Influence of Axial Load Ratio on Shear Behavior of Through-Diaphragm Connections of Concrete-Filled Square Steel Tubular Columns

Nonlinear finite element analysis and parametric studies were carried out to study the influence of axial load ratio on the shear behavior of the through-diaphragm connections of concrete-filled square steel tubular columns. The analysis reveals that smaller axial load ratio can improve the shear bearing capacity and ductility while larger axial load ratio will decrease the shear behavior of the through-diaphragm connections. The parametric studies indicate that the axial load ratio should be limited to less than 0.4 and its influence should be considered in the analysis and design of such connections.

Axial length/corneal radius of curvature ratio and refractive development evaluation in 3-to 4-year-old children: the Shanghai Pudong Eye Study

AIM: To measure and analysis axial length(AL)/corneal radius of curvature(CRC) ratio and other refractive parameters, provide a medical reference range for refractive development evaluation and earlier visual impairment screening of 3 to 4 y kindergarten students.METHODS: Between April and June 2017, a total of 4350 participants aged 3-to 4-year-old(8700 eyes) from 10 cluster random sampling kindergartens in Shanghai, Pudong District were involved. According to the measurement and analysis of the unaided visual acuity(VA), AL, CRC, AL/CRC ratio, astigmatism and other refractive parameters, the data distribution and reference range were obtained.RESULTS: Uncorrected VA of examined children was 0.23±0.08(logMAR, mean±SD) [95% confidence interval(CI) range ≤0.36];AL was 22.10±0.79 mm(95%CI 20.55-23.65);CRC was 7.86±0.26 mm(95%CI, 7.35-8.37);AL/CRC ratio was 2.81±0.12(95%CI, 2.57-3.05). The median of astigmatism was-0.5 D, a total of 56.3% had astigmatism <-0.50 D, 85.3%<-1.00 D, 6.7%>-1.50 D;71% were astigmatism with the rule. Eye-specific analyses were conducted. Statistical difference of VA was in right and left eyes. There were no significant differences between two eyes of AL, CRC, AL/CRC ratio and astigmatism(P>0.05).CONCLUSION: VA and AL/CRC ratio reference could be used to assess refractive development in children and screening uncorrected refractive errors or amblyopia. Astigmatism needs to be considered in the diagnosis.

Influence of axial stress on rockburst in deep tunnels: insight from model experiment

Frequent rockburst disasters in deep-buried engineering projects severely impact construction. To explore the influence of axial stress on rockburst in deep-buried tunnels, large-scale true triaxial rockburst experiments were conducted under four different axial stress ratio conditions (ηt, axial loading stress/vertical loading stress) using a self-developed true triaxial loading device under the condition of "pre-loading before excavation". The influence of axial stress on the rockburst process and failure characteristics in deep tunnels was studied using a combination of real-time video monitoring, rockburst debris sieving, and acoustic emission monitoring. The results indicate: (1) all four specimens subjected to different axial stress ratio loading conditions exhibited three stages of macroscopic failure: small particle ejection, flake spalling, and large fragment ejection. Ultimately, "V"-shaped notches appeared on both sides of the tunnel. (2) The failure stress, fragment volume, and fragment size distribution of the rockburst specimens exhibited a clear two-stage failure characteristic with increasing axial stress ratio. In the lower axial stress ratio stage (ηt ≤ 0.7), the increase in the axial stress ratio enhances lateral confinement, thereby increasing the crack initiation strength of the surrounding rock, inhibiting crack formation and propagation, and thus suppressing damage to the surrounding rock of the tunnel. In the higher axial stress ratio stage (ηt > 0.7), the increase in axial stress ratio makes the Poisson effect of the surrounding rock more pronounced, promoting the generation and propagation of cracks along the tunnel axis direction, thereby promoting damage to the surrounding rock. (3) Based on the analysis of acoustic emission parameters (fracture properties), it can be concluded that in the lower axial stress ratio stage (ηt ≤ 0.7), an increase in the axial stress ratio leads to a higher proportion of shear fracture in rockburst damage. Conversely, in the higher axial stress ratio stage (ηt > 0.7), the increase in axial stress ratio gradually reduces the proportion of shear fracture in rockburst damage.

