Stress-Strain Relationship and Failure Criterion for Concrete after Freezing and Thawing Cycles

The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out. Based on the damage mechanics theory, the dsmage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained. Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies tile rationality of tile damage-based one-dimensional stress-strain relationship proposed.

Stress-strain relationship of unsaturated cohesive soil

A moisture-content based constitutive model was proposed based on the hyperbolic model as an attempt to move towards the implementation of unsaturated soil mechanics into routine geotechnical engineering practice. The stress-strain behavior of in-situ soil at a depth of 5 m was investigated by conducting undrained triaxial compression tests using the remolded soil samples. The test results show that the stress-strain relationship of unsaturated cohesive soil is still hyperbolic. The values of parameters a and b given in the model decrease with increasing the confining pressure for soil samples with the same moisture content and increase with increasing the moisture content for soil samples under the same confining pressure. The relationships between parameters a, b and moisture content were studied for confining pressures of 100, 150, 200 and 250 kPa. The comparison between the measured and predicted stress-strain curves for an additional group of soil samples, having a moisture content of 25.4%, shows that the proposed moisture content-dependent hyperbolic model provides a good prediction of stress-strain behavior of unsaturated cohesive soil.

Nonlinear model characterizing stress-strain relationship and permeability change of contact compression fracture at closing stage

Understanding the stress-strain relationship and permeability change for contact compression fracture at closing stage has been a hot issue for a long time.Previous investigations of this topic were mainly focused on experimental tests;however,theoretical approaches were rarely reported.Based on this,this paper focuses on the contact fracture at closing stage when rock is uniaxially loaded,and then a theoretical model is proposed.Based on the change of fracture elasticity modulus,it shows that as crack apertures are gradually reduced in the loading process,the permeability of rock sample will decrease progressively.This scenario shows that theoretical computation matches well with the experimental results.Finally,the effects of ratio of sample size to fracture aperture(n).pore pressure(P),and initial aperture(b) on stress-strain relationship and permeability change for contact compression fracture at closing stage are analyzed.

Effect of Engineering Character on Stress-Strain Relationship in Post-Peak Area

Constitutive experiments are the base of all rock mechanics works. The effect of engineering character on constitutive law is a new problem of rock mechanics. The results of series specimens based on the uniaxial and plane strain compression experiments were presented and discussed. It is found that engineering or experiment character has obvious effects on stress-strain relationship and especially on mechanic parameters in post-peak area. And the law of size effect of softening materials was also discussed.

Mechanical Properties and Stress Strain Relationship Models for Bamboo Scrimber

In order to investigate the basic mechanical properties and stress strain relationship model for bamboo scrimber manufactured based on a new technique,a large quantities of experiments have been carried out.Based on the analysis of the test results,the following conclusions can be drawn.Two main typical failure modes were classified for bamboo scrimber specimens both under tension parallel to grain and tension perpendicular to grain.Brittle failure happened for all tensile tests.The slope values for the elastic stages have bigger discreteness compared with those for the specimens under tensile parallel to grain.The failure modes for bamboo scrimber specimens under compression parallel to grain could be divided into four.Only one main failure mode happened both for the bending specimens and the shear specimens.With the COV values of 28.64 and 25.72 respectively,the values for the strength and elastic modulus under tensile perpendicular to grain have the largest discreteness for bamboo scrimber.From the point of CHV values,the relationship among the mechanical parameters for bamboo scrimber were proposed based on the test results.Compared with other green building materials,bamboo scrimber manufactured based on a new technique has better mechanical performance and could be used in construction area.Three stress strain relationship models which are four-linear model,quadratic function model,and cubic function model were proposed for bamboo scrimber specimens manufactured based on a new technique.The latter two models gives better prediction for stress strain relationship in elastic plastic stage.

A novel binary effective medium model to describe the prepeak stressstrain relationship of combined bodies of rock-like material and rock

Combined bodies of rock-like material and rock are widely encountered in geotechnical engineering,such as tunnels and mines.The existing theoretical models describing the stress-strain relationship of a combined body lack a binary feature.Based on effective medium theory,this paper presents the governing equation of the“elastic modulus”for combined and single bodies under triaxial compressive tests.A binary effective medium model is then established.Based on the compressive experiment of concretegranite combined bodies,the feasibility of determining the stress threshold based on crack axial strain is discussed,and the model is verified.The model is further extended to coal-rock combined bodies of more diverse types,and the variation laws of the compressive mechanical parameters are then discussed.The results show that the fitting accuracy of the model with the experimental curves of the concretegranite combined bodies and various types of coal-rock combined bodies are over 95%.The crack axial strain method can replace the crack volumetric strain method,which clarifies the physical meanings of the model parameters.The variation laws of matrix parameters and crack parameters are discussed in depth and are expected to be more widely used in geotechnical engineering.

