

控制桥梁振动响应是保证高速列车安全稳定运行的关键,遵循梁体不发生共振或较大位移响应的原则,提出了简支梁桥基频限值频域分析法。首先基于移动荷载列模型,通过傅里叶变换得到了桥梁振动响应谱和移动荷载谱,并从时域角度验证了谱的正确性;然后通过引入间跨比γ和无量纲速度κ,探究了在不同移动荷载列作用下桥梁自由振动发生最大位移响应时,无量纲速度κ和间跨比γ之间的关系;其次根据γ-κ关系曲线分析了24 m、32 m、40 m简支梁桥最大位移响应下的无量纲速度κ;最后为了避免列车激励下桥梁发生共振或较大位移响应,参考国际铁路联盟基频限值规范,基于移动荷载谱给出了移动荷载列在不同设计时速下24 m、32 m、40 m简支梁桥基频限值建议值。研究表明:移动荷载幅值谱与时域计算的桥梁自由振动位移幅值响应规律一致;单节车长25 m左右的移动荷载列以共振速度激励桥梁时,24 m、32 m简支梁桥自由振动都能达到最大位移响应,而40 m简支梁桥仅产生较大位移响应,且在列车运营速度范围内达不到产生最大位移的条件;桥梁基频限值随着列车时速的增加而增大,当最大设计时速400 km/h时24 m、32 m、40 m简支梁桥基频建议下限值分别为6.00 Hz、4.94 Hz、5.66 Hz。

峰前峰后循环加卸载对砂岩动力特性的影响

为深入分析砂岩峰前和峰后不同阶段的动力特性规律,开展单轴分级循环加卸载试验,综合分析下限应力对砂岩峰前峰后不同加卸载阶段的表观弹性模量、滞回圈面积、阻尼比、阻尼系数及动弹性模量等相关动力参数的影响。研究结果表明:①岩样在峰后因内部损伤加深和累积,相同下限应力下滞回曲线位于峰前右侧,且应变量增幅和最大应变增幅均随下限应力的增加而逐渐减小,说明峰后岩样虽然强度已达到极限状态,但只要岩石未完全破坏失稳,其致密性仍可以在高应力条件下的循环加卸载中得到增强。②砂岩在峰前峰后循环加卸载下的变化过程,可以通过表观弹性模量曲线斜率a值的变化得以体现,低下限应力循环加卸载试验中,致密性增强系数a_(1)>致密性劣化系数a_(2),斜率a均为正值,轴向应力对岩石整体的压密作用明显强于劣化损伤作用;随着下限应力升高,a_(2)的降低速率高于a_(1)的升高速率,a值逐渐减小甚至变为负值,说明轴向应力对岩石整体的压密作用逐渐弱于劣化损伤作用。③4组不同下限应力条件下,岩样峰后的滞回圈面积、阻尼比、阻尼系数均高于峰前状态,而动弹性模量低于峰前状态,说明岩样在峰后循环加卸载过程中内部劣化损伤程度高于峰前。

室内人造板甲醛释放承载限量验证研究

通过实验测定不同类型的人造板在不同条件下的甲醛释放量,验证了人造板极限甲醛释放量最热月平均温度、最高月平均湿度校正系数,实际检测结果偏差为-25.7%~29.2%,基本符合温湿度校正系数换算数学模型。同时通过典型装修工程室内人造板甲醛释放量和使用量分析,以及实际室内空气甲醛含量检测,验证了人造板理论甲醛极限承载限量计算结果与实际检测结果基本相符。

非线性加载路径下金属薄板成形极限研究进展

成形极限图是评判金属薄板局部成形能力的重要工具,研究非线性加载路径下的成形极限图对提高实际生产过程中工艺设计的合理性和板料的成形性具有重要意义。总结分析了国内外学者对非线性加载路径下金属薄板成形极限的研究进展,主要包括试验方法、理论预测模型及路径无关成形极限图3个方面。重点研究了不同试验方法的适用范围及优缺点,阐述了多种预测非线性加载路径下成形极限图的理论模型及应用实例,并归纳了当前在应变路径无关的成形极限图方面取得的研究成果。最后,从上述3个方面总结了当前更具潜力的研究方向,并对未来的发展趋势以及面临的困难和挑战进行了展望。