The Anatomic Study on Replacement of Artificial Atlanto-odontoid Joint through Transoral Approach

In order to provide anatomical basis for transoral approach （TOA） in dealing with the ventro lesions of craniocervical junction, and the design and application of artificial atlanto-odontoid joint, microsurgical dissecting was performed on 8 fresh craniocervical specimens layer by layer through transoropharyngeal approach. The stratification of posterior pharyngeal wall, course of vertebral artery, adjacent relationship of atlas and axis and correlative anatomical parameters of replacement of artificial atlanto-odontoid joint were observed. Besides, 32 sets of atlanto-axial joint in adults＇ fresh bony specimens were measured with a digital caliper and a goniometer, including the width of bony window of anterior arch of atlas, the .width of bony window of axis vertebra, the distance between superior and inferior two atlas screw inserting points, the distance between two axis screw inserting points etc. It was found that the width of atlas and axis which could be exposed were 40.2±3.5 mm and 39.3±3.7 mm respectively. The width and height of posterior pharyngeal wall which could be exposed were 40.1±5.2 mm and 50.2±4.6 mm respectively. The distance between superior and inferior two atlas screw inserting points was 28.0±2.9 mm and 24.0±3.5 mm respectively, and the distance of bilateral axis screw inserting points was 18.0±1.2 mm. The operative exposure position through TOA ranged from inferior part of the clivus to the superior part of the C3 vertebral body. Posterior pharyngeal wall consisted of 5 layers and two interspaces： mucosa, submucosa, superficial muscular layer, anterior fascia of vertebrae, anterior muscular layer of vertebrae and posterior interspace of pharynx, anterior interspace of vertebrae. This study revealed that it had the advantages of short operative distance, good exposure and sufficient decompression in dealing with the ventro lesions from the upper cervical to the lower clivus through the TOA. The replacement of artificial atlanto-odontoid joint is suitable and feasible. The design of artificial atlanto-odontoid joint should be based on the above data.

Crack initiation stress and strain of jointed rock containing multi-cracks under uniaxial compressive loading: A particle flow code approach

The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.

Numerical Analysis of Local Joint Flexibility of K-joints with External Plates Under Axial Loads in Offshore Tubular Structures

The Local Joint Flexibility(_(LJF))of steel K-joints reinforced with external plates under axial loads is investigated in this paper.For this aim,firstly,a finite element(FE)model was produced and verified with the results of several experimental tests.In the next step,a set of 150 FE models was generated to assess the effect of the brace angle(θ),the stiffener plate size(ηandλ),and the joint geometry(γ,τ,ξ,andβ)on the_(LJF)factor(f_(LJF)).The results showed that using the external plates can decrease 81%of the f_(LJF).Moreover,the reinforcing effect of the reinforcing plate on the f_(LJF)is more remarkable in the joints with smallerβ.Also,the effect of theγon the f_(LJF)ratio can be ignored.Despite the important effect of the f_(LJF)on the behavior of tubular joints,there is not available any study or equation on the f_(LJF)in any reinforced K-joints under axial load.Consequently,using the present FE results,a design parametric equation is proposed.The equation can reasonably predict the f_(LJF)in the reinforced K-joints under axial load.

On the calibration of a shear stress criterion for rock joints to represent the full stress-strain profile

