Application of semi-analytical finite element method to analyze the bearing capacity of asphalt pavements under moving loads

To facilitate long term infrastructure asset management systems, it is necessary to determine the bearing capacity of pavements. Currently it is common to conduct such measurements in a stationary manner, however the evaluation with stationary loading does not correspond to reality a tendency towards continuous and high speed measurements in recent years can be observed. The computational program SAFEM was developed with the objective of evaluating the dynamic response of asphalt under moving loads and is based on a semi-analytic element method. In this research project SAFEM is compared to commercial finite element software ABAQUS and field measurements to verify the computational accuracy. The computational accuracy of SAFEM was found to be high enough to be viable whilst boasting a computational time far shorter than ABAQUS. Thus, SAFEM appears to be a feasible approach to determine the dynamic response of pavements under dynamic loads and is a useful tool for infrastructure administrations to analyze the pavement bearing capacity.     

Thiopave改性沥青路面力学响应研究

基于Thiopave改性沥青路面良好的高低温稳定性,采用有限元软件对典型半刚性基层沥青面层进行计算,得到不同沥青面层层底力学响应,并对计算结果进行对比研究,得到的主要结论如下：Thiopave沥青路面层底弯拉应力显著大于SBS沥青及基质沥青路面,路表轮隙中心处弯沉值小于SBS沥青及基质沥青路面;随着SEAM掺量的增加,...     

索膜结构非线性有限元找形荷载全过程分析

基于索模结构非线性有限元理论,膜单元采用考虑小应变大位移的平面三角形单元,索单元采用考虑大变形的二节点直线杆单元,引入支座提升方法和杨氏小模量理论,给出了一种索膜结构找形的方法。随后应用通用有限元软件ANSYS,对某高校看台膜结构进行了找形分析,并依照新的膜结构技术规程,进行了荷载分析。找形及荷载分析结果符合规程要求,证实了该方法的有效性和可行性。     

Effect of anisotropic characteristics on the mechanical behavior of asphalt concrete overlay

Asphalt concrete (AC) overlays placed over old asphalt pavement have become an alternative to repairing and reinforcing pavements. The strength contributed by the AC overlay is strongly influenced by the anisotropic properties of the pavement material. This study was conducted to analyze the influence of anisotropy, modulus gradient properties, and the condition of the AC overlay and old pavement contact plane on the mechanical behaviors of AC overlays, as well as to quantify the influence of the degree of anisotropy on the mechanical behaviors of AC overlay by a sensitivity analysis (SA). The mechanical behaviors of the AC overlay were numerically obtained using the three-dimensional finite element method with the aid of ABAQUS, a commercial program. Variations in the AC overlay’s modulus as a function of temperature as well as the contact state between the AC overlay and AC layer were considered. The SA is based on standardized regression coefficients method. Comparing the mechanical behavior in terms of surface deflection, stress, and strain of the anisotropy model against those corresponding to the isotropic model under static loads show that the anisotropic properties had greater effects on the mechanical behavior of the AC overlay. In addition, the maximum shear stress in the AC overlay was the most significant output parameter affected by the degree of anisotropy. Therefore, future research concerning the reinforcement and repair of pavements should consider the anisotropic properties of the pavement materials.     

移动荷载作用下半刚性基层沥青路面动力响应

基于弹性层状体系理论,使用有限元计算软件ANSYS10.0计算了移动荷载作用下半刚性基层沥青路面的动力响应,分析了半刚性基层沥青路面在不同车速车辆动荷载作用下动力响应的变化规律,并得出了相关的结论。     

路面结构应力分析的非线性有限单元法

本文提出了一个考虑材料非线性的多层路面应力分析的有限单元法。材料的非线性参数采用三轴试验确定。非线性分析的方法,除采用一般的变刚度法之外,还采用了改进的BFGS法。实际计算表明,这个方法比变刚度法有更大的适用性。为验证非线性分析结果的正确性,我们将分析结果与利用足尺试验路面的实测位移值进行了比较,并同时与线性弹性理沦解作了对比。     