Effect of Hub-Ratio on Performance of Asymmetric Dual-Rotor Small Axial Fan

Currently, domestic and abroad scholars put more attention on contra-rotating dual-rotor axial fan. But there is less scholars study on asymmetric dual-rotor small axial fan, which is one of the contra-rotating dual-rotor axial fans. Like axial fan, many factors have influence on the performance of the asymmetric dual-rotor small axial flow fan, such as the wheel hub ratio, blade shape, blade number, stagger angle and the tip clearance. Because wheel hub ratio has great impact on the performance of the fan, we choose the size of wheel hub ratio as a variable factor to study the model change. There is a different wheel hub ratio between front stage impeller and rear stage of asymmetric dual-rotor small axial fan, so it is very beneficial to select the greater wind area that the fan area of external diameter minuses the area occupied by the blades and the hub as front stage impeller. In this paper, the hub-ratio of front stage impeller is 0.72, and that of rear stage is 0.72, 0.67 and 0.62 respectively along with the front stage impeller. Three kinds of models with different hub ratio of rear stage are simulated using the CFD software and the static characteristics are obtained. Based on the experimental test results, the internal flow field of the asymmetric dual-rotor small axial fan is analyzed in detail, the impact trends of different hub-ratio on the performance of asymmetric dual-rotor small axial fan are obtained and the argument of structure optimization for dual-rotor small axial fan is provided.

Preparation and Properties of Carbon Fiber Chiral Materials

The chiral materials were prepared by using the carbon fiber helices as chiral inclusions, and the composite of Fe3O4 and polyaniline as matrix. The electromagnetic properties, including the rotation angles, the axial ratios and the complex chirality parameters, were measured by using a circular waveguide method in the 8.5-11.0 GHz frequency range. The dependence of these electromagnetic properties on the frequency and the concentration of the Fe3O4 in the composite matrix were analyzed. The results show that an appropriate concentration of Fe3O4 in the matrix is useful in improving the electromagnetic properties of the chiral material.

配置630MPa高强钢筋混凝土柱抗震性能试验研究

为研究高强配筋对方形截面混凝土柱抗震性能的影响,对6根配置有屈服强度为630、600、500、400MPa钢筋的边长为300mm的方形截面混凝土柱进行了拟静力加载试验,试验变量为钢筋强度、轴压比和纵向钢筋配筋率,对各试件的最终破坏形态、承载力、位移延性、滞回曲线、刚度退化曲线和耗能曲线进行分析。试验结果表明:配置600MPa和630MPa钢筋的混凝土柱与配置400MPa和500MPa钢筋的混凝土柱均发生弯曲破坏;600MPa和630MPa纵筋和箍筋与混凝土具有良好的协同作用,使混凝土柱能充分发挥材料性能,有较为饱和的滞回曲线,并具有良好的震后恢复性;纵筋配筋率的增加能有效提高配置高强钢筋混凝土柱的位移延性,增强耗能能力;适当的试件轴压比能使其具有相对较好的耗能和抗震能力。

基于多轴向铺层设计的FRP拉挤方管螺栓节点抗拉性能研究

在基于构件-节点一体化设计优化出的多轴向铺层基础上,进一步探究了铺层(单轴向铺层UD、多轴向铺层MD1、单轴向和多轴向相邻铺层MD2及多轴向中混碳铺层BC)以及几何尺寸(端距和排距)对FRP拉挤方管螺栓节点抗拉性能的影响。试验结果表明,多轴向布(MD1和MD2)的加入使节点极限承载力提升50%以上,极限位移增大至2倍以上,极大改善了节点承载和节点延性。采用MD2铺层能够获得最大节点承载力;BC铺层没有提升节点承载力但使节点刚度增大了7%~30%。端距和排距对UD方管螺栓节点的破坏模式无明显影响,均呈现剪切或劈裂破坏模式。当端径比增加至4时,多轴向方管螺栓节点破坏模式开始或完全转变为延性挤压破坏;随着排距的增大,两孔共同挤压受力过程延长,实现了更高延性、更高承载力的节点性能。建议多轴向BFRP拉挤方管螺栓节点的端径比和排径比取为4以上。

Seismic ductility of very-high-strength-concrete short columns subject to combined axial loading and cyclic lateral loading

The seismic ductility of reinforced very-high-strength-concrete （VHSC） short columns was studied by combinatively applying axial load and low cyclic lateral load on specimens to simulate seismic impact. Twelve specimens with concrete compressive strength ranging from 95.6 MPa to 118.6 MPa and a shear-span ratio of 2.0 were tested for shear failure pattern and fear force-displacement hysteretic responses. Combinative application of axial load and low cyclic lateral load to VHSC short columns incurs shear failure. The displacement ductility is much smaller when the axial load ratio is larger; whereas a larger stirrup ratio is accompanied with a better displacement ductility. The relationship of displacement ductility factor,μ△, with stirrup characteristic value, λv, and test axial load ratio, nt, is μ△=（1＋8λv）/（0.33＋nt）. By this relationship and relevant codes for aseismatic design, the axial load ratio limits for aseismatic design of reinforced VHSC （C95 to C100） short columns for frame construction are respectively 0.5, 0.6, and 0.7 for seismic classes Ⅰ, Ⅱ, and Ⅲ; corresponding minimum characteristic values of stirrups are calculated according to the required characteristic values of at least 1.273 times of experimental results. These data are very useful to aseismatic engineering.

