Study on the effect of the infill walls on the seismic performance of a reinforced concrete frame

Motivated by the seismic damage observed to reinforced concrete (RC) frame structures during the Wenchuan earthquake, the effect of infill walls on the seismic performance of a RC frame is studied in this paper. Infill walls, especially those made of masonry, offer some amount of stiffness and strength. Therefore, the effect of infill walls should be considered during the design of RC frames. In this study, an analysis of the recorded ground motion in the Wenchuan earthquake is performed. Then, a numerical model is developed to simulate the infill walls. Finally, nonlinear dynamic analysis is carried out on a RC frame with and without infill walls, respectively, by using CANNY software. Through a comparative analysis, the following conclusions can be drawn. The failure mode of the frame with infill walls is in accordance with the seismic damage failure pattern, which is strong beam and weak column mode. This indicates that the infill walls change the failure pattern of the frame, and it is necessary to consider them in the seismic design of the RC frame. The numerical model presented in this paper can effectively simulate the effect of infill walls on the RC frame.     

Consolidation and deformation around stone columns: Numerical evaluation of analytical solutions

Coupled finite element analyses of the consolidation and deformation around stone columns have been performed to assess the accuracy of different analytical solutions. The numerical model reproduces the hypotheses of the closed-form solutions. In the model, a rigid load is applied to a unit cell formed by a fully penetrating column and its surrounding soil, and simple elastic or elasto-plastic soil models are used. The surface settlement, the dissipation of the pore pressure and the vertical stress concentration on the column are studied. These soil responses are accurately estimated with closed-form solutions that properly include the radial and plastic strains in the column. However, the surrounding soil does not yield for usual conditions, which reasonably justifies the elastic soil behavior assumed in the analytical solutions. The differences between drained and consolidation analyses are also evaluated. Comparing the numerical results with the closed-form solutions illustrates the implications of the assumptions of each approach.     

P350微色谱柱在线分离富集-火焰原子吸收光谱法测定矿石中痕量金

在王水介质条件下,用自行设计的微色谱柱在线分离富集系统分离富集矿石样品中的痕量金,采用火焰原子吸收光谱法进行测定。在原子吸收光谱仪吸喷溶液的流路上,用P350微色谱柱研究了金的分离富集条件,采用快速吸附和快速洗脱技术,以盐酸溶液为淋洗液,亚硫酸钠溶液为洗脱液,测定一个样品整个分离和测定过程仅需1 min,成功地克服了火焰原子吸收光谱法测定金灵敏度低的缺点。方法的相对标准偏差小于3.2%,检出限为0.078μg/g。与现行离线分离富集方法相比,建立的方法具有高效、快速、成本低廉的优点,经实际样品验证获得了较为满意的结果。     

Prediction of Flowing Bottomhole Pressures for Two-Phase Coalbed Methane Wells

A method is proposed to predict the flowing bottomhole pressures(FBHPs)for two-phase coalbed methane(CBM)wells.The mathematical models for both gas column pressure and two-phase fluid column pressure were developed based on the well liquid flow equation.FBHPs during the production were predicted by considering the effect of entrained liquid on gravitational gradients.Comparison of calculated BHPs by Cullender-Smith and proposed method was also studied.The results show that the proposed algorithm gives the desired accuracy of calculating BHPs in the lowproductivity and low-pressure CBM wells.FBHP is resulted from the combined action of wellhead pressure,gas column pressure and fluid column pressure.Variation of kinetic energy term,compressibility and friction factors with depth increments and liquid holdup with velocity should be considered to simulate the real BHPs adequately.BHP is a function of depth of each column segment.The small errors of less than 1.5%between the calculated and measured values are obtained with each segment within 25 m.Adjusting BHPs can effectively increase production pressure drop,which is beneficial to CBM desorption and enhances reservoir productivity.The increment of pressure drop from 5.37 MPa2 to 8.66 MPa2 leads to an increase of CBM production from 3270 m3/d to 6700 m3/d and is attributed to a decrease in BHP from 2.25 MPa to 1.33 MPa.     

Studies on the determination of shear wave velocity in sands

Laboratory investigations such as resonant column, cyclic triaxial, and torsional shear tests are usually conducted on undisturbed and reconstituted sand samples in order to determine their shear modulus, which can be used to compute shear wave velocity. However, these methods are extremely cumbersome and indirect, they employ cost-intensive instrumentation, and they require trained manpower. These problems can be overcome by using bender elements, which yield the shear wave velocity of sands directly, easily, and quite rapidly. In this context, efforts made by earlier researchers in developing empirical relationships (based on bender elements and resonant column techniques) which can be employed to compute shear wave velocity in sands are worth consideration. Although these relationships take into account parameters like effective stress and void ratio, they do not directly incorporate fundamental characteristics of sands such as their state (i.e. dry or saturated) and the particle size. Thus a generalized relationship, which can be used to compute shear wave velocity in sands in either the dry or saturated state, has been developed. Experiments were conducted on samples of sand and glass beads of different sizes and the results were used to demonstrate the utility and efficiency of the relationship. Details of the methodology developed for this purpose are also presented in this paper.     

