Failure behavior around a circular opening in a rock mass with non-persistent joints:A parallel-bond stress corrosion approach

The stability of underground excavations is influenced by discontinuities interspaced in surrounding rock masses as well as the stress condition. In this work, a numerical study was undertaken on the failure behavior around a circular opening in a rock mass having non-persistent open joints using PFC software package. A parallel-bond stress corrosion(PSC) approach was incorporated to drive the failure of rock mass around the circular opening, such that the whole progressive failure process after excavation was reproduced. Based on the determined micro parameters for intact material and joint segments, the failure process around the circular opening agrees very well with that obtained through laboratory experiment. A subsequent parametric study was then carried out to look into the influence of lateral pressure coefficient, joint dip angle and joint persistency on the failure pattern and crack evolution of the rock mass around the circular opening. Three failure patterns identified are step path failure, planar failure and rotation failure depending on the lateral pressure coefficient. Moreover, the increment of joint dip angle and joint persistency aggravates the rock mass failure around the opening. This study offers guideline on stability estimation of underground excavations.

Ultimate Load Capacity and Reinforcement of Circular-Hollow-Section N-Joint

Experimental research and numerical analysis were applied to study the ultimate load capacity(ULC) and reinforcement of circular-hollow-section N-joint.Four specimens were tested under static load.The ULC of each specimen was obtained and the detailed failure conditions were discussed.Based on the results, both welding a plate on the chord member and filling concrete in the chord member are effective to reinforce the N-joint, but it is suggested that these two methods should not be applied simultaneously.Moreover, considering the four important influence factors of ULC of the joints, the ratio of chord diameter to chord thickness, the ratio of diagonal member diameter to chord member diameter, the axial load on the chord member and the gap size between the two brace members, a new prediction formula of ULC of N-joint was put forward based on numerical analysis results.The new formula was proved to be more accurate than the current Chinese design code in a wide range.

Elasto-plastic Analysis of Circular Tunnels in Jointed Rock Masses Satisfy the Hoek-Brown Failure Criterion

The relationship between the Hoek-Brown parameters and the mechanical response of circular tunnels is il-lustrated. Closed-form and approximate solutions are given for the extent of the plastic zone and the stress and dis-placement fields under axisymmetrical and asymmetric stress conditions. For the same rock masses and under axisym-metrical stress conditions,the radius of the plastic zone in terms of Hoek-Brown criterion is generally an approximation of the radius in terms of the Mohr-Coulomb criterion. The radius in terms of the Hoek-Brown criterion is larger under low stress conditions. For poor quality rock masses (GSI<25),measures (such as grouting,setting rock bolts,etc.) that improve the GSI of rock masses are effective in improving the stability of tunnels. It is not advisable to improve the sta-bility of the tunnels by providing a small support resistance p through shotcrete,except for very poor quality jointed rock masses. Without reference to the quality of the rock mass,the disturbance factor D should not less than 0.5. Meas-ures which disturb rock masses during tunnel construction should be taken carefully when the tunnel depth increases.

Who Gets up or Gets out?——A joint circular to urge textile industry to be restructured and upgraded

Ten governmental organizations recently issued a joint circular (No.762-2006, State Development & Reform Commission) to guide Chinese textile growth in the next five years (2006-2010). The circular, seriously taken as guideline policy, is given out amid aggravating factors for resources, environment, trade disputes, structural problems and other challenging issues that Chinese textile industry is supposed to address in

Ultimate Bearing Capacity of Hollow Spherical Joints Welded with Circular Pipes under Eccentric Loads

The hollow spherical joints welded with circular pipes applied to the National Swimming Center of China are subjected to large bending moments, but the influence of bending moments is not considered in the design equations in Technical Specification for Latticed Shells. Based on the von Mises yield criterion, multilinear isotropic hardening rule and associated flow rule, the elasto-plastic finite element model is put forward to analyze the behavior of the joints, and a calculation method for the joints under bending moments or eccentric loads is proposed. It is shown by the analytical results of joint that the stiffening rib can improve the ultimate bearing capacity by 10% for joints under axial tensile load, by 40% for joints under axial compressive load, and by 50% for joints under bending moment. The unified calculation equations for joints with or without stiffening rib are put forward, which can be applied to calculating the ultimate bearing capacity of the hollow spherical joints with circular pipes under eccentric loads.