Behavior and design method of square-tubed reinforced concrete short columns under axial compression

The behavior of square-tubed reinforced concrete (STRC) short columns subjected to axial compression was studied in detail with an accurate nonlinear finite element model (FEM) . Different width to thickness ratios (D/t = 50 150) of the steel tube and the compressive strength of concrete (C80 and C50) were adopted in this research. The axial load strength,steel tube strain and load-shortening response were determined from FEM and the analysis results from FEM were compared with those from experiment. The analysis and test results indicate that the concrete strength little affectes the confinement of the steel tube on the concrete. The transverse stress of the tube at the axial load point increases with the increment in the width to thickness ratio. Based on the results from FEM and experiment,a formula for the prediction of the axial load strength was proposed in this paper.

配筋PVA-钢混杂纤维增强水泥基复合材料梁柱边节点抗震性能试验研究

改善工程材料韧性和耐久性,提高框架梁柱节点抵抗变形和破坏的能力,是提高框架结构抗震韧性的有效途径之一。采用PVA-钢混杂纤维增强水泥基复合材料代替普通混凝土应用到梁柱边节点,考虑轴压比和加密区体积配箍率的影响,设计6个配筋PVA-钢混杂纤维增强水泥基复合材料、1个配筋单掺PVA纤维增强水泥基复合材料和1个钢筋混凝土梁柱边节点试件进行拟静力试验,分析其破坏形态、滞回曲线、骨架曲线、延性、耗能能力、钢筋应变和梁端塑性铰区转角,探讨混杂纤维的加入对梁柱边节点抗震性能的影响。结果表明:与钢筋混凝土节点和单掺PVA纤维增强水泥基复合材料节点相比,PVA-钢混杂纤维增强水泥基复合材料节点的承载力高、变形能力大、延性好、耗能能力强,抗震性能显著提升。当试验轴压比从0.12增加到0.24,梁端塑性铰区产生一定的外移,塑性性能发挥更充分,同时试件的变形能力、延性、耗能能力增加。在加密区体积配箍率减小的情况下,试件仍表现出良好的抗震性能。

Multi-point airfoil optimization for axial-flow fan

Airfoil is the element of fan blade design. It is strongly anticipated to design a fan of ave- raged high performance over a wide operation range. Multi-point optimization design of airfoil for axial flow fan was proposed over specific operation range. Weighted objective function of airfoil lift-drag ratio was constructed for several operation points around the designing one. Airfoil was defined by parametric B-spline curve of limited shape controlling points. Results show that normal standard airfoils have remained spaces to be optimized under specific operation conditions. Airfoil performance is sensitive to flow′s Reynolds number and cascade solidity. Predicting flow transition along airfoil profile is essential to search for optimized one. Optimized airfoil of wide operation range is possible to obtain with prescribed fitness function. Obtainments of multi-point optimization may be relatively lower at design point, but positive obtainments are achieved at off-design ones. Resulted airfoil is specially suitable for axial flow fans operating frequently at off-design point such as air condition coolers.

一种宽带圆极化缝隙天线的研究与设计

设计了一种结构简单的宽带圆极化缝隙天线,由单层介质基板和两层金属构成,覆盖WiMAX、WLAN和5G通信的sub6 GHz频段。通过在方形缝隙拐角处分别添加两个矩形贴片和一个倒L枝节,实现宽带圆极化辐射。天线采用微带耦合馈电的方式,通过调整T形微带馈线的长度和矩形贴片的宽度,进一步展宽了天线的带宽。测试结果表明,天线的−10 dB阻抗带宽为1.91~7.14 GHz,轴比带宽为2.5~6.3 GHz,相对轴比带宽为86.4%,峰值增益在5.5 GHz处达到5.5 dBic。

