基于性能的几种钢结构支撑框架体系应用研究

采用SAP2000（V11.0.8 Advanced C）有限元分析软件,对12层钢结构框架建筑进行基于性能的Pushover能力谱法分析,考虑了纯框架、中心支撑框架、偏心支撑框架、隅撑支撑框架4种结构体系,结果表明：相对于纯框架和中心支撑框架,偏心支撑框架和隅撑支撑框架具有更优越的力学性能和更好的经济效益,设计中宜优先考虑使用。     

Pressure distribution on the anatomic landmarks of the knee and the effect of kneepads

This study examines stress transmitted to anatomic landmarks of the knee (patella, combined patella tendon and tibial tubercle) while in static kneeling postures without kneepads and while wearing two kneepads commonly worn in the mining industry. Ten subjects (7 male, 3 female) simulated postures utilized in low-seam mines: kneeling in full flexion; kneeling at 90° of knee flexion; and kneeling on one knee while in one of three kneepad states (no kneepads, non-articulated kneepads, and articulated kneepads). For each posture, peak and mean pressure on the anatomic landmarks of the knee were obtained. The majority of the pressure was found to be transmitted to the knee via the combined patellar tendon and tibial tubercle rather than through the patella. While the kneepads tested decreased the maximum pressure experienced at the combined patellar tendon and tibial tubercle, peak pressures of greater than 25 psi were still experienced over structures commonly injured in mining (e.g. bursa sac - bursitis/Miner’s Knee). The major conclusion of this study is that novel kneepad designs that redistribute the stresses at the knee across a greater surface area and to other regions of the leg away from key structures of the knee are needed.     

Pull-Out Response of a Steel Post Inserted in a Pre-Drilled HDPE Cylinder: Analytical and Finite Element Analyses Using Pressure-Dependent Friction

Abstract

For the aim of fixing and stabilizing the Total Knee Arthroplasty (TKA) tibial component, pull-out strength of the post is one of the most important factors to be considered. The material properties of bone, coupled with the principal dimensions of bone/post assembly such as diameter, interference fit and implantation length, may affect the pull-out strength of the post fixation. In this study, a cylindrical stainless steel post inserted in a pre-drilled High Density Polyethylene (HDPE) cylinder with an initial interference fit was taken as a model to assess the contribution of post fixation to the initial stability of TKA tibial component. Pull-out experiments were carried out for different initial interference fits and implantation lengths. Under pull-out loading, the micro-slip initiation and propagation at the post/cylinder interface was found to be progressive and was modeled using Coulomb friction at the interface. In order to examine the experimental ultimate pull-out force results, an analytical model was developed. The analytical model was fitted to the experimental results by adjusting the friction coefficient for the considered ranges of initial interference fit and implantation length. It was found that friction coefficient depends on initial interference fit (Δr) as well as on the initial contact pressure (σ0). For the considered interference fit values Δr = 01 mm, Δr = 02 mm and Δr = 03 mm (σ₀ = 1362 MPa, σ₀ = 2724 MPa and σ₀ = 4086 MPa), the values of adjusted friction coefficient are 0.091, 0.067 and 0.058, respectively. Finite Element simulation was also carried out for the pull-out test using the ABAQUS program. It was found that numerical, analytical and experimental results are all in good agreement.     

The effects of knee angles on subjective discomfort ratings, heart rates, and muscle fatigue of lower extremities in static-sustaining tasks

The purpose of this study was to investigate the effects of knee-flexion angles on subjective discomfort ratings, heart rates, and muscle fatigue using median frequency (MDF) in a static-sustaining task. Thirty healthy participants maintained 13 postures including standing, squatting, sitting, and kneeling postures and then MDFs from the erector spinae, biceps femoris, vastus medialis, gastrocnemius, and tibialis anterior muscles, subjective discomfort, and heart rates were collected every 3 min during a sustained 15 min task. Results showed that the discomfort, heart rate and muscle fatigue were significantly influenced by the body postures. In general, standing and sitting postures showed less discomfort as well as lower heart rates, whereas squatting postures (KF120, KF90, KF60) had higher discomfort and heart rates. Three MDF change trends were reported associated with postures in this study. First, there were less changes of MDFs for standing and sitting postures; second, all patterns of MDFs for KF 150 and KF120 decreased, and lastly some MDFs had increasing trends and others showed decreasing trends for KF30, KF30T, and kneeling postures.     

Knee injuries in motor vehicle collisions: a study of the National Accident Sampling System database for the years 1979-1995

A detailed study of knee injuries recorded in the 1979–1995 National Accident Sampling System database maintained by the National Highway Traffic Safety Administration was conducted. Injuries to other body regions were also considered in order to illustrate the relative frequency of knee injuries. This study demonstrated that knee injuries constitute ≈10% of all injuries recorded every year. However, the majority of these injuries were of low severity (i.e. contusions, abrasions, lacerations) with an abbreviated injury score (AIS) of 1. Most knee injuries occurred following a frontal collision with no intrusion. The study also indicated most knee fractures occur in crashes where the vehicle velocity differences (ΔVs) were less than 45 kmph, with some occurring at ΔVs as low as 10 kmph. Serious non-fracture knee injuries (i.e. ligament tears) rated AIS 2 accounted for 20 out of every 1000 injuries and predominantly occurred at ΔVs below 25 kmph. In this study it was noted that women were more likely to experience a knee contusion than men. This study further suggests that knee impact scenarios have remained relatively constant over the years as the knee injury rates showed little variation. The rate of lap and shoulder belt use was lower in occupants who experienced a knee injury vs. the rate in the overall database and airbags were present in only a small number of cases. As this study largely included only vehicles without airbags it provides a good baseline for analysis of the influence of the airbag on knee injury trends in the future.     