Conventional numerical solutions developed to describe the geomechanical behavior of rock interfaces subjected to differential load emphasize peak and residual shear strengths.The detailed analysis of preand post-peak shear stress-displacement behavior is central to various time-dependent and dynamic rock mechanic problems such as rockbursts and structural instabilities in highly stressed conditions.The complete stress-displacement surface(CSDS)model was developed to describe analytically the pre-and post-peak behavior of rock interfaces under differential loads.Original formulations of the CSDS model required extensive curve-fitting iterations which limited its practical applicability and transparent integration into engineering tools.The present work proposes modifications to the CSDS model aimed at developing a comprehensive and modern calibration protocol to describe the complete shear stressdisplacement behavior of rock interfaces under differential loads.The proposed update to the CSDS model incorporates the concept of mobilized shear strength to enhance the post-peak formulations.Barton’s concepts of joint roughness coefficient(JRC)and joint compressive strength(JCS)are incorporated to facilitate empirical estimations for peak shear stress and normal closure relations.Triaxial/uniaxial compression test and direct shear test results are used to validate the updated model and exemplify the proposed calibration method.The results illustrate that the revised model successfully predicts the post-peak and complete axial stressestrain and shear stressedisplacement curves for rock joints.

An Error Equivalent Model of Revolute Joints with Clearances for Antenna Pointing Mechanisms

Joint clearances in antenna pointing mechanisms lead to uncertainty in function deviation. Current studies mainly focus on radial clearance of revolute joints, while axial clearance has rarely been taken into consideration. In fact, own?ing to errors from machining and assembly, thermal deformation and so forth, practically, axial clearance is inevitable in the joint. In this study, an error equivalent model(EEM) of revolute joints is proposed with considering both radial and axial clearances. Compared to the planar model of revolute joints only considering radial clearance, the journal motion inside the bearing is more abundant and matches the reality better in the EEM. The model is also extended for analyzing the error distribution of a spatial dual?axis("X–Y" type) antenna pointing mechanism of Spot?beam antennas which especially demand a high pointing accuracy. Three case studies are performed which illustrates the internal relation between radial clearance and axial clearance. It is found that when the axial clearance is big enough, the physical journal can freely realize both translational motion and rotational motion. While if the axial clearance is limited, the motion of the physical journal will be restricted. Analysis results indicate that the consideration of both radial and axial clearances in the revolute joint describes the journal motion inside the bearing more precise. To further validate the proposed model, a model of the EEM is designed and fabricated. Some suggestions on the design of revolute joints are also provided.

Seismic performance of steel reinforced ultra high-strength concrete composite frame joints

To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.

Entire deformational characteristics and strain localization of jointed rock specimen in plane strain compression

Shear band (SB), axial, lateral and volumetric strains as well as Poisson’s ratio of anisotropic jointed rock specimen (JRS) were modeled by Fast Lagrangian Analysis of Continua (FLAC). Failure criterion of rock was a composited Mohr-Coulomb criterion with tension cut-off. An inclined joint was treated as square elements of ideal plastic material beyond the peak strength. Several FISH functions were written to automatically find the addresses of elements in the joint and to calculate the entire deformational characteristics of plane strain JRS. The results show that for moderate joint inclination (JI), strain is only concentrated into the joint governing the behavior of JRS, leading to ideal plastic responses in axial and lateral directions. For higher JI, the post-peak stress-axial and lateral strain curves become steeper as JI increases owing to the increase of new SB’s length. Lateral expansion and precursor to the unstable failure are the most apparent, resulting in the highest Poisson’s ratio and even negative volumetric strain. For lower JI, the entire post-peak deformational characteristics are independent of JI. The lowest lateral expansion occurs, leading to the lowest Poisson’s ratio and positive volumetric strain all along. The present prediction on anisotropic strength in plane strain compression qualitatively agrees with the results in triaxial tests of rocks. The JI calculated by Jaeger’s formula overestimates that related to the minimum strength. Advantages of the present numerical model over the Jaeger’s model are pointed out.

Experimental Studies on Seismic Behavior of Exterior SRUHSC Joints

To investigate the seismic behavior of the joints,six steel reinforced ultra high strength concrete( SRUHSC) frame exterior joints were tested. Three levels of axial compressive ratio varying from 0.25 to 0.45 were investigated to determine how this variable might influence the performance of the joints including failure mode,ductility,energy dissipation capacity,stiffness degradation,shear strength and shear deformation by the quasi-static cyclic test on SRUHSC exterior joints. This research program suggests that the design of joint should make full use of the joint panel deformation to dissipate energy of earthquake. It is tested that the value of 0.38 as a dividing point about the effect of axial compression ratio on the seismic performance of SRUHSC exterior joints should be taken into account in design. In addition,the increase of volumetric ratio of stirrup could possess the ductility for adequate response to unexpected strong earthquakes and a recommended value of minimum volumetric ratio of stirrup with high axial-load level is pointed out.

