桩基弦振效应的数值模拟与性能分析     

罗靖  邹荣华 《荆门职业技术学院学报》2008,23(6)

文章利用C 语言编制了ANSYS到FLAC的接口程序,模拟了砂土粘聚力、内摩擦角、标贯数、桩长细比、动荷载等因素对液化砂土中桩的弦振效应的影响,得出了相关的规律曲线及各因素影响的敏感曲线.研究结果表明,桩基弦振效应随砂土粘聚力、内摩擦角、标贯数、动荷载频率、桩弹性模量的增加而减小,随桩长细比、动荷栽振幅增加而增大.  相似文献   

Formwork lateral pressure of precast normal-concrete composite shear walls infilled with self-compacting concrete     

YAO Rong  YE Yan-hua 《重庆大学学报(英文版)》2018,17(2):39-48

Wall cracking and mold expanding due to concrete vibrations can be effectively solved through the application of precast normal-concrete composite shear walls infilled with self-compacting concrete (SCC). However, the high liquidity of SCC will induce a higher lateral pressure. Therefore, it is important to obtain a better understanding of the template lateral pressure. In this work, nine composite shear walls were experimentally investigated, focusing on the effects of two parameters, i.e., the casting rate and the section width of the formwork. The time-varying pressure was monitored during the SCC pouring. It is found that the increase of casting rate from 3.2 m/h to 10.3 m/h resulted in a higher maximum lateral pressure. The higher casting rate led to a longer time required for the lateral pressure to drop to a steady value. There was no correlation between the section width and the rate of decrease in the initial formwork pressure and stable value. Based on the test results, a formula considering the effect of casting speed for the calculation of SCC formwork pressure was established to fill the gap in the current standards and for engineering applications.  相似文献   

Cultivating sustained teachers’ professional learning within a centralised education system     

Imran Shaari  Victor Lim  David Hung  Yew Meng Kwan 《School Effectiveness & School Improvement》2018,29(1):22-42

This study investigates how sustained professional learning for teachers within a centralised system was cultivated. Specifically, the sustained professional learning was initiated by officers from the headquarters (HQ) and involved interested teachers across schools in Singapore. Qualitative instruments were used to collect and analyse the data in examining the partnerships perceived by the participants. The enablers responsible to bring about sustained professional learning are proposed. A contribution of this study is to clarify how resources in the HQ and its schools can be bridged. Deliberate bridging of resources is critical particularly at the initial stage of the partnerships. This bridging is made possible through dedicated appointed champions. The appointed champions are passionate about the educational innovations and are willing to invest their time to understand the teachers’ needs. This paper argues that the enablers can offer opportunities for lateral networks to be forged within a hierarchical system.  相似文献   

The relationship between leg preference and knee mechanics during sidestepping in collegiate female footballers     

Scott R. Brown  Henry Wang  D. Clark Dickin  Kaitlyn J. Weiss 《Sports biomechanics / International Society of Biomechanics in Sports》2014,13(4):351-361

This study examined the relationship between leg preference and knee mechanics in females during sidestepping. Three-dimensional data were recorded on 16 female collegiate footballers during a planned 45° sidestep manoeuvre with their preferred and non-preferred kicking leg. Knee kinematics and kinetics during initial contact, weight acceptance, peak push-off, and final push-off phases of sidestepping were analysed in both legs. The preferred leg showed trivial to small increases (ES = 0.19–0.36) in knee flexion angle at initial contact, weight acceptance, and peak push-off, and small increases (ES = 0.21–0.34) in peak power production and peak knee extension velocity. The non-preferred leg showed a trivial increase (ES = 0.10) in knee abduction angle during weight acceptance; small to moderate increases (ES = 0.22–0.64) in knee internal rotation angle at weight acceptance, peak push-off, and final push-off; a small increase (ES = 0.22) in knee abductor moment; and trivial increases (ES = 0.09–0.14) in peak power absorption and peak knee flexion velocity. The results of this study show that differences do exist between the preferred and non-preferred leg in females. The findings of this study will increase the knowledge base of anterior cruciate ligament injury in females and can aid in the design of more appropriate neuromuscular, plyometric, and strength training protocols for injury prevention.  相似文献   

Assessment of causal effects of physical activity on neurodegenerative diseases: A Mendelian randomization study     

Peng-Fei Wu  Hui Lu  Xiaoting Zhou  Xuchen Liang  Ruizhuo Li  Wan Zhang  Danyang Li  Kun Xia 《运动与健康科学(英文)》2021,10(4):454

BackgroundPhysical activity has been hypothesized to play a protective role in neurodegenerative diseases. However, effect estimates previously derived from observational studies were prone to confounding or reverse causation.MethodsWe performed a two-sample Mendelian randomization (MR) analysis to explore the causal association of accelerometer-measured physical activity with 3 common neurodegenerative diseases: Alzheimer''s disease (AD), Parkinson''s disease (PD), and amyotrophic lateral sclerosis (ALS). We selected genetic instrumental variants reaching genome-wide significance (p < 5 × 10⁻⁸) from 2 largest meta-analyses of about 91,100 UK Biobank participants. Summary statistics for AD, PD, and ALS were retrieved from the up-to-date studies in European ancestry led by the international consortia. The random-effect, inverse-variance weighted MR was employed as the primary method, while MR pleiotropy residual sum and outlier (MR-PRESSO), weighted median, and MR-Egger were implemented as sensitivity tests. All statistical analyses were performed using the R programming language (Version 3.6.1; R Foundation for Statistical Computing, Vienna, Austria).ResultsPrimary MR analysis and replication analysis utilized 5 and 8 instrumental variables, which explained 0.2% and 0.4% variance in physical activity, respectively. In each set, one variant at 17q21 was significantly associated with PD, and MR sensitivity analyses indicated them it as an outlier and source of heterogeneity and pleiotropy. Primary results with the removal of outlier variants suggested odds ratios (ORs) of neurodegenerative diseases per unit increase in objectively measured physical activity were 1.52 for AD (95% confidence interval (95%CI): 0.88–2.63, p = 0.13) and 3.35 for PD (95%CI: 1.32–8.48, p = 0.01), while inconsistent results were shown in the replication set for AD (OR = 1.06, 95%CI: 1.01–1.12, p = 0.02) and PD (OR = 0.99, 95%CI: 0.88–0.12, p = 0.97). Similarly, the beneficial effect of physical activity on ALS (OR = 0.51, 95%CI: 0.29–0.91, p = 0.02) was not confirmed in the replication analysis (OR = 0.96, 95%CI: 0.91–1.02, p = 0.22).ConclusionGenetically predicted physical activity was not robustly associated with risk of neurodegenerative disorders. Triangulating evidence across other studies is necessary in order to elucidate whether enhancing physical activity is an effective approach in preventing the onset of AD, PD, or ALS.  相似文献