Mechanical properties and supporting effect of CRLD bolts under static pull test conditions

A device for supporting soft rock masses combined with a constant resistance structure characterized by constant resistance and large deformation at the end of a steel bar, known as the constant resistance and large deformation（CRLD） bolt, has recently been developed to counteract soft rock swelling that often occurs during deep mining. In order to further study the mechanical properties of the CRLD bolt, we investigated its mechanical properties by comparison with the conventional strength bolt（rebar） using static pull tests on many aspects, including supporting capacity, elongation, radial deformation, and energy absorption. The tests verified that the mechanical defects of the rebar, which include the decrease of bolt diameter, reduction of supporting capacity, and emergence and evolution of fracture until failure during the whole pull process, were caused by the Poisson＇s ratio effect. Due to the special structure set on the CRLD bolt, the bolt presents a seemingly unusual phenomenon of the negative Poisson＇s ratio effect, i.e., the diameter of the constant resistance structure increases while under-pulling. It is the very effect that ensures the extraordinary mechanical properties, including high resistance, large elongation, and strong energy absorption. According to the comparison and analysis of numerical simulation and field test, we can conclude that the CRLD bolt works better than the rebar bolt.

Uncertainty analysis of ship model vertical center of gravity and transverse moment of inertia test

The usability of test results of ship model vertical center of gravity and transverse moment of inertia is generally depends on its uncertainty. Referring to the guidelines for uncertainty analysis in examination of liquid dynamic recommended by International Towing Tank Conference （ ITTC）, the results were analyzed, bias limits and precision limits were calculated and total uncertainty was estimated. The total uncertainty of six tests on ship model vertical center of gravity is is 0. 16% of the mean value, and the total uncertainty of six tests on ship model transverse moment of inertia is 5.66% of the mean value. The test results show that the total uncertainty of both the multiple tests and the single test is from the precision limits of ship model vertical center of gravity and transverse moment of inertia tests. Thus, the improved measurement system stability can enormously decrease the total uncertainty of multiple tests and the single test.

Laboratory pull-out tests on fully grouted rock bolts and cable bolts:Results and lessons learned

Laboratory pull-out tests were conducted on the following rock bolts and cable bolts:steel rebars,smooth steel bars,fiberglass reinforced polymer threaded bolts,flexible cable bolts,IR5/IN special cable bolts and Mini-cage cable bolts.The diameter of the tested bolts was between 16 mm and 26 mm.The bolts were grouted in a sandstone sample using resin or cement grouts.The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample.In most tests,the rate of displacement was about 0.02 mm/s.The tests were performed using a pull-out bench that allows testing a wide range of parameters.This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response(rock bolts and cable bolts).It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole,which cannot be neglected when the test results are used to assess the bolt-grout or the grouterock interface.

Shake-table testing of a self-centering precast reinforced concrete frame with shear walls

The seismic performance of a self-centering precast reinforced concrete （RC） frame with shear walls was investigated in this paper. The lateral force resistance was provided by self-centering precast RC shear walls （SPCW）, which utilize a combination ofunbonded prestressed post-tensioned （PT） tendons and mild steel reinforcing bars for flexural resistance across base joints. The structures concentrated deformations at the bottom joints and the unbonded PT tendons provided the self-centering restoring force. A 1/3-scale model of a five-story self-centering RC frame with shear walls was designed and tested on a shake-table under a series of bi-directional earthquake excitations with increasing intensity. The acceleration response, roof displacement, inter-story drifts, residual drifts, shear force ratios, hysteresis curves, and local behaviour of the test specimen were analysed and evaluated. The results demonstrated that seismic performance of the test specimen was satisfactory in the plane of the shear wall; however, the structure sustained inter-story drift levels up to 2.45%. Negligible residual drifts were recorded after all applied earthquake excitations. Based on the shake-table test results, it is feasible to apply and popularize a self-centering precast RC frame with shear walls as a structural system in seismic regions.

