Experimental research on behavior of 460 MPa high strength steel I-section columns under cyclic loading

To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.

Effects of geometric configuration on droplet generation in Y-junctions and anti-Y-junctions microchannels

Droplets generation in Y-junctions and anti-Yjunctions microchannels are experimentally studied using a high speed digital microscopic system and numerical simulation.Geometric configuration of a microchannel,such as Y-angle（90°,135°,-90° and-135°）,channel depth and other factors have been taken into consideration.It is found that droplets generated in anti-Y-junctions have a smaller size and a shorter generation cycle compared with those in Yjunctions under the same experimental conditions.Through observing the internal velocity field,the vortex appearing in continuous phase in anti-Y-junctions is one of the key factors for the difference of droplet size and generation cycle.It is found that droplet size is bigger and generation cycle is longer when the absolute angle value of the intersection between the continuous and the dispersed phases（i.e.,the angle between the main channel and the continuous phase or the dispersed phase channel） increases.The droplet＇s size is influenced by the Y-angle,which varies with the channel depth in Y-junctions.The Y-angle has a positive effect on the droplet generation cycle,but a smaller height-width ratio will enhance the impact of a continuous and dispersed phase＇s intersection angle on the droplet generation cycle in Y-junctions microchannels.

Experimental research on oil fi lm thickness and its microwave scattering during emulsifi cation

Synthetic Aperture Radar(SAR) plays a major role in identifying oil spills on the sea surface.However,obtaining information of oil spill thickness(volume) is still a challenge.Emulsification is an important process affecting the thickness and normalized radar cross section(NRCS) of oil film.Experiments of crude oil emulsification with C-band fully-polarized scatterometer were conducted combining airborne hyperspectral imaging spectrometer and 3 D laser scanner observation data,to provide experimental parameters and method to support accurate remote sensing monitoring on marine oil spill.It is further proved that through quantitative homogeneous emulsified oil spill experiments,to a certain extent,the NRCS of oil film increased during the emulsification process of crude oil.The backscattering mechanism of crude oil emulsification was explored using a semi-empirical model(SEM);the change of oil film NRCS was modulated by its dielectric constant and surface roughness,in which the dielectric constant showed a dominant effect.The relationship between thickness and NRCS of oil film was studied under two experimental conditions.The differences of NRCS between oil film and adjacent seawater(Δσ~0) and the damping ratio(DR) were found to have a linear relationship with oil thickness,which were best in the vertical polarization mode(VV) at 45° incident angle during the quantitative crude oil homogeneous emulsification process.In the natural emulsification process of continuous oil spill in which oil film was mixed with both crude oil and emulsified oil,an empirical equation of oil film thickness is preliminarily established.The Δσ~0,DR,and the empirical equation of oil film thickness were applied to the marine continuous oil spill incident on a 19-3 oil platform with spaceborne SAR image and successfully explained the distribution of the relative thickness of the oil film.

Prevalence and Correlates of Elevated Blood Pressure in Chinese Children Aged 6-13 Years: a Nationwide School-Based Survey

Objective To estimate the prevalence of elevated blood pressure（EBP） in Chinese children and identify individual and family factors associated with EBP. Methods A nationwide cross-sectional study was conducted in 2010 using stratified cluster sampling. Participants＇ blood pressure was measured, and their parents completed a questionnaire on personal and family characteristics. Prevalence and correlates of EBP were assessed. Results Among a total of 24,333 participants, 20.2% of boys and 16.3% of girls had EBP. The prevalence of EBP increased with the ascending trend of waist circumference, Waist-to-height ratio, and body mass index. The adjusted prevalence ratios（aP Rs） for obese boys and girls were 2.50 and 2.97, respectively. Fewer urban boys（16.2%） had EBP than rural boys（21.7%）. Boys with a family history of hypertension were 12% more likely to have EBP. Children whose mothers received a college education tended to have lower likelihood of EBP; with an aP R was 0.85 among boys and 0.78 among girls. Conclusion EBP is common among obese students and those who have a family history of hypertension. A negative association between mothers＇ education levels and EBP risk in children was found.

