高速移动列车荷载作用下成层地基-轨道耦合系统的动力响应

为研究层状地基-轨道耦合系统在高速移动列车荷载作用下的动力响应问题,建立了求解层状地基-轨道动力相互作用的2.5维间接边界元方法。方法选取垂直轨道方向的截面,在频率-波数域内进行边界单元的离散和求解,然后通过傅里叶变换方法求得时间-空间域内的动力响应。方法具有降维、自动满足辐射条件的优点。文中通过与已有结果的比较验证了方法的正确性,并以均匀半空间地基、基岩上单一土层地基和多层土地基情况为模型进行了数值计算分析。研究表明成层地基与均匀半空间地基情况轨道和地基振动响应存在本质差异;成层地基列车移动临界速度的确定需考虑成层地基中面波的频散和多模态特性。     

基于SBFEM任意角度混合型裂纹断裂能计算的J积分方法研究

混合型裂纹断裂能(GF)是裂纹扩展的判据之一,是裂纹扩展方向分析的基础。以往平面问题断裂能J积分方法的研究只是局限于Ⅰ型或是Ⅱ型,裂纹方向为水平方向。推导了Ⅰ-Ⅱ混合型裂纹任意角度时线弹性材料J积分与应力强度因子(SIF)K之间的关系,提出将比例边界有限元法(SBFEM)用于J积分的求解。在数值计算中,通过用SBFEM、有限元法(FEM)和用推导公式计算J积分的对比,验证推导公式的正确性,同时也说明SBFEM计算J积分是精确的、方便的。根据数值计算的结果,对计算边界与裂纹的距离、计算单元的尺寸以及积分路径等诸因素对精度的影响进行一定分析。     

地基-基础-支护结构-上部结构动力相互作用体系的计算分析研究

利用通用有限元程序ANSYS针对地基-基础-支护结构-上部结构动力相互作用体系进行了计算分析，探讨了支护结构的存在对高层建筑抗震性能的影响，计算中土体的本构模型采用等效线性模型，利用粘-弹性人工边界作为土体的侧向边界，并研究了支护排桩长度和刚度、上部结构刚度以及基础型式等参数对动力相互作用体系的动力特性及地震反应的影响。     

多层地基Terzaghi一维固结解

分析了传统Terzaghi一维固结方程的求解方法的缺点及局限性,提出了结合传递矩阵的分析技术来求解多层地基Terzaghi一维固结问题的方法。运用Laplace变换法求解Terzaghi一维固结方程,得到了单层地基的初参数解及传递矩阵,然后用传递矩阵法推导出多层地基Terzaghi一维固结问题理论解答,并就单层固结与多层固结分析进行了相应的数值计算,得到了简明的解析解。结果表明:提出的计算方法计算工作量小,精度高,适于工程应用。     

弹性地基中三维动力问题的耦合粘性边界

根据波在地基的3个方向(x、y、z轴)都可以进行传播的特点,假定了地基中质点沿3个方向的振动表达式,通过胡克定律和波动理论,推导了弹性地基中三维动力问题的耦合粘性边界的公式。数值计算结果与理论精确解的比较表明:有限区域的有限元与截断边界的耦合粘性边界结合,能够较准确地求解弹性半空间的三维波动问题。本文耦合粘性边界是和频率无关的,可以适用于频域和时域的计算。     

结构-地基开放系统动力相互作用问题的高效解法

应用黏弹性人工边界将结构-地基开放系统转化为近似的封闭系统,利用等效地震波动输入方法将波动散射问题化为波源问题,再采用振型叠加法对近似封闭系统进行分析,由此建立了一种结构-地基开放系统动力反应问题的高效计算方法。采用高效算法分别计算了二维弹性半空间波源问题和地震作用下结构-地基动力相互作用问题算例,并与采用常规的直接时域逐步积分法给出的计算结果进行了对比,由此讨论了高效算法的特点。与常规直接动力分析方法相比,高效算法可以在确保模拟精度的同时,有效降低计算工作量、节省计算时间,并且结构-地基动力相互作用系统的模型越大、自由度越多,高效算法的优越性就越突出,从而为大型结构-地基系统动力相互作用问题数值分析提供了一种高效而精度足够的解法。     

层状地基中盾构隧道开挖非均匀收敛引起临近管道变形预测

采用弹性层状地基模型来考虑地基土体的非均质性,并针对隧道开挖边界引入椭圆化非等量径向土体位移模式;采用基于位移控制技术的边界单元方法来求解土体自由位移场,提出层状地基中盾构隧道开挖非均匀收敛引起临近管道变形影响的位移控制分析方法。结合位移控制有限元数值模拟和既有离心模型试验结果进行对比分析,验证该方法的有效性。算例分析结果表明,土体自由位移场计算对管道纵向变形性能的评估具有较大影响;对于非均质层状地基,如果采用以往的将不同土体参数近似折算成平均值,进而按照弹性均质地基进行求解会带来较大的计算误差。研究成果可为合理制定城市地铁隧道施工对周围环境影响的保护措施提供一定理论依据。     