基于主成分分析淮北五道沟日尺度地温对气象要素的响应

为探讨淮北地区地温对气象要素的响应关系,对未来地温进行预测,利用五道沟水文实验站1986-2021年0-320cm深度土壤内9个土层地温和8个逐日气象要素(平均气温、水面蒸发、日照时数、降水量、1.5m高度平均风速、平均空气相对湿度、绝对湿度和水汽压力差)实测资料,分析地温与气象要素的相关关系,利用主成分分析法对8个气象要素进行数据降维,以提取出的主成分作为输入构建PCA-BP地温模拟模型,并与仅使用平均气温作为输入的BP神经网络模型进行对比分析。结果表明:(1)除平均气温外,地温还受水面蒸发、绝对湿度、水汽压力差等气象要素影响,气象要素对地温的影响随土壤深度的增加而减弱。深层地温对气象要素的响应表现出时滞性特点,滞后时间随土层深度增加而增加。(2)0-80cm处PCA-BP地温模型在预测未来1、3、7d后地温时精度较高,R^(2)(决定系数)均高于0.79。由于地温对气象要素响应的滞后性,预测天数增加时,PCA-BP地温模型对深层地温的预测精度提高。(3)引入新的气象要素作为输入,可提高地温预测模型的精度;与仅使用平均气温作为输入的BP模型对比,PCA-BP模型在预测未来3d和7d后地温表现更优。

Stress-strain relationship for reactive powder concrete with recycled powder under uniaxial compression

The recycled powder(RP)from construction wastes can be used to partially replace cement in the preparation of reactive powder concrete.In this paper,reactive powder concrete mixtures with RP partially replacing cement,and natural sand instead of quartz,are developed.Standard curing is used,instead of steam curing that is normally requested by standard for reactive powder concrete.The influences of RP replacement ratio(0%,10%,20%,30%),silica fume proportion(10%,15%,20%),and steel fiber proportion(0%,1%,2%)are investigated.The effects of RP,silica fume,and steel fiber proportion on compressive strength,elastic modulus,and relative absorption energy are analyzed,and theoretical models for compressive strength,elastic modulus,and relative absorption energy are established.A constitutive model for the uniaxial compressive stress-strain relationship of reactive powder concrete with RP is developed.With the increase of RP replacement ratio from 0% to 30%,the compressive strength decreases by 42% and elastic modulus decreases by 24%.

岩石应力–应变滞后现象的定量研究

从应力–应变滞后回线"X"形的切线模量出发,探讨岩石滞后的定量描述。高应力作用下岩石的应力–应变滞后回线的形状是尖叶状的,反映在正弦波应力作用下应变的相位在加、卸载反转点处发生改变;滞后回线的切线模量和泊松比呈不对称的"X"形,且在加、卸载反转点处是不连续的。这种岩石在应力–应变图中出现的滞后回线是由于循环荷载时应力和应变的相位不同步造成的。理论计算和实验结果表明,岩石应力–应变滞后回线切线模量"X"形切线模量的夹角θ′与岩石的耗散角有确定性关系,θ′同样也反映岩石的滞后程度,它与岩石的耗散角在衡量岩石的滞后方面具有同等价值。

基于MFD的路网宏观交通状态及影响因素研究

从城市路网交通管理与控制的需求出发,引入交通流宏观基本图(MFD)模型,基于实测和仿真数据,开展对北京市西三环实际路网的宏观交通状态、时变特征以及影响因素研究.文中首先介绍了MFD模型及其矢量算法,利用实测数据建立西三环路网的MFD,基于Van Aerde模型标定路网交通流特征参数,对比分析路网平均流量-平均密度关系的时段分布差异,并得到宏观交通流的"磁滞现象";其次,证明了交通密度分布的不均衡性是影响路网宏观交通状态的根本因素;最后,利用Integration仿真研究了路网结构、交通需求以及出行路径对路网车流密度分布、宏观交通状态及其变化趋势的影响,以期为宏观交通控制、拥堵治理措施的制定提供决策支持.

均线滞后的时序自回归股市态势预测算法

针对艾略特波浪理论中的W形态,给出一种均线滞后性的量化方法,并提出融合均线滞后特征的时序自回归股市态势预测算法(DSMA).算法首先基于波浪理论提取W形态,给出W形态结点的量化表示形式;然后引入均线滞后性,并计算均线滞后程度;最后,利用贝叶斯网络表示融入均线滞后性的W形态结构关系,将各结点的局部关系代入AR模型中实现对股市态势的预测.在实际数据上进行了算法比较分析,实验结果表明算法具有更高预测精度.