冷弯薄壁型钢纯弯构件截面分类

为研究冷弯薄壁卷边槽钢纯弯构件截面分类,基于试验数据验证后的有限元模型,对不同板件宽厚比下冷弯薄壁卷边槽钢纯弯构件进行了大量的参数分析。结果表明:抗弯承载力随翼缘与腹板宽厚比的减小而增大。在考虑翼缘与腹板相关作用的前提下,基于截面承载力得出板件截面宽厚比限值,提出了冷弯薄壁卷边槽钢纯弯构件截面分类方法。

底部填芯预制节段拼装桥墩抗震性能数值仿真分析

为促进预制节段拼装桥墩在山区复杂环境及强震地区的应用,提出了一种底部填芯的预制节段拼装桥墩,采用ABAQUS有限元模型讨论了填芯段高度、初始张拉力和耗能钢筋配筋率等关键参数对底部填芯预制节段拼装桥墩抗震性能的影响规律。研究结果表明:随着填芯段高度的增大,底部填芯预制节段拼装桥墩的承载能力和耗能能力显著提高,但残余位移和填芯段上部接缝开口宽度也增大;随着初始张拉力的增大,底部填芯预制节段拼装桥墩承载能力和耗能能力略有提高,残余位移和墩底混凝土损伤程度基本不变;随着耗能钢筋配筋率的增大,底部填芯预制节段拼装桥墩承载能力和耗能能力提高,但填芯段上部接缝开口宽度增大。研究结果可为底部填芯预制节段拼装桥墩合理构造提供参考,促进预制拼装桥墩在山区复杂环境和强震地区的应用。

不同影响因素下巷道变形特征模拟研究

以王晁煤矿16层煤开采巷道为背景,基于正交试验通过FLAC^(3D)数值模拟软件建立巷道变形破裂演化的计算模型,系统研究了不同巷道断面形状、巷道断面尺寸、巷道断面宽高比对巷道围岩变形、破坏和应力演化规律的影响。模拟结果表明,各参数对巷道变形破坏影响的显著性次序为巷道断面大小>断面形状>断面宽高比;巷道断面大小是影响巷道变形破坏的最主要因素,断面大小与巷道的变形和破坏呈正相关;椭圆形断面巷道最为稳固,塑性区发育高度和最大垂直位移量显著小于直墙半圆拱断面巷道与矩形断面巷道;断面宽高比对巷道变形破坏影响较小,但对最大垂直应力的产生影响较大。研究揭示了不同巷道断面对巷道围岩变形破坏演化规律,可为煤矿巷道设计提供参考。

对《砌体结构设计规范》中高厚比修正系数等问题的探讨

文章指出了《砌体结构设计规范》(GB 50003—2011)中关于带门窗洞口砌体墙允许高厚比的修正系数μ2的计算精度不足,并根据弹性稳定理论,提出了两端铰接变截面柱临界荷载Pcr的正确表达式,通过理论计算和有限元模拟对其给予了证明,此外,还推导了门窗洞口最不利布置时的μ2表达式。在此基础上,提出了比《砌体结构设计规范》(GB 50003—2011)更合理的有洞口墙体的允许高厚比修正系数μ2计算公式,同时对μ2的相关应用细则提出了修正建议。以修正后的两端铰接柱临界荷载Pcr为基础,提出了规范中变截面柱下段计算长度H0的更合理形式,为便于工程应用,最后对规范中有吊车房屋变截面柱计算长度的应用条款提出了修改建议。

锻造毛坯形状优化设计的研究

近几年来 ,锻造形状优化得到了众多学者的关注。本文对单工序锻造问题的毛坯形状优化进行了研究。以毛坯高径比为优化设计变量 ,目标函数取为实际锻件超出预定理想直线部分的体积 ,以黄金分割法进行优化迭代 ,给出了目标函数的表示方法及计算表达式。并对一典型的轴对称H型锻件的毛坯形状进行了优化设计 。

水平地震作用方向对异形柱结构整体分析的影响

钢筋混凝土异形柱由于截面几何性质的特殊性,在进行该类结构的抗震计算时,地震作用方向是一个不可忽视的因素,通过对异形柱截面和异形柱结构的计算结果分析,说明了无论是在异形柱框架结构中,还是一般结构中部分采用了异形柱,都应根据具体情况考虑地震作用方向的不利影响。

