Low-Cyclic Fatigue Behavior of Reinforced Concrete Columns Subjected to Non-Symmetric Displacement Cycling

For the sake of setting up more rational damage criteria for RC structures based on the relationship between displacement amplitude after yielding and low-cyclic fatigue life, this paper Presents six RC columns test results focusing on development of cumulative damage and low-cyclic fatigue life varying with displacement amplitude and positive/ negative displacement ratio. On this basis, expression is provided to describe the relation between low-cyclic fatigue life and positive/negative displacements amplitude ratio under different displacement levels.     

The mechanical behavior of structured and homogenized soil under repeated loading

Soil deformation is increasingly important in crop production since nowadays weights of agricultural machines exceed the bearing capacity of most soils. Often this is counteracted by distributing the weight over more axles leading to an increase in wheeling frequency. Machine passages during one year can, depending on the crop and equipment used, range between two and five times for the majority of the field and up to twenty times and more for a wheeling track. These add up to hundreds of loading events for a crop‐rotation period. In this study, we investigated the effect of multiple loading with the same load in a cyclic‐compression test on soil‐pore‐volume change. The tests were conducted on homogenized soil samples with varying texture and undisturbed soil samples from a field experimental site comparing conventional and conservation‐tillage systems. Of particular interest was the question whether there is significant plastic soil deformation for soil stresses that remained sufficiently below the precompression stress, which is commonly neglected. Our results show that especially for cohesive soils, the assumption of fully elasticity in the recompression range may not be justified since those soils show distinct cyclic‐creep behavior. We found that deformation under cyclic loading follows a logarithmic law. We used the slope of the logarithmic fit of void‐ratio changes vs. loading cycles as a parameter to characterize the sensitivity of soils to cyclic compression. The results suggest that for characterizing the mechanical stability of soils that show cyclic creep, we have (with respect to long‐term deformation effects) to consider both precompression stress and cyclic compressibility.     

Effects of agriculture development on vole dynamics and conservation of Montagu''s harrier in western French wetlands

Nesting populations of Montagu's harrier (Circus pygargus) are declining in most parts of Europe; in France, western marshes remain the most important nesting sites in terms of breeding pairs. In this open field landscape dominated by grasslands, the common vole (Microtus arvalis) displays regular population outbreaks and constitutes a favourite prey of this raptor. Twelve years of field data indicate significant variations in nesting population size and young harriers produced, which correlate with yearly differences in vole densities. Up to 10 years ago, these marshes were traditionally used as extensive pastures but recent agricultural changes have resulted in almost 50% of the pastures being converted to drained agricultural production, as already observed in many localities of this region next to our study area. Our data, together with previous data collected from 1968 in this region, demonstrate that agricultural changes have resulted in a decrease of frequency and intensity of vole population peaks. A summer density of 100 voles/ha appears as a threshold value to support a good breeding success of harriers. These modifications of the vole fluctuation pattern suggest that nesting populations of Montagu's harrier from western French marshes could be endangered in future under these current trends in agricultural changes.     

EXPERIMNTAL RESEARCH ON THE CRACK RESISTANCE AND BEARING CAPACITY OF PRESTRESSED BRICK MASONRY WALLS UNDER CYCLIC LOADING

By comparing the tests of prestressed and nonprestressed brick masonry walls with peripheral beams and Constructional columns, under cyclic lateral loading,the apperaence and development of Cracks,failure mechanism,hysteretic behavior,strength,stiffness,ductility and ener-gy dissipation of the brick rnasonry walls arc studied.Only the crack resistance and bearing capacity of walls are discussed in this paper.It is shown that prestressing on brick masonry wall can obviotisly improve its seismic behavior.Morcover,calculating methods for the crack resistance and the ultimate bearing capacity are presented,and the caculating results are identical with the tests.     

不同促腐菌剂对有机废弃物堆肥效果的研究

为了促进当地农业有机废弃物资源的循环利用,以牛粪、鸡粪、食用菌渣为堆肥原料并协调碳氮比为30∶1,添加不同的微生物菌剂进行堆肥,研究堆肥过程中的温度、pH值、全氮、铵态氮、硝态氮和发芽指数的变化趋势,比较不同菌剂处理在堆肥前后养分含量的差异。结果表明,枯草芽孢菌剂和EM菌剂处理堆肥初期升温快,发酵基和速腐剂处理堆肥初期升温相对缓慢;枯草芽孢菌剂处理高温阶段温度基本上维持在70℃上下,堆肥前后氮素损失率最大为33.18%,发芽指数最低,而EM菌剂处理的高温阶段温度维持在55~68℃,氮素损失率最小为10.73%,发芽指数在堆肥21 d为51.55%,达到了基本腐熟,堆肥35 d为84.27%,达到了完全腐熟,堆肥腐熟快于其他处理。因此,在利用牛粪等有机废弃物进行高温好氧堆肥过程中,需要选择具有多种微生物能够相互协调作用并适应高温堆肥的菌剂,并且菌剂用量适宜,以达到减少氮素损失,提高堆肥的效果。     

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.     

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。     

An Empirical Study and Forecast of the Cyclic Fluctuation of Real Estate Investment in China

As one of the key factors affecting the real estate,the development investment exerts leading influence on the real estate industry,which has become the pillar industry in the economic development of China.This paper aims to show the evolution route,the inner rule and the mechanism of the cyclic fluctuation of the real estate investment in China,and to give a reasonable short-term forecast of the investment based on the establishment of the ARIMA model,in order to contribute to a nicer performance of the industry in the future.     

Damage Constitutive Relationship of Coupled Plasticity-creep for Magnesium Alloy

Based on a simple mechanical model and an appropriate definition of generalized time,a constitutive equation is obtained for coupled plasticity and creep behavior of materials.A damage evolution based on a spherical void model for mixed hardening materials is obtained by means of Gurson's model.The damage evolution law is embedded in the adopted constitutive equation,and a damage constitutive equation is obtained for coupled plasticity and creep behavior of die-casting magnesium alloy.The response of magnesium alloy subjected to cyclic loads is analyzed.The validity of the proposed model is demonstrated by the satisfactory agreement between the experimental and calculated results.