Experimental Study Creep Characteristics on Creep and Cyclic of Saturated Soft Clay

Several long term creep and cyclic creep tests of Shanghai soft clay are performed in the laboratory. Test results have been obtained under various combinations of confining stresses, deviation static stress ratios and deviation cyclic stress ratios. The results reveal that the axial creep strain increases with the increase of deviation static stress ratio under a constant confining stress, while it also increases with the increase of confining stress under a constant deviation stress ratio. Such a phenomenon is similar to that from the cyclic creep tests, but the following creep strain increase will be significantly reduced after a period of cyclic loading. The results will benefit the expressway, railroad and underground constructions.     

高速铁路隧道基底软岩动力累积损伤特性

利用相似材料模拟高速铁路隧道基底软岩,采用荷载控制和非对称正弦波循环加载方式对软岩试件进行动三轴疲劳与损伤检测综合试验。通过试验结果分析,建立了软岩3参数多项式疲劳寿命计算模型和4参数多项式累积损伤参量计算模型,获得了软岩疲劳损伤特性,即：软岩疲劳破坏表现为端部拉-剪复合破坏和中部压-剪复合破坏两种模式;疲劳破坏全过程表现为初始微孔隙压密、裂纹发生与稳定扩展以及损伤裂纹加速发展3个发展阶段;软岩疲劳寿命主要取决于本身强度和动应力水平,强度愈高、动力应力水平愈低,其疲劳寿命就越长;当动应力水平相同时,软岩疲劳寿命与其弹性模量呈线性增长关系。     

Analyses of Interlayer Stresses and Strain Transfer in Smart Laminated Structures

A new model is proposed to analyze the strain/stress transfer relation between host materials and piezoceramic sensors/actuators under bending and axial stress loading. The finite thickness of the adhesive is taken into account. The physical layers of the piezoceramic, adhesive and structure material are further subdivided into thinner layers as fine as necessary in order to improve the accuracy of stress analysis. In each thin layer the in-plane stresses are assumed to vary linearly across the thickness. By satisfying equilibrium equations, constitutive equations and displacement-strain relations, all components of stress, strain and displacement can be expressed as functions of the in-plane forces and the moments of the thin layers. The differential equations governing the in-plane forces and the moments are obtained. Then, this analytical model is used to predict strain transfer from the structure material to the sensor. It is found, both experimentally and theoretically, that the axial strain of the host material is considerably larger than the strain of the sensor, which is directly related to the output voltage. By introducing the so-called strain transfer factor, a relationship between the output voltage of the sensor and the strain of the measured material is derived. The model is used to predict interlayer stress distributions and strain transfer, which are induced by actuator strain. The result was compared with existing experiments and FEM. There is stress concentration between the actuator and adhesive around the edge of the smart structures, which may cause debonding under high stress loading.     

沉积作用及应力历史对自重应力和沉降的影响

土体的沉积作用和应力历史会影响土体自重应力的确定,也会影响地基最终沉降量的确定。鉴于e-lnp比e-lgp坐标图能更方便、精确地描述线性问题,根据e-lnp坐标图推导沉积作用对成层土、正常固结土、超固结土的自重应力与沉降影响的计算式。用该计算式对昆明滇池国际会展中心部分深厚软土地基的自重应力和最终沉降量进行计算,并用计算结果和不考虑沉积作用及应力历史影响的计算结果进行对比分析,结果表明,沉积作用对深厚软粘土自重应力和最终沉降量计算值的影响非常显著,并且土体厚度越厚、上覆荷载越大,其影响越明显。     

The Micro/Macro Mechanic Analysis of PD3 Pearlitic Steel with Layered Microstructures

A micro/macroscopic analysis of PD3 pearlitic steel with layered microstructure is carried on.Based on the compatibilit conditions of stress and strain at the interface between two layers as well as the mixed law of composites,constitutive equations of an effective homogeneous inclusion are obtained.combining these equations with the K B W self consistent model,the micro macroscopic transition has been estabilished.It turns out that the analysis is capable of determining the overall responses of materials as well as local stress evolution in microstructure under monotonic and cyclic loading.It is found that stress in the thin cementite layer is very high.This is caused by intersification of the local plastic flow of the soft ferrite layer in which more loading is transferred cycle by cycle to the hard phase.Furthermore,a strength dimension law that the strength is inversely proportional to the square root of the layer thickness is developed to explain the high strength of the cementite layer.     