轴力对预应力高强混凝土管桩抗震性能的影响

目的研究轴力和往复荷载作用下预应力高强混凝土管桩的抗震性能,为预应力高强混凝土管桩的设计和实际工程应用提供参考依据。方法应用ABAQUS有限元软件对预应力高强混凝土管桩进行有限元模拟,并与已有试验结果对比,两者吻合良好,验证了模型的准确性。在此基础上,研究轴压比和有无普通钢筋及普通钢筋直径对预应力高强混凝土管桩滞回曲线、骨架曲线、刚度退化、延性及耗能能力的影响。结果配置普通钢筋可以提高预应力高强混凝土管桩的承载能力和延性,对刚度影响不大;随着轴压比的增加,预应力高强混凝土管桩的承载能力逐渐提高,但延性变差,轴压比为0.45时,预应力高强混凝土管桩发生脆性破坏。结论配置普通钢筋可以有效改善预应力高强混凝土管桩的抗震性能,预应力高强混凝土管桩的轴压比不宜超过0.3。

Dem与轴率比预测3-14岁儿童屈光状态效率的比较

目的:研究Dem、轴率比与3-14岁儿童屈光状态的关系,比较Dem、轴率比预测近视的效率,探寻定量预测儿童屈光状态更为有效的方法。方法:横断面研究。收集2021-03/2022-12就诊于西安市第一医院眼科门诊的3-14岁儿童共519例519眼(均取右眼数据)。于睫状肌麻痹验光前采集眼球生物测量数据,记录眼轴长度(AL)、角膜曲率(K值)、Dem、睫状肌麻痹后等效球镜度数(SER)等,SER≤-0.50 D判断为近视。结果:3-14岁儿童SER与Dem呈正相关(r=0.88,P<0.01),与AL/CR比值呈负相关(r=-0.87,P<0.01)。Dem、AL/CR截点分别为20.40 D、3.02,当Dem≤20.40 D或AL/CR≥3.02时可判断为近视。Dem每减小1 D,SER减小0.57 D,AL/CR每增加0.06,SER减小1.00 D。ROC曲线下面积(AUC)Dem(0.958)>AL/CR(0.940)。结论:3-14岁儿童SER与Dem呈正相关,与AL/CR呈负相关,预判近视的效率Dem优于AL/CR。眼球生物测量仪可直接提供Dem,且Dem与SER量效关系更便于计算,用于预测儿童SER更为便捷。

圆中空夹层不锈钢管水泥砂浆短柱轴压性能研究

海洋工程平台塔架结构中,圆形截面中空双钢管是主要受力构件,工程界十分关注其受压性能和耐腐蚀性能。为研究圆中空夹层不锈钢管水泥砂浆短柱的轴压力学性能,以外不锈钢管壁厚、内碳素钢管直径和是否含夹层水泥砂浆为试验变量,共设计了12个短柱试件。分析各试件的破坏情况、荷载-位移曲线、承载力、变形能力及应变特征,研究不同变量对极限承载力的影响规律。结果表明:试件破坏形态为外钢管端部或中部局部屈曲破坏;随着不锈钢管壁厚的增大,试件的轴压承载力近似呈线性增长;夹层水泥砂浆对试件力学性能影响较大,可有效提高试件承载力,抑制外不锈钢管的变形,提高试件延性;对于含夹层水泥砂浆的试件,承载力随空心率增大而减小,不含夹层水泥砂浆的试件,承载力随空心率增大而增大。根据国内外规范以及相关学者提出的理论公式,计算了试件的极限承载力,并与试验承载力进行了对比分析,给出了设计建议。

轴压比对波纹侧板-方钢管混凝土柱抗震性能的影响研究

为研究轴压比对波纹侧板-方钢管混凝土柱抗震性能的影响,使用ABAQUS软件建立了组合结构柱的有限元模型,通过破坏形态和滞回曲线等对模型的准确性进行了验证,运用参数模型讨论了不同轴压比对试件的破坏形态、滞回曲线、骨架曲线、压弯承载力和延性系数的影响。结果表明,随着轴压比增大,方钢管的高应力高度逐渐升高,波纹板的应力由水平分布变化为斜向分布;提高轴压比会使试件的压弯承载力和延性系数呈先升高后降低的趋势,建议轴压比不应超过0.30,满足规范中对延性系数的要求并在一定程度上提高结构的压弯承载力。通过合理控制轴压比,可以提升波纹侧板-方钢管混凝土柱抗震性,确保其在实际应用中的安全性和稳定性。

