带初始裂缝钢筋与混凝土粘结破坏机理

钢筋与混凝土之间的粘结是保障钢筋混凝土结构实现其建筑功能(安全性、适用性和耐久性)的关键影响因素之一.通过实验室模拟不同工作环境中带有不同初始裂缝宽度、以及不同水灰比铰梁试件,经海水浸泡180 d干湿循环或大气环境180 d等环境作用下,对钢筋与混凝土粘结性能进行研究.本文主要分析钢筋与混凝土之间粘结破坏机理.本文试验研究结果表明:(1)钢筋与混凝土粘结破坏主要表现为混凝土沿纵筋方向劈裂破坏(贯穿劈裂破坏和部分劈裂破坏);(2)带预制裂缝试件钢筋与混凝土粘结受预制裂缝的影响,钢筋与混凝土的粘结应力分布改变,钢筋与混凝土的粘结破坏为部分劈裂破坏;(3)如果试件中的钢筋不能提供足够拉力时,会发生钢筋受拉屈服的破坏而钢筋与混凝土的粘结不破坏.     

BP神经网络在粉煤灰混凝土极限粘结应力预测中的应用

研究粉煤灰混凝土与钢筋的粘结性能是非常必要的,而且这将对粉煤灰混凝土的广泛应用也非常有利.应用BP神经网络对粉煤灰混凝土极限粘结应力进行预测,表明该预测方法预测精度高,高效可行,具有一定的优越性,不仅为粉煤灰混凝土极限粘结应力的获得提供了新方法,而且为寻求关于粉煤灰混凝土粘结性能的各影响因素之间内在的和整体的规律提供了新的思路.     

钢筋内贴片中心拔出试件制作方法

详细介绍了钢筋内贴片中心拔出试件的制作方法。中心拔出试验是研究钢筋与混凝土间粘结性能的有效方法,通过钢筋内贴应变片可以测得锚固区内不同位置的钢筋应力,进而揭示钢筋与混凝土的粘结特点。     

混凝土粘结质量对其多轴强度影响的数值分析

以测试混凝土抗压强度的试件为数值分析的对象,考虑试件内部存在贯穿整个试件1-2mm厚的细砂、中砂或粗砂形成的薄弱层缺陷,使得骨料与胶凝材料粘结不充分,针对混凝土的二、三轴强度,进行数值模拟分析,分析结果表明：由于缺陷的存在,不只是降低了材料的强度,同时也改变了分析试件的应力状态.当胶凝砂砾石材料施工方法不当时,骨料与胶凝材料粘结不充分现象是较难避免的,不容忽视;通过试件粘结质量对混凝土影响的分析,提供研究胶凝砂砾石材料筑坝问题的一种思路.     

碳纤维布与混凝土粘结耐久性能研究

完成了8个试件在不同的胶结剂、不同的环境情况下碳纤维布与混凝土的粘结性能试验,统计分析了冻融环境对碳纤维布与混凝土粘结质量的影响,描述了混凝土与碳纤维布剪切破坏的特点。     

FRP加固锈蚀钢筋混凝土梁的受弯性能分析(英文)

采用Ansys有限元软件对8根不同锈蚀率的FRP片材加固钢筋混凝土梁的受弯性能进行数值分析,研究纵筋锈蚀率对FRP加固梁的裂纹开展、破坏模式、承载能力以及延性和变形能力的影响.研究结果表明:低钢筋锈蚀率的梁发生受压区混凝土压碎破坏;中等锈蚀率的梁钢筋屈服后,钢筋与混凝土界面发生黏结滑移,最后FRP剥离破坏;高锈蚀率的梁钢筋没有达到屈服强度便发生黏结滑移,最后发生受压区混凝土压碎破坏.钢筋锈蚀越严重,FRP加固钢筋混凝土梁的承载力降低得越多.试件RCB-1(锈蚀率为0)的承载力为115 kN,而试件RCB-7(锈蚀率为20%)的承载力仅为42 kN.与FRP加固未锈蚀的钢筋混凝土梁相比,FRP加固锈蚀钢筋混凝土梁的变形能力较高.试件RCB-1和试件RCB-7的最大跨中挠度分别为20 mm和35 mm,而试件RCB-5(锈蚀率为10%)的最大跨中挠度达到了60 mm.     