A better estimation of wave arrival time in water distribution networks using WAvelet kNEe (WANE)

A transient pressure wave is a sudden pressure change that occurs in a short time, which can be induced by sudden changes in valve and pump operation, and pipe bursts in a Water Distribution Network (WDN). An accurate estimation of a transient wave arrival time is crucial because it facilitates pipe condition assessment, hydraulic model calibration, and accurate localization of pipe burst events. Due to the noisy and highly fluctuating nature of the pressure signals, estimating an accurate transient pressure wave arrival time is not a trivial task. Among many methodologies proposed for detecting abrupt pressure changes, Discrete Wavelet Transform (DWT) and Cumulative Sum (CUSUM) were the two most popular approaches. However, several limitations involved with these two approaches can easily lead to unsatisfactory results. Moreover, some of the existing methodologies were only tested on either a single pipeline, engineered events, or a small sample size of events, making these methodologies suitable and accurate only for a limited number of scenarios. Driven by these limitations, a novel approach is proposed to estimate the wave arrival time in water distribution networks (WDNs). The backbone of this approach is the integration of wavelet decomposition and a knee point detection algorithm, thus gaining the name WAvelet kNEe (WANE). Through a comparative study against the other methodologies using 90 recorded transient events detected in a real WDN, WANE is found to provide the best wave arrival time estimation, with a Root Mean Square Error (RMSE) of 0.4 s. Based on the result, our estimation error is at least 15 s lesser than the other methodologies. With an improved wave arrival time estimation, WANE has the potential to minimize the response time of repair crews, service disruption time, as well as the associated water losses due to a pipe break.     

A sequentially-defined stiffness model of the knee

A new procedure is proposed to obtain a stiffness model of the knee, i.e. a model of the joint when static external loads are applied to the tibia and femur. A sequential approach is used to generalise a kinematic model of the passive motion of the articulation previously presented by the authors. The procedure is devised in such a way that the restraining function of the articular components which guide the passive motion of the joint is preserved after generalisation. As a result, the new stiffness model can replicate the passive motion with the same accuracy as the previous kinematic model, and it can also replicate the relative motion of the tibia and femur when the knee is loaded by static external loads. The proposed procedure is applied to a specimen and the relevant stiffness model is devised. The motion of the model under several loading conditions is then compared with the original motion of the specimen and with data obtained from the literature, in order to show the accuracy of the model and the potential of the proposed procedure.     

Studies of the knee of the cosmic rays primary spectrum through measurements in the 10–10 eV energy range

In this contribution I review the most recent results obtained by experiments studying the primary cosmic rays spectrum at energies around the knee, i.e. the change of slope observed at .The main results are: the change of slope has been observed in the spectra of all secondary components of extensive air showers. The primary chemical composition gets heavier above the knee. Almost all experiments, with the exception of TIBET ASγ, attribute the change of slope to the light component of cosmic rays. The arrival directions of cosmic rays are highly isotropic.These results favor an astrophysical explanation of the knee either as the maximum energy achievable in galactic sources or of end of the containment inside galactic magnetic fields. Nevertheless the scenario is neither complete nor univocally accepted and relevant informations can be obtained studying the 10¹⁶–10¹⁸ eV energy range.     

晚期弥漫型色素沉着绒毛结节性滑膜炎行全膝关节置换的初步探讨

目的:探讨晚期弥漫型色素沉着绒毛结节性滑膜炎(Pigmented Villonodular Synovitis,PVNS)行全膝关节置换治疗(Total knee arthroplasty,TKA)及其临床疗效。方法:对2003年2月至2010年10月年收治的16例发生于单侧膝关节(左膝11例,右膝5例)的弥漫型PVNS行滑膜切除术后的TKA。其中男性5例,女性11例,年龄37至66岁,平均57.2岁;4名患者有膝关节外伤史及1至2次患侧膝关节手术史,余病例发病前均无明显诱因;术前平均屈伸活动度为:屈:101°(75°至120°)、伸:-6°(-10°至0°);HSS评分:59.2±7.3。结果:1例患者出现了下肢深静脉血栓、1例患者术后功能恢复较差,余病例均取得较满意的功能恢复。末次随访平均活动度:屈:125°(95°至130°)、伸:-1°(-5°至0°),HSS评分:85.3±8.1,与术前相比有统计学意义(P0.05)。术后随访21至83个月,平均47个月,均未见PVNS复发及假体松动。结论:MRI在该疾病诊断、明确病变范围、术后评估各方面起着重要的作用。对于软骨破坏严重的晚期弥漫型PVNS,TKA应作为首选治疗,但相比其他疾病的TKA治疗,术中需注意更多细节的处理。而术后至抗凝药物应用的间隔时间是否应适度延长、术后是否需应用局部放射治疗仍有待进一步研究。     

An optimal control model for determining articular contact forces at the human knee during rising from a static squat position

A two-dimensional dynamic model of the knee joint was incorporated into a four-segment, eight-muscle model of the human body to determine the muscle, ligament, and articular contact forces transmitted at the knee as humans stand up from a static squatting position. Our optimal control model predicted peak tibiofemoral contact forces 8 times as high as body weight. Furthermore, ligament forces, especially those in the anterior-cruciate, were nearly body weight as knee flexion approached 90 degrees. Ligament and tibiofemoral contact loads were dominated by the forces exerted by muscles during the movement.