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.

Pull-out tests and slope stability analyses of nailing systems comprising single and multi rebars with grouted cement

The pull-out capacities for soil nailing systems comprising of one single 29 mm diameter(type A) and four 16 mm diameter(type B) rebars with grouted cement were examined.A field test and numerical analysis for the type A and type B systems were carried out to investigate the pull-out capacities and the slope stability reinforcement efficiency in soil and rock slopes.The results of the pull-out tests show the mobilized shear force and load transfer characteristics with respect to soil depth.The load-displacement relationship was examined for both type A and type B systems.Slope stability analyses were carried out to study the relationships between soil and nail reinforcement and bending stiffness as well as combined axial tension and shear forces.Factors of safety were calculated in relation to the number of nails and their outside diameters.Both soil and rock slopes were included in this evaluation.

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.

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.

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.

Effects of different pull-out loading rates on mechanical behaviors and acoustic emission responses of fully grouted bolts

Due to the influence of mining disturbance stress,it is of great significance to better understand the bearing characteristics of fully grouted bolts under different pull-out loading rates.For this purpose,a series of laboratory pull-out tests were conducted to comprehensively investigate the effects of different pull-out loading rates on the mechanical performance and failure characteristics of fully grouted bolts.The results show that the mechanical performance of the anchored specimen presents obvious loading rate dependence and shear enhancement characteristics.With the increase of the pull-out loading rates,the maximum pull-out load increases,the displacement and time corresponding to the maximum pull-out load decrease.The accumulated acoustic emission(AE)counts,AE energy and AE events all decrease with the increase of the pull-out loading rates.The AE peak frequency has obvious divisional distribution characteristics and the amplitude is mainly distributed between 50-80 dB.With the increase of the pull-out loading rates,the local strain of the anchoring interface increases and the failure of the anchoring interface transfers to the interior of the resin grout.The accumulated AE counts are used to evaluate the damage parameter of the anchoring interface during the whole pull-out process.The analytical results are in good agreement with the experimental results.The research results may provide guidance for the support design and performance monitoring of fully grouted bolts.

Loading characteristics of mechanical rib bolts determined through testing and numerical modeling

Underground coal mines use mechanical bolts in addition to other types of bolts to control the rib deformation and to stabilize the yielded coal ribs.Limited research has been conducted to understand the performance of the mechanical bolts in coal ribs.Researchers from the National Institute for Occupational Safety and Health(NIOSH)conducted this work to understand the loading characteristics of mechanical bolts(stiffness and capacity)installed in coal ribs at five underground coal mines.Standard pull-out tests were performed in this study to define the loading characteristics of mechanical rib bolts.Different installation torques were applied to the tested bolts based on the strength of the coal seam.A typical tri-linear load-deformation response for mechanical bolts was obtained from these tests.It was found that the anchorage capacity depended mainly on the coal strength.Guidelines for modeling mechanical bolts have been developed using the tri-linear load-deformation response.The outcome of this research provides essential data for rib support design.

Bond Property Test of Reinforced Concrete with All Soaking and Impressed Current Method Corrosion

In order to research the bond properties between corroded reinforcement bars and concrete,reinforcement bars with different diameters and different types and concrete with different strength levels were treated specially with all soaking and impressed current method,and the bond properties were measured with the pull-out test.The comparative analysis of the bond properties of corroded reinforcement bars was carried out.The results showed that the types of reinforcement bars and concrete had great influence on the bond strength.The corrosion and volume expansion of reinforcement bars made concrete in tensile condition,which tended to produce cracks in parallel reinforced direction.The typical bond failure of plain reinforcement bars was pull-out,while the typical bond failure of ribbed reinforcement bars was split.The bond strength between corroded reinforcement bars and concrete increased with the increase of concrete strength.The bond strength of plain and ribbed reinforcement bars showed a decreasing trend after the first increase with the increase of the extent of corrosion.Through the test,the coefficients of the bond strength of plain and ribbed reinforcement bars were given,respectively.

Investigating Earth Reaction to Pull-Out Process of Frictional Rock Bolts Using Distinct Element Method

The reaction of earth to pull-out process of frictional rock bolts was here modeled by the distinct element method (DEM). Ten frictional bolts were prepared;the expanding shells of five bolts included convex edges and the others had the shells with concave bits. The strength of bolts was measured by applying a standard pull-out test;the results confirmed that the strength of shells with convex edges was remarkably more than the strength of other shells. Furthermore, a two-dimensional DEM model of the test was developed by a particle flow code;the obtained results showed that the reaction of rock particles to the contacts occurring between the convex edges and earth was considerably more than those of the concave bits. In the other words, the convex edges transferred the pull-out force into a large area of the surrounded rock, causing these bolts to have the highest resistance against earth movements.

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.