Test Center测试平台中合成频谱仪插件的设计和实现

合成仪器是一种模块化的硬件和软件测试方案,在自动测试系统中占据重要地位。本文介绍了合成仪器的概念、体系架构及特点,以及Test Center测试平台中的仪器插件,详细地阐述了如何设计和实现Test Center合成频谱仪插件。

Research on location of underground explosion center based on distributed testing system

Distributed testing system has strong applicability in the field of dynamic testing,which can centrally manage the testing equipment in different locations through the local area network,and meet the new requirements of the test.Based on the theory of seismic location,the location of underground explosion center was studied.The applicability of seismic location theory to the location of underground explosion center was verified by simulating the underground explosion with LS-DYNA simulation platform.Combined with distributed testing system theory and weighting method,the optimal distribution method of test points was summarized through data analysis.

Test-retest strength reliability of the Electronic Push/Pull Dynamometer (EPPD) in the measurement of the quadriceps and hamstring muscles on a new chair

Background: Test-retest strength reliability of the Electronic Push/Pull Dynamometer (EPPD) in the measurement of the extensor and flexor muscles on a new constructed chair. The objective of the study was to assess reliability of Electronic Push/Pull Dynamometer in the measurement of the knee flexion and extension at 90° and 60° on a new constructed chair. The aims of the author: To assess reliability of Electronic Push/Pull Dynamometer in the measurement of the knee flexion and extension at 90° and 60° on a new constructed chair. Design: A test-retest reliability study. Subjects: One hundred healthy students male and female (mean age, 21y). Methods: Maximum isometric strength of the quadriceps and hamstring muscle groups was measured using the EPPD were recorded at 60° and 90° for 3 trials on 2 occasions. Reliability was assessed with the Intraclass correlation coefficient (ICC), mean and standard deviation (SD) of measurements, and smallest real differences were calculated for the maximum and for the mean and work of the 3 repetitions. Results: Mean strength ranged from 50.44 kg for knee flexion to 55.76 kg for knee extension 50.44 kg to 61.98 kg at 90° hip flexion. Test-retest reliability Intraclass correlation coefficients (ICCs) ranged from 0.85 to 0.99. ICCs for test-retest reliability ranged from 0.780 to 0.998. Conclusions: The results of the reliability study indicate that the EPPD in reliable dynamometer to use in determining lower limb muscle force production. It can be used to measure disease progression and to evaluate changes in knee extension and flexion strength at the individual patient level.

六层自复位钢筋混凝土框架结构振动台试验研究

为研究多层自复位框架结构整体抗震性能,进行一个1/4缩尺比六层自复位框架结构模型的模拟地震振动台试验,研究该结构的动力特性及其在7度多遇至7度极罕遇4个水准地震作用下的动力反应和破坏情况。试验结果表明:在多遇以及设计基本地震作用下,结构构件无可见裂缝和损伤;随着输入地震动峰值的增加,结构损伤增加,但损伤主要集中在梁、柱端的表面混凝土,构件自身几乎没有损伤,表明自复位混凝土框架结构的抗震性能良好;在7度罕遇地震作用下,主体结构最大层间位移角为1/62,自复位框架的节点开始张开;在7度极罕遇地震作用下,模型节点张开更加明显,角钢进入屈服阶段,而主体结构的最大残余位移角仅为1/2533,证明结构具有很强的自复位能力。

带扇叶形锚固板钢筋机械锚固性能试验研究

为避免型钢混凝土节点钢筋锚固时导致的大量型钢穿孔或钢筋焊接,设计一种新型扇叶形锚固板,并通过带扇叶形锚固板钢筋中心拔出试验,分析锚固板形式、钢筋直径、锚固长度对带锚固板钢筋机械锚固性能的影响。试验结果表明:带扇叶型锚固板钢筋可避开抗剪栓钉,具有施工方便的优点,同时拥有良好的锚固性能;当钢筋锚固长度为5d~7d时,发生混凝土劈裂破坏,当锚固长度为8d~12d时,发生钢筋拉断破坏,且钢筋的锚固系数大于1.25,具有良好的锚固性能;带扇叶形锚固板钢筋极限粘结强度随钢筋直径、钢筋锚固长度增大而减小,建议钢筋的锚固长度取为8d;提出了适用于带扇叶形锚固板钢筋极限粘结强度的计算公式,能较准确地反映扇叶形锚固板对混凝土产生的挤压和劈裂作用。

