Local Strain Measurement within Tendon

Abstract:  Tendon is a dense connective tissue, responsible for transmitting the forces generated by muscles to the skeleton. It is composed of a hierarchical arrangement of crimped collagen fibres, interspersed with proteoglycan matrix and cells, known as tenocytes. During physiological loading, tendons are subjected to strains in the region of 5–6%, which result in the straightening and realignment of the collagen fibres, generating variable local strain fields within the tendon. This study demonstrates a technique for analysing local strains within viable tendon explants, during both loading and unloading of the tissue. Samples were strained in a custom-designed rig, allowing real-time visualisation of cell nuclei, used as local discrete markers, on a confocal microscope. Results indicated that local strains within the fascicle are smaller than the applied strains, never exceeding 1.2%, even at 8% gross applied strain. By contrast, the sliding of adjacent collagen units was recorded at each strain increment in this study, reaching a mean maximum of 3.9% of the applied displacement. Loading–unloading studies indicated that sliding behaviour is reversible up to strains of 5%, and provides the major extension mechanism within the rat-tail tendon. This technique can be extended to further analyse shearing behaviour within the matrix.     

体外CFRP筋预应力混凝土箱梁长期受力性能试验研究

碳纤维(CFRP)筋具有优异的物理力学性能,可用于替代传统的预应力钢筋。制作了体外配置碳纤维筋预应力混凝土箱梁模型,对持续均布荷载作用箱梁的截面应力重分布、长期挠曲变形及裂缝发展等规律进行了1001 d的试验观测。基于素混凝土柱体的实测徐变系数,运用双线性法和曲率法分别对试验箱梁的长期挠曲变形进行预测。试验结果表明:受压钢筋应变较初值增长225%～268%,受拉钢筋的应变较初值增长36.2～38.6%,混凝土表面压应变较初值增长164%～224%。按现行设计规范计算长期荷载作用特征裂缝宽度较实测值偏小11.8%～55.5%。跨中长期挠曲变形实测值为初始变形的2.32～2.42倍,较现行设计规范取值偏大18.5%。     

Molecular Mechanisms of Fetal Tendon Regeneration Versus Adult Fibrous Repair

Tendinopathies are painful, disabling conditions that afflict 25% of the adult human population. Filling an unmet need for realistic large-animal models, we here present an ovine model of tendon injury for the comparative study of adult scarring repair and fetal regeneration. Complete regeneration of the fetal tendon within 28 days is demonstrated, while adult tendon defects remained macroscopically and histologically evident five months post-injury. In addition to a comprehensive histological assessment, proteome analyses of secretomes were performed. Confirming histological data, a specific and pronounced inflammation accompanied by activation of neutrophils in adult tendon defects was observed, corroborated by the significant up-regulation of pro-inflammatory factors, neutrophil attracting chemokines, the release of potentially tissue-damaging antimicrobial and extracellular matrix-degrading enzymes, and a response to oxidative stress. In contrast, secreted proteins of injured fetal tendons included proteins initiating the resolution of inflammation or promoting functional extracellular matrix production. These results demonstrate the power and relevance of our novel ovine fetal tendon regeneration model, which thus promises to accelerate research in the field. First insights from the model already support our molecular understanding of successful fetal tendon healing processes and may guide improved therapeutic strategies.     

大内跨小边跨框架结构预应力筋优化布置方法

预应力筋的优化布置是大内跨小边跨的多跨预应力混凝土框架结构合理设计计算的关键.为满足控制截面承载力最大的需要,以往常将大跨所需预应力筋布置为连续曲线,并按水平直线延伸通过其相邻的两小跨,按这种布置方式仅使大跨内产生竖向向上的预应力等效荷载,可较好平衡大跨的竖向外荷载;而若将大跨及相邻的两小跨统一考虑,预应力筋按连续曲线布置,张拉产生的预应力等效荷载不但可有效平衡大跨的竖向外荷载而且也可平衡小跨的竖向外荷载,可以使荷载平衡得到优化实现.以一典型工程为例,分析了在相同条件下两种预应力筋布置过程中张拉引起的综合弯矩、主弯矩和次弯矩的分布和量值上差异,比较了两类布筋形式对正截面承载力计算结果的影响,验证了对大内跨小边跨框架结构统一考虑后整体上按三段连续正反抛物线预应力筋布置的合理性.     

新型多自由度假手的研制

介绍了一种新型多自由度假手的机械结构、运动方式及其静力学分析．假手的主要结构部件由光敏树 脂制成,使用小型直流伺服电机作为驱动器．手指采用欠驱动及腱驱动方式．该假手具有拟人的外观、较低的整体 重量和对被抓物体外形的适应能力．文章研究了假手的运动特点及接触力规律,通过仿真对假手的接触受力规律进 行了校验．最后通过实验,对假手的运动规律与抓握能力进行了验证．     

预应力FRP筋混凝土梁在低周反复荷载下的恢复力模型

作为一种新型建筑材料,FRP具有轻质、高强、耐腐蚀等优点,非常适合作为预应力筋材料.通过4根预应力FRP筋混凝土梁在低周反复荷载下的试验研究,根据预应力FRP筋混凝土梁在低周反复荷载下滞回曲线的特点,提出了适合于预应力FRP筋混凝土梁的弯矩-曲率恢复力模型,并与试验结果进行了比较,计算模型与试验结果吻合良好。     

用基因遗传算法设计主动控制结构控制机构的最优布置

通过对高层建筑结构主动控制算法和控制机构布置准则的分析，建立了控制机构布置的优化模型，改进了遗传搜索优化算法，并以一栋受主动锚索控制机构控制的建筑结构为例进行了数值计算和分析，结果表明本文的方法可行，优化速度较快。     

垫脚加锚-高拱坝加固增稳的高效方法

本文首先介绍一种加固高拱坝的高效方法—垫脚加锚法 ,并阐述预应力锚索的锚固机理 ,然后对李家峡拱坝的垫脚加锚布置作了介绍。李家峡拱坝垫脚加锚前后的地质力学模型试验成果和整体三维非线性有限元分析成果表明垫脚加锚确有很好的加固增稳效果     

龙滩水电站左岸进水口边坡锚固预应力的实测研究

介绍了龙滩左岸进水口边坡预应力锚索监测成果，重点分析了锚固力损失和异常的原因。锚固力损失偏大的主要原因是:钻孔的精度和锚索的安装质量等引起锚索在张拉过程中的偏心，造成锁定损失偏大，部分钢绞线随着荷载的增大，松弛损失量也迅速加大;另外，受开挖等外界因素影响使锚索的受荷状态发生变化，锚固介质受到冲击或锚固结构的荷载发生变化等，均导致锚索预应力的损失（降低）。边坡下切过程中，由于地质条件较差使岩体产生变形是预应力锚索在运行过程中出现锚固力超张拉值的主要原因。