压电陶瓷驱动器的迟滞非线性规律

探究压电陶瓷的迟滞非线性规律,为进一步修正迟滞非线性提供参考依据和理论基础。通过实验测量得到迟滞模型并对实验数据分析,拟合出上升轨迹的修正直线,求出其在相同位移下与上升、下降轨迹的电压差作为补偿电压,发现两条轨迹采样点上的输入电压与补偿电压满足近似多项式关系;分别选定5,10和15 V不同步长进行驱动实验。实验结果:上升轨迹(下降轨迹)多项式参数R-square=0.999 2(0.999 9),RMSE=0.083(0.080 86);R-square=0.999 7(0.999 9),RMSE=0.057 39(0.094 99);R-square=0.995 2(0.999 8),RMSE=0.291 6(0.165 5)。实验结论:两条轨迹的R-square近似为1,RMSE较接近0,重复性误差在1.13%~2.63%,输入电压与补偿电压满足近似多项式关系,拟合程度和匹配性较高,且重复性较好,具有可预测性,从而为进一步修正压电陶瓷驱动器的迟滞非线性提供了参考依据和理论基础。

单非晶丝磁芯双绕组新型磁传感器理论与实验研究

采用旋转水中淬火纺丝法制备的钴基非晶态合金丝作为磁敏感材料,提出了一种采用单非晶丝磁芯双绕组结构,多谐振荡桥励磁,对弱磁场进行检测的高灵敏度、高线性度新型磁传感器。通过建立敏感磁芯的理想磁滞回线模型并根据电路理论及电磁场理论,推出了传感器的输出信号与待测磁场、振荡桥元件参数、线圈匝数、敏感磁芯的磁参数及磁芯几何参数的关系,通过实验证实了在传感器线性检测区域内理论结果的正确性,从而为优化传感器性能提供了理论依据。文中给出了研制的磁传感器对外磁场的检测结果。

北京地区降水量与GNSS基准站垂向位移时空相关性特性研究

降水量直接影响地表质量的重分布,引起固体地球的弹性形变,而这种地表负荷引起的地壳形变能够通过GNSS基准站垂向位移直接反应。本文通过北京地区4个中国大陆构造环境监测网(陆态网)站点2011年至2015年的垂向位移数据和对应的日降水量数据,完成了两者的时空相关性特性分析。研究表明,GNSS基准站垂向位移与站点对应降水量存在密切的相关性,通过数据实验分析其存在约6个月的滞后期,降雨量对地表沉降的正负相关性并不固定,且数学模型对垂直分量变化能够起到一定的预测作用。

弹簧-阻尼型模拟人胸廓在心肺复苏按压下的力学特性

目的测试以变刚度弹簧组与阻尼器并联结构作为阻力部件的模拟胸廓在心肺复苏按压下的按压力-胸骨位移关系，并与现有的心肺复苏模拟人、“典型人”参数及1例真人试验数据比较。方法自制测量机构，采用2005国际心肺复苏指南标准对模拟胸廓及多种模拟人进行按压操作，获得按压力与位移的动态数据，同时对已发表的“典型人”和1例采用图像处理算法提取的真人数据，分别做出力-位移滞回曲线，并采用麦夸特法（Levenberg—Marquardt）＋通用全局优化法进行曲线参数优化，获得相应的参数。结果获得了模拟人、新型胸廓、“典型人”和1例真人的参数及滞回曲线图。对滞回曲线和曲线参数进行了分析比较。结论以变刚度弹簧组与阻尼器并联结构作为阻力部件的模拟胸廓较真实地模拟了人体胸廓在心肺复苏按压下的力学特性，较现有的各款国内外模拟人更接近于真人数据和“典型人”参数。

水位波动下沙介质中饱和度-毛细压力关系滞后研究

通过对气-水两相沙介质中干燥和湿润交替过程中的饱和度-毛细压力(S-p)关系的测定,研究了干燥和湿润交替过程中沙介质内非湿润相流体(空气)运移滞后问题。研究结果表明干燥和湿润过程之间的滞后程度受沙介质干燥-湿润循环次数影响不明显;滞后程度随着循环过程中湿润过程初始水饱和度的增加而逐渐减少。通过利用Van Genuchten(VG)模型对S-p关系进行的拟合和分析发现,水位波动引起的所有干燥过程中,反映侵入压大小的α值均很接近,从实测数据及拟合参数两方面均表明了沙介质的侵入压大致是一常数,不受干燥过程的路径和初始水饱和度的影响;湿润过程中参数α随着本过程初始水饱和度的升高而不断降低,这也表明了参数α值与干燥过程与湿润过程之间滞后性存在正相关。VG模型不但可以描述一般的S-p关系曲线,同时也可用于水位波动复杂条件下干燥和湿润过程中S-p关系的描述。