Experimental analysis of the deformation of sandstone under cyclic pore water pressure and wavelet transformation

To explore the characteristics of deformation of sandstone under cyclic pore water pressure, the experiments with different axial stresses (60%, 70% and 80% of peak intensity) of sandstone subjected to cyclic pore water loading are investigated by using MTS815 rock mechanics testing system, and irregular small deformation in deformation curve of sandstone are also processed by wavelet transformation of Matlab. The results show that with the increase of constant axial stress, fatigue deformation under cyclic pore water pressure will accelerate the failure of the sandstone. With the increase of the number of cyclic pore water pressure, the deformation evolution of the plastic-loop is illustrated as sparse-dense-sparse. The deformation curves of sandstone under cyclic pore water pressure affected by many factors are decomposed, reconfigurable processed and evaluated by using wavelet transformation, which indicates that the basic curve with optimal decomposition scale fits well with the experimental curves and reveals the deformation evolution of sandstone.     

Predicting Damage Rate of Asphalt Pavement for the Fatigue Performance Cracking with Axial Loading

The damage rate of asphalt pavement for the fatigue performance cracking is studied with axial loading by the relationshi Pof surface cueved index with Falling Weight Deflection basin, bottom pulling strain of asphalt surface and aumbers of axial loading. The predicting result of standard axial loading and more-classified loading is very different, so as its increasing rate with the time going. It fits real circumstance to predict the fatigue character of asphalt pavement according to more-classified loading and could be an effective measurement for predicting fatigue life of asphalt pavement ruder axial loading.     

Experimental Analysis on Beam-column Behavior of Steel-concrete Composite Pylon

Ten specimens with perforated ribs, which can be divided into two series, were made to observe the behavior of steel-concrete composite pylon under axial load and cyclic load respectively. The experiment reveals the ultimate capacity and failure mode of two types of specimens under the cyclic load with different actual axial load level. Furthermore, it can be concluded from the results that the failure mode can be divided into two types, that is compression failure and tension failure. And the behavior of those specimens under cyclic load is influenced significantly under high axial load or without axial load at all. In addition, perforated ribs will prevent the plates under compression from overall buckling effectively based on the observation that the wavelength of plate is limited between two neighboring perforated ribs. At last, comparison on the interaction behaviors of the axial load (N) versus moment (M) is made between the results of experiment and calculation according to the criteria.     

水压力环境中混凝土经历循环荷载后的抗压强度

研究了水压力环境中混凝土在经历循环荷载后的动态压缩强度,分析了水压力和循环次数对混凝土强度的影响。试验应变速率为10^-5/s、10^-4/s、10^-3/s和10^-2/s,水压为0~10 MPa。试验结果表明,在不同水压力下饱和混凝土的强度都随应变速率提高而增加,也随水压力提高呈增加地趋势。在相同水压力下,应变速率越高,混凝土强度提高越显著。饱和混凝土经过循环荷载后,其强度随荷载循环次数的增加呈现出先提高后降低的现象。应变速率越高,混凝土强度最大时所对应的荷载循环次数也相应增加。还构建了饱和混凝土强度与应变速率、水压力的关系,其与试验数据吻合较好。进一步引入了管道孔隙模型,并基于汞压法的原理和孔隙分布特点,考虑混凝土孔隙的微观结构解释了孔隙水对混凝土强度的作用机理。     

