水平和竖向力作用下厂房纵向支撑的设计要求     

童根树  李东 《科技通报》2006,22(2):241-246

纵向框架支撑有两个主要作用:抵抗水平力和保证框架纵向刚度。从整体稳定性角度,考虑交叉支撑和柱顶横系杆的相互影响:通过研究理想体系得到支撑的刚度要求;考虑实际框架中构件初始缺陷,得到水平和竖向荷载共同作用下支撑体系的强度要求。可以发现支撑为保持框架稳定性的承载力要求和抵抗水平力的承载力要求不能直接叠加,水平力降低了框架的抗侧刚度,增大了对支撑的承载力要求。拟合得到水平和竖向力共同作用下支撑承载力要求的计算公式。  相似文献   

Soreness-related changes in three-dimensional running biomechanics following eccentric knee extensor exercise     

Max R. Paquette  Shelby A. Peel  Brian K. Schilling  Dan A. Melcher  Richard J. Bloomer 《European Journal of Sport Science》2017,17(5):546-554

Runners often experience delayed onset muscle soreness (DOMS), especially of the knee extensors, following prolonged running. Sagittal knee joint biomechanics are altered in the presence of knee extensor DOMS but it is unclear how muscle soreness affects lower limb biomechanics in other planes of motion. The purpose of this study was to assess the effects of knee extensor DOMS on three-dimensional (3D) lower limb biomechanics during running. Thirty-three healthy men (25.8?±?6.8 years; 84.1?±?9.2?kg; 1.77?±?0.07?m) completed an isolated eccentric knee extensor damaging protocol to elicit DOMS. Biomechanics of over-ground running at a set speed of 3.35?m?s^?1±5% were measured before eccentric exercise (baseline) and, 24?h and 48?h following exercise in the presence of knee extensor DOMS. Knee flexion ROM was reduced at 48?h (P?=?0.01; d?=?0.26), and peak knee extensor moment was reduced at 24?h (P?=?0.001; d?=?0.49) and 48?h (P?<?0.001; d?=?0.68) compared to baseline. Frontal and transverse plane biomechanics were unaffected by the presence of DOMS (P?>?0.05). Peak positive ankle and knee joint powers and, peak negative knee joint power were all reduced from baseline to 24?h and 48?h (P?<?0.05). These findings suggest that knee extensor DOMS greatly influences sagittal knee joint angular kinetics and, reduces sagittal power production at the ankle joint. However, knee extensor DOMS does not affect frontal and transverse plane lower limb joint biomechanics during running.  相似文献   

肌肉疲劳后不同恢复手段介入效益的对比实验研究     

张帆 《武汉体育学院学报》2017,51(12):88-95

目的：探讨肌肉疲劳后,被动(Passive Recovery,PR)、主动(Active Recovery,AR)、振动(Vibration Recovery,VR)和冰敷(Cryotherapy Recovery,CR)等不同恢复方式对肌肉表现(最大肌力MVC、爆发力MP、肌肉激活程度sEMG)和力学特性(肌肉硬度MS、肿胀程度SD)的影响及差异。方法：20名身体健康的普通男性大学生为受试者,平均年龄(20.4±2.3 yrs.),平均身高(173.5±3.4 cm),平均体重(68.7±3.9 kg)。先测量非惯用手肱二头肌的SD、MS、MVC和sEMG,之后进行肘关节屈曲45°/s向心与离心收缩运动直至疲劳,再进行后测。其后以随机方式进行其中1种恢复,10 min恢复后立即进行后测,各恢复方式间隔7天。以单因素重复测量方差分析检验SD、MS、MVC和sEMG在不同检测时间点的差异及恢复效果。结果：10 min VR和CR均有约15%的力量恢复效果,其中VR介入后sEMG的恢复效果显著高达(32.50±16.10%)。另外,CR可以缓解疲劳后的SD,但AR后SD(28.51±2.79 cm)显著高于疲劳前(27.93±2.93 cm),且MS(11.14±1.58 mm/2kg)相较于疲劳后(11.59±1.40 mm/2kg)也显著下降。结论：CR与VR均可有效帮助疲劳后的肌力恢复,2组间恢复效果无显著差异;同比之下AR则无法改善肌肉疲劳的恢复,甚至造成SD增加且MS降低。  相似文献