短肢剪力墙抗震性能理论分析与数值模拟

为研究短肢剪力墙的抗震性能，首先考虑边缘约束构件的影响，利用平截面假定和短肢剪力墙正截面界限配筋，建立了短肢剪力墙墙肢轴压比限值的理论计算公式，并对短肢剪力墙抗震性能研究的试验进行数值模拟．然后利用轴压比计算理论获得试验试件的轴压比限值，通过改变短肢剪力墙数值模型的墙肢轴压比数值，分别研究短肢剪力墙墙肢轴压比在大于或小于墙肢轴压比限值时对其抗震性能的影响．最后结合数值模拟分析了短肢剪力墙在不同截面高厚比下的抗震性能．研究表明：骨架曲线各特征点的计算值与试验值的比值在0．86～1．08之间，数值模拟结果与试验结果吻合较好；短肢剪力墙墙肢轴压比小于轴压比限值时，轴压比每提高0．1，其最大水平承载力提高约7．81％，延性降低约4．52％；短肢剪力墙墙肢轴压比大于轴压比限值时，轴压比每提高0．1，其最大水平承载力降低约5．50％，延性降低约6．85％，同时验证了墙肢轴压比限值计算理论的准确性；截面面积相同时，墙肢截面高厚比越大，其抗震性能越好．

薄壁及加劲圆钢管的抗弯性能研究

风力发电作为一种可再生能源在国内外得到了迅速的推广和应用,而塔筒是风力发电设备的重要承载构件,其设计对于结构的安全至关重要。塔筒常采用薄壁圆形截面,主要承受弯矩作用,而国内外对其研究较少,文章针对大径厚比薄壁圆钢管的受弯性能进行研究,完成6个大径厚比薄壁圆钢管和4个加劲薄壁圆钢管的抗弯性能试验,试件的主要设计参数为径厚比和加劲肋,构件的径厚比从100变化到300;同时采用有限元分析钢管初始几何缺陷对受弯承载力的影响。研究结果表明:径厚比较大时,钢管受压区出现局部屈曲,将显著降低构件的延性,同时降低其承载力;加劲肋的设置有效限制了受压区钢管的局部屈曲,改变了构件的破坏模式,提高了构件的延性和承载力。初始几何缺陷会降低构件的抗弯承载力,随着径厚比的增加降低的幅度逐渐增大,因此在实际工程中要严格限制钢管的初始几何缺陷幅值。

H形截面压弯钢构件板组弹塑性相关屈曲分析

建立轴压力和水平荷载作用下焊接H形截面钢构件有限元分析模型以模拟板组弹塑性相关屈曲性能,改变轴压比、翼缘宽厚比、腹板高厚比及翼缘-腹板厚度比等参数,进行一系列非特厚实截面钢构件弹塑性局部相关屈曲非线性有限元分析,获得一系列极限弯矩比与这些参数的相关曲线,表明极限弯矩比随轴压比和翼缘宽厚比增大而明显降低.得到精度较高的正则化极限弯矩比拟合公式,基于整体和局部等稳原则导出板组容许宽厚比相关曲线.在某些条件下,钢结构设计规范的翼缘和腹板宽厚比限值可能超出容许宽厚比相关曲线限定的参数范围.

方形分离器入口高宽比及直段高度对分离性能的影响

为了研究结构参数对方形分离器性能的影响,设计了15个不同入口高宽比(a/b)和直段高度(h)的入口带加速段的方形分离器,每一个分离器都具有相同的直段边长(D),入口高宽比的变化范围为3.8~10.6,直段高度的变化范围为1.8D^2.8D。在大型冷态试验台上相同的运行工况下,测试了它们的分离器效率及阻力。结果表明:随着入口高宽比的增大,分离效率先增大后减小,在a/b=8时分离效率最高;随着直段高度的增大,分离效率先减小后增大,在h=2.3D时效率最低。分离器阻力随着入口高宽比增大而增大,随着直段高度的减小而减小。二者优化值为a/b=8和h=1.8D,对应的分离器阻力为1.22 kPa。

H型钢楔形薄壁构件的局部屈曲性能分析

用三维退化曲壳元离散H型钢楔形薄壁构件 ,对其进行了考虑双重非线性的全过程分析 ,提出了评价H型钢楔形薄壁构件局部屈曲性能的特征荷载。考察了平均腹板宽厚比、楔率等参数对H型钢楔形薄壁构件屈曲后强度的影响 。