A CONSTITUTIVE LAW FOR CYCLIC BEHAVIOR OF A CLASS OF TWO-PHASE STEELS

Based on a thermomechanically consistent mechanical model, the constitutive law for a class of complex two-phase materials with locking-in inter-phase residual stress capability is proposed. The developed model contains the current plastic strain in its hereditary integral so that the main features of the above materials subjected to cyclic loading can be well described. The developed model can include both the endochronic constitutive equation and Bower' s empirical formula as special cases. The cyclic plasticity and ratcheting of OFHC copper (single-phase material) and rail steel BS1l(two-phase material)are analyzed and compared with experimental results     

A Constitutive Model for Structured Clays based onTwo Different Types of Overconsolidation

Structure has a major influence on the stress strain relation of soil, which implies that the constitutive model should reflect the its structure. Based on the investigation , the over consolidation (OC) of the soils was made up of two different types, which were structure induced OC and stress induced OC. And then the structure induced OC and stress induced OC were united. Structure induced OC index was used to represent the degree of structure and the cam clay model was extended. The shape of the yield surface was the same as cam clay model, whise the size was equal to the sum of the structure induced OC and stress induced OC. And the change in size of the yield surface was decerminated by the volume harden function and the structural damage function. The associated flow rule was adopted in the model. Afterwards constitutive model for structured clays was presented. The concept of the model is clear and the parameters are simple. The ability of the model is good by firstly application and it can describe the character of the structured soils.     

结构消(耗)能元件芯材SN490B本构关系数值模拟

采用消(耗)能元件的结构在遭受地震作用时,元件芯材首先屈服进入塑性阶段,利用其滞回变形消耗地震输入能量,保护主体结构,元件芯材本构关系的数值模拟是对采用消(耗)能元件结构进行抗震分析与设计的基础。为更真实地模拟结构消(耗)能元件芯材在单调和循环荷载下的本构响应,更准确地对采用消(耗)能元件结构进行结构弹塑性地震响应分析,对常用作消(耗)能元件芯材的日本高延性钢材SN490B的单调、循环加载本构及循环骨架曲线进行了数值模拟,包括：采用Esmaeily-Xiao二次流塑性模型模拟材料在单调荷载作用下弹性段、屈服段、强化段和二次流塑段4个阶段;采用混合强化模型模拟材料循环荷载作用下的本构响应,运用大型通用有限元软件ABAQUS结合数值模拟参数对16种不同循环加载制度下的循环加载试验进行模拟,并与试验结果进行对比;采用Ramberg-Osgood模型、无量纲化的Ramberg-Osgood模型及两段式模型模拟循环骨架曲线。研究结果表明：所采用数学模型可以较好地模拟SN490B钢材单调、循环加载本构响应及循环骨架曲线,数值模拟与试验结果拟合较好。     

A Comparative Study of Confined Concrete Models under Cyclic Loading

In this paper,four models are selected as the representatives and applied to nonlinear dynamic analysis program for space frames which is based on the beam-column elements using the finite element flexibility method and the fiber model.Park's test on combined axial and bending columns under cyclic loading are taken as the calibrations,comparisons to material and structural member level are drawn and the analytical results of various models are discussed.     

Integration Strategy for Thermal-Elastic-Plastic Models of Concrete under Plane Stress

Plastic strain was determined at multiple time increments.The strain was caused by stress and temperature.The yield function in high-temperature states is the function of temperature and plastic strain.The calculation efficiency would be decreased and much more calculation would be needed if a conventional method,such as the radial return method,was used.In the case of axial stress states,the temperature path was difficult to determine at various time intervals.Initial value equations were obtained with the Drucker-Prager function of plane stress concrete.This method can solve the previously mentioned problems efficiently when used with the Runge-Kutta integration strategy.A program was developed with an updated co-varying coordinate finite element method based on the S-R decomposition theorem.Computational results show that the integration strategy is highly accurate and efficient.     

