Effect of stocking on juvenile wood stiffness for three <Emphasis Type="Italic">Eucalyptus</Emphasis> species

The effects of stocking on wood stiffness (MoE) for three Eucalyptus species are quantified using a 6-year-old trial established in New South Wales, Australia. An acoustic time-of-flight tool measured the velocity between two probes in the outerwood, from which the stiffness was estimated. Four stocking levels (714, 1,250, 1,667 and 3,333 sph) were examined. Stiffness varied significantly between all species, with E. cloeziana showing the highest stiffness (14.2–15.7 GPa), followed by E. pilularis (12.2–13.5 GPa) and E. dunnii (10.7–12.6 GPa). There was a stiffness increase (around 11%) between 714 and 1,250 stems/ha for all species but thereafter differences between stockings were not always significant. Trees were also assessed for basic density, dbh, total height, crown area, green crown height and stem slenderness (height/dbh). Only stem slenderness had a significant association (0.41 ± 0.17) with stiffness. These findings suggest that, where stiffness is a priority, forest managers could reduce establishment costs with low stockings (around 1,250 stems/ha).

Influence and Its Application of Soil on the Mode of Cantilever Retaining Wall

The modal parameters are the key indexes for the damnification diagnosis and state evaluation. But for the complexities of the structure and soil interaction effect mechanism of cantilever retaining wall system, there is still no appropriate ways to simulate the modal parameters effectively at the moment. To solve the existing problem, practical modal parameters of structure system were obtained by field impulse hammering modal test. Compared them with the modal parameters of structure system ignoring the soil influence, it was concluded that the soil influence can not be ignored. And with the consideration of soil influence, calculation methods of additional stiffness and mass were analysed and modal analysis with the finite element method was undertaken for the retaining wall as well. It was approved that the calculating method for soil influence and impulse hammering modal test is feasible with good agreement with data from field test. Finally, the main disabled modes of the retaining wall, the modal parameters characteristics under damage state and health diagnosis methods were studies and a fast, simple, lossless and effective modal analysis evaluation method was proposed for the health diagnosis of cantilever retaining wall.     

An improved method for and error evaluation of modal pushover analysis

Based on evaluation of the basic principle and error of the modal pushover analysis method, an improved method is suggested by selecting rational values of stiffness reduction parameters of beams and columns in a reinforced concrete frame corresponding to the global target displacement ductility ratio. A 10 story and a 16 story reinforced concrete plane frame are designed as examples to investigate the influence of higher modes. Nonlinear seismic responses of the two frames under excitations of seven earthquake waves of varying earthquake intensities are selected to be the reference points for a comparison study. The changing rules of the results of modal pushover analysis and modified modal pushover analysis with respect to various natural fundamental periods and different earthquake intensities are studied. Research results show that the error of modal pushover analysis and modified modal pushover analysis will not increase with a larger fundamental period, which implies that modal pushover analysis can cover the effect of higher modes reasonably. When the degree of nonlinearity of the structure is more severe, the modified modal pushover analysis we suggest could decrease the error of normal modal pushover analysis to a certain extent.     

结构设计中应该重视的问题

结构设计中应该引起重视的问题很多,作者着重就结构总体参数控制的意义、方法及注意事项等问题进行了简述。     

Effect of decay on shear performance of dowel-type timber joints

Monotonic and reversed cyclic loading tests were conducted on dowel-type timber joints with varying degrees of wood decay due to Fomitopsis palustris (Berk. et Curt.), a brown rot fungus, and the effect of decay on various shear performances of dowel-type joints was investigated. For joints affected by the brown rot fungus, the initial stiffness, yield load, and maximum load of dowel-type joints were significantly decreased, even with a small mass loss of wood. The reductions in shear performance were the largest for initial stiffness, followed by yield load and maximum load, in that order. For a 1% reduction of the yield load, initial stiffness and maximum load showed reductions of 1.15% and 0.77%, respectively. When dowel-type joints that had been exposed to the brown rot fungus were subjected to reversed cyclic loading, the gap between the dowel and the lead hole of the wood was increased and equivalent viscous damping was decreased. These results indicate that decay around the dowel lead hole especially affects the load-displacement behavior at small displacement level, and dowel-type joints under cyclic loading have very low resistance to forces acting on the wooden structure. Part of this report was presented at the 5th Symposium on Timber Bridges of the Japan Society of Civil Engineers, Tokyo, July 2006; the 56th Annual Meeting of the Japan Wood Research Society, Akita, August 2006; and the Annual Meeting of the Architectural Institute of Japan, Fukuoka, August 2007     