高校分析测试中心的发展与现状

高校分析测试中心作为理工科院校教学和科研的重要支撑平台,其良性建设与稳定发展对于学科建设和科研成果的取得至关重要。大型仪器设备的高效采购与运行、实验人员分析测试能力的提升以及个人发展、队伍建设和完善的管理制度,都是确保分析测试中心发挥重要作用的关键因素。文章以武汉纺织大学分析测试中心为例,深入探讨其在这些方面存在的问题,并提出相应的改进建议,为高校分析测试中心的发展提供参考。

五轴加工中心多维力随动加载模拟实验平台设计

针对数控机床可靠性实验装置加载维度不足、难以工程化应用等问题,该文设计了五轴加工中心多维力随动加载模拟实验平台。通过开展多维力随动加载模拟实验,分析不同主轴转速、橡胶圈厚度、切削深度对圆锥台试件切削加工过程中所受切削力的影响规律,验证了该实验平台的可行性及多维加载能力。实验结果表明在稳定切削阶段,综合切削力随着橡胶圈厚度增大而减小,随切削深度增大而增大,切削深度与橡胶圈厚度的比值过大或过小,均易引起切削力波动。当主轴转速为1000 r/min、橡胶圈厚度为3 mm时,五轴加工中心所受综合切削力波动最小,是加载实验最佳的橡胶圈厚度。

Design and theoretical analysis of test system for propellants' gas pressure in warhead

Aiming at harsh environment of cluster bombs center tube explosion dispersion and difficulties in installation of traditional test systems,a storage test system based on 16-bit ultra-low power microcontroller MSP430 is designed in order to acquire gas pressure during cluster bombs dispersion.To meet the requirement of low power consumption,the working states of system＇s modules during data acquisition are elaborated and the equation to calculate the gas pressure change during cylindrical center tube opening the hatch is deduced.The field test is conducted and good test results are obtained.

土工格栅单向和循环拉拔特性研究

【目标】研究路基填土中土工格栅筋材特性及其固土机理,分析法向应力、压实度和拉拔速率对筋材抗疲劳性能的影响。【方法】开展了一系列大型单向拉拔试验、单向循环拉拔试验、双向循环拉拔试验,对法向应力、压实度和拉拔速率等相关参数进行了分析。在完成单向循环拉拔试验和双向循环拉拔试验后,再次对筋材进行单向拉拔试验,以对比分析筋材在循环反复荷载下的力学特性。【结果】土工格栅拉拔阻力与法向应力和压实度均呈正相关关系,提高法向应力和压实度均能提高筋材的拉拔强度。提高压实度,更容易促进填土与筋材的嵌固作用,发挥出加筋优势,提高加筋土的抗剪强度和力学稳定性。在1.5 mm/min拉拔速率下,筋材的峰值拉拔阻力最高,未出现筋材拉拔阻力随着拉拔速率变化持续增大或减小的一般规律。拉拔速率与筋材拉拔阻力存在一个阈值,增大拉拔速率会使筋材更快速地发挥功效,致使拉拔阻力更快达到峰值,这也导致筋材性能没有充分发挥,未达到理想强度便进入应变硬化阶段。在循环拉拔试验中,随着循环次数增加,残余应变减少且拉拔峰值阻力增高。第2次循环之后,筋材拉拔阻力增加速度变缓,残余应变差异较小。【结论】参与循环拉拔试验的筋材拉拔峰值阻力均有所提高,参与双向循环拉拔试验的筋材力学性质表现得更为稳定。

