APPLICATION OF STOCHASTIC FINITE ELEMENT METHOD TO STRENGTH AND STABILITY ANALYSIS OF EARTH DAMS

This paper applies the stochastic finite element method to analyse the statistics of stresses in earth dams and assess the safety and reliability of the dams. Formulations of the stochastic finite element method are briefly reviewed and the procedure for assessing dam's strength and stability is described. As an example, a detailed analysis for an actual dam Nululin dam is performed. A practical method for studying built-dams based on the prototype observation data is described.

Finite element analysis of slope stability by expanding the mobilized principal stress Mohr's circles-Development, encoding and validation

In recent years,finite element analysis is increasingly being proposed in slope stability problems as a competitive method to traditional limit equilibrium methods(LEMs)which are known for their inherent deficiencies.However,the application of finite element method(FEM)to slope stability as a strength reduction method(SRM)or as finite element limit analysis(FELA)is not always a success for the drawbacks that characterize both methods.To increase the performance of finite element analysis in this problem,a new approach is proposed in this paper.It consists in gradually expanding the mobilized stress Mohr’s circles until the soil failure occurs according to a prescribed non-convergence criterion.The present approach called stress deviator increasing method(SDIM)is considered rigorous for three main reasons.Firstly,it preserves the definition of the factor of safety(FOS)as the ratio of soil shear strength to the mobilized shear stress.Secondly,it maintains the progressive development of shear stress resulting from the increase in the principal stress deviator on the same plane,on which the shear strength takes place.Thirdly,by introducing the concept of equivalent stress loading,the resulting trial stresses are checked against the violation of the actual yield criterion formed with the real strength parameters rather than those reduced by a trial factor.The new numerical procedure was encoded in a Fortran computer code called S^(4)DINA and verified by several examples.Comparisons with other numerical methods such as the SRM,gravity increasing method(GIM)or even FELA by assessing both the FOS and contours of equivalent plastic strains showed promising results.

Strength reduction and step-loading finite element approaches in geotechnical engineering

The finite element limit analysis method has the advantages of both numerical and traditional limit equilibrium techniques and it is particularly useful to geotechnical engineering.This method has been developed in China,following well-accepted international procedures,to enhance understanding of stability issues in a number of geotechnical settings.Great advancements have been made in basic theory,the improvement of computational precision,and the broadening of practical applications.This paper presents the results of research on（1） the efficient design of embedded anti-slide piles,（2） the stability analysis of reservoir slopes with strength reduction theory,and（3） the determination of the ultimate bearing capacity of foundations using step-loading FEM（overloading）.These three applications are evidence of the design improvements and benefits made possible in geotechnical engineering by finite element modeling.

An Integrated Structural Strength Analysis Method for Spar Type Floating Wind Turbine

An integrated structural strength analysis method for a Spar type floating wind turbine is proposed in this paper,and technical issues related to turbine structure modeling and stress combination are also addressed.The NREL-5MW ＂Hywind＂ Spar type wind turbine is adopted as study object.Time-domain dynamic coupled simulations are performed by a fully-coupled aero-hydro-servo-elastic tool,FAST,on the purpose of obtaining the dynamic characteristics of the floating wind turbine,and determining parameters for design load cases of finite element calculation.Then design load cases are identified,and finite element analyses are performed for these design load cases.The structural stresses due to wave-induced loads and wind-induced loads are calculated,and then combined to assess the structural strength of the floating wind turbine.The feasibility of the proposed structural strength analysis method for floating wind turbines is then validated.

Light weight analysis of a skeleton vehicle frame using BS960 super-high-strength steel

Static strength finite element analysis was conducted to decrease the weight of a skeleton vehicle＇s frame. Results indicated that the maximum stress occurs on the front beam ＇s variable section area. Dynamic sensitivity analysis elucidated the relationship between the maximum stress and the thickness of a particular beam,e. g.,top,middle,and bottom beam. Displacement was analyzed by the key part that influenced the maximum stress. Finally,the new plan using BS960 super-high-strength beam steel and the preferred beam thickness was compared with the original plan. New combinations of beam thickness were introduced on the basis of different purposes; the maximum responding light w eight ratio was 21%.

Fatigue Strength and Modal Analysis of Bogie Frame for DMUs Exported to Tunisia

The equivalent stress at key positions of Bogie Frame for DMUs Exported to Tunisia is obtained by using simulation analysis. The evaluation of static strength and fatigue strength is checked referring to UIC specification and Goodman sketch for welding materials. In addition, the modal analysis of the frame is made, and the vibrational modal of frame in given frequency domain is predetermined to evaluate the dynamical behavior of the frame in order to meet the dynamical design requirements. The results show that the key points of the calculated frame of the equivalent stress are less than allowable stress, and thus it could provide a theoretical foundation for the optimized design of frame structure and safety of industrial production.