基于ADAMS的双横臂扭杆弹簧独立悬架线刚度计算

运用空间机构运动学方法建立某皮卡车双横臂扭杆弹簧独立悬架的数学模型,根据力学分析给出其垂直线刚度的计算方法。同时还应用ADAMS软件建立同种悬架的多体动力学模型,对双横臂扭杆弹簧独立悬架垂直线刚度随车轮上下摆动的变化进行动态仿真分析。采用两种方法计算、仿真结果的一致性表明这两种方法都是分析双横臂扭杆弹簧悬架垂直线刚度行之有效的方法,也说明了文中所建的模型和提出的计算方法都是正确的。     

轻型慢性乙型肝炎湿热蕴结证与肝郁脾虚证肝组织纤维化分级及肝脏硬度值的比较

目的 比较轻型慢性乙型肝炎（chronic hepatitis B,CHB）湿热蕴结证与肝郁脾虚证患者肝组织纤维化分级、肝脏硬度值的差异。方法 回顾性分析161例轻型CHB患者的临床资料,依据中医辨证分型,分为湿热蕴结证组和肝郁脾虚证组,采用倾向得分匹配法（propensity score matching,PSM）按1：1匹配后,比较两组间肝组织纤维化分级、肝脏硬度值的差异。结果 （1）倾向得分匹配后,共纳入116例轻度CHB,分为湿热蕴结证和肝郁脾虚证组,各58例,两组间临床基本特征差异无统计学意义（P>0.05）;（2）89.7%（104/116）轻型CHB患者肝组织纤维化分级为S0-2,湿热蕴结证肝组织纤维化程度明显重于肝郁脾虚证（P<0.05）;（3）湿热蕴结证组肝硬度值（LSM）明显高于肝郁脾虚证（P<0.05）。结论 轻型CHB患者病程早期,湿热蕴结证较肝郁脾虚证其纤维化程度重,启动抗病毒治疗时,及时运用中医辨治抗肝纤维化,力求及早延缓、阻断纤维化进展。     

强化复合地板刚度预测

应用复合材料经典层合板理论,分析了强化复合地板刚度计算,并使用电阻应变片测得试件在受轴向拉伸或纯弯曲载荷时,其上、下表面的应变ε_x和ε_y,从而对柔度系数的实验值和预测值,正则化柔度系数与弹性常数进行了验证。结果表明,预测值与实验值相对误差较小,建立的强化复合地板刚度计算模型能较好地符合实际情况。图1表5参8     

切削加工机器人刚度模型研究

通过对机器人臂杆的分析研究,把机器人臂杆当作一个柔性杆进行处理,分别求出其拉伸、扭转和弯曲的挠度,运用误差参数建立运动学模型,从而求得臂杆末端挠度的映射模型,并结合机器人各关节传动误差在机器人操作末端上的挠度误差映射,最终在机器人操作末端叠加关节挠度和臂杆挠度,通过刚度的定义求解出机器人总的操作空间刚度。建立的机器人刚度模型可为机器人切削加工过程中刀具的误差补偿提供依据。     

介电弹性体圆柱形驱动器静态特性分析

介电弹性体驱动器的工作条件本质上属于静态操作范围。针对介电弹性体膜材料特性及圆柱形驱动器具体结构对其静态特性的影响,对圆柱形驱动器轴向力的主要影响因素进行了研究。采用超弹性材料Yeoh模型及ABAQUS仿真软件分析了因介电弹性体膜的横向侧边收缩、卷绕后的周向松弛、层间挤压导致的驱动器轴向力变化情况。与实际驱动器的结构尺寸对比表明,驱动器卷绕后的膜层周向松弛对驱动器轴向力影响最大,误差达25.9%,考虑后两项影响因素后计算出的驱动器轴向力与实际误差小于5%;最后对圆柱形驱动器的静态刚度进行了分析,实验结果表明在大位移拉伸时需考虑薄膜滑移因素的影响。