Impact of Temperature in Air-conditioned Room on Blood Rheological Characteristics

Based on the reversed cyclic loading tests of 21 nearly full-size interior joints in completed reinforced concrete frames,the law of bond deterioration of beam bars crossing the joint is tested and analyzed,which is influenced by the axial load ratio,shear-compression ratio,reinforced bar strength,concrete strength and the relative length of beam bars crossing the joint. By the nonlinear fitting method, the formula of the bond stress r between steel crossing interior joints and concrete under different loading step is obtained. According to the loading approach, the propositional formula of the relative length of beam bars crossing the joint hc/d is presented, which is influenced by axial load ratio, shear-compression ratio ,reinforced bar strength and concrete strength.     

On Elasto-Plastic Consolidation Settlement of Saturated Soft Clay

The specific properties of soft clay are characterized by higher void ratio, lower permeability and higher compressibility, the consolidation settlement of soft clay is affected by the imposed stress history, the stress paths, the consolidation pressure and the soil properties. In this paper, the porous media theory based on the mixture theory was applied in the study on the consolidation settlement of soft clay, which was more rigorous than the conventional consolidation settlement theory and the coupling between soil and water can be taken into account in the analysis.     

A Hypoplastic Macro-Element Model for Circular Shallow Foundations of Offshore Wind Turbines Under Combined Loading

The foundation for offshore wind turbines is subjected to vertical loading caused by structural weight and horizontal loading and moment due to wind- or wave-induced loading. Furthermore, it sustains torque from rotor blades. Based on the framework of hypoplasticity theory, the available general yield function and plastic potential function, a macro-element model for circular shallow foundations on sands under six-degree-of-freedom combined loading has been developed. In this model, to correctly reproduce the mechanical response of offshore foundations under cyclic loading, the concept of equivalent inter-granular strain is introduced into the relationship of generalized forces as well as its corresponding displacements. The performance of the proposed macro-element model is demonstrated by comparing the model predictions with available experimental data from a series of model tests.     

Effects of Vibration History on Modulus and Damping of Clay

Aiming at evaluating the effects of vibration history on dynamic characteristics of normally consolidated clay, a series of multi-cycled cyclic shear tests were conducted on 16 soil samples under consolidation pressure of 50 kPa, 100 kPa, 300 kPa and 500 kPa respectively. The experimental results reveal that, on the stage of drainage and consolidation, with the development of duration shear modulus curve ascends while damping curve descends; this trend became significant as consolidation pressure increased. The variation tends to be stable in 25 hours. When subjected to cyclic loading controlled by constant strain amplitude, both the modulus and damping of soil samples change significantly during the first 50 cycles, and then the differences become moderate afterwards, in which the damping curve acts in hyperbolical type. It is also found that there exists a clear sign of pre-straining that affects damping more significantly than modulus.     

Simple Shear Test of Interface between Sand and Structure under High Stress

By using a simple shear apparatus that is developed from RMT-150B,a series of simple shear tests of interface between saturated sand and structure under high normal stress were carried out to study constitutive law and shearing stiffness of interface to provide some theoretical evidences for design and calculation of projects concerned with mechanical problem of interface.In test,sand was consolidated in upper shearing box firstly,then,shear was started and testing data was recorded under high and constant normal stress.During the process,sand can deform relatively freely.It is shown that the relation curve between shear stress and shear displacement under high normal stress in simple shear tests is different from that in direct shear tests,and the complete shearing deformation process of interface under high stress can be described as a nonlinear elastic-perfect plastic form;Weibull distribution with three parameters can overcome the mathematical deficiencies of hyperbola in NEPP.The new model which is established by substituting Weibull distribution for the hyperbola of NEPP better agrees with the testing data.The regressive results of the initial shearing stiffness demonstrate that the linear function is slightly better than power function to express the relation between the initial shearing stiffness and normal stress.Based on the new interface model,the formula of tangential shearing stiffness is proposed,meantime,the change trend of tangential shearing stiffness of the new model is compared with that of NEPP.