Co-variance matrix adaptation evolution strategy for pavement backcalculation

The falling weight deflectometer (FWD) is the foremost and widely accepted tool for characterizing the deflection basins of pavements in a non-destructive manner. The FWD pavement deflection data are used to determine the in situ mechanical properties (elastic moduli) of the pavement layers through inverse analysis, a process commonly referred to as backcalculation (B/C). Several B/C methodologies have been proposed over the years, each with individual strengths and weaknesses. Hybrid methods (combining two methods or more) are recently proposed for overcoming problems posed by stand-alone methods, while extracting and compounding the benefits that are individually offered. This paper proposes a novel hybrid strategy that integrates co-variance matrix Adaptation (CMA) evolution strategy, Finite element (FE) modeling with neural networks (NN) non-linear mapping for backcalculation of non-linear, stress dependent pavement layer moduli. The resulting strategy, referred as CMANIA (CMA with neural networks for inverse analysis) is applied for asphalt pavement moduli backcalculation and is compared with a conventional B/C approach. Results demonstrate the superiority of this method in terms of higher accuracy, achieving nearer to global solutions, better computational speed, and robustness in predicting the pavement layer moduli over the conventional methods.     

沥青路面车辙变形的三维粘弹性动力有限元分析

基于车辆对路面的动力作用,建立路面不平整度引起的汽车动荷载简化模型,通过室内高温蠕变试验获得不同沥青面层材料的粘弹性模型,以弹粘塑性理论、动力学基本理论和有限元方法作为理论基础,采用动力有限元分析方法对沥青路面车辙进行了计算与预估,并分析了车辆轮胎压力、车速、作用时间、路面温度及轴载作用次数对沥青路面车辙深度的影响。通过河北邯郸~长治高速公路实体工程验证表明,采用基于动力有限元方法的车辙理论计算值与实测值误差仅为8%~9.5%,具有较高精度,研究成果为进一步完善车辙计算方法及工程应用提供理论依据。     

Instantaneous pavement condition evaluation using non-destructive neuro-evolutionary approach

In this paper, a hybrid neural network (NN)-genetic algorithm (GA) based non-destructive pavement auscultation method for instantaneous airfield infrastructure condition assessment is discussed. NNs are employed for finite element aided forward prediction of pavement surface deflections resulting from non-destructive test impulse loading and the GAs are used for global optimisation of the pavement structural parameters by matching the NN predicted deflections with the measured pavement response. This hybrid approach takes advantage of the non-linear estimation capability provided by neural networks trained using finite element (FE) solutions in modelling the stress-dependent behaviour of unbound pavement geo-materials while improving the robustness to measurement uncertainty through the application of genetic algorithms. The performance of the developed hybrid pavement auscultation technique is evaluated through extensive field studies conducted at a state-of-the-art full-scale airfield pavement test facility. The results show that this approach is promising for real-time condition evaluation of airfield pavement infrastructure systems.     

子模型法在大跨径斜拉桥桥面结构分析中的应用

在对大跨径混凝土桥梁整体结构有限元分析的基础上 ,应用子模型法对大跨径混凝土斜拉桥梁桥面板局部进行了有限元结构受力分析 ,分析轴向不同位置桥面板结构的变形特点及应变状态 ,并与所建立的普通路面模型基层弯沉进行对比分析 ,从桥面板弯沉及应变角度分析大跨径混凝土箱梁桥面铺装对沥青混凝土的性能要求 ,并总结了大跨径桥梁桥面铺装的力学分析方法 ,为大跨径混凝土桥梁沥青桥面铺装的设计提供参考依据。     

水泥混凝土路面板模量反算的一种新方法--惰性弯沉法

路面结构层模量反算方法有多种,但都因反算解的唯一性问题而使反算结果误差太大.为了提高反算精度,本文提出了"惰性点"的概念.发现在混凝土路面的弯沉盆上,存在一个其弯沉值几乎不随面层模量变化而改变的点,该点即被定义为惰性点.该点的发现,为唯一确定路面结构层模量提供了理论基础.     

