地基-非线性结构相互作用空间效应的超谐和亚谐共振研究

建立了考虑空间效应的无质量基础-地基-结构相互作用模型,将模型简化为三个自由度体系,得到了考虑结构水平侧移和扭转位移相耦合的振动方程,用多尺度法研究了体系在强激励下的超谐共振和亚谐共振行为,通过算例分析得到了一些不同于线性体系的结论,为结构非线性分析提供了更深刻的理论依据。     

较小剪跨比带暗柱T形柱抗震性能试验研究

提出了带暗柱Ｔ形柱,进行了４根较小剪跨比的Ｔ形柱抗震性能试验,分析了轴压比对承载力,刚度,片断生的影响以及设暗柱对提高Ｔ表柱抗震能力的作用。最后进行了理论计算,计算值与实测值符合较好。     

基于滞回曲线以及结构动力方程的混凝土结构抗震稳定性分析

为准确全面地量化分析研究土木工程建筑中混凝土结构抗震稳定性,提出基于滞回曲线以及结构动力方程的混凝土结构抗震稳定性分析方法。首先采用滞回曲线描述混凝土结构在地震作用下的损伤情况,对滞回曲线模型拐点进行有效操作,确保动力方程对混凝土结构抗震稳定性进行有效分析。其次采用基于混凝土结构动力方程的抗震稳定性分析方法,对地震地面运动模型以及结构分析模型来分析混凝土结构的随机地震反应情况,得到混凝土结构随机反应的汇总量,在此基础上通过双参数的结构破坏模型,基于结构稳定性原理,获取运算混凝土结构抗震稳定性的概率表达式,再基于该表达式分析混凝土结构的抗震稳定性情况。实验结果说明,所提方法能够对土木工程建筑中不同类型混凝土构件抗震稳定性进行有效分析,分析结果准确且全面。     

Measurement of iodine-129 in seawater samples collected from the Japan Sea area using accelerator mass spectrometry: Contribution of nuclear fuel reprocessing plants

The concentrations of ¹²⁹I in seawater samples from two sites (off Sekine and the Toyama Bay) in the Japan Sea were determined by accelerator mass spectrometry. The observed concentrations exceed amounts expected from natural origin and globally distributed fallout due to nuclear weapons testing. Because the fraction of natural origin and global fallout is 2% and 8.9–13.8%, respectively, the residual more than 80% of the concentration must come primarily from nuclear fuel reprocessing plants. This result indicates a rapid distribution of ¹²⁹I through atmospheric transport on a global scale. The depth distribution of ¹²⁹I at the Toyama Bay in the Japan Sea shows that the ¹²⁹I maximum is in the mixed layer and that concentrations decrease with depth. The inventory of ¹²⁹I in water column is four times higher than that measured in the Gulf of Mexico which has almost the same depth at the Toyama Bay. This higher inventory probably reflects: (1) the rapid water sinking in the Japan Sea, (2) the difference of distance in sampling locations with respect to major ¹²⁹I releasing plants and (3) the strong increase in emissions from nuclear fuel reprocessing plants after the profile of the Gulf of Mexico was taken.     

Development of stochastic dynamic Nash game model for reservoir operation II. The value of players’ information availability and cooperative behaviors

Stochastic dynamic game models can be applied to derive optimal reservoir operation policies by considering interactions among water users and reservoir operator, their preferences, their levels of information availability and cooperative behaviors. The stochastic dynamic game model with perfect information (PSDNG) has been developed by [Ganji A, Khalili D, Karamouz M. Development of stochastic dynamic Nash game model for reservoir operation. I. The symmetric stochastic model with perfect information. Adv Water Resour, this issue]. This paper develops four additional versions of stochastic dynamic game model of water users interactions based on the cooperative behavior and hydrologic information availability of beneficiary sectors of reservoir systems. It is shown that the proposed models are quite capable of providing appropriate reservoir operating policies when compared with alternative operating models, as indicated by several reservoir performance characteristics. Among the proposed models, the selected model by considering cooperative behavior and additional hydrologic information (about the randomness nature of reservoir operation parameters), as exercised by reservoir operator, provides the highest attained level of performance and efficiency. Furthermore, the selected model is more realistic since it also considers actual behavior of water users and reservoir operator in the analysis.     