单板焊接空心球节点受拉承载性能研究

单板焊接空心球节点常用做弦支穹顶上部结构连接拉杆或拉索的节点,单板主要承受拉力并传递至焊接空心球,为了满足工程设计的要求,需对其受拉承载性能进行研究.通过试验,研究了不同参数的单板焊接空心球节点轴拉状态下的受力性能和破坏机理,建立有限元模型并进行验证,该模型能较好地反映单板焊接空心球节点轴拉性能,通过有限元模型参数化分析揭示了节点尺寸、加劲肋、单板尺寸等参数对其力学性能的影响规律,并提出单板焊接空心球轴拉承载力计算公式.研究结果表明:单板焊接空心球在轴拉作用下为应力集中导致的剪切强度破坏,破坏发生在单板端部与空心球连接处,表现为焊接空心球被撕裂;有限元应力云图得出破坏时沿着单板平面内拉力方向的剪应力起主要作用;单板焊接空心球节点的受拉承载力随单板宽度及空心球壁厚的增大而明显增大,空心球直径的增大会使承载力略有降低,单板的厚度增加使节点承载力略有提高,单板的高度对节点承载力的影响较小,空心球内设置加劲肋能使承载力提高至少20%;基于参数化提出的单板焊接空心球节点的受拉承载力计算公式能简便地计算出单板焊接空心球节点的承载力,相对误差在±15%以内,满足工程设计误差要求.研究工作可为今后外接单板的焊接空心球节点分析设计提供参考.

配筋PVA-钢混杂纤维增强水泥基复合材料梁柱边节点抗震性能试验研究

改善工程材料韧性和耐久性,提高框架梁柱节点抵抗变形和破坏的能力,是提高框架结构抗震韧性的有效途径之一。采用PVA-钢混杂纤维增强水泥基复合材料代替普通混凝土应用到梁柱边节点,考虑轴压比和加密区体积配箍率的影响,设计6个配筋PVA-钢混杂纤维增强水泥基复合材料、1个配筋单掺PVA纤维增强水泥基复合材料和1个钢筋混凝土梁柱边节点试件进行拟静力试验,分析其破坏形态、滞回曲线、骨架曲线、延性、耗能能力、钢筋应变和梁端塑性铰区转角,探讨混杂纤维的加入对梁柱边节点抗震性能的影响。结果表明:与钢筋混凝土节点和单掺PVA纤维增强水泥基复合材料节点相比,PVA-钢混杂纤维增强水泥基复合材料节点的承载力高、变形能力大、延性好、耗能能力强,抗震性能显著提升。当试验轴压比从0.12增加到0.24,梁端塑性铰区产生一定的外移,塑性性能发挥更充分,同时试件的变形能力、延性、耗能能力增加。在加密区体积配箍率减小的情况下,试件仍表现出良好的抗震性能。

Seismic Behavor of RC Beam-Column Joint with Additional Bars under Cyclic Loading

The behavior of Beam-Column Joints in moment resisting frame structures are susceptible to damage caused by seismic effects due to poor performance of the joint.A good number of researches were carried out to understand the complex mechanism of RC joints which are considered in seismic design code practices presently adopted.The traditional construction detailing of transverse reinforcement have shown serious joint failure. This paper introduces a new design philosophy involving the use of additional diagonal bars within the joint particularly suitable for low to medium seismic effects in earthquake zones throughout the world.In lieu to this study,ten(10) full-scale interior beam-column specimens were constructed with various additional reinforcement details and configurations as will be discussed in the later.The experiment provided adequate results to proof the idea of additional bars as suitable approach in reinforced concrete structures where earthquake is eminent.While compared with overall cracking observation during the test,the specimen with additional bars (diagonal and straight) had shown few cracks on the column than the ones without.Furthermore,concrete confinement is certainly an important design method as recommended by certain international codes.