横观各向同性层状地基上埋置刚性条带基础动力刚度矩阵求解

提出了求解横观各向同性层状地基埋置刚性条带基础动力刚度矩阵的精确算法。算法利用空间变换方法求解得到了横观各向同性层状地基表面或内部任意点的动力位移响应,针对开挖基础求解开挖区域内节点群的动力柔度矩阵,最后利用容积算法求解埋置刚性条带基础动力刚度矩阵。此算法采用精细积分算法求解频率–波数域内层状地基的动力柔度系数,对层状地基的层数和厚度均没有任何限制。此外,算法基于维数较小的矩阵(2×2)运算,数值计算稳定,求解效率较高,数值算例验证了所提算法的精确性及对横观各向同性多层地基的广泛适用性。     

基础型式对均质岩坡—基础—上部结构共同作用影响分析

随我国山地城镇建设中,一些建筑需建于岩质边坡地基之上,建筑结构与岩坡地基之间的共同作用成为一个现实的研究课题。通过有限元数值分析的方法,对岩坡地基与上部结构及基础共同作用受力中基础型式的影响问题进行了计算分析,其中岩坡地基为10m高的直立边坡,上部结构为10层框架结构,基础型式考虑了独立基础、条形基础、筏形基础、桩基础4种情况。分析中上部结构、基础与岩坡地基满足三者的受力平衡和变形协调条件。研究了4种基础型式下考虑相互作用后的岩坡地基强度变形情况及上部框架结构及基础内力和变形情况,得出了一些有益的结论,对相关工程实践具有参考意义。     

地基-结构动力相互作用对基础隔震效果的影响

以多层基础隔震框架为研究对象,利用有限元分析方法,研究地基-结构相互作用效应对基础隔震结构隔震效果的影响。对考虑和不考虑SSI效应时隔震体系的动力特性和地震响应的差异进行对比,并对地基-结构相互作用效应各组成因素对隔震后地震响应的影响规律进行分析。分析结果表明,地基-结构相互作用效应对基础隔震结构存在影响,在工程设计中,隔震结构不应忽略地基-结构相互作用效应的影响。     

冲刷作用下层状横观各向同性土中群桩水平振动响应

采用有限元(FEM)与间接边界元(BEM)耦合法,求解冲刷作用下层状横观各向同性地基中高承台群桩的水平振动响应。采用三节点梁单元对群桩进行离散;然后,基于层状横观地基频域内的解答,以及考虑桩–桩相互作用,建立了地基积分方程;再通过对积分方程离散和数值求解,得到地基的柔度矩阵;根据桩土之间的协调条件,推导出群桩与地基共同作用的方程;通过引入各基桩桩顶的边界条件,获得共同作用方程的解答。最后,通过相关数值算例,验证本文理论及结果的正确性,并讨论冲刷深度对群桩水平振动响应的影响。     

解析层元法求解层状地基非轴对称荷载问题

从弹性层状地基非轴对称问题的解析解出发,推导出Hankel积分变换域内单层地基的解析层元,即对称的精确刚度矩阵;然后根据有限层法原理组合相邻层元得到总刚度矩阵,并结合边界条件,求解总刚度矩阵形成的代数方程,得到层状地基非轴对称问题在Hankel积分变换域内的解答;最后应用Hankel逆变换技术,得到物理域内的解。编制了相应的计算程序,分析了非轴对称荷载作用下多层地基沿径向的地表水平位移性状。     

Improved numerical method for time domain dynamic structure-foundation interaction analysis based on scaled boundary finite element method

Based on the reduced set of base function in scaled boundary finite element method (SBFEM), an improved time domain numerical approach for the dynamic structure-foundation interaction analysis was proposed. With reasonable choice of the number of base functions, the degrees of freedom on the structure-foundation interface were reduced and the associated computation for the calculation of convolution integral was greatly reduced. The results of this proposed approach applied to the calculation of a gravity dam and an arch dam. The acceleration frequency response functions were calculated and the influences affected by different reduced set of base functions as well as full set were compared. It was found that a higher degree of reduced set of base functions resulted in a significant increase of computational efficiency but a little bit of loss in accuracy. When the reduced set was decreased by 60%, the efficiency may be increased to up to five times, while the loss of accuracy of peak value of response will be less than 4%. It may be concluded that the proposed approach is suitable for large-scale structure-foundation interaction analysis.     