Radiographic Circularity of Capitellum and Its Relation to the Range of Motion

Background: The shape of the capitellum has been traditionally described in anatomy books as part of a sphere. Alteration in the capitellar morphology following pathologies such as fractures, osteochondrosis, and degenerative arthritis has been associated with less optimum functional results. Aim: To define the relationship between the sphericity of the capitellar morphology as measured on trauma series plain radiographs and the elbow range of motion. Methods: 40 patients were included in the study. All patients recruited from the upper limb clinics presented with non-elbow joint-related complaints. The elbow range of motion was measured using a standardized technique. Digital anteroposterior and lateral radiographs of patients’ elbows were used to measure capitellar circularity using the ImageJ processing program and circularity calculation equation. Correlation analyses were conducted between the degree of capitellar sphericity and elbow range of motion. Results: The results of measurements from the anteroposterior radiographs showed a positive correlation between increased circularity and an increase in the range of flexion, pronation, and supination. The range of extension decreased with the increased circularity of the capitellum. This trend was repeated with measures of lateral radiographs but was statistically not significant. Conclusion: Native capitellar circularity has an impact on the elbow range of motion. This should be put into consideration when dealing with pathologies that affect capitellar morphology.

非编码RNA在颞下颌关节炎中的研究进展

颞下颌关节炎(temporomandibular joint osteoarthritis,TMJOA)是一种临床常见疾病,但发病机制尚不明确且缺乏有效的治疗手段,给患者带来很大困扰。因此,探究TMJOA的发病机制,寻找有效的治疗方法具有重要意义。近年来的研究表明,非编码RNA(noncoding RNA,ncRNA)参与调控TMJOA的发生、发展,在其诊断和治疗方面具有巨大潜力,因此有望成为新的诊断标志物和治疗靶标。本文将对ncRNA在TMJOA中的研究进展作一综述。

基于循环孔洞扩张模型的X型圆管节点超低周疲劳寿命预测

海洋工程钢结构在服役过程中,受风、浪、流或地震等极端循环载荷的影响,易发生超低周疲劳断裂破坏,造成人员伤亡及财产损失,因此超低周疲劳断裂分析及寿命预测对于海工结构安全性评估至关重要。然而,现阶段基于累积损伤理论提出的多种超低周疲劳寿命预测模型无法对多尺度节点实现统一预测,造成了实际工程应用的不便。因此文中基于循环孔洞扩张模型开展X型圆管节点超低周疲劳寿命预测。首先,开发了基于循环孔洞扩张模型的VUSDFLD程序,实现ABAQUS与FORTRAN子程序联合应用,利用有限元分析验证循环孔洞扩张模型在X型圆管节点超低周疲劳断裂分析中的有效性;其次,根据多组X型圆管节点超低周疲劳断裂有限元分析结果,在宏观层面提出了一种基于Manson-Coffin公式的超低周疲劳寿命预测公式;最后,依据Miner理论,将适用于等幅加载的超低周疲劳寿命公式扩展至变幅加载情况,验证了多种节点尺寸下超低周疲劳公式的适用性,为工程应用提供了理论依据。

支管轴压下高强钢圆管X形节点的承载力计算公式

研究了支管受压的Q460、Q690、Q960高强钢圆管X形节点的静力性能。采用经试验数据验证的有限元模型进行节点有限元参数分析,研究高强钢牌号、支管与主管外径之比(β)、主管外径与其管壁厚度之比(2γ)、主管轴向应力比(n)对节点性能的影响;与有限元参数分析和文献中试验结果对比,评价我国钢结构设计标准计算公式的适用性。结果表明,节点发生主管塑性破坏,节点承载力多由主管局部变形限值(3%主管外径)确定;多数情况下钢结构设计标准计算公式高估了高强钢圆管X形节点的承载力;主管受到压力或较大拉力时均会降低节点承载力。最后,针对不同钢材牌号的圆管X形节点给出了建议的2γ范围。基于主管塑性破坏,提出了考虑高强钢屈服强度、主管拉压效应的圆管X形节点承载力计算公式。

带接缝圆形地下连续墙室内模型试验研究

为研究圆形基坑开挖过程中带接缝时圆形地连墙的内力以及变形特征,考虑接缝数量、墙体直径、有无内衬等工况,通过室内模型试验,采用ABAQUS建立三维数值模型,对模型试验中圆形基坑分步开挖时地连墙的受力特点进行了模拟分析。结果表明,存在接缝时,圆形地连墙仍具有空间拱效应,产生的环向压应力明显大于竖向应力;墙体侧向位移值很小,墙后土体沉降值较小,环向应力与环向位移变化规律基本一致,呈现中间大两头小的分布形式;墙体直径对地连墙的空间拱效应影响最大,接缝数量次之,内衬影响最小。

圆谐Joint变换光学图像识别的研究

圆谐Joint变换光学图像识别的研究@冯选旗@刘聚成@王涛...