Intergrain contact density indices for granular mixes I： Framework

Mechanical behavior such as stress-strain response, shear strength, resistance to liquefaction, modulus, and shear wave velocity of granular mixes containing coarse and fine grains is dependent on intergrain contact density of the soil. The global void ratio e is a poor index of contact density for such soils. The contact density depends on void ratio, fine grain content （Cv）, size disparity between particles, and gradation among other factors. A simple analysis of a two-sized particle system with large size disparity is used to develop an understanding of the effects of Cv, e, and gradation of coarse and fine grained soils in the soil mix on intergrain contact density. An equivalent intergranular void ratio （ec）oq is introduced as a useful intergrain contact density for soils at fines content of less than a threshold value Crth. Beyond this value, an equivalent interfine void ratio （ef）eq is introduced as a primary intergrain contact density index. At higher values of Cv beyond a limiting value of fine grains content CVL, an interfine void ratio ef is introduced as the primary contact density index. Relevant equivalent relative density indices （Drc）eq and （Drf）eq are also presented. Experimental data show that these new indices correlate well with steady state strength, liquefaction resistance, and shear wave velocities of sands, silty sands, sandy silts, and gravelly sand mixes.     

Dynamic performance of angle-steel concrete columns under low cyclic loading-I： Experimental study

This paper describes low cyclic loading testing of nine angle-steel concrete column （ASCC） specimens. In the tests, the influence of the shear-span ratio, axial compression ratio and shear steel plate ratio on the hysteretic behavior, energy dissipation, strength degradation, stiffness degradation, skeleton curve and ductility of the ASCCs is studied. Based on the test results, some conclusions are presented. The P-A and sectional M -φ hysteretic models for the ASCCs are presented in a companion paper （Zheng and Ji, 2008）.     

共振柱试验的非线性拟合研究

土体动力参数是表征土动力特性的重要指标,对抗震计算具有重要影响。利用GCTS共振柱仪对淤泥、黏土、粉质黏土和粉砂进行共振柱试验,对Hardin—Drnevich提出的双曲线模型的模量比表达式进行线性拟合与改进的非线性拟合对比研究。结果表明：改进的非线性拟合得到的曲线较线性拟合曲线更加接近原始数据点;在低应变处,非线性拟合残差小于线性拟合残差,随着应变增加非线性拟合的残差接近线性拟合残差,在大应变处线性拟合残差小于非线性拟合的残差;改进的非线性拟合的最大动剪切模量G_dmax和参考剪应变γ_r的标准误差及置信区间宽度均比线性拟合的结果小;拟合优度评价指标表明改进非线性拟合效果优于线性拟合效果。将线性拟合结果作为非线性拟合方法的初始值的改进方法较线性拟合方法具有更高的准确性和稳定性,并具有更高的应用价值。     

Intergrain contact density indices for granular mixes-Ⅱ:Liquefaction resistance

Whether the presence of non-plastic silt in a granular mix soil impact its liquefaction potential and how to evaluate liquefaction resistance of sand containing different amounts of silt contents are both controversial issues. This paper presents the results of an experimental evaluation to address these issues. Two parameters, namely, equivalent intergranular void ratio (ec)eq and equivalent interfine void ratio (ef)eq, proposed in a companion paper (Thevanayagam, 2007) as indices of active grain contacts in a granular mix, are used to characterize liquefaction resistance of sands and silty sands. Results indicate that, at the same global void ratio (e), liquefaction resistance of silty sand decreases with an increase in fines content (CF) up to a threshold value (CFth). This is due to a reduction in intergrain contact density between the coarse grains. Beyond CFth, with further addition of fines, the interfine contacts become significant while the inter-coarse grain contacts diminish and coarse grains become dispersed. At the same e, the liquefaction resistance increases and the soil becomes stronger with a further increase in silt content. Beyond a limiting fines content (CFL), the liquefaction resistance is controlled by interfine contacts only. When CF＜CFth, at the same (ec)eq, the liquefaction resistance of silty sand is comparable to that of the host clean sand at a void ratio equal to (ec)eq. When CF＞CFth, at the same (ef)eq, the cyclic strength of a sandy silt is comparable to the host silt at a void ratio equal to (ef)eq.