Multi-domain equivalent method for prediction of elastic modulus of complex fractured rock mass

Reliable estimation of deformation and failure behaviors of fractured rock mass is important for practical engineering design.This study proposes a multi-domain equivalent method for fracture network to estimate the deformation properties of complex fractured rock mass.It comprehends both the advantages of the discrete fracture network model and the equivalent continuum model to capture the features of discontinuities explicitly while reducing computational intensity.The complex fracture network is stochastically split into a number of subfracture networks according to the domain,length or angle.An analytical solution is derived to infer theoretically the relationship between the elastic moduli of the original complex fractured rock mass and the split subfractured rock masses by introducing a correction term based on the deformation superposition principle.Numerical simulations are conducted to determine the elastic moduli of split subfractured rock masses using universal distinct element code(UDEC),while the elastic modulus of the original model is estimated based on the currently proposed analytical relationship.The results show that the estimation accuracy with the current domainbased splitting model is far superior compared to those with the other two splitting models.Thus,the estimation method of elastic modulus of complex fractured rock mass based on domain splitting mode of fracture network is identified as the multi-domain equivalent method proposed in this paper.The reliability of this method is evaluated,and its high computational efficiency is demonstrated through exemplification with regard to different geometric configurations for stochastically artificial discrete fracture network.The proposed multi-domain equivalent method constructs the theoretical framework except for the regression analysis hypothesis compared to the density-reduced model equivalent method.

Method to analyze wrinkled membranes with zero shear modulus and equivalent stiffness

To solve the problems of divergence,low accuracy and project application of membrane wrinkling analysis,an analysis method of zero shear modulus and equivalent stiffness was proposed.This method is an improvement to the previous method (Method I) of local coordinate transposition and stiffness equivalence.The new method is derived and the feasibility is theoretically proved.A small-scale membrane structure is analyzed by the two methods,and the results show that the computational efficiency of the new method (Method II) is approximately 23 times that of Method I.When Method II is applied to a large-scale membrane stadium structure,it is found that this new method can quickly make the second principal stress of one way wrinkled elements zero,and make the two principal stresses of two-way wrinkled elements zero as well.It could attain the correct load responses right after the appearance of wrinkled elements,which indicates that Method II can be applied to wrinkling analysis of large-scale membrane structures.

Macro and meso analysis of jointed rock mass triaxial compression test by using equivalent rock mass(ERM) technique

Methods that can efficiently model the effects of rock joints on rock mass behavior can be beneficial in rock engineering. The suitability of equivalent rock mass(ERM) technique based upon particle methods is investigated. The ERM methodology is first validated by comparing calculated and experimental data of lab triaxial compression test on a set of cylindrical rock mass samples, each containing a single joint oriented in various dip angles. The simulated results are then used to study the stress-strain nonlinearity and failure mechanism as a function of the joint dip angle and confining stress. The anisotropy and size effects are also investigated by using multi-scale cubic ERM models subjected to triaxial compression test. The deformation and failure behavior are found to be influenced by joint degradation, the micro-crack formation in the intact rock, the interaction between two joints, and the interactions of micro-cracks and joints.

Deformation-based longitudinal equivalent stiffness beam model for shield tunnel and its application in seismic deformation method

In the longitudinal seismic deformation method for shield tunnels,one of the most commonly used is the longitudinal equivalent stiffness beam model(LES)for simulating the mechanical behavior of the lining.In this model,axial deformation and bending deformation are independent,so the equivalent stiffness is a constant value.However,the actual situation is that axial deformation and bending deformation occur simultaneously,which is not considered in LES.At present,we are not clear about the effect on the calculation results when axial deformation and bending deformation occur simultaneously.Therefore,in this paper,we improve the traditional LES by taking the relative deformation as a load and considering the coordinated deformation of axial and bending degrees of freedom.This improved model is called DNLES,and its neutral axis equations are an explicit expression.Then,we propose an iterative algorithm to solve the calculation model of the DNLES-based longitudinal seismic deformation method.Through a calculation example,we find that the internal forces based on LES are notably underestimated than those of DNLES in the compression bending zone,while are overestimated in the tension bending zone.When considering the combined effect,the maximum bending moment reached 13.7 times that of the LES model,and the axial pressure and tension were about 1.14 and 0.96 times,respectively.Further analysis reveals the coordinated deformation process in the axial and bending directions of the shield tunnel,which leads to a consequent change in equivalent stiffness.This explains why,in the longitudinal seismic deformation method,the traditional LES may result in unreasonable calculation results.