Energy dissipation in engineered sand of large damping ratio

Many geotechnical problems such as seismic resistant designs and machine vibrations require the installation of dampers or isolators to control the amplitude of vibrations. Engineered fills designed with increased capability of dissipating energy can provide a more economical approach to control excessive vibrations. This study presents a novel technique to increase the damping ratio of sand without affecting its stiffness and shear strength. The increase in damping ratio is evaluated by performing resonant column tests on the engineered sand. The damping ratio of the sand is increased by adding a controlled amount of viscoelastic material to the voids. The resonant column tests indicate that the damping ratio of the sand can be increased manifold without affecting the shear modulus. The micromechanical evaluation of the results shows a good correlation between the particle surface area in contact with the pore-mixture and the damping ratio of the sand. The suitability of engineered sand as foundation material is also evaluated by performing direct shear tests. The direct shear tests on mixtures indicate similar or better shear strength parameters compared to pure sand.     

Dynamic shear modulus of undisturbed soil under different consolidation ratios and its effects on surface ground motion

The dynamic shear modulus for three types of undisturbed soil under different consolidation ratios is presented by using the resonant column test method. Its effects on surface ground motion is illustrated by calculation. The test results indicate that the power function is a suitable form for describing the relationship between the ratio of the maximum dynamic shear modulus due to anisotropic and isotropic consolidations and the increment of the consolidation ratio. When compared to sand, the increment of the maximum dynamic shear modulus for undisturbed soil due to anisotropic consolidation is much larger. Using a one-dimensional equivalent linearization method, the earthquake influence factor and the characteristic period of the surface acceleration are calculated for two soil layers subjected to several typical earthquake waves. The calculated results show that the difference in nonlinear properties due to different consolidation ratios is generally not very notable, but the degree of its influence on the surface acceleration spectrum is remarkable for the occurrence of strong earthquakes. When compared to isotropic consolidation, the consideration of actual anisotropic consolidation causes the characteristic period to decrease and the earthquake influence factor to increase.     

高墩抗震梁桥单墩模型地震时程响应分析

直接基于经典的欧拉梁理论,推导针对规则高墩梁桥单墩模型弹性阶段地震时程响应的半解析计算步骤,考虑梁墩铰接的形式,在墩底引入等效基础弹簧变形协调条件,解析的获得各阶实模态和频率方程,用牛顿法搜索各阶频率．应用振型叠加法求解体系的地震时程响应。最后应用该方法对一高墩梁桥单墩模型的地震响应进行分析,与离散模型的有限元时程积分的结果比较表明了方法的有效性。     

Comparison of variability and change rate in tropospheric NO2 column obtained from satellite products across China during 1997–2015

ABSTRACT

Tropospheric NO₂ column (TNC) products retrieved from five satellites including GOME/ERS-2 (H, 1997–2002), SCIAMACHY (S, 2003–2011), OMI (O, 2005–2015), GOME-2/METOP_A (A, 2007–2013) and GOME-2/METOP_B (B, 2013–2015) were compared in terms of their spatiotemporal variability and changes over China. The temporal series of H suggested an increasing trend of TNC from 1997 to 2002, those of S, O and A revealed further increasing trends until the highest level of TNC was reached in 2011, but decreasing trends were detected by those of O and B from 2011 to 2015. Seasonally, TNC was the highest in winter and the lowest in summer. Variability and changes from satellite TNC products are also analyzed in different regions of China. Spatially, it was the highest in North China and the lowest in Tibetan Plateau based on five datasets. Overall, TNCs from A, B and S were higher than that from O; and TNC from S was larger than that from A at the country level. The higher TNC the region has, the larger difference satellite products would show. However, different datasets reached a good agreement in the spatial pattern of trends in TNC with highly significant increasing trends detected in North China.     

规则梁桥单墩-质点隔震体系地震时程响应半解析法

本文基于带集中参数边界条件的分布参数连续梁理论,推导规则隔震梁桥单墩-质点(SCM)地震时程响应的计算步骤.在控制方程边界条件引入等效基础弹簧和墩顶隔震层变形协调条件,解析地获得各阶实模态,用牛顿法搜索各阶频率.为了处理隔震层非比例阻尼产生的耦联效应,由能量法分配各阶实振型的隔震层附加阻尼比,实现体系的实模态近似解耦,应用振型叠加法求解体系的地震时程响应.最后应用该方法对一规则隔震梁桥SCM体系的地震响应进行分析,与有限元时程积分的结果进行比较,表明此方法的有效性.计算结果表明,采用墩顶隔震策略的单墩-质点体系能显著减小结构响应,具有良好的减震效果.