植物根系固土试验研究进展

植物根系固土技术在防治土体滑坡中具有重要作用。为深入了解植物根系与土壤相互作用机理,基于现有研究成果,利用VOSviewer软件对2000—2023年植物根系固土领域文献进行关键词聚类分析,得出植物根系固土试验研究常用的方法有根土复合体剪切试验、单根抗拉试验、根系构型试验和原位拉拔试验,分类归纳4种试验方法的适用性及应用情况。详细梳理各试验方法的研究进展,总结根系参数、土壤性质和环境条件对固土效果的影响。未来研究需优化试验方法,更准确地模拟实际条件中根土复合体的受力,以提高试验研究结论的准确性和代表性。

HS-ECC与带肋钢筋黏结滑移性能试验研究

为了对高强超高延性水泥基复合材料(HS-ECC)和钢筋的黏结滑移性能进行系统性研究,文章通过对7组试件的中心拔出试验,探究PE纤维掺量(0、1%和1.5%)、钢筋直径d(16 mm和20 mm)和保护层厚度(1d、2d、4d、5d)对HS-ECC和带肋钢筋黏结滑移性能的影响。结果表明:PE纤维的掺入可以有效抑制拉拔试件的脆性破坏,具有延性的劈裂-拔出破坏为主要破坏模式;黏结强度随PE纤维掺量增加呈现线性上升的趋势,纤维掺量从0增加到1.5%,黏结强度增幅为93%;黏结强度随着钢筋直径的增大而减小,因此在钢筋HS-ECC结构中钢筋直径不宜过大;黏结强度随保护层厚度的增大呈现先上升后趋于稳定的趋势,临界保护层厚度为4d。

一种非接触式R-test测量仪球心坐标计算方法

R-test测量仪是用于五轴数控机床转动轴结构误差测量的专用设备,其通过测量球相对测量坐标系的位置变化进行误差辨识。在测量坐标系中,测量球球心坐标计算的准确性和稳定性是保证测量精度的重要前提。为进行测量球球心坐标的精确计算,构建了非接触式R-test测量仪的结构模型并建立了球心坐标计算方程组。以球心坐标计算方程组为基础,简化得到用于球心坐标求解的非线性方程组并构建其目标函数,然后采用差分进化算法提高球心坐标求解的精度。最后,在GF Mikron UCP800五轴机床上进行对比实验,将测量球球心坐标的计算结果与机床实际坐标进行对比,验证所提出球心坐标计算方法的精度和可靠性。

Epidemiology of Nosocomial Bacteremia Due to Bacteria from the “<i>Burkholderia cepacia</i>Complex” at Libreville University Hospital Center

Introduction: Burkholderia cepacia is a non-fermenting emergent bacterium common in nosocomial infections and can cause life-threatening infections whose multidrug resistance makes them a serious threat in hospitals. The aim of this study was to determine the prevalence of B. cepacia infections during nosocomial infections at Libreville University teaching hospital. Methodology: In this cross-sectional study, lasting 19 months, 412 blood cultures were analyzed. The BacT/ALERT 3D (Biomerieux, France) was used to detect the positivity of blood culture flasks and the Viteck 2 compact (Biomerieux, France) for the identification of germs and the study of their susceptibility to antibiotics. Results: Our study population consisted of 412 patients. The sex-ratio M/F was 1.06 in favor of the male gender (n = 201, 51%). The age of the patients varied between 0 and 82 years. The bacteremia of B. cepacia mainly affected children under 15 years of age with a prevalence of 7% (n = 28). The pediatric ward was more represented with a frequency of 36% (n = 10). The antibiotic sensitivity profile showed high resistance of 100% for aminoglycosides (amikacin, tobramycin, and gentamycin), tetracycline, beta-lactams (Amoxicillin, Imipenem, Ticarcillin, Cefoxitin and Cefotaxime), and ciprofloxacin. However, four molecules were active on B. cepacia (Levofloxacin 100%, Trimethoprim + sulfamethoxazole 92.3%, ceftazidime 80% and cefepime 35%). Conclusion: Ultimately, infection and multi-resistance due to Burkholderia cepacia calls for a review of hospital hygiene in the pediatric ward and a review of antibiotic therapy in young children.