26655例体检人群中肥胖指数与慢性肾脏病联系的横断面调查（英文）

目的:探讨大样本体检人群中慢性肾脏病(chronic kidney disease,CKD)与肥胖指数(体质量指数,腰围,腰围身高比)之间的联系。方法:按规定标准纳入2013年6月至2014年2月在中南大学湘雅三医院健康管理中心参加健康体检的26 655例个体,收集相关人体学资料及生化指标,进行logistic回归分析等统计学分析。结果:男性及女性个体中CKD的流行率分别是9.6%及3.1%。多因素logistic回归分析显示在糖尿病及高血压男性人群中,体质量指数、腰围、腰围/身高是CKD的独立危险因素。而在女性人群中,肥胖指数并非CKD的独立危险因素(P<0.01)。受试者工作特征(receiver operating characteristic,ROC)曲线分析显示在糖尿病男性人群中体质量指数、腰围、腰围/身高截点值分别为28.7kg/m^2,90.7cm及0.56时预测CKD的敏感性分别是24.8%,58.5%,45.5%,特异性分别是83.3%,54.4%,69.6%,其曲线下面积分别为0.56,0.57,0.59。而在高血压男性人群中体质量指数、腰围、腰围/身高截点值分别为27.0kg/m^2,91.2 cm及0.54时预测CKD的敏感性分别是41.0%,47.0%,50.1%,特异性分别是68.0%,63.0%,61.4%,其曲线下面积分别为0.54,0.56,0.57。结论:在糖尿病及高血压男性人群中,体质量指数,腰围,腰围/身高与CKD风险增加相关,然而肥胖指数预测CKD的效应有限。

反复荷载作用下矩形钢管混凝土柱的滞回性能研究

文中首先建立了钢管与核心混凝土界面的粘结-滑移滞回模型、考虑包辛格效应的钢材单轴滞回模型和考虑矩形钢管约束效应后内填混凝土的单轴应力-应变滞回模型。在截面纤维模型的基础上,建立了考虑界面粘结-滑移的矩形钢管混凝土柱分析模型,用Fortran语言编制了相应的全过程分析程序。考虑轴压比和截面高宽比两个因素,对19个矩形钢管混凝土试件进行了数值模拟计算,并对荷载-位移滞回关系进行了初步的理论分析。

基于XFEM的混凝土楔入劈拉断裂过程模拟分析

为研究混凝土的楔入劈拉断裂特性,采用扩展有限元法数值模拟了不同缝高比、不同截面高度的混凝土楔入劈拉试件断裂过程,研究了混凝土楔入劈拉试件裂缝扩展特性和尺寸效应。结果表明,起裂韧度受初始缝高比和试件截面高度的影响较小,但不具有明显的尺寸效应;当缝高比大于0.5或截面高度大于500mm时,失稳韧度才不具有尺寸效应。结果可为混凝土断裂特性研究提供参考。

压边力曲线对极限拉深高度的影响

运用ANSYS模拟软件对不同压边力曲线在筒形件拉深过程中的影响进行分析。分析发现,能够达到筒形件极限拉深高度,并且不发生起皱和破裂的压边力有一个数值范围,范围中的压边力曲线可以作任何类型的变化。但不同类型的压边力曲线愈接近压边力数值范围内的下限值,压边力曲线的变化幅度愈小,拉深件的危险断面处,厚度愈大或厚度减薄率愈小,厚度和厚度减薄率在数值上也愈趋于一致,对提高拉深过程的稳定性和拉深件质量最为有利。

钢筋混凝土受弯构件正截面抗裂相似性研究

引入结构仿真模型试验相似理论,提出了钢筋混凝土受弯构件正截面抗裂弯矩的相似比计算方法。根据试验研究成果提出了考虑截面高度、混凝土保护层厚度与配筋率等参数的截面抵抗矩塑性系数计算公式。通过大型钢筋混凝土梁及其模型试验梁的正截面抗裂弯矩对比试验,证明所提公式可用于原型和模型构件之间正截面的抗裂换算,为模型试验设计提供了科研依据。