钢筋混凝土销栓作用的疲劳承载性能试验研究（英文）

为研究钢筋销栓作用的疲劳承载性能,制作了9个钢筋混凝土试件分别进行静载试验和疲劳加载试验.试件共分为2组,首先通过6个试件的静载试验确定销栓作用的极限承载力,其钢筋直径分别为12,20和25 mm;然后通过3个试件的疲劳加载试验来研究疲劳荷载作用下销栓作用承载性能的衰减特征及疲劳破坏形态.试验结果表明,在疲劳加载的过程中,疲劳损伤的积累会降低销栓作用的承载能力.在正常使用状态下,即极限承载力的55%,随着疲劳循环次数的增加,销栓作用的破坏模式会发生转化.疲劳破坏形态表现为钢筋的瞬时断裂,其疲劳寿命由钢筋和混凝土的材料性能所决定.基于试验结果,可以将钢筋销栓作用的疲劳破坏过程分为2个阶段,分别为损伤积累阶段和瞬时断裂阶段.     

钢纤维与混凝土粘结强度试验方法研究

钢纤维与混凝土的界面粘结强度决定钢纤维的增强、增韧效应,本文首次探讨了钢纤维与混凝土基体的粘结强度试验方法,介绍了试验采用的试件形状、固定钢纤维位置的器具以及加载装置等,并且介绍了试件的制作过程、试验步骤以及确定粘结强度的方法。试验采用的试件形状、制作过程简单,加载装置加工简单,避免了制作特殊形状的试模和复杂的加载工具和夹具。试验简单易行,费用低。     

钢筋与混凝土粘结滑移本构关系研究现状

国内外学者一直致力于研究钢筋与混凝土的粘结滑移本构关系,试图得到比较一致的结论,但由于钢筋与混凝土间传力机理复杂、影响因素多,目前尚无可以通用的公式。文章就普通钢筋混凝土和锈蚀后的钢筋混凝土两种情况下的粘结滑移本构关系的研究现状进行了阐述。     

高强钢筋约束混凝土柱的抗震性能

以普通钢筋(400 MPa)和高强钢筋(1000 MPa)为约束箍筋,通过低周反复水平加载试验,对比分析了6组不同配筋率和间距的高强钢筋约束混凝土柱的轴压破坏形态和抗震性能.结果表明:普通钢筋约束混凝土试件的位移延性分别低于相同配筋率下的高强钢筋约束混凝土试件;无论是在相同配箍率还是在相同箍筋间距条件下,高强钢筋约束高...     

Cu-Zr基金属玻璃的形成能力及力学性能研究

用铜模吸注方法制备了不同直径的Cu47.5Zr47.5Nb5金属玻璃,并用X-Ray对制备的金属玻璃进行了结构测定,同时对金属玻璃进行了压缩实验及断口分析。实验结果表明,Cu-Zr基金属玻璃的形成能力受到Nb的加入和吸铸直径的影响:相对于直径为2mm的金属玻璃,直径为3mm及5mm的金属玻璃的塑性和压缩强度都有明显的降低,其综合性能明显下降,表明直径对合金性能的影响相当大。     

Rib height selection for roughness-enhanced tube

1 Introduction A well known method to increase heat transfer from a surface is to roughen the surface by use of regular geometric roughness elements, such as transversely-ridged tube, spirally-ridged tube or converging-diverging tube, etc., on the surface…     

Theoretical and experimental research on heat transfer performance of the semi-open heat pipe