内加强环式圆钢管混凝土柱-钢蜂窝梁节点抗震性能研究

目的 研究内加强环式圆钢管混凝土柱-钢蜂窝梁节点的抗震性能,为工程应用提供参考。方法 采用ABAQUS软件建立节点模型,对比其与内加强环式圆钢管混凝土柱-钢实腹梁的抗震性能,分析不同因素对节点抗震性能的影响。结果 与内加强环式圆钢管混凝土柱-钢实腹梁相比,两者抗震性能相近;梁柱线刚度比和钢材牌号对抗震性能影响较大,但梁柱线刚度比对节点的承载力和耗能能力影响最大,最大相差分别为169.3%和29%,钢材牌号对节点的延性影响最大,最大相差41.2%;含钢率、内加强环宽度和厚度对抗震性能影响不大,但对延性、耗能能力、屈服和极限位移影响较明显。结论 内加强环式圆钢管混凝土柱-钢蜂窝梁节点具有可行性,符合“强柱弱梁”的抗震设计要求。

青藏高原建立农业循环经济探索

青藏高原是中国最大、世界海拔最高的高原,被称为“世界屋脊”。拥有全世界最高、最年轻而水平地带性和垂直地带性紧密结合的自然地理单元、丰富的野生动植物资源和水资源。由于其地理位置和历史文化的特殊性,使得青藏高原的生态系统、经济发展模式和传统社会文化存在特殊性。该文通过搜集资料、逐步分析,发现经济发展为青藏高原生态带来极大的危害。而生态的破坏必然会阻碍经济的发展,尤其是农业经济。建立循环经济迫在眉睫,所谓农业循环经济,就是在加强生态农业建设的同时提高经济效益。经研究发现,循环经济是缓解资源压力、促进资源可持续发展的有效方法。加强政府的领导,调动居民的积极性,实施“共同管理模式”,以“循环型”代替“消耗型”农业发展模式,是实现循环经济的重要方法。

某不规则钢框架结构及其梁-柱节点分析

介绍了一栋不规则2层钢框架结构体系,该项目基于建筑要求,钢框架梁、柱要求全部采用圆钢管型截面。由于实际工程中框架梁、柱截面全部采用圆管型截面的钢框架结构研究与应用较少,故为满足设计的需要,并确保结构体系的安全及可靠,在设计过程中对该结构体系及节点进行了一些分析与研究,以解决设计中的难点所在。分析结果表明,经过周到合理的分析,并配以恰当的构造措施,圆管型框架梁完全可运用到钢框架结构设计当中,圆管型截面的钢框架梁-柱节点具有良好的抗震性能。结构设计中若判断构件以受弯为主,箱形或工字型截面有较好的经济性。

X形圆钢管相贯节点平面内受弯抗震性能试验研究

为了研究X形圆钢管相贯节点的平面内受弯抗震性能,进行了支主管直径比β不同的2个正交X形节点(支主管夹角θ=90°)和2个斜交X形节点(θ=55°)的平面内受弯滞回性能试验,并进行了有限元分析。结果表明:四个X形节点均表现出良好的抗震性能,均为相贯线附近主管管壁开裂破坏,均以主管管壁的塑性变形及开裂后裂纹扩散为主要抗震耗能模式。对比之下,提高支主管直径比β能显著提高X形节点的平面内抗弯承载力、延性和耗能能力;正交节点在正、负弯矩作用下的承载力及延性均较接近;斜交节点在负弯矩作用下的承载力大于在正弯矩作用下的承载力,但其在正弯矩作用下的延性更好;β较大斜交节点在正、负弯矩作用下的承载力及延性的差异比β较小时更明显;无论是β较大还是β较小的X形节点,斜交节点的能量耗散系数小于相应的正交节点;当夹角θ较小(≤55°)时,采用因子1/sinθ略偏保守地估计支主管斜交对节点负向平面内抗弯承载力的加强作用,但高估了支主管斜交对β较大节点的正向平面内抗弯承载力的加强作用。