沥青路面动态黏弹反演研究

对沥青路面结构进行动态黏弹反演, 正向分析采用谱单元法,采用典型路面结构分析验证了谱单元法动态黏弹分析的正确性;采用实测和计算得到的路表弯沉整体时程曲线的均方误差作为反演误差控制方程,以序列二次规划算法作为优化算法,对路面结构层力学参数进行优化。对半刚性基层和复合式基层两种沥青路面结构动态进行黏弹反演,结果表明：利用谱单元法对沥青路面进行动态黏弹响应分析,可以极大地提高计算效率,动态反演可充分利用弯沉时程曲线的数据信息,反演得到的动态模量、相位角数主曲线组成完整的黏弹力学参数,可以更全面地描述沥青层的力学特性以及荷载作用频率和温度场的影响。动态黏弹反演方法可以弥补传统反演结果无法得到的力学参数主曲线的缺陷,为沥青路面分析及质量评定提供了有效的方法。     

ATPB抑制沥青路面反射裂缝的研究

通过有限元法计算了半刚性基层沥青路面和铺设ATPB沥青路面结构的应力强度因子,并利用Paris公式预估了这两种路面结构的疲劳寿命,结果表明,ATPB可有效抑制半刚性基层沥青路面的反射裂缝。     

Large deflection analysis of flexible plates by the meshless finite point method

The classical finite difference technique and methods based on series expansions can only be adopted for solving plates with simple geometry, loading and boundary conditions. In contrast, the finite element method has been widely used for general analysis of bending and flexible plates (coupled bending and in-plane effects). Lack of stress continuity and relatively expensive mesh generation and remeshing schemes have led to the emergence of meshless methods, such as the finite point method (FPM). FPM is a strong form solution which combines the moving least square interpolation technique on a domain of irregularly distributed points with a point collocation scheme to derive system governing equations. In this study, coupled nonlinear partial differential equations of fourth order are solved to analyse large deflection behaviour of plates subjected to lateral and in-plane loadings. Several plate problems are solved and compared with analytical solution and other available numerical results to assess the performance of the proposed approach.     

Performance of geosynthetic-reinforced flexible pavements in full-scale field trials

The paper presents the results of a series of full-scale trials carried out in Thailand examining the performance of geosynthetics as reinforcement for flexible pavements. The geosynthetics were embedded at different pavement depths and the structural response was monitored across four test sections by means of strain gauges, pressure sensors, deflection points and deflection plates. The results show that all reinforcement configurations helped reduce the vertical static stresses developed at the base of the pavement by up to 66% and by up to 72% for dynamic stresses. The performance enhancement expected to prolong the lifespan of the base layers. The reinforcement layers closer to the base experienced the highest lateral strains of up to 0.13%, providing evidence that geosynthetics can also effectively reduce lateral spreading. All reinforcement configurations helped enhance rut resistance with maximum traffic benefit ratio (TBR) of 13.70, effectiveness ratio (EF) of 12.70 and minimum rutting reduction ratio (RRR) of 0.74. The best configuration included a geotextile within the asphalt concrete layer and a geogrid under the base layer. Non-linear finite element analyses of the test sections predicted very well the strains and stresses in the pavement. The study provides a benchmark for future studies in this field and concludes that geosynthetics can help increase maintenance periods and extend the lifetime of flexible pavements.     