This paper focuses on the heat transfer performance of semi-open heat pipe which is a new type of heat pipe. After analyzing its condensation heat transfer mechanisms theoretically, several semi-open heat pipes in different length ratios and upper hole diameters are studied experimentally and compared with the same dimensions closed heat pipes. Experimental results show that the heat transfer performance of semi-open heat pipe becomes better by increasing heat transfer rate. At the first transitional point, the heat transfer performance of semi-open heat pipe approaches the level of the closed heat pipe. It is suitable to choose upper small hole about 1 mm in diameter and length ratio larger than 0.6 for the semi-open heat pipe.     

Numerical investigation on wheel-turnout rail dynamic interaction excited by wheel diameter difference in high-speed railway

The wheel-rail relationship in turnout is more complicated than that in ordinary track. Profile wear and machining errors of the wheelset cause deviations of the rolling radius on different wheels. Therefore, wheelsets move to the direction of smaller diameter wheels in search of a new stable state and to change the condition before entering the turnout. The main aim of the present work is to examine the wheel-turnout rail dynamic interaction combined with the static contact behaviour. Calculations are performed on a high-speed vehicle CRH2 and the No. 12 turnout of the passenger dedicated line. The wheel-turnout contact geometric relationship and normal contact behaviour under wheel diameter difference are assessed by the trace principle and finite element method. A high-speed vehicle-turnout coupling dynamic model is established based on SIMPACK software to analyse the wheel-rail dynamic interaction, riding comfort, and wear. Both the wheel diameter amplitudes and distribution patterns are accounted for. The simulation shows that wheel diameter difference can greatly disturb the positions’ variation of wheel-rail contact points and affect the normal contact behaviour on switch rails by changing the load transition position. The effect of wheel diameter difference on wheel-turnout rail dynamic interaction can be divided into three according to its amplitude: when the wheel diameter difference is within 0–1.5 mm, the wheel flange comes into contact with the switch rail in advance, causing a rapidly increased lateral wheel-rail force; when it is within 1.5–2.5 mm, trains are subject to instability under equivalent in-phase wheel diameter difference; when it is larger than 2.5 mm, the continuous flange-switch rail contact helps strengthen the vehicle stability, but increases the wheel-rail wear. It is recommended to control the wheel diameter difference to within 2.5 mm but limit it to 2 mm if it is distributed in-phase.     

Vaginal introital diameter in the evaluation of sexual abuse

Physical objective markers to aid in the diagnosis of sexual abuse are few. We therefore studied 242 females, ages 1 through 12 years, to determine if the vaginal introital diameter is useful in evaluating a child for sexual abuse. The children were divided into three groups: Group I, history of sexual contact and/or Neisseria gonorrhoeae; Group II, no history of sexual contact but at risk; and Group III, nonabused. A vaginal introital transverse diameter of greater than 4 mm was more prevalent among children in Group I (94%) than in Group II, (5%); or in Group III (0%) (chi 2, p less than .001). Eighty-eight percent of children who complained of penile-vaginal penetration had a vaginal introital diameter greater than 4 mm as compared to 18% of children with no penetration (chi 2, p less than .001). Forty-six percent of children who complained of fondling with penetration had a vaginal introital diameter of greater than 4 mm as compared to 14% in those without a history of penetration (chi 2, p less than .008). Fifty-eight percent of children with more than one encounter had a vaginal introital diameter greater than 4 mm as compared to 29% in those with one encounter (chi 2, p less than .006). In a logarithmic regression analysis, the greatest proportion of children with a vaginal introital diameter greater than 4 mm was observed in the penile-vaginal contact group (chi 2, p less than .00003). The test is not very sensitive but highly specific. The sensitivity drops precipitously at greater than 5 mm without losing the specificity. A vaginal introital diameter of greater than 4 mm is highly associated with sexual contact in children less than 13 years of age.     

