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.

Analysis of steel-concrete composite structure with overlap slab of Xingguang bridge

Finite element modeling methods of steel-concrete composite structure with overlap slab were investigated. A two-step finite element method was presented. It was applied to analyze an extra long span composite bridge. The conversion of structure system and the mechanical behavior of the bridge were analyzed with two different construction methods. The stresses of steel beams, precast slabs and in-situ-place concrete under the total load were compared. The results show that steel-concrete composite structure with overlap slab has many advantages, the construction method that the top in-situ concrete and the concrete in construction joints are cast respectively is rather reasonable than the one that the top in-situ concrete and the concrete in construction joints are cast at the same time, and the two-step finite element method is affective to such large-scale structures.

Wave propagation of laminated composite plates via GPU-based wavelet finite element method

This paper presents a novel parallel implementation technology for wave-based structural health monitoring (SHM) in laminated composite plates. The wavelet-based B-spline wavelet on he interval (BSWI) element is constructed according to Hamilton’s principle, and the element by element algorithm is parallelly executed on graphics processing unit (GPU) using compute unified device architecture (CUDA) to get the responses in full wave field accurately. By means of the Fourier spectral analysis method,the Mindlin plate theory is selected for wave modeling of laminated composite plates while the Kirchhoff plate theory predicts unreasonably phase and group velocities. Numerical examples involving wave propagation in laminated composite plates without and with crack are performed and discussed in detail. The parallel implementation on GPU is accelerated 146 times comparing with the same wave motion problem executed on central processing unit (CPU). The validity and accuracy of the proposed parallel implementation are also demonstrated by comparing with conventional finite element method (FEM) and the computation time has been reduced from hours to minutes. The damage size and location have been successfully determined according to wave propagation results based on delay-and-sum (DAS). The results show that the proposed parallel implementation of wavelet finite element method (WFEM) is very appropriate and efficient for wave-based SHM in laminated composite plates.

Nonlinear finite-element-based structural system failure probability analysis methodology for gravity dams considering correlated failure modes

The structural system failure probability(SFP) is a valuable tool for evaluating the global safety level of concrete gravity dams.Traditional methods for estimating the failure probabilities are based on defined mathematical descriptions,namely,limit state functions of failure modes.Several problems are to be solved in the use of traditional methods for gravity dams.One is how to define the limit state function really reflecting the mechanical mechanism of the failure mode;another is how to understand the relationship among failure modes and enable the probability of the whole structure to be determined.Performing SFP analysis for a gravity dam system is a challenging task.This work proposes a novel nonlinear finite-element-based SFP analysis method for gravity dams.Firstly,reasonable nonlinear constitutive modes for dam concrete,concrete/rock interface and rock foundation are respectively introduced according to corresponding mechanical mechanisms.Meanwhile the response surface(RS) method is used to model limit state functions of main failure modes through the Monte Carlo(MC) simulation results of the dam-interface-foundation interaction finite element(FE) analysis.Secondly,a numerical SFP method is studied to compute the probabilities of several failure modes efficiently by simple matrix integration operations.Then,the nonlinear FE-based SFP analysis methodology for gravity dams considering correlated failure modes with the additional sensitivity analysis is proposed.Finally,a comprehensive computational platform for interfacing the proposed method with the open source FE code Code Aster is developed via a freely available MATLAB software tool(FERUM).This methodology is demonstrated by a case study of an existing gravity dam analysis,in which the dominant failure modes are identified,and the corresponding performance functions are established.Then,the dam failure probability of the structural system is obtained by the proposed method considering the correlation relationship of main failure modes on the basis of the mechanical mechanism analysis with the MC-FE simulations.

Time-domain Finite Element Method for Transient Electric Field and Transient Charge Density on Dielectric Interface

This paper is devoted to solving the transient electric field and transient charge density on the dielectric interface under the electroquasistatic(EQS)field conditions with high accuracy.The proposed method is suitable for both 2-D and 3-D applications.Firstly,the governing equations represented by scalar electric potential are discretized by the nodal finite element method(FEM)in space and the finite difference method in time.Secondly,the transient constrained electric field equation on the boundary(TCEFEB)is derived to calculate the normal component of the transient electric field intensities on the Dirichlet boundary and dielectric interface as well as the transient charge density on the dielectric interface.Finally,a 2-D numerical example is employed to demonstrate the validity of the proposed method.Furthermore,the comparisons of the numerical accuracy of the proposed method in this paper with the existing FEMs for electric field intensity and charge density on the dielectric interface are conducted.The results show that the numerical accuracy of the proposed method for calculating the normal component of transient electric field intensities on the Dirichlet boundary and dielectric interface as well as the transient charge density on the dielectric interface is close to that of nodal electric potential and an order of magnitude higher than those of existing FEMs.