AN EQUIVALENT CONTINUUM METHOD OF LATTICE STRUCTURES

An equivalent continuum method is developed to analyze the effective stiffness of three-dimensional stretching dominated lattice materials. The strength and three-dimensional plastic yield surfaces are calculated for the equivalent continuum. A yielding model is formulated and compared with the results of other models. The bedding-in effect is considered to include the compliance of the lattice joints. The predicted stiffness and strength are in good agreement with the experimental data, validating the present model in the prediction of the mechanical properties of stretching dominated lattice structures.

Testing method of rock structural plane using digital drilling

The rock mass consists of rock blocks and structural planes,which can reduce its integrity and strength.Therefore,accurately obtaining the characteristics of the rock mass structural plane is a prerequisite for evaluating stability and designing supports in underground engineering.Currently,there are no effective testing methods for the characteristic parameters of the rock mass structural plane in underground engineering.The paper presents the digital drilling technology as a new testing method of rock mass structural planes.Flawed rock specimens with cracks of varying widths and angles were used to simulate the rock mass structural planes,and the multifunctional rock mass digital drilling test system was employed to carry out the digital drilling tests.The analysis focuses on the variation laws of drilling parameters,such as drilling pressure and drilling torque,affected by the characteristics of prefabricated cracks,and clarifies the degradation mechanism of rock equivalent compressive strength.Additionally,an identification model for the characteristic parameters of rock mass structural planes during drilling is established.The test results indicate that the average difference of the characteristics of prefabricated cracks identified by the equivalent compressive strength is 2.45°and 0.82 mm,respectively.The identification model while drilling is verified to be correct due to the high identification accuracy.Based on this,a method for testing the characteristic parameters of the surrounding rock structural plane while drilling is proposed.The research offers a theoretical and methodological foundation for precise in situ identification of structural planes of the surrounding rock in underground engineering.

Seepage simulation of high concrete-faced rockfill dams based on generalized equivalent continuum model

This research focused on the three-dimensional(3 D) seepage field simulation of a high concrete-faced rockfill dam(CFRD) under complex hydraulic conditions. A generalized equivalent continuum model of fractured rock mass was used for equivalent continuous seepage field analysis based on the improved node virtual flow method. Using a high CFRD as an example, the generalized equivalent continuum range was determined, and a finite element model was established based on the terrain and geological conditions, as well as structural face characteristics of the dam area. The equivalent seepage coefficients of different material zones or positions in the dam foundation were calculated with the Snow model or inverse analysis. Then, the 3 D seepage field in the dam area was calculated under the normal water storage conditions, and the corresponding water head distribution, seepage flow, seepage gradient, and seepage characteristics in the dam area were analyzed. The results show that the generalized equivalent continuum model can effectively simulate overall seepage patterns of the CFRD under complex hydraulic conditions and provide a reference for seepage analysis of similar CFRDs.

Inner damage identification and residual strength assessment of a 3D printed tunnel with marble-like cementitious materials using piezoelectric transducers

Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious materials was first fabricated using the three-dimensional(3D)printing technique and then loaded to simulate its failure mode in the laboratory.Lead zirconate titanate piezoelectric(PZT)transducers were embedded in the surrounding rock around the tunnel in the process of 3D printing.A 3D monitoring network was formed to locate damage areas and evaluate damage extent during loading.Results show that as the load increased,main cracks firstly appeared above the tunnel roof and below the floor,and then they coalesced into the tunnel boundary.Finally,the tunnel model was broken into several parts.The resonant frequency and the peak of the conductance signature firstly shifted rightwards with loading due to the sealing of microcracks,and then shifted backwards after new cracks appeared.An overall increase in the root-mean-square deviation(RMSD)calculated from conductance signatures of all the PZT transducers was observed as the load(damage)increased.Damage-dependent equivalent stiffness parameters(ESPs)were calculated from the real and imaginary signatures of each PZT at different damage states.Satisfactory agreement between equivalent and experimental ESP values was achieved.Also,the relationship between the change of the ESP and the residual strength was obtained.The method paves the way for damage identification and residual strength estimation of other 3D printed structures in civil engineering.