Finite element analyses of slope stability problems using non-associated plasticity

In recent years, finite element analyses have increasingly been utilized for slope stability problems. In comparison to limit equilibrium methods, numerical analyses do not require any definition of the failure mechanism a priori and enable the determination of the safety level more accurately. The paper compares the performances of strength reduction finite element analysis(SRFEA) with finite element limit analysis(FELA), whereby the focus is related to non-associated plasticity. Displacement-based finite element analyses using a strength reduction technique suffer from numerical instabilities when using non-associated plasticity, especially when dealing with high friction angles but moderate dilatancy angles. The FELA on the other hand provides rigorous upper and lower bounds of the factor of safety(FoS) but is restricted to associated flow rules. Suggestions to overcome this problem, proposed by Davis(1968), lead to conservative FoSs; therefore, an enhanced procedure has been investigated. When using the modified approach, both the SRFEA and the FELA provide very similar results. Further studies highlight the advantages of using an adaptive mesh refinement to determine FoSs. Additionally, it is shown that the initial stress field does not affect the FoS when using a Mohr-Coulomb failure criterion.

3D FEM analysis for layered rock considering anisotropy of shear strength

An empirical expression of cohesion （C） and friction angle （Ф） for layered rock was suggested. This expression was compared with a test result made by the former researchers. The constitutive relationship of a transversely isotropic medium and Mohr-Coulomb criterion in which C and Ф vary with directions were employed, and a relative 3D elasto-plastic FEM code was developed, in which the important thing was to adopt a search-trial method to find the orientation angle （p） of shear failure plane （or weakest shear plane） with respect to the major principal stress as well as the corresponding C and Ф Taking an underground opening as the calculation object, the numerical analyses were carried out by using the FEM code for two cases of transversely isotropic rock and isotropic rock, respectively, and the computation results were compared. The results show that when the rock is a transversely isotropic one, the distributions of displacements, plastic zones and stress contours in the surrounding rock will be non-axisymmetric along the tunnel＇s vertical axis, which is very different from that of isotropic rock. The stability of the tunnel in transversely isotropic rock is relatively low.

Structural Strength Analysis of a Tri-Floater Floating Foundation for Offshore VAWT

Vertical axis wind turbines(VAWTs) are advantageous for the development of large-scale offshore wind power because the drive system is located at the bottom of the turbine. This study investigates the structural strength of a tri-floater floating foundation supporting a 2.6 MW Darrieus VAWT. Finite element models of the floating foundation were developed using space plate-beam elements. The environmental loads, such as the aerodynamic loads, static wind loads, and wave-current loads, were considered. The general strengths of the floating foundation were calculated for the normal operating case(a cut-out wind speed of 25 m s^(-1) and blade rotation of 12 r min^(-1) were used to analyze the most unfavorable loads) and an extreme case(wind speed of 40 m s^(-1) and parked blades), and the weak components of the structure were analyzed. The results show that the floating foundation meets the strength requirements and the structural stress is highest when the wave, wind, and current are in a collinear direction. The main and secondary supporting bars transmit the loads between the stand columns and the tower foundation, and their stresses are higher than those in the other components. In the actual design, these supporting bars should be strengthened. The aerodynamic loads are very important and should be considered in the structural strength analysis of the floating foundation and the floating wind turbine system.

Stability analysis of a concrete gravity dam and its foundation

The stability of dams and their foundations is an important problem to which dam engineers have paid close attention over the years. This paper presented two methods to analyze the stability of a gravity dam and its foundation. The direct analysis method was based on a rigid limit equilibrium method which regarded both dam and the rock foundation as undeformable rigid bodies. In this method, the safety factor of potential sliding surfaces was computed directly. The second method, the indirect analysis method, was based on elasto-plastic theory and employs nonlinear finite element method (FEM) in the analysis of stresses and deformation in the dam and its foundation. The determination of the safety degree of the structure was based on the convergence and abrupt the change criterion. The results obtained showed that structures' constituent material behavior played an active role in the failure of engineered structures in addition to the imposed load.

Multi-factor sensitivity analysis on the stability of submarine hydrate-bearing slope

There are many factors affecting the instability of the submarine hydrate-bearing slope (SHBS),and the interaction with hydrate is very complicated.In this paper,the mechanical mechanism of the static liquefaction and instability of submarine slope caused by the dissociation of natural gas hydrate (NGH) resulting in the rapid increase of pore pressure of gas hydrate-bearing sediments (GHBS) and the decrease of effective stress are analyzed based on the time series and type of SHBS.Then,taking the typical submarine slope in the northern South China Sea as an example,four important factors affecting the stability of SHBS are selected,such as the degree of hydrate dissociation,the depth of hydrate burial,the thickness of hydrate,and the depth of seawater.According to the principle of orthogonal method,25 orthogonal test schemes with 4 factors and 5 levels are designed and the safety factors of submarine slope stability of each scheme are calculated by using the strength reduction finite element method.By means of the orthogonal design range analysis and the variance analysis,sensitivity of influential factors on stability of SHBS are obtained.The results show that the degree of hydrate dissociation is the most sensitive,followed by hydrate burial depth,the thickness of hydrate and the depth of seawater.Finally,the concept of gas hydrate critical burial depth is put forward according to the influence law of gas hydrate burial depth,and the numerical simulation for specific submarine slope is carried out,which indicates the existence of critical burial depth.