Influence of Shim Layers on Progressive Failure of a Composite Componentin Composite-Aluminum Bolted Joint in Aerospace Structural Assembly

The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)structural solid elements assembled model of a carbon fiber-reinforced polymer(CFRP)-aluminum single-lap joint with a titanium(Ti-6 Al-4 V)fastener and a washer generated with the commercial finite element(FE)software package,ABAQUS/Standard.A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure.The assembled 3 DFE model simulated,as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate,aluminum alloy 7075-T651 substrate,liquid shim(Hysol EA 9394),solid peelable fiberglass shim,a titanium fastener,and a washer.In distinction to previous investigations,the influence of shim layers(liquid shim and solid peelable fiberglass shim)inserted in-between the faying surfaces(CFRP and aluminum alloy substrates)were investigated by both numerical simulations and experimental work.The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1)The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure;liquid shim series(0.3,0.5 and 0.7 mm thicknesses)prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim;(2)The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life;and(3)Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.

Analysis of a New Composite Material for Watercraft Manufacturing

In this paper, we investigate the properties of an alternative material for use in marine engineering, namely a rigid and light sandwich-structured composite made of expanded polystyrene and fiberglass. Not only does this material have an improved section modulus, but it is also inexpensive, light, easy to manipulate, and commercially available in various sizes. Using a computer program based on the finite element method, we calculated the hogging and sagging stresses and strains acting on a prismatic boat model composed of this material, and determined the minimum sizes and maximum permissible stresses to avoid deformation. Finally, we calculated the structural weight of the resulting vessel for comparison with another structure of comparable dimensions constructed from the commonly used core material Divinycell.

Behavior of steel-concrete composite slabs subjected to standard fire

Finite element method is employed to calculate the temperature fields for two kinds of steel concrete composite slabs: composite slab with profiled steel sheeting and LJMB composite slab. The calculated results are in good agreement with those of tests. Fire resistance of the two kinds of composite slabs is calculated by using a numeric method. The results show that: due to heat absorbing of concrete, the performance of composite slabs under fire is better than that of unprotected steel structure, and fire resistance of composite slabs mentioned in this paper is at least 30 min subjected to standard fire. Parameters related to the fire resistance are discussed. It was found that with increasing of concrete strength and thickness of slab, fire resistance increases, and with increasing of steel strength and steel ratio, fire resistance decreases. Also thickness of fire proof is calculated by a numeric method. The results obtained in this paper may be referenced for practical engineering.

THE INFLUENCE OF SHRINKAGE AND MOISTURE DIFFUSION ON IDEALIZED TOOTH STRUCTURE INVOLVING DEBONDING DAMAGE

This study highlights the joint effect of early polymerization shrinkage and long-term moisture diffusion on the behavior of the restoration-tooth structure. The interphase debonding between particle and polymer resin in dental composite is taken into account by introducing the damage variable. The idealized model is designed and constructed for representing the restorationtooth structure, which consists of enamel, dentin, composite and interphase, each considered as homogenous material. The simulation is carried out using the general-purpose finite element software package, ABAQUS incorporated with a user subroutine for definition of damaged material behavior. The influence of Young's moduli of composite and interphase on stress and displacement is discussed. The compensating effect of water sorption on the polymerization shrinkage is examined with and without involving damage evolution. A comparison is made between the influence of hyper-, equi- and hypo-water sorption. Interfacial failure in the specific regions as well as cuspal movement has been predicated. The damage evolving in dental composite reduces the rigidity of composite, thus in turn reducing consequent stress and increasing consequent displacement. The development of stresses at the restoration-tooth interface can have a detrimental effect on the longevity of a restoration.

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

锚杆倒肋式风机基础受力性能的数值模拟

为了解决风机基础施工成本高、施工难度大等问题,提出了一种新型锚杆倒肋式风机基础。利用有限元分析软件ABAQUS对该新型风机基础与传统梁板式风机基础在极端运行荷载工况下的混凝土应力、钢筋应力、基础位移以及基础倾斜率进行数值模拟分析,并进一步讨论二者的混凝土用量、钢筋用量、土方开挖量。结果表明,锚杆的添加以及倒肋的结构设计使锚杆倒肋式风机基础的受力性能、经济性等方面明显优于传统梁板式风机基础,具有较好的应用前景。

