Experimental Study on Shear Strength of High Strength Concrete Columns

On basis of the experiment on sixteen high strength concrete columns, their shear behaviors are analysed. The effects of shear-span ratio and axial compression ratio on failure behavior, cracking shear and shear strength are analysed. The authors have discussed the suitability of the design equations for shear strength in the code. This experimental study on shear strength of high strength concrete frame columns is the first one in this field at home and the results can be served as reference for the code of high strength concrete design.     

Shunt Active Power Filiter for Harmonic Compensation in DC Side of HVDC Transmission System

A shunt active power filiter(APF) used for harmonic treatment isintroduced in this paper. Basic circuit-theory and main configuration are analyzed. Control scheme and its realization are discussed. Computer simulation is used to verity theoretical analysis. It shows that APF is an interesting alternative for hasmonic treatment compared with conventional passive filter.     

Hydrofracturing Breakdown Modes Under Different In-Situ Stress States

An analysis is made for various kinds of possible breakdown modes during hydrofracture,and the corresponding breakdown pressure,from which a method is given to distinguish which kind of failure mode practically occured. The analysis shows that the initial failure mode at the wellbore wall may be the pure tension failure or shear failure according to different stress states and mechanical properties of rock,therefore there are two different stress state configurations resulting in vertical shear fractures.     

直流电场处理树种在陕西飞播造林效果

用直流电场处理油松种子，进行发芽试验和飞播造林试验，结果表明：经直流电场处理的油松种子，可提前１￣２ｄ发芽，提高发芽成苗率１０％￣２５％。     

中原地区丹红杨插干造林技术研究

丹红杨是中国林业科学研究院2003年培育成功的新一代超速生抗虫杨,雌株。耐桑天牛、易生根、速生（年胸径生长量达5.8 cm,年平均高生长量4.9 m）。为了提高丹红杨的造林成活率,进行了杨树插干深栽造林试验。试验结果表明,丹红杨采用插干深栽造林方法与传统的带根植苗造林相比,具有成本低、成活率高、生长量大等特点,是一种比...     

华北地区采用无机氮测试和植株速测进行夏玉米氮肥推荐

A field experiment with a split-plot design was carried out at Dongbeiwang Farm in Beijing Municipality to establish reliable N fertilizer recommendation indices for summer maize (Zea mays L.) in northern China using the soil Nmin(mineral N) test as well as the plant nitrate and SPAD (portable chlorophyll meter readings) tests. The results showed that Nrnin sollwert (NS) 60 kg N ha^-1 at the third leaf stage and N rate of 40 to 120 kg N ha^-1 at the tenth leaf stage could meet the N requirement of summer maize with a target yield of 5.5-6 t ha^-1. Sap nitrate concentrations and SPAD chlorophyll meter readings in the latest expanded maize leaves at the tenth leaf stage were positively correlated with NS levels, indicating that plant nitrate and SPAD tests reflected the N nutritional status of maize well. Considering that winter wheat subsequently utilized N after the summer maize harvest, the 0-90 cm soil Nmin (74 kg N ha^-1) and apparent N loss (12 kg N ha^-1) in the NS60＋40 treatment were controlled at environmentally acceptable levels. Therefore NS60＋40, giving a total N supply of 100 kg N ha^-1, was considered the optimal N fertilizer input for summer maize under these experimental conditions.     

播种造林种基盘基质的改良研究

 为提高干旱半干旱地区植被恢复中的种子发芽率、成活率和初期生长量,提出了局部改善植物生长环境的技术,即播种造林的种基盘绿化技术。实验研究了添加物对种基盘基质水分特性的影响和使用种基盘绿化技术对植物生长的影响。结果表明:通过添加土壤活性改良剂,可以提高种基盘基质的透水性和吸水速率,降低其表面蒸发量,并能促进植物的地上部生长;添加土壤侵蚀防止剂,对种基盘基质的透水性及植物的生长没有显著的影响,但对于维持种基盘形状、提高施工效果很有帮助;通过种基盘进行播种造林,可以增加根的生长粗度,并能促进植物根系向土壤深处发展,从而有利于提高苗木的抗旱能力。     

模拟自然降雨条件下植物根系增强边坡土体抗剪强度特征

该研究以位于青藏高原东北部黄土区的西宁盆地作为试验区,采用柠条锦鸡儿(Caragana korshinskii Kom.)、霸王(Zygophyllum xanthoxylon(Bunge)Maxim.)、垂穗披碱草(Elymus nutans Griseb.)、细茎冰草(Agropyron trachycaulum(Linn.)Gaertn.)的单播种植,以及柠条锦鸡儿分别与细茎冰草、垂穗披碱草混播种植等2种方式,开展了原位模拟降雨试验并采用直接剪切试验,系统分析了模拟降雨试验前后试验区边坡表层以下3个不同位置处复合体抗剪强度大小及其随深度变化规律。结果表明:模拟降雨试验前,由柠条锦鸡儿与细茎冰草、垂穗披碱草混播的边坡a层(0~20 cm)根-土复合体黏聚力分别为19.5、18.9 k Pa,均较相同条件下单播边坡a层复合体黏聚力大;混播种植边坡各层根-土复合体黏聚力均较模拟降雨试验后裸坡a层土体黏聚力大,其中柠条锦鸡儿与细茎冰草混播边坡、垂穗披碱草混播边坡模拟降雨试验后,a层复合体黏聚力分别较裸坡a层黏聚力的增幅为30.65%~56.45%;柠条锦鸡儿、霸王、垂穗披碱草、细茎冰草单播边坡b层复合体黏聚力增幅为4.17%~38.89%;柠条锦鸡儿分别与细茎冰草、垂穗披碱草混播边坡b层黏聚力增幅为29.17%~34.72%;边坡c层土体黏聚力增幅相对不及a层、b层显著,反映了草本起到浅层加筋作用,灌木则起到深部锚固作用。     

Modeling of Punching Failure Initiated by Concrete Splitting at Longitudinal Bar Level for Slabs without shear reinforcement

A new punching failure model has been developed for thinner slabs (≤120 mm thick) yet with a larger reinforcement ratio (＞085). On the assumption that the trigger of ultimate failure is the loss of dowel action caused by concrete splitting along the horizontal surface at longitudinal bar level, an equilibrium equation was established and an upper bound solution was obtained. The computation of punching shear capacity shows that for a total of 194 specimens collected, the mean and the coefficient of variation are 1072 and 0.250 respectively. As for the 116 members (out of all 194 ones) with the above character, it is found that there is little change of the mean (equal to 1017) yet an apparent decrease in the coefficient of variation (equal to 0184), which justifies the proposed hypothesis and refined mode in estimating punching resistance of such members.