发动机燃油泵附件的管路动力学等效设计及实现

燃油泵附件的管路空间构型复杂,在振动环境试验中直接模拟难以实现。为满足试验要求,采用系统等效缩减/扩展过程(SEREP)方法对管路进行动力学等效设计,选取管路上特定结点为主自由度,并将原管路模型缩减至主自由度模型上,得到缩减质量和刚度矩阵;对子振型矩阵采用SVD分解,使得缩减质量和刚度矩阵进一步简化,得到低阶管路模型的新缩减质量和刚度矩阵参数;提出“质量球—梁弹簧”结构模型,分别用“质量球”和“梁弹簧”来映射缩减的质量和刚度矩阵,进而确定等效设计加工参数;通过实例验证等效设计方法的可行性。结果表明:等效管路与原管路的第一阶频率误差大多在10%以内,满足工程应用要求。

基于等效刚度法优化的风力机叶片刚度计算

风力机叶片刚度由于非线性且截面变化程度大的特点,针对叶片建模初期刚度的评估问题通常采用刚度展项分布图体现叶片刚度,存在评估叶片刚度的参考参数不够直接、宏观的问题。基于变刚度梁挠度计算的等效刚度法,将叶片等效成变截面悬臂梁,根据叶片特征合理选取边界条件,以叶片建模的截面数据特点为基础,优化原始等效刚度法的计算方式,使该方法更加贴合叶片模型,从而适用于叶片,达到方法优化的目的。利用ANSYS有限元软件进行叶片的预应力模拟实验,得出叶片的挠度模拟数值,以该模拟计算的挠度值为参考,验证优化后方法的有效性。结果表明:优化后的等效刚度法得到的刚度值,在低均布载荷值22.5 Pa下理论计算的挠度值与试验挠度值的误差达到9.68%,减小原始方法计算的误差贴近叶片模型,可用于叶片刚度估算,为叶片的刚度计算提供新方法。

圆形深基坑环梁径向等效刚度系数研究

弹性支点法是我国现行规范推荐的深基坑支护结构计算方法。在弹性支点法基础上,针对圆形深基坑环梁作为支护桩弹性支点的刚度系数提出明确算法,达到更合理地计算支护结构内力和位移的目的。通过弹塑性力学厚壁圆筒理论,得到环梁径向位移公式,进而推导出环梁径向等效刚度系数和环梁换算截面的等效材料抗力计算公式。将径向等效刚度系数和等效材料抗力作为弹性支点的参数,计算支护结构内力和位移。采用此方法计算沈阳某圆形深基坑支护结构的内力和位移。结果表明:采用等效刚度系数的二维弹性支点法计算得到的支护结构的内力与位移,与现场监测数据比较吻合,比三维有限元计算结果更安全,比常规刚度系数计算结果更经济合理。

Janus-Helmholtz换能器的振动模态谐振频率理论分析研究

Janus-Helmholtz换能器利用驱动振子纵向谐振与Helmholtz谐振腔的液腔谐振耦合,具有大功率、宽带声发射特性.传统观点认为导纳曲线中低频谐振峰对应液腔谐振频率,而高频谐振峰对应纵振动谐振频率,然而大量的实验研究发现该结论存疑.本文结合一只Janus-Helmholtz换能器实验样机的实验结果,运用等效电路法结合有限元法分析并求解了驱动振子纵向模态的谐振频率,使用有限元法分析并求解了Helmholtz谐振腔的液腔谐振频率.研究结果表明,与传统观点相反,导纳曲线中第1个谐振峰为驱动振子的纵向谐振,第2个谐振峰为Helmholtz谐振腔的液腔谐振;Janus换能器4个大尺寸辐射面带来的可观辐射质量是造成纵向振动谐振频率在水中大幅度下降的原因;Janus-Helmholtz换能器中存在两个等体积的Helmholtz共振腔而非传统认为的仅存在一个共振腔.这些结论对于正确认识Janus-Helmholtz换能器的结构及性能特性起到了正本清源的作用,也为优化创新该换能器的结构、改善换能器的声发射特性提供了技术支撑.