正交异性钢-钢纤维混凝土组合桥面板疲劳极限状态研究

为了解正交异性钢-钢纤维混凝土(Steel Fiber Reinforced Concrete,SFRC)组合桥面板的疲劳性能及失效机理,以川南城际铁路临港长江大桥为背景,设计、制作正交异性钢-SFRC组合桥面板足尺模型进行疲劳试验,采用ANSYS软件建立试件有限元模型,研究关键细节的疲劳应力和开裂等情况。基于有限元模型,分析不同设计参数(钢顶板厚度、栓钉布置、SFRC抗拉强度及层厚)下组合桥面板疲劳极限状态的失效模式,并提出了主要控制参数取值建议。结果表明:200万次疲劳加载后足尺模型的实测最大裂缝宽度为0.136 mm,出现在SFRC层上缘,钢结构未开裂,组合桥面板疲劳性能良好;组合桥面板疲劳极限状态主要由SFRC层开裂控制,钢顶板厚度、栓钉布置对组合桥面板疲劳性能的影响较小,SFRC抗拉强度和层厚对组合桥面板疲劳性能影响较大,为主要控制参数;在常规正交异性钢桥面板上铺设薄层(厚度不超过50 mm)SFRC时,SFRC抗拉强度不应小于5 MPa,在常规正交异性钢桥面板上铺设普通SFRC(钢纤维体积含量不高于1%,抗拉强度不高于3 MPa)时,SFRC层厚不宜低于100 mm。

含大石块泥石流冲击作用下框架结构房屋动力响应研究

基于光滑粒子流体动力学-有限元法(smoothed particle hydrodynamics-finite element method,SPH-FEM)耦合的数值方法,分别从结构破坏形态、冲击力时程、关键点位移和速度、系统能量等方面,研究含大石块泥石流冲击作用下框架结构房屋的动力响应和破坏机理。计算结果表明:SPH-FEM耦合方法能够较好地模拟泥石流冲击爬高、绕流扩散、淤积稳定过程。考虑了三种泥石流强度等级,在低、中强度冲击情况下,框架房屋填充墙受到破坏,房屋结构整体保持稳定;在高强度冲击情况下,可以观察到框架房屋的逐步倒塌过程,框架柱损坏模式体现了剪切破坏或塑性铰链失效机制。对于房屋结构而言,泥石流的冲击破坏能力主要来自龙头的冲击力,龙身冲击力相对于龙头降幅约34.2%,大石块的集中作用是结构柱体局部破坏的主要原因。系统能量主要通过泥石流动能转化为结构内能(17.8%)和摩擦耗能(82.8%)。

30 m预应力UHPC箱梁抗弯性能试验及结构优化研究

为了解大尺寸预应力UHPC箱梁的抗弯性能,以预应力UHPC公路桥——河北石磁跨线桥为背景,设计、制作1片长30 m的足尺预应力UHPC箱梁模型进行四点弯曲试验,结合有限元计算结果,分析试验现象及裂缝分布、跨中荷载~位移曲线、受拉区UHPC及筋材应力~应变曲线。在此基础上分别考虑普通钢筋配筋情况、预应力筋数、腹板厚度和底板厚度等参数对预应力UHPC箱梁进行结构优化设计研究。结果表明:箱梁破坏时受压区UHPC未压溃、受拉区钢纤维被拔出,裂缝贯通底板;根据荷载~位移曲线,箱梁受力可分为弹性阶段、裂缝发展阶段、裂缝快速发展阶段和破坏阶段;根据应力~应变曲线,受拉区UHPC在纵筋屈服时仍能贡献抗拉能力;试验现象及力学指标实测值均说明了预应力UHPC箱梁抗弯能力还有很大富裕空间,可进一步优化。完全不配置普通钢筋的预应力UHPC箱梁仍能满足抗弯承载能力极限状态设计要求;底部预应力筋数增多可有效提高受压区UHPC的抗压强度利用率;腹板厚度过薄会造成腹板主拉应力过大问题,不宜薄于8 cm;采用体外预应力的方法可有效减薄底板所需厚度。

增材制造钛基金字塔点阵结构对镁/钛双金属复合材料界面强化的优化

采用超声辅助固-液复合铸造的方法,通过在界面处采用增材制造的钛基金字塔型点阵材料制备镁/钛异种双金属复合材料。采用正交法对点阵结构参数进行优化。结果表明,优化后的点阵结构参数为:杆直径(d)1 mm,杆长与杆直径比(l/d)3,上节点和下节点直径与杆直径比(d_(1)/d,d_(2)/d)均为2.5,其中l/dd是影响接头失效强度的最显著因素,最优点阵结构参数下镁/钛双金属接头的失效强度为77.3 MPa。实验结果和有限元分析表明:随着点阵结构长径比的增加,镁/钛双金属接头的失效强度先增加后减小,当长径比为3时,失效强度达到最大。