Study on Welding-Bead Bonding Strength of Laser-Stacking Copper-Aluminum Heterogeneous Electrode Plates

In this paper,two types of copper-aluminum heterogeneous electrode plates are stacked and the finite element analysis(FEA)models of two different laser welding conditions are built by using SYSWELD welding simulation software to calculate the depth of the welding bead and the temperature distribution of the welding surface.Then,the residual stress analysis data of the welded area are exported and the residual stress is applied to the welded specimen for CAE analysis to ensure that the welding bonding strength meets the design target of a shear force of 500 N or higher.The copper-aluminum laser-stacking simulation technique in this paper can be applied to the manufacturing of copper-aluminum heterogeneous laser-welded electrodes and series-connected electrodes of automotive lithium-ion power battery modules,providing an effective analysis method for welding bonding-strength.

高温下焊接Q960钢H形截面柱局部稳定设计方法

为考察焊接Q960钢H形截面轴心受压柱局部稳定性能,采用ABAQUS软件建立有限元模型,经试验数据验证后,分析翼缘宽厚比、腹板高厚比、构件温度、构件长细比、初始几何缺陷和残余应力等参数对焊接Q960钢H形截面轴心受压柱局部屈曲强度的影响。研究表明,轴心受压柱的局部屈曲承载力主要与截面尺寸及构件温度有关。采用多国规范对试验试件的局部屈曲承载力进行计算,发现现有规范的设计方法不适用于高温下焊接Q960钢H形截面轴心受压柱局部屈曲承载力的计算。根据有限元分析结果提出焊接Q960钢H形截面轴心受压柱局部屈曲设计方法,与试验数据和有限元分析结果的对比表明所提方法能较准确地计算焊接Q960钢H形截面轴心受压柱不同温度下的局部屈曲承载力。

不同去柱工况下多层钢框架结构抗连续倒塌机理研究

为探究不同去柱工况对多层钢框架结构抗连续倒塌性能影响,分别对中柱失效和角柱失效工况的2层2跨钢框架梁-柱子结构进行Pushdown加载试验,研究其在倒塌过程中的抗力曲线和破坏模式。试验结果表明:中柱失效下钢框架主要依靠弯曲机制和悬链线机制抵抗外加荷载,且悬链线机制具有一定的滞后性;而角柱失效下钢框架主要依靠弯曲机制抵抗倒塌,且由于空腹效应的存在,可以有效提高结构的抗倒塌承载力。随后通过有限元软件ANSYS/LS-DYNA对所研究试件进行数值模拟,并对现实场景中可能出现的6种去柱工况分别进行抗连续倒塌分析。通过对比6种去柱工况钢框架结构的抗力曲线和抗倒塌风险可知:不同去柱工况下的钢框架结构水平约束条件不同,从而空腹效应发展也不尽相同;考虑空腹效应并考虑单位面积结构的承载力时,邻角柱失效与邻边柱失效工况下的钢框架结构具有较高的倒塌风险。

基于强度折减法的河漫滩软土浅埋偏压连拱隧道洞口边坡稳定性研究

以南京市乌龙山大跨浅埋偏压连拱隧道为背景,基于有限元强度折减法分析了隧道施工过程中洞口边坡的安全系数和塑性区分布特征,探明了不同坡角和隧道埋深下边坡稳定性情况与破坏模式发展规律,并提出相应施工建议。结果表明:边坡角度越大、隧道埋深越小时,隧道开挖过程中上覆边坡的安全系数越低。及时施作隧道衬砌能大幅度提高坡体稳定性,但当隧洞顶部埋深超过洞高的1.5倍后,衬砌加固效果相对有限;当边坡角度为60°时,坡体潜在滑动面将沿隧道浅埋侧拱顶附近产生,当隧道洞顶埋深达1.5倍洞高时,边坡破坏面不再经过隧道,而是分布于拱顶上方;针对隧道洞口段安全性较差问题,建议根据不同隧道埋深和边坡角度采用不同范围的坡表注浆加固方案。当隧道埋深>1.5倍洞高时,无须坡表注浆;当隧道埋深<1.5倍洞高且边坡角度<60°时,应在隧道浅埋侧施工前对坡脚至中隔墙区域进行注浆,且加固深度不应小于隧道拱腰埋深;当边坡角度达60°时,深埋和浅埋侧隧道施工前均需进行坡表注浆。