轴力作用下焊接方管Π型节点的极限承载力分析

目前规范中还未规定Π型构造形式的方管节点承载力计算公式。该文在经过试验验证有限元分析准确性的基础上,基于两种方管不同区域的材料本构关系模型,利用Abaqus软件对85组在轴力作用下的节点进行了数值模拟,得到了方管Π型节点在轴力作用下的极限承载力。随后,通过参数化分析和多元回归,得出影响Π型节点极限承载力的因素以及修正的承载力计算公式。结果表明,支管-主管宽度比β对节点极限承载力和初始刚度影响较大,增大支管宽度,能够显著提高节点的极限承载力,支管上施加的荷载由主管上表面的抗弯、抗剪作用和主管侧壁共同承担,节点的破坏模式也取决于β;主管宽厚比2γ越大,意味着主管上翼缘和支管连接区域变得更加细长,降低了主管上翼缘的抗弯刚度,节点承载力和初始刚度因此降低;支管-主管高宽比η和支管间距g对节点极限承载力有一定影响,增大支管截面的高度和支管间隙,即增大了沿主管纵向方向的支管、主管相交区域,使得支管在主管翼缘更宽的区域传递荷载,节点的塑性区域更大,材料利用更充分,因此提高了节点的承载能力;支管-主管厚度比τ对节点极限承载力和初始刚度影响不大,支管的壁厚增加,提高了支管的承载力,但节点最终破坏是主管上翼缘达到屈服破坏而并非支管破坏,因此支管厚度的变化对节点承载能力影响不明显。根据有限元模型的分析结果,通过曲线拟合提出了计算方管Π型节点极限承载力的参数方程,并对该方程的准确性进行了评价,为这类节点的进一步研究和工程应用提供了参考。

载流导线激励弹性约束轴向变速运动梁主-参联合共振

研究了两端弹性约束轴向变速运动梁的主-参联合共振问题。根据哈密顿原理,推导导电梁在平行载流导线激发磁场中的磁弹性非线性振动方程。由两端弹性约束边界条件得到振型函数,再对方程进行伽辽金积分法离散,然后利用多尺度法得到稳态运动的近似解析解,并对稳态解的稳定性进行了分析。通过算例,用数值方法对解析解结果进行验证,并分析不同参数对共振振幅及频率的影响。结果表明,系统发生主-参联合共振时,弹簧刚度和外激励力主要影响系统振幅,而轴向速度、电流、轴向力对振幅和共振频率都有影响;系统的稳定区域随弹簧刚度的增大而增加。

外部能场辅助搅拌摩擦焊接技术综述

外部能场辅助搅拌摩擦焊接是一种改进型固相焊接方法,在航空航天、汽车制造、能源领域等方面得到了广泛应用,通过引入外部能场,可以改善焊接接头的组织和性能,提高焊接质量和效率。本文对外部能场辅助搅拌摩擦焊接技术进行了分类,综述了能场的选择和控制、工艺参数的优化等,阐述了外部能场对焊接温度、轴向载荷、接头组织性能的影响,最后总结了外部能场辅助搅拌摩擦焊接技术未来的发展趋势。

基于ANSYS的复式膨胀节强度和轴向刚度有限元分析

通过ANSYS有限元分析,研究了复式膨胀节在同时受内压及轴向位移时的强度和轴向刚度.建立了复式膨胀节的二维轴对称模型,并考虑了非线性对复式膨胀节的影响,将分析结果与EJMA工程近似法计算结果进行对比,表明ANSYS有限元结果更接近实际情况,采用工程近似法分析复式膨胀节时存在一定误差.