基于化学激活荧光素酶表达基因法和标准方法评估动物源性固态食品中17种二噁英类化合物毒性当量的相关性比较

为使化学激活荧光素酶表达基因法(CALUX)在动物源性固态食品中二噁英类化合物毒性当量筛查中具有更好的适用性,使其能够与标准方法高分辨气相色谱-高分辨质谱法(HRGC-HRGC)的评估结果相互转换,分别基于CALUX和HRGC-HRGC评估了肉类、海鲜类和配方乳粉这3类典型动物源性固态食品中7种2,3,7,8-取代的多氯代二苯并二噁英(PCDDs)和10种2,3,7,8-取代的多氯代二苯并呋喃(PCDFs)的毒性当量,分析两种方法测定结果的相关性,并确定换算关系和适宜样品类型。结果表明:基于HRGC-HRMS得到的样品中17种目标物的毒性当量(TEQ)下限值为0.001~0.106 pg·g^(-1),TEQ上限值为0.004~0.242 pg·g^(-1),远低于欧盟法规EC 1881/2006规定的限量值(3.5 pg·g^(-1));基于CALUX得到的肉类样品中17种目标物的毒性当量(BEQ)值为0.74~1.30 pg·g^(-1),海鲜类样品中17种目标物的BEQ值为0.31~0.63 pg·g^(-1),配方乳粉样品中17种目标物的BEQ值为0.043~0.074 pg·g^(-1);肉类和配方乳粉样品的BEQ值与TEQ值的相关性较差,而海鲜类样品的BEQ值与TEQ上限值相关性较好。

高层结构基于稳定极限状态的整体抗震可靠度分析及应用

对于高层建筑结构,重力二阶效应对结构稳定性的不利影响显著。建立了基于等效刚重比退化率的整体稳定能力极限状态方程,提出了基于随机响应面法的整体抗震可靠度分析方法。以框架-核心筒结构为例进行整体稳定能力极限状态抗震可靠度分析,并与当前设计规范相适应的变形能力抗震可靠度分析结果进行对比。结果表明:整体稳定能力抗震可靠度指标可以有效地评估结构的抗震可靠性,与变形能力抗震可靠度指标具有较好的一致性。考虑材料强度和地震作用随机性,提出的方法可应用于高层建筑设计结构方案比选、既有高层结构的可靠性鉴定分析以及对加固方案有效性的评估。

HPGPC-RID法测定右旋糖酐20分子量及其分布的可行性研究

目的 建立高效凝胶渗透色谱-示差折光检测器(HPGPC-RID)测定右旋糖酐20分子量及其分布的方法,并对该方法进行可行性研究。方法 对新建方法进行专属性、准确度、重复性及耐用性验证,并评价新建方法与《中国药典》2020版(二部)收录方法检测结果的等效性。结果 新建方法专属性、准确度、重复性、耐用性良好,且与药典方法等效,可用于右旋糖酐20分子量及其分布的测定。与此同时,新建方法能避免药典方法中硫酸钠(Na_(2)SO_(4))峰对右旋糖酐20峰的干扰。结论 相比于药典方法,新建方法对右旋糖酐20分子量及其分布测定具有更好的适用性。

A force control high-order single-step-β method (HSM) for substructure pseudo-dynamic testing

This paper proposes a new technique which introduces the high-order single-step-β method(HSM)into the experimental study on the substructure pseudo-dynamic testing(SPDT).The technique is based on the proposed concept of equivalent shear stiffness which can meet the requirement of the HSM algorithm.A study is done to theoretically validate the technique by the numerical analysis of two-storey shear building structure,in comparison of the proposed substructure pseudo-dynamic testing algorithm with the central difference method(CDM).Then,a full-scale SPDT model,the three-storey frame-supported reinforced concrete short-limb masonry shear wall structure,is designed and tested to simulate the seismic response of the corresponding six-storey structure and verify the proposed force control HSM technique.Meanwhile,the techniques of both stiffness correction and force control are suggested to control algorithmic error,control error and measurement error.The results indicate that the force control HSM can be used in the full-scale multi-degree-of-freedom(MDOF)substructure pseudo-dynamic testing before descent segment of structure restoring force properties.