高温后烧结普通砖砌体剪压复合抗剪性能试验研究

为了研究砖砌体结构在高温后的剪压复合受力性能,制作了84个砌体试件,进行了在不同高温后不同轴压比下的抗剪试验,得出砌体在高温后的抗剪强度和轴压比之间的变化规律,对高温后砌体试件在不同轴压比情况下的延性进行了分析。结果表明:在相同温度下,随着轴压比增大,砌体抗剪强度增大;轴压比一定时,随着温度升高,砌体抗剪强度减小。在0.1~0.5轴压比范围内,同一温度下,随着轴压比增加,砌体的延性不断增大;轴压比相同时,随着温度的升高,砌体延性逐渐降低。以常温下相同压应力为基准,200℃以内,轴压比为0.3时试件出现剪压破坏;400℃以上,轴压比为0.2时试件出现剪压破坏,高温使砌体剪压段提前。基于变摩擦系数的剪摩理论,计算出普通砖砌体抗剪强度公式的变摩擦系数;结合高温后砖砌体纯剪强度公式,得到以温度为变量的高温后砖砌体剪压复合抗剪强度计算公式。

承插式连接预制拼装桥墩抗震性能试验研究

为研究不同连接构造、轴压比和承插深度对承插式连接预制拼装桥墩(简称“承插式桥墩”)抗震性能的影响,制作1组现浇桥墩试件和3组承插式桥墩试件开展拟静力试验。对比试件破坏模式、滞回曲线、骨架曲线及特征值、耗能能力、刚度特性和残余位移、纵筋应变,分析承插式桥墩与现浇桥墩抗震性能差异以及增设钢榫进行结构优化后桥墩抗震性能改善效果。结果表明:承插式桥墩与现浇桥墩试件破坏模式、损伤范围、承载能力、耗能能力、残余位移和钢筋应变沿梁高分布相近;提高承插式桥墩轴压比,能提高桥墩承载能力,降低延性和累积耗能能力,破坏时残余位移远小于其它构件,具有可靠的自复位能力;提高承插深度,会增大桥墩承载能力和耗能能力;墩底增设钢榫能增强承插式桥墩与承台间的连接,承载能力、延性、耗能能力等与承插式和现浇桥墩保持一致,但各加载位移下的累积耗能较高,有助于提高承插式桥墩的耗能能力,具有良好的抗震性能。

相对密实度和固结应力比对北部湾海砂动力特性影响的试验研究

北部湾地区拥有丰富的海洋资源,海洋工程在这一地区的发展日益重要,了解海砂在不同固结应力比和密实度条件下的动力特性,对于海岸线保护、港口建设、堤防工程等都至关重要。为探究北部湾海砂的动力特性,针对北部湾海砂开展了一系列的固结不排水循环动三轴试验,分析了相对密实度和固结应力比对北部湾海砂的轴向累积应变、动弹性模量、动孔压以及滞回曲线的影响。研究表明:在相同振次水平下,随着固结应力比和相对密实度的增大,海砂的轴向累积应变随之减小;动孔压随着固结应力比的增大线性减小,在低相对密实度(Dr≤50%)下,动孔压随振次的增大而增大,在高相对密实度(Dr=70%)下,动孔压随振次先增后减;动弹性模量随着振次的增加出现刚度软化现象,增大相对密实度与固结应力比,较明显地减缓了动弹性模量的衰减速率;随着固结应力比和相对密实度的增大,滞回曲线包围的面积减小,滞回曲线由不封闭曲线转为封闭曲线。这些研究成果可以为北部湾围填海工程提供一定的参考。

负载下活性粉末混凝土钢筋网加固足尺混凝土柱轴压性能试验研究

为提高负载下钢筋混凝土(RC)柱的轴心抗压性能,使用活性粉末混凝土钢筋网(RPCSM)对负载下的RC足尺柱进行加固,设计制作了7根RC方柱试件,其中1根未加固对比柱、1根端部箍筋加密加固柱、2根RPCSM加固柱、3根端部箍筋加密RPCSM加固柱。考虑加固层厚度、钢筋网配筋率和端部箍筋加密对轴心受压RC柱性能的影响,进行了试验研究并分析了各试件的破坏模式、荷载-变形关系和应变变化规律。结果表明:加固柱的承载力提高了2.81~3.82倍;原混凝土柱与RPCSM加固层界面粘结可靠,共同工作良好;随着钢筋网配筋率的提高以及加固层厚度的增加,端部箍筋加密后整体性的提高,承载力和轴向变形能力提高,但延性有所下降。结合规范和破坏机理,给出了承载力计算公式,以促进该加固技术的推广。