T_(1)灰阶反转图评估中轴型脊柱关节炎骶髂关节结构性病变的价值

【目的】探讨T_(1)灰阶反转(rT_(1))图对中轴型脊柱关节炎(ax-SpA)骶髂关节结构性病变的诊断价值。【方法】回顾性搜集我院2020年2月至2022年12月在1周内行骶髂关节MRI及CT检查并符合ax-SpA诊断标准的患者52例,共计104个骶髂关节。两名放射科医师基于常规T_(1)WI、rT_(1)、T_(1)WI+rT_(1)三组图像,分别评估ax-SpA骶髂关节结构病变:骨侵蚀、骨质硬化、关节间隙改变,在斜冠状位图像上将骶髂关节分为前、中、后3部分,每部分分骶面、髂面,共6个区域,并按拟定评分规则对上述3种结构性病变进行评分,其中1名医师间隔1月后再次进行评分。由第3名肌骨影像专科医师同样使用上述方法评估CT图像作为参考标准。使用组内相关系数(ICC)分析医师间及医师内分别评估各病变评分一致性;采用Friedman M检验比较三组图像对各病变评分与CT评分的差异;以CT为参考标准,采用诊断性试验分析计算三组图像诊断骨侵蚀、骨质硬化及关节间隙改变的准确率、灵敏度、特异度,并采用McNemar检验比较rT_(1)、T_(1)WI+rT_(1)与T_(1)WI的差异。【结果】三组图像评分各类结构病变医师间、医师内一致性好,其中以T_(1)WI+rT_(1)的一致性最优,评估各类病变ICC≥0.85695%CI(0.794,0.900),优于rT_(1)及T_(1)WI[rT_(1):ICC≥0.81995%CI(0.745,0.874),T_(1)WI:ICC≥0.75495%CI(0.656,0.827)];T_(1)WI+rT_(1)对各病变的评分结果与CT评分结果相当,rT_(1)对骨侵蚀、关节间隙改变评分与CT相当(P>0.05)。相较T_(1)WI,T_(1)WI+rT_(1)诊断各病变均有更高的准确率及灵敏度(准确率骨侵蚀:90.3%vs 76.9%;灵敏度骨侵蚀:91.6%vs 76.1%;准确率骨质硬化:89.4%vs 80.8%;灵敏度骨质硬化:84.6%vs 73.9%;准确率关节间隙改变:86.5%vs 73.1%;灵敏度关节间隙改变:84.9%vs 60.4%;P<0.05);rT_(1)提高了对骨侵蚀、关节间隙改变诊断的准确性和灵敏度(准确率骨侵蚀:87.5%vs 76.9%;灵敏度骨侵蚀:88.7%vs 76.1%;准确率关节间隙改变:85.6%vs 73.1%;灵敏度关节间隙改变:83.0%vs 60.4%;P<0.05)。【结论】rT_(1)能提高ax-SpA骶髂关节结构性病变的诊断效能,T_(1)WI+rT_(1)效能更优。

双耳板焊接空心球节点轴拉力学性能研究

目的探究双耳板焊接空心球节点的受拉力学特性,揭示破坏机理并探讨影响其承载力的主要因素。方法针对8个双耳板焊接空心球节点进行轴心受拉极限承载力试验,并采用ABAQUS有限元分析软件对节点进行参数化数值分析,重点讨论节点几何尺寸对其承载力的影响。结果在轴向拉力作用下,双耳板焊接空心球节点破坏形式分为空心球开裂破坏,耳板与空心球连接处焊缝失效,且个别试件出现球面局部起皮;空心球与耳板连接端部处应力集中明显,随着荷载增大,在空心球与耳板连接处沿径向逐步进入屈服阶段。结论节点轴拉极限承载力,与空心球直径、耳板宽度与球外径比、耳板厚度与球壁厚度比呈正相关,与空心球径厚比呈负相关,且上述影响因素中空心球壁厚与耳板厚度比对承载力影响相对较小。