川西南公路顺层边坡桩锚组合结构加固分析——以乐西高速ZK9+352~ZK9+526边坡为例

四川盆地周边地形地质条件复杂,公路建设中顺层边坡的工程病害频现。通过工程地质分析和数值计算,基于滑面损伤本构模型,研究顺层边坡支护前后滑面应力、位移和边坡稳定性系数等特征量的变化规律,验证桩锚组合结构加固顺层边坡的适用性;通过施工全周期现场监测,获取边坡深部位移、抗滑桩桩身弯矩和锚索应力的时效特征。结果表明:开挖扰动下顺层边坡具渐进性失稳破坏特征;自坡脚沿滑面向后缘,位移呈指数型平滑递减,剪应力先增大后降低,滑面损伤变量自剪应力峰值位置开始同频衰减;采用桩锚组合结构加固顺层边坡后,滑面位移最大值降低88.62%,最大损伤变量降低84.75%,稳定系数提高25.20%;坡体深部位移、抗滑桩桩身弯矩、锚索应力等监测验证了桩锚组合结构加固的有效作用。

钢与混凝土组合弯梁桥不同施工方法对结构内力的影响

随着经济和交通建设的发展,组合弯梁桥逐渐成为城市桥梁建设中的优选桥型。组合弯梁桥与直桥的受力特点不同,不同的施工方法涉及不同的体系转换问题,因此施工方法的选择会对结构的力学性能产生影响。基于组合弯梁桥的三种施工方法——先简支后连续、先支点后跨中和满堂支架施工,通过有限元软件模拟不同施工方法的施工过程,研究了不同施工方法对组合弯梁桥结构力学性能的影响,针对预制组合弯梁桥提出合理主梁、横梁施工方法,对组合弯梁桥从结构受力角度选择合理的主梁施工方法具有指导意义。

双三角点阵夹芯结构低速冲击下的动态响应与失效机制

采用非线性有限元仿真方法研究双三角点阵夹芯结构抗冲击性能,使用直径为16 mm的半球形冲击器以不同的冲击能量分别对夹芯板的节点和基底位置进行冲击,研究了点阵夹芯板的失效机理和动态响应,以及各个变量对夹芯板的抗冲击性能的影响规律。结果表明:双三角点阵夹芯结构的主要失效形式为面板的基体拉伸破裂;芯子的失效形式受自身结构和受力方式影响,主要为脆性坍塌断裂和塑性变形。载荷-时间曲线表明,冲头能量与冲击位置对夹芯板的损伤失效行为有着显著的影响。相同冲击能量下,与基底冲击相比,夹芯板在节点冲击时的损伤程度及载荷峰值都更优,抗冲击性能更加优异;高冲击能量下,节点冲击的吸能效果更优,但二者载荷变化趋势却越来越相似。

面向某太阳能无人机机翼的梁结构设计制造与验证

太阳能无人机机翼具有典型的低翼载荷、大柔度、大展弦比特征,翼梁作为机翼的主承力结构,其承载能力与重量要求十分严格。如何提高翼梁结构承载效率,达到承载能力与重量的综合平衡,并实现大尺寸复合材料翼梁的整体化设计与制造,是太阳能无人机翼梁结构研究中的关键技术问题。本文首先针对太阳能无人机复合材料翼梁设计提出了一种快速选型及优化设计方法,该方法通过计算梁不同截面的承载能力来确定设计参数,同时考虑了铺层对称性、应变约束及稳定性约束,能够避免在方案阶段建立全机有限元模型并进行反复迭代计算,从而提高了翼梁结构的设计效率。其次,针对大尺寸复合材料圆管梁结构,提出了一种新型的专用成型方法,基于阴模成型实现了翼梁整体化制造并保证了制件成型质量,为类似的大型复合材料结构的制造工艺提供了参考。最后,开展了2 m量级圆管梁静力试验,典型截面的应变结果与设计结果误差不超过10%,验证了此快速优化设计方法的适用性。

桥面板施工顺序对钢-混组合梁桥的受力影响研究及优化

为分析桥面板施工顺序对钢-混组合梁桥成桥受力性能的影响并优化现有的桥面板施工顺序,基于钢-混组合梁桥的受力过程,以交通部颁发的装配化钢-混组合梁通用图为依托,选取3×40 m钢-混组合连续梁桥为对象进行研究。采用桥梁博士软件建立钢-混组合梁桥有限元模型,以桥面板施工工序和结构体系转换时间为变量,分析7种桥面板施工顺序下的结构受力性能。结果表明:钢-混组合截面的受力模式分为一次受力状态和分阶段受力状态,其中采用一次受力状态的施工顺序具有施工方便、成桥整体刚度大、钢梁应力小的优点,但存在支点处桥面板拉应力过大的缺点;分阶段受力状态的施工顺序能有效降低支点处桥面板拉应力,但成桥钢梁应力偏大,结构刚度不足。针对采用上述2种受力模式的施工顺序不能兼顾结构成桥性能(钢梁应力、整体刚度等)较优与控制支点桥面板拉应力的问题,提出优化的混合受力状态的施工顺序,该顺序既保留了一次受力状态较优的成桥性能又显著降低了支点处桥面板拉应力,兼顾了上述2种受力模式的优点,可为钢-混组合梁桥的设计和施工提供参考。