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。

2021-2022年江阴市公共场所微生物检测结果分析

目的分析旅店、洗浴中心、超市的微生物检测结果。方法根据《公共场所卫生监测技术规范》和《公共场所卫生标准监测检验方法》要求,对3类公共场所(旅店、洗浴中心、超市)共2372份样品进行微生物检测。结果通过对2021年-2022年空气和公共用品用具微生物检测结果进行分析后,2021年共计检测1124份样本,其中合格样本1110份,合格率为98.75%;2022年共计检测1248份样本,其中合格样本为1248份,合格率为100.00%。2022年空气和公共用品用具微生物检测结果高于2021年(x^(2)值=13.586,P<0.05)。结论与2021年相比,2022年江阴市公共场所微生物检测合格率有较高的提升。然而,需要保持警惕,加强卫生管理,以确保公共场所的环境卫生和人员健康。

基于CMA 认证构建实验室安全体系研究

分析测试中心作为公共科研与教学服务的实验室平台,存在着人员流动大、测试量多、安全风险高的特点,测试中心的安全管理对于学校和社会的稳定至关重要。基于CMA认证中实验室安全的标准及要求,依托高校大型仪器设备共享平台,围绕实验室安全管理机制、实验室标准化工作、安全教育和准入制度等方面开展了一系列工作,以此来优化测试中心的安全管理体系,保障了实验室稳定高效且安全的运行,为实验室安全建设提供一些参考与借鉴。

4Cr13模具钢探伤缺陷的成因分析及控制

针对某公司模铸产线生产的4Cr13钢种探伤不合存在的缺陷问题,采用扫描电镜和能谱仪对钢样进行了成因分析。结果表明,探伤缺陷分为钢板头尾部的点状缺陷和中心区域的线状缺陷,点状缺陷主要以CaO与Al2O3为主的钙铝酸盐夹杂物形式存在,中心区域线状缺陷由钢锭内部缩孔或疏松造成。通过优化RH处理工艺、优化锭型使用、延长镇静时间等改进措施,4Cr13厚板探伤不合率由改进前的平均33.5%下降至改进后的4.5%,得到了显著改善。

高校分析测试中心实验室安全管理体系的构建

高校分析测试中心是实验教学、科研和社会服务的重要场所,是大型仪器共享平台的重要基地,因此,学校对分析测试中心实验室的安全管理提出了更高的要求。文章针对分析测试中心实验室的特点及安全管理现状进行分析,从管理制度的建立、安全教育培训的强化、定期监督巡查以及应急响应体系的建立等方面去探讨分析测试中心实验室安全管理体系的构建,并提出实验室安全管理持续改进的措施,为其他高校分析测试中心实验室安全管理提供参考。

平面KK型矩形钢管节点静力试验研究

依托某主题广场月牙形艺廊单层网壳钢屋架结构,选取其最不利受力节点,设计了中心插板节点和毂节点两种KK型矩形钢管节点,分别对其足尺模型进行静载试验,测试分析模型节点区域的应变及应力分布规律,对比分析支管端部的位移变化。结果表明:1)设计荷载水平下,两个节点均满足受力要求;毂节点和中心插板节点的最大试验荷载约为等效设计荷载的2.85倍和3.25倍,节点安全储备较高;2)在最大试验荷载作用下,两个节点支管根部与中心构件相贯焊缝附近部分均不同程度地屈服,毂节点圆筒内加劲肋焊缝局部出现开裂;3)相同荷载作用下,中心插板节点相应位置应力应变水平相对较低,故中心插板节点的承载强度较高;4)由试验荷载-位移曲线分析得出毂节点的各肢平均位移比中心插板节点约大13.3%,表明中心插板节点弹性刚度较大。

变摩擦装配式自复位复合墙抗震性能研究

针对自复位墙体耗能不足及大位移角时损伤严重的问题,介绍了一种变摩擦装配式自复位复合墙.墙体由变摩擦阻尼器、钢脚、预应力筋和复合墙构成:变摩擦阻尼器的摩擦力随滑移量的增加而增加,具有良好的耗能能力;钢脚提高了墙角抗压强度并提供了变摩擦阻尼器安装空间;预应力筋为墙体提供了自复位能力和部分承载能力;复合墙具有轻质、高强、绿色环保的特点.为进一步研究该墙体的抗震性能,对3块自复位复合墙进行了低周往复试验,分析不同初始预应力、碟簧组合形式对试件破坏形态、滞回特征、承载力、刚度退化、自复位能力和耗能能力的影响.研究结果表明:试件仅在墙底部出现少量混凝土表皮剥落,表现出良好的低损伤特点;试件在1.0%位移角时最大残余位移角为0.85%,表现出自复位特点;各试件的单圈耗能随着位移角的增加而迅速增加,表现出良好的耗能能力;初始预应力提高至1.9倍,导致承载力增加至1.3倍,而残余位移角降低至60%;阻尼器碟簧组合的并联数量增加至2倍,导致墙体的承载力增加至1.5倍,耗能能力增加至2倍,残余位移角增加至4.6倍.此外,建立了自复位复合墙数值分析模型,数值模型分析结果与试验结果较为吻合.随后进行了参数分析,发现预应力筋根数、螺栓初始预紧力和钢脚宽度对墙体的承载能力或耗能能力具有较大影响.