回热器流阻对脉管制冷机稳定特性的影响

基于流体网络理论,研究了通过改变回热器流阻对由双向进气阀诱发的直流流动进行抑制的可行性,计算结果表明,增加回热器流阻可以有效地抑制直流,进而有望提高脉管制冷机在高温区的稳定性能.在此基础上,采用不同的回热器填料布置方式,对脉管制冷机的稳定特性开展实验研究,通过采用直径0.25 mm的铅丸代替回热器冷端(0.3回热器长度)247目不锈钢丝网的方法,实现了制冷机在80 K温区长时间稳定工作.该研究为解决脉管制冷机存在的高温区性能不稳定提供了新的途径.     

纤维与沥青胶浆粘附性新型测试仪器的应用

为推广应用自制的新型沥青胶浆纤维拉拔试验机,使用其对沥青胶浆和玄武岩纤维之间的粘附性进行了研究,并采用最大粘结强度来表征二者的粘附性.采用两种不同产地的玄武岩纤维,在4种粉胶比(0.8、1.0、1.2、1.4)、3种纤维埋置长度(12、20、30 mm)下进行试验,并采用灰色关联分析等方法对试验数据进行了分析.结果 表...     

Performance of Catalytically Active Membrane Reactors with Different A/V Ratios

Although the performance of membrane reactors(MR) is highly affected by the ratio of membrane area-toreaction volume, there are few studies on this effect owing to the difficulties associated with reactor manufacture. In this study, an MR with high A/V ratio, a diameter of 35 m,and a height of 0.8 mm was fabricated. Separation performance of this MR was investigated in an n-butanol/water system. Esterification of acetic acid and n-butanol was used as the model reaction to investigate the performance of catalytically active membrane reactors(CAMR)with different A/V ratios. The reaction conversion was 38.59% in the CAMR with the high A/V ratio of 12,497/m,which was much higher than that in other CAMRs, for reaction time of 60 min and W/Vfratio of 0.093 g/mL.Excellent catalytic stability of the CAMR was confirmed by performing long-term stability experiments.     

边坡高扬程虹吸排水管流态特征研究

研究目的：从实验及理论角度闸述边坡高扬程虹吸排水容易断流造成虹吸中断的原凶,并提供解决方案,实观虹吸排水的长期有效。创新要点研究方法重要结论：利用物理模型实验,结合理论解析推导,得到了高扬程虹吸排水管顶部流态特抓及其与管径的关系,解决了高扬程虹吸排水容易断流造成虹吸中断问题,保证了虹吸排水技术住边坡治理工程中的长期有效性。通过物理模型试验,揭示虹吸水流经过管顶区段的兰利,流型特征（见图4）;利用热力学理论推导,得到了虹吸水流绛过管顶区段由贴壁流向弹状流转变的临界管住,址公式（23）。管中形成气液共吲移动的完整掸状流是灾脱虹吸排水长期稳定的关键,虹吸水流绛过管硕区段由贴壁流向弹状流转变时存扯临界管仵。保讹边坡工群中虹吸排水长期稳定的管径以3．6mm为宜。     

U形垂直埋管直接膨胀式地源热泵的性能分析

首先,对直接膨胀式地源热泵的性能进行了理论分析.与常规地源热泵相比,直接膨胀式地源热泵的地埋管换热器热阻更小,在制冷工况下具有更低的冷凝温度,在制热工况下具有更高的蒸发温度,因此它具有更高的性能系数.直接膨胀式地源热泵系统无需二次换热回路和循环水泵,因此具有更高的系统性能系数.然后,根据实测数据对直接膨胀式地源热泵实验系统的性能进行了分析.该实验系统建立在中国湘潭,其U形垂直地埋管换热器置于水井之中,地埋管换热器的长度为42m,外径为12.7mm.测试结果表明,在制热工况下此直接膨胀式地源热泵系统的性能系数最大值为5.95,平均值为4.72.