前交叉韧带损伤患者膝关节前交叉韧带重建术中采用股骨椭圆隧道技术的效果

目的观察前交叉韧带损伤患者在膝关节前交叉韧带重建术中采用股骨椭圆隧道技术对移植物、膝关节功能的影响。方法选择2019年1月至2021年6月该院收治的80例前交叉韧带损伤患者为研究对象,均接受关节镜下膝关节前交叉韧带单束解剖重建术治疗。根据术中制备股骨隧道方法的不同分为观察组与对照组,每组40例。对照组采用圆隧道技术,观察组采用椭圆隧道技术。术后3、6、12个月定期随访,比较两组术后移植物情况、移植物成熟度、膝关节功能及并发症发生情况。结果术后12个月时,观察组移植物滑膜覆盖情况、移植物张力情况优于对照组,差异均有统计学意义(P<0.05)。术后3个月时,两组近、中、远端的移植物信号/噪声比(SNQ)比较,差异均无统计学意义(P>0.05)。术后6、12个月时,观察组近、中、远端SNQ均低于对照组,差异均有统计学意(P<0.05)。术后3个月时,两组Tegner评分比较,差异无统计学意义(P>0.05),观察组Lysholm、膝关节功能指数(IKDC)评分高于对照组,KT-1000测量值大于对照组,差异均有统计学意义(P<0.05)。术后6、12个月时,观察组Tegner、Lysholm、IKDC评分高于对照组,KT-1000测量值大于对照组,差异均有统计学意义(P<0.05)。两组并发症发生情况比较,差异无统计学意义(P>0.05)。结论前交叉韧带损伤患者在膝关节前交叉韧带重建术中采用股骨椭圆隧道技术制备股骨隧道,患者移植物滑膜覆盖情况、移植物张力情况更好,且对移植物成熟度、膝关节功能的远期效果更具优势。

星载天线支撑桁架的结构设计、模型研制及实验

制备能可靠收展的高收纳比、动力学性能优良的支撑结构是大型星载天线技术发展的关键需求之一。针对环形天线反射器的支撑结构提出改进方案,通过设计支撑桁架的接头结构使其适用于多种单胞数目,为环形天线支撑桁架的地面动力学实验提供便利。首先对支撑桁架进行三维建模及运动仿真,验证方案的可行性,然后分别研制出了可展桁架实物模型,最后进行了支撑结构展开实验,验证了可展支撑桁架结构设计的可行性。

C臂正位圆孔压杆技术在股骨髓内钉远端锁定螺钉中的临床应用

目的探讨C臂正位圆孔压杆技术在股骨髓内钉远端锁定螺钉中的临床应用效果。方法选取2019年2月—2022年6月收治的86例股骨干骨折患者作为研究对象,按照随机数字表法将其分为对照组和研究组,各组均43例;两组均行股骨髓内钉远端锁定螺钉固定,对照组术中以徒手技术锁钉,研究组术中以C臂正位圆孔压杆技术锁钉;比较两组一次锁钉成功率、围手术期相关指标、膝关节功能及并发症发生情况。结果研究组一次锁钉成功率高于对照组,差异有统计学意义(P<0.05);研究组远端锁定透视时间、远端锁定成功时间及骨折愈合时间均短于对照组,差异有统计学意义(P<0.05);研究组膝关节功能优于对照组,差异有统计学意义(P<0.05);两组患者并发症发生率比较,差异无统计学意义(P>0.05)。结论股骨髓内钉远端锁定螺钉固定术中采用C臂正位圆孔压杆技术固定可提高一次锁钉成功率,缩短锁定时间,促使膝关节功能恢复。

TX型和TT型圆管节点轴向承载力的影响因素分析

空间管节点几何构形多样,受力复杂,影响其承载性能的因素较多.本文采用有限元软件ANSYS,选用SHELL181壳体单元建模计算,并考虑了焊缝的影响,分析了荷载路径、弦管轴向应力对TX型圆管节点轴向承载力的影响,以及弦管长度和边界条件对TT型圆管节点轴向承载力的影响.

基于均匀圆阵的近场源三维参数估计

基于均匀圆阵,提出一种近场源距离-方位角-俯仰角联合估计算法。利用阵元观测数据,构造一组高阶累积量矩阵,通过矩阵联合对角化技术得到阵列流形矩阵的估计。根据阵列流形矩阵的估计以及近场和远场条件下方位角相同的结论,获得方位角的估计。利用阵列流形矩阵和方位角的估计,得到距离和俯仰角的估计。该方法无需二维频域峰值搜索或参数配对。计算机仿真验证了算法的有效性。