岩土常规三轴Drucker-Prager准则

随着三维数值极限分析得到日益关注,亟需发展适用于岩土常规三轴应力状态的Drucker-Prager(DP)准则。当前尚无适用于岩土常规三轴条件的DP准则的精确解,而是使用近似的等面积圆DP-3_(1)准则,该准则偏安全。基于岩土三剪能量准则,推导了该准则最高点(即该准则与摩尔-库仑准则的切点)对应的罗德角的表达式,进而通过最高点建立了岩土常规三轴DP-3_(2)准则,并将其应用于常规三轴条件下土体的极限荷载计算与边坡稳定性分析。研究表明:DP-3_(2)准则计算的常规三轴下土体极限荷载为实测值的87%~97%,DP-3_(2)准则与DP-3_(1)准则计算的极限荷载之比可达1.19,且随着围压减小、黏聚力c增大或者内摩擦角φ增大,二者计算结果的差异增大;DP-3_(2)准则计算的土质边坡稳定安全系数为DP-3_(1)准则计算结果的1.01~1.04倍,且二者差异随着坡度增大而增大。这些结果表明DP-3_(2)准则适用于岩土常规三轴应力状态下的数值极限分析。

冷弯薄壁折叠翼缘C形不锈钢构件受弯性能分析

为了在同成本下获得更高效的截面形式,利用ABAQUS对前期六组V形加劲C形截面奥氏体304不锈钢受弯构件建立有限元简化数值分析模型,将得到的结果与试验结果进行了对比验证。对应上述六组受弯构件设计了四组与其用钢量相同,但尺寸分布不同的折叠翼缘不锈钢受弯构件,共24组;探讨了折叠翼缘截面不锈钢受弯构件在四点受弯作用下的构件承载性能,并将其与C形截面不锈钢受弯构件的承载性能进行了对比。利用现有的设计计算方法计算了24组折叠翼缘截面受弯构件的极限承载力,并将其与有限元得到的结果进行了比较。对比发现:相同用钢量的情况下,当折叠翼缘截面腹板高度与斜翼缘在腹板平面内的投影长度值之和较C形截面腹板高度提升12%以上时,折叠翼缘截面不锈钢梁的极限承载性能比C形截面更优异,截面形式更加高效。现有的计算方法计算腹板V形加劲的折叠翼缘受弯构件得到的结果比较理想,误差较小;而对于平翼缘V形加劲且宽度较小的构件,计算得到的结果偏大,不能准确地预测构件的极限承载能力。

碰撞冲击载荷下船用LNG燃料罐的结构强度评价

针对LNG燃料船舶在碰撞事故发生情况下的LNG燃料罐结构安全问题,应用有限元方法建立有限元分析模型,并参照规范形成碰撞载荷计算及加载、结构强度评价等方法,提出碰撞冲击载荷作用下船用LNG燃料罐结构安全评价的解决方案。以18 m~3船用LNG燃料罐作为研究对象进行仿真计算分析,评估碰撞载荷作用下LNG燃料罐筒体、封头、内外容器间的支撑结构及鞍座等部件的应力水平和总体结构安全状况。结果表明,该船用燃料罐各构件应力均小于规范中的许用值,强度满足要求,符合行业规范,验证有限元分析方法在LNG燃料罐结构强度评价的可行性;内容器是工况条件下最容易失效的结构,其最大应力可达123.63 MPa,与许用值相差13.07 MPa。

自卸车车架有限元分析与轻量化设计

自卸车车架的轻量化一直是整车厂的设计目标之一,车架轻量化不仅可以节约材料和成本,也可以减少油耗,提高经济性。文章以某型自卸车为研究对象,运用ANSYS软件对车架进行三种工况静力学分析,根据仿真分析数据对车架进行轻量化设计,选取最佳优化方案,对轻量化的车架进行静态和模态分析,验证其是否满足使用要求,分析及轻量化设计自卸车车架对增加自卸车辆的整车使用寿命,对提高其安全可靠性和经济性有一定的工程实践意义。

基于强度折减黄土路基高边坡稳定性分析与设计优化

为开展黄土路基高边坡的治理工作,保障交通安全,文章基于有限元强度折减法,开展边坡稳定性分析研究。首先,基于数值模拟,构建路基高边坡有限元模型,标定力学参数。其次,利用有限元强度折减法,从等效塑性应变贯通、收敛计算、边坡位移突变等方面开展边坡稳定性计算分析。最后,依托荣乌高速黄土路基高边坡工程治理实例,开展路基边坡合理断面和边坡防护研究。结果表明:采用简化Bishop计算的安全系数相对偏于安全,提出的稳定性计算方法更加准确且符合实际。