非对称刚构-连续组合体系梁桥受力特性研究

为给非对称刚构-连续组合体系梁桥的设计与应用提供理论基础,以渝湘复线高速长头河特大桥主桥为背景,引入非对称比例系数研究不对称程度对非对称刚构-连续组合梁桥力学特性的影响,提出采用在连续墩处设置组合阻尼支承体系改善该体系梁桥连续墩处主梁在横向风荷载作用下受力不利的问题。保持该桥主跨跨径180 m不变,调整刚构侧和连续侧单侧主梁长度在主跨范围内的占比,采用MIDAS Civil软件建立10个不同非对称比例系数的刚构-连续组合体系梁桥有限元模型,分析不同模型在恒载、汽车荷载、温度荷载、收缩徐变等作用下的主梁内力和支座反力,以及组合阻尼支座不同水平等效刚度对主梁受力的影响。结果表明:非对称刚构-连续组合体系梁桥不对称程度对结构内力影响最大的荷载为收缩徐变;非对称比例系数m>0.2时需适当加大连续墩处主梁梁高、延长小边跨长度以减小非对称性的不利影响,m最大限值建议采用0.3;在连续墩处设置组合阻尼支承体系,利用阻尼位移使主梁协调变形,能有效降低横向风荷载引起的主梁弯矩和应力幅。

基于轴压刚度等效的“柱中柱”(CIC)系统等代设计方法研究

为克服传统钢管混凝土柱作为竖向承载构件功能单一的不足,使其兼具结构减振(震)控制的作用,文章基于TMD系统振动控制的概念,对钢管混凝土柱进行改进,提出一种具有“承载-减振(震)”双功能的“柱中柱”系统,以进一步增强结构的抗震性能。文章主要介绍了“柱中柱”系统的组成和控制机理,并基于钢管混凝土统一理论,采用叠加原理推导“柱中柱”系统的截面轴压组合刚度和轴压极限承载力的理论公式,最终建立该系统基于轴压刚度等效的等代设计方法;同时,根据等代设计流程,选取典型的钢管混凝土构件进行算例分析,以检验等代设计方法的准确性。结果表明,采用叠加原理便于建立“柱中柱”系统的截面轴压组合刚度和轴压极限承载力理论公式,提出的等代设计方法具有良好的准确性,可为今后的工程设计与分析提供参考。

三角剪切型压电加速度传感器固有频率计算及优化

针对应用于高温环境的剪切型压电加速度传感器,建立了固有频率的计算模型,研究了刚度和几何结构参数对加速度传感器固有频率的影响。研究结果表明:该模型计算结果和有限元仿真结果基本一致。三角支柱的法向刚度对传感器整体刚度的影响最大。中心支柱的几何尺寸对固有频率影响最大,质量块的长宽以及压电片高度对固有频率也有较大影响。优化后的传感器实物样品,固有频率较优化前实现了约20%的提升,符合理论变化趋势。该计算模型和计算结果有助于优化三角剪切型压电加速度传感器。

基于GSI的深部节理化岩体工作面稳定性分析

针对节理岩体力学参数选取困难问题,基于地质强度指标GSI,结合损伤力学原理和广义Hoek-Brown准则构建考虑节理强度的节理岩体力学模型,对深部节理化岩体工作面进行了稳定性分析。结果表明:所给出的节理等效系数能较好地描述节理间距与GSI之间的关系,节理岩体的破碎程度对工作面的稳定性产生了影响,随着岩体破碎程度的提高,工作面易发生顶板冒落、煤壁片帮等现象;当岩体较为破碎时,顶板失稳主要由节理的发育、贯通引起;岩体的完整性较好时,顶板的稳定性受采空区悬臂段顶板的影响较大。