Theoretical prediction of ground movements induced by tunnelling in multi-layered soils

The theoretical predictions of ground movements induced by tunnelling are usually based on the assumptions that the ground is homogeneous. Actually, layered formations with different soil properties are usually encountered in situ and effects of soil stratification should be taken into account. This paper presents the displacement controlled boundary integral method aimed specially at investigating the effect of soil stratification on the tunnelling-induced ground movements. The modified elastic layered half-space model is combined with the method to consider the soil non-homogeneous characters, whereas the Kelvin and Mindlin solution based on homogeneous materials are employed previously. The applicability of the proposed method is verified with other available published results as well as the displacement controlled finite element analysis. Surface settlements and lateral displacements induced by tunnelling on the layered soil condition are compared with those based on the homogeneous soil. The results discussed in this paper show that the soil stratification, neglected in previous solutions, have a significant influence on the tunnelling-induced ground movements in multi-layered soils.     

层状地基中群桩的水平振动特性

采用动力Winkler地基模型模拟桩土之间的动力相互作用,并运用传递矩阵法考虑地基土的分层特性,提出了计算层状地基中单桩和群桩动力阻抗函数的一种简化方法。在计算动力相互作用因子时考虑了“被动桩”与周围土体之间的相互作用。最后将相互作用因子和群桩阻抗的本文解与精确解进行了对比,同时与有关现场试验结果作了比较,验证了本文方法的有效性。     

混凝土坝-基岩地震动力相互作用时域有限元分析

混凝土坝地震响应分析是坝工安全评估的关键一步。坝与基岩动力相互作用对混凝土坝地震响应具有重要影响。因此,建立一个可考虑坝与基岩动力相互作用影响的数值分析方法是十分必要的。给出了分析混凝土坝–基岩系统地震响应的时域有限元法。在时域有限元分析中,地震波的输入以及地基辐射阻尼的模拟常常是2个十分重要的课题。基于柱面波动方程提出了能同时实现地震动输入和模拟地基辐射阻尼的方法,这种方法非常简单有效,几个数值算例验证了方法的精度和有效性。最后,对混凝土重力坝地震响应进行了数值分析,结果表明无限地基辐射阻尼的影响是显著的。     

A simplified analysis method for the influence of tunneling on grouped piles

One of key issues of tunneling in urban areas is to assess the likely impact on adjacent piled buildings of tunnel construction. Simple and reliable predictions of tunneling-induced bending and axial stresses in pile foundations are important to the safety of tunneling. In this paper, a simple two-stage analysis method for determining the response of pile groups caused by tunneling was presented. At the first stage, an analytical solution proposed by Loganathan and Poulos [Loganathan, N., Poulos, H.G., 1998. Analytical prediction for tunneling-induced ground movement in clays. J. Geotech. Geoenviron. Eng., ASCE 124 (9), 846–856] is used to estimate the free-field vertical and lateral soil movements induced by tunneling. At the second stage, assuming no slippage at the soil-pile interface, the Winkler model is first adopted for simulating the pile-soil interaction, combined with finite difference method in the case of multi-layered soils. Then, shielding effect is considered for the interaction between two passive piles using a logarithmic attenuation function suggested by Randolph and Wroth [Randolph, M.F., Wroth, C.P., 1979. Analysis of the vertical deformation of pile groups. Géotechnique 29 (4), 423–439] for vertical response and Mindlin’s solution for lateral response. Finally, the response of a passive pile group due to tunneling is obtained by the superposition principle. Solutions obtained by the proposed approach for the analysis of single piles and piled groups subjected to ground movements induced by tunneling are compared with those using the boundary element program GEPAN. Comparisons are also made between the observed behavior of centrifuge model tests as well as field measurements and those computed by the proposed method. It is demonstrated that the present method can in general give a satisfactory prediction of the response of passive piles subjected to tunneling.     

Earthquake analysis of arch and gravity dams including the effects of foundation inhomogeneity

Dam-foundation interaction plays an important role in the design of earthquake-resistant concrete arch and gravity dams. Geological conditions of the dam canyon are usually very complicated; however, in the literature, the damfoundation interaction analysis is often carried out based on the premise of a homogeneous unbounded foundation. In this paper, the effect of foundation inhomogeneity on the seismic response of arch and gravity dams was studied by means of scaled boundary finite element method (SBFEM). In order to satisfy the similarity requirement of SBFEM and simplify the computational effort, a subdomain approach and a conical representation of an unbounded foundation were proposed. The way of partitioning the domain and the selection of open angle and bottom radius of the cone model on the accuracy of the result were examined. Numerical examples show that the proposed approach is rational and efficient. Cases of foundation inhomogeneity with stiffness varying in accordance with an exponential function along the radial direction, and cases of foundation inhomogeneity with stiffness discontinuity and with weak interlayer strata on the earthquake response of concrete arch dams as well as gravity dams were analyzed. It was found that a homogeneous idealization of the unbounded foundation may sometimes greatly underestimate the maximum earthquake stress response of the dam. Therefore, taking into account the effect of foundation inhomogeneity for the earthquake safety assessment of concrete arch and gravity dams has great significance.