循环张拉作用下新型多节泡土钉抗拔性能现场试验研究

新型多节泡土钉具有拉拔硬化特征,相比传统土钉,其在土质边坡中抗拔性能更优。为了探究实际工况条件下新型多节泡土钉的边坡加固性能,并与传统土钉进行比较,开展7组新型多节泡土钉及传统土钉现场循环张拉试验,研究注浆工艺、节泡间距及埋深对土钉抗拔力及其发挥速率的影响规律,进而探明了每一循环下土钉弹、塑性拉拔位移占比,并分析其内在机理。试验结果表明:循环张拉作用下,注浆工艺对土钉的抗拔力影响显著,采用改进式压密注浆工艺和直接压密注浆工艺的土钉抗拔力远远超出传统注浆工艺,且初期的拉拔硬化现象更明显。采用改进式压密注浆工艺的土钉抗拔力发挥速率最快,直接压密注浆工艺次之,传统注浆工艺最小。从总体趋势上看,新型多节泡土钉抗拔力发挥速率在降低,传统土钉抗拔力发挥速率在升高。采用改进式压密注浆工艺虽然不能提升土钉弹性拉拔位移的占比,却能显著提高极限抗拔力;节泡间距对多节泡土钉抗拔力和抗拔力发挥速率影响较小,主要受到土钉周围土体强度的影响;埋深影响多节泡土钉的极限抗拔力,埋深越大,极限抗拔力和初始抗拔力发挥速率越大,同时抗拔力发挥速率随拉拔位移递减的趋势也更加明显。研究成果对提高新型多节泡土钉加固性能和优化工程应用提供指导。

叶轮中心淹没深度对特低扬程下立式泵装置流道水力性能的影响

为提高特低扬程泵站立式轴流泵装置的水力性能,该研究对叶轮直径为3.0、2.5、2.0、1.5 m的立式轴流泵装置在不同叶轮中心淹没深度下的进、出水流道流场分别进行了三维湍流流动数值计算,并对流道流场和水头损失进行了分析比较;对某特低扬程泵站在叶轮中心淹没深度为3.08、2.38、1.68 m下的立式轴流泵装置水力性能分别进行了数值计算及比较,并进行了泵装置模型试验验证。研究结果表明:叶轮中心淹没深度对肘形进水流道的水流流态及水头损失的影响很小,但对虹吸式出水流道的流态和水头损失影响较大;随着叶轮中心淹没深度的增大,虹吸式出水流道内的流态逐渐改善,流道水头损失基本呈下降趋势,泵装置效率逐渐增大,特低扬程工况下泵装置模型试验最优工况点的效率达75.92%,泵装置能量性能数值模拟结果与模型试验结果基本一致。研究结果可为特低扬程泵站采用立式泵装置的设计提供一定参考依据。

沙漠砂混凝土与钢筋黏结性能试验研究

在我国西部沙漠砂资源丰富的背景下,探究沙漠砂对钢筋与混凝土黏结性能的影响,制作中心拉拔试验,通过对不同沙漠砂取代率和不同粉煤灰掺量下的钢筋与混凝土的黏结强度进行试验研究。根据黏结滑移曲线,分析沙漠砂取代率和粉煤灰掺量对钢筋和混凝土黏结强度、极限位移、破坏模式的影响。研究结果表明:直径16 mm钢筋混凝土试件在锚固长度较短导致脆性劈裂破坏的情况下,钢筋与混凝土的黏结强度随沙漠砂取代率的增加呈先上升后下降的趋势;粉煤灰掺量为20%时,对两者的黏结强度提升最大。