基于Preisach理论形状记忆合金电阻-应变滞回模型

随着对形状记忆合金(SMA)研究的不断深入,其几种特殊性质得到了越来越广泛的应用。其中关于SMA电阻-应变滞回模型的研究,已经受到国内外学者高度重视。由于SMA的电阻与应变之间存在有规律性的关系,可以利用这种关系,把SMA作为传感器应用到结构的健康监测中去。但实验表明SMA的电阻-应变关系具有较强的非线性性质,表现出明显的滞回特性。利用Preisach理论建立SMA的电阻-应变模型。在实验的基础上,通过训练得到SMA的电阻-应变表达式,并利用另一组实验数据验证了该方法的有效性,为进一步开展利用SMA电阻特性的结构健康诊断研究奠定了基础。

高寒山区冰川河流悬移泥沙的输移特征

[目的]分析不同区域冰川河流的水沙关系、输沙量及其对气候变化的响应,并对泥沙侵蚀强度进行评估,为高寒山区冰川河流的水沙动态研究提供理论基础。[方法]选取绒布河和科其喀尔河作为研究对象,在消融期间(2018年5—10月)对冰川河进行野外观测和水样采集。考虑气温和降水的影响,采用水文模型法对绒布河径流量进行模拟,结合水沙关系曲线、泥沙滞后环及回归模型对冰川河流的悬移泥沙输移及其影响因素进行分析。[结果]气温是影响高寒山区冰川河流悬移泥沙运输的主要因素;绒布河和科其喀尔河消融期的径流模数约7.36×10^(5),6.82×10^(5) m^(3)/(km^(2)·a),输沙模数分别为200 t/(km^(2)·a)和890 t/(km^(2)·a)。[结论]绒布冰川对气候变化更加敏感,消融强度大,泥沙主要来源于融水与降水对河道底部与坡面的侵蚀,但是可侵蚀沉积物和水力条件不足,造成该地区输沙模数低于其他冰川;科其喀尔河地处西北干旱区,泥沙输移量主要是由泥沙来源决定的,随着气温的升高,大量冰碛物被输送到下游,侵蚀强度明显高于其他大多数冰川。

分级循环荷载下泥岩和砂岩的阻尼特性试验研究

为研究岩石在不同应力水平循环荷载作用下轴向与径向变形的应力应变滞后关系及径向阻尼比与轴向阻尼比的关系,在MTS815岩石力学试验系统上对饱和泥岩与饱和砂岩进行变幅分级循环荷载试验。研究结果表明:同一岩石在循环荷载作用下的径向滞回环与轴向滞回环形状保持一致;对于砂岩,在加载时应变相位超前于应力相位,在卸载时应变相位滞后于应力相位,由此导致滞回环加卸载段都呈下凸状;对于泥岩,在加载时应变相位同步或滞后于应力相位,在卸载时应变相位滞后于应力相位。应力幅值不变时,随着循环次数的增加,阻尼比趋向于稳定,应力幅值越大,阻尼比越大。泥岩的阻尼比大于砂岩的阻尼比,泥岩和砂岩的径向阻尼比都大于轴向阻尼比,且在循环加载的初始阶段,泥岩和砂岩的径向阻尼比增长速率较快。随着径向应变与轴向应变比的增大,径向阻尼比与轴向阻尼比的比值逐渐减小,两者之间的关系为线性关系。

场次暴雨条件下濂水流域水沙关系探究

为探究场次暴雨条件下流域的水沙关系,该研究以赣南濂水流域为对象,基于1965—2020年的水文气象数据和土地利用数据,运用聚类分析、判别分析和Spearman相关分析等,在场次暴雨条件下,分析不同洪水类型、不同时段下的水沙特征及水沙关系,并对水沙滞回关系进行探究。结果表明:流域120场暴雨洪水划分为3种类型,发生频率由高到低依次为:Ⅲ型(短历时、小径流、低洪峰)、Ⅰ型(长历时、中径流、中洪峰)、Ⅱ型(中历时、大径流、高洪峰)。整个研究期划分的5个时段中,1996-2005年、2006-2020年的输沙特征值增幅较大,且单位径流的输沙能力大幅上升。不同洪水类型下的各水沙环路曲线比例差异较大;在不同时段下,逆时针型、“8”字型曲线分别在1996-2005年、2006-2020年的比例最高,分别为43.0%、55.6%,这与流域内果园大面积开发导致的沙源位置及数量的改变有着密切关系。研究成果可为流域的水沙管理及调控提供科学依据。