榫卯-灌浆套筒混合连接装配式方墩轴压性能研究

已有研究表明,榫卯-灌浆套筒混合连接装配式方墩(简称混合连接拼装桥墩)的抗震性能接近于整体现浇桥墩。为进一步探讨混合连接拼装桥墩的轴压性能,以钢管的长度、直径以及壁厚等为变化参数,进行1个整体现浇桥墩(编号ZT)和4个混合连接拼装桥墩(编号GTA-0~GTD-0)的轴压承载力试验,结果表明,GTA-0~GTD-0试件的承载力比ZT试件提高了10.1%~14.4%,其延性系数均大于ZT试件;GTA-0~GTD-0试件的轴压承载力随钢管直径和长度的增大而增大,而钢管壁厚对于试件承载力的影响较小;拼装桥墩的破坏位置随着钢管长度的增加而上移,逐渐接近于整体现浇桥墩,但二者的破坏模式基本相同。

冷弯型钢钢管混凝土柱-钢梁装配式节点抗震性能研究

为考察多高层框架结构体系中新型冷弯型钢装配式钢管混凝土柱-冷弯型钢拼合梁节点的抗震性能,设计并制作了一组足尺节点试件,对其进行不同轴压比下的拟静力试验.结合ABAQUS有限元分析,以轴压比、钢管柱壁厚、内填充混凝土强度等级为主要参数,研究节点试件在低周往复水平荷载作用下的破坏形态、滞回曲线、骨架曲线、承载力、耗能能力、刚度退化等抗震性能.结果表明:在冷弯型钢柱内填充混凝土时,新型冷弯型钢装配式梁柱节点的承载力和耗能能力相比于空钢管柱节点整体有所提高,节点延性增加,节点仍保持“强柱弱梁”的失效模式.在低轴压比(0.2)下,钢管柱壁厚的增加对节点的耗能能力与承载力有一定的提升,其延性也有所增加;混凝土强度等级的变化对本文所研究“强柱”构造下的节点抗震性能几乎无影响,节点的滞回曲线基本一致,骨架曲线基本重合,节点的破坏形态保持不变,随着混凝土强度等级的增加,节点延性有所降低.但在高轴压比(0.8)下,钢管柱壁厚为2 mm和3 mm时柱刚度过弱,节点出现柱端压弯破坏;当钢管柱壁厚增加到4 mm时,节点破坏形态转变为梁端塑性铰破坏,因此应注意限制梁柱线刚度比,保证“强柱弱梁”的失效模式.本文研究成果对该新型节点用于多高层框架结构体系中的适用性及设计构造有一定参考意义.

轴压比和面承板厚度对混合节点抗震性能的影响

为了研究新型柱全截面隔板式钢筋混凝土柱-钢梁(RCS)混合框架节点形式的抗震性能,考虑不同轴压比和面承板厚度的影响,对2组共6个3/4比例的梁柱节点进行低周往复加载试验研究.试验中所有试件均发生设计预期的节点剪切破坏,滞回曲线呈弓型,表明节点具有良好的抗震性能.试件最终因节点区的混凝土开裂剥落而丧失承载力.试验结果表明,当轴压比为0~0.25时,随着轴压比的增大,RCS节点开裂荷载有所增大,峰值荷载前斜裂缝数量减少、宽度减小,试件的承载力、刚度和耗能能力均有所提高.节点域柱纵筋黏结应力随轴压比增大而减小,表明节点域内黏结状况有明显改善.相较于单向面承板试件,双向面承板试件在承载能力、延性和耗能能力方面均表现出显著提高;当双向面承板厚度由6 mm增加至10 mm时,试件峰值承载力和刚度的提升幅度相对有限.