Airfield pavement deterioration assessment using stress-dependent neural network models

In this study, an artificial neural network (ANN)-based approach was employed to backcalculate the asphalt concrete and non-linear stress-dependent subgrade moduli from non-destructive test (NDT) data acquired at the Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) during full-scale traffic testing. The ANN models were trained with results from an axisymmetric finite element pavement structural model. Using the ANN-predicted moduli based on the NDT test results, the relative severity effects of simulated Boeing 777 (B777) and Boeing 747 (B747) aircraft gear trafficking on the structural deterioration of NAPTF flexible pavement test sections were characterized. The results indicate the potential of using lower force amplitude NDT test data for routine airport pavement structural evaluation, as long as they generate sufficient deflections for reliable data acquisition. Therefore, NDT tests that employ force amplitudes at prototypical aircraft loading may not be necessary to evaluate airport pavements.     

固化剂水泥稳定土基层沥青路面结构数值分析

采用路邦固化剂水泥稳定土作为某高速公路路面结构的基层材料,应用三维有限元软件计算了该路面结构在四种典型车型额定荷载、欠载、超载等荷载工况作用下的力学响应,重点分析了路面弯沉和水平、竖向应力等数据。结果表明:采用路邦固化剂水泥稳定土作为基层材料的沥青路面结构具有较强的路面承受能力,采用固化剂作基层稳定材料是可行的。     

Analysis of fatigue crack growth behavior in asphalt concrete material in wearing course

Fatigue crack is a main form of structural damage in flexible pavements. Under the action of repeated vehicular loading, deterioration of the asphalt concrete materials in pavements, caused by the accumulation and growth of micro and macro cracks, gradually takes place. The indirect tensile fatigue testing (ITFT) was carried out on three types of asphalt concrete materials comprising a high stiffness Gilsonite modified wearing course (GM-ACWC), stone mastic asphalt (SMA) and conventional asphalt concrete wearing course (ACWC) to establish fatigue damage model and failure criteria. Fatigue damage model, based on continuum damage approach, to describe the formation of micro-cracks and crack propagation was developed for the wearing course materials. With the fatigue damage model, finite element analysis was carried out to study the crack resisting performance of the three wearing course materials in a flexible pavement structure.     

Effect of principal stress axis rotation on cyclic plastic deformation characteristics of unsaturated base course material

It is generally observed that the stress state induced through traffic loads inside the substructure of pavements cannot be exactly reproduced in laboratory element tests. Moreover, there are not sufficient studies that examine the behavior of granular material under unsaturated conditions, although such conditions are very prevalent in pavement structures. In this research, an attempt is made to determine the cyclic plastic deformation characteristics of unsaturated granular base course material, and to examine the effect of the rotation of the principal stress axis (experienced by pavement elements under traffic loads) on the mechanical behavior of unsaturated granular base course material by applying various loading methods. A series of laboratory element tests using a multi-ring shear apparatus, which can take into account the rotation of the principal stress axis, were carried out on granular base course material under different moisture contents. The experimental results show that the moisture content has an obvious effect on both the shear behavior and the cyclic plastic deformation of granular base course material. However, the moisture content for the maximum deformation of granular base course material varies according to the loading method. It is also explained that cyclic plastic deformation considerably increases due to the rotation of the principal stress axis under repeated axial and shear loading tests. Therefore, the principal stress axis rotation has a significant influence on the cyclic plastic deformation of unsaturated granular base course material.     

贝克曼梁弯沉车弯沉测定的影响因素分析

贝克曼粱弯沉仪测定路面弯沉一直以来是我国公路工程路面弯沉检测和竣工、交工验收的标准方法,提高其测量精度对路面弯沉评价的公正性和合理性具有重要意义.弯沉车荷载以及后轴轮胎的类型、胎面花纹、层级、轮胎压力和轮胎尺寸对贝克曼梁方法测定路面弯沉均有影响,在轮胎因素中轮胎的宽度对弯沉测定结果影响最大.现场测试规程中对弯沉车的荷载等进行了规定,但是对测定车轮胎要求相对不足,分析认为需要对弯沉车的后轴轮胎也应提出要求.针对目前工程上弯沉车选择的随意性,提出了弯沉车选择的建议.