冲击回波法检测预应力束孔管道压浆质量

详细阐述了冲击回波检测方法的原理及其在土木工程中的应用,结合厦门市某大桥,采用冲击回波法对箱梁预应力束孔管道的压浆质量进行无损检测.首先在完全灌浆的预应力钢束管道位置和正常混凝土位置(即无波纹管位置)进行测试,获得混凝土内部压浆密实和无预应力管道时的两组冲击回波频谱图,作为与测点检测结果进行对比的基础,根据时频谱图的分析结果可以预测钢束管道内的压浆质量,判断孔道中是否有空隙存在.经检测与分析表明,冲击回波法是可行的,适用于预应力束孔管道的压浆质量检测.     

预应力管道压浆质量检测方法研究

详细阐述了电磁波法和冲击回波法的原理以及其在桥梁预应力管道压浆质量检测中的实际应运,结合实际桥梁,采用这两种方法的仪器对梁板预应力管道压浆质量进行检测。     

浅析桥梁预应力管道真空辅助压浆施工技术及应用

近年来,随着我国交通业的不断发展,各类路桥工程随之不断增多。施工技术是确保桥梁施工质量的关键环节,为此,在具体工程中必须选用最为合理、可行的施工技术。在预应力钢筋混凝土桥梁结构中,预应力束的耐久性主要取决于张拉后管道压浆的施工质量,正因如此,使得真空辅助压浆技术被广泛应用于桥梁预应力施工中。基于此点,本文就桥梁预应力管道真空辅助压浆施工技术的及应用进行研究。     

真空压浆法在预应力砼箱梁或T梁施工中的应用

为了保证预应力砼箱梁或T梁的钢绞线在张拉后处在一个良好的受力状态,应及时将预应力管道进行封闭,以防止预应力钢绞力暴露在空气中产生腐蚀。因此,管道压浆的作用就显得非同小可了,考虑到现行箱梁及T梁施工中普遍采用真空压浆,故此对真空压浆施工应注意的一些要求进行共同探讨。     

后张法预应力管道压浆技术探讨

后张法预应力技术在桥梁工程中是我国工程领域中已经相当成熟的旋工工艺,管道压浆技术是后张法预应力施工中关键的环节之一。本文简要探讨了管道压浆技术的基本施工工艺、施工质量控制及常见问题的防止。     

小议超声透射法对混凝土钻孔灌注桩完整眭检测

桥梁的桩基础在混凝土浇筑完成后,无法对其进行原位破坏性检测,因此既不破坏桩身,又能检测成桩质量的混凝土桩基完整性检测技术就显得尤为重要。本文根据笔者的工程经验,简要介绍了超声波透射法桩基检测技术。     

一发三收式桩基声波透射检测技术及数值模拟分析

桩基声测管倾斜会使得桩身混凝土超声波波速计算结果出现误差,影响桩身质量检测结果,为此提出一种一发三收式声波透射检测技术。该技术通过固定各声波接收换能器的间距,根据几何关系,使用检测得到的超声波声时和接收换能器的间距,即可计算得到桩身混凝土超声波波速,使其不再依赖于超声波发射端和接收端的间距,也不再需要拟合声测管管身曲线。通过有限元软件模拟接收换能器间距和声测管倾斜程度对检测结果精度的影响,结果表明该技术可以良好地适应超声波接收换能器间距和声测管倾斜斜率的变化,稳定保持较高的波速计算精度,解决声测管倾斜、偏位时造成的声速计算误差。     

跨孔超声波透射法在桥梁灌注桩检测中的应用

跨孔超声波透射法是无破损检测桩基完整性最行之有效的方法之一,它具有结果准确、测试成本较低,检测快捷等优点。本文主要介绍跨孔超声波透射法的原理、检测操作要领,并结合工程实际介绍检测评定的方法,最后对跨孔超声波透射法检测中存在的一些问题进行探讨。     

管道真空压浆技术在后张法预应力体系中的应用

本文从施工控制的角度出发,对后张法预应力砼工程中采用的管道真空压浆技术进行了详细描述,并指出应在具体施工中严格控制压浆工作的有关细节,以供业内同行日后在进行类似工程的施工控制时能相互借鉴学习。     

桥梁桩基超声波透射法应用探讨

跨孔超声波透射法是无破损检测桩基完整性最行之有效的方法之一,它具有结果准确、测试成本较低,检测快捷等优点。本文主要介绍跨孔超声波透射法的原理、检测操作要领,并结合工程实际介绍检测评定的方法,最后对跨孔超声波透射法检测中存在的一些问题进行探讨。     

冲击荷载作用下装配式钢筋混凝土梁力学性能研究

为了研究装配式钢筋混凝土梁（简称PC梁）的抗冲击力学性能,通过对5根PC梁和1根作为对比的现浇钢筋混凝土梁（简称RC梁）进行落锤冲击试验,研究了不同拼装位置和套筒灌浆料饱满度对PC梁的抗冲击性能影响。详细地分析了各个试件的破坏形态、冲击力、支座反力、跨中位移、整体变形耗能能力等性能。结果表明:1）冲击作用位置,拼装位置以及冲击荷载强度共同影响构件的破坏形态。随着冲击位置远离于构件拼装位置,PC梁破坏形态、接触刚度、整体抗冲击刚度等力学性能均接近于RC梁的力学性能,其抗冲击性能的设计可以参考RC梁进行设计;2）相同强度的冲击荷载作用下,预制试件拼装位置与冲击位置相同时,PC梁破坏形态表现为拼装处严重的局部破坏,刚度退化较大,整体变形耗能不如其他拼装位置的梁以及RC梁,考虑此工况的构件需采取合理的措施,提高其抗冲击能力;3）套筒灌浆饱满度对梁的抗冲击性能有影响较大,其决定PC梁的破坏形态以及刚度;4）拼装位置处交接面的边界条件是影响PC梁抗冲击性能数值分析是否准确的关键因素。     

预应力混凝土箱梁桥竖向预应力孔道对腹板截面

以两片安装竖向筋试验简支梁为基础,进行了预应力混凝土箱梁桥竖向预应力孔道对腹板截面削弱的研究,试验表明在不灌浆情况下梁开裂荷载提前,箍筋应力、混凝土表面主拉应增加明显,同时对试验梁进行了有限元分析,试验结果与有限元分析一致。研究表明加强竖向预应力灌浆质量的检测与管理对防止预应力混凝土箱梁桥的开裂有重要意义,同时为分析这类桥的开裂原因提供了理论与试验依据。     

Propagation of Bessel beams from a dielectric to a conducting medium

Recently, the use of Bessel beams in evaluating the possibility of using them for a new generation of ground penetrating radar systems has been considered. Therefore, an analysis of the propagation of Bessel beams in conducting media is worthwhile. We present here an analysis of this type. Specifically, for normal incidence we analyze the propagation of a Bessel beam coming from a perfect dielectric and impinging on a conducting medium, i.e., the propagation of a Bessel beam generated by refracted inhomogeneous waves. The remarkable and unexpected result is that the incident Bessel beam does not change its shape even when propagating in the conducting medium.     

整体结构中两跨钢梁火灾变形性能的试验研究

为研究整体结构中钢梁的抗火性能,利用自行研制的试验炉和相关测试装置,对三层三跨足尺钢框架楼中三层顶一两跨连续梁进行受火试验研究,试验中钢梁受火,钢柱和节点不受火。试验量测了炉体内烟气温度、钢梁和混凝土楼板四等分点处截面沿厚度不同点的温度场、位于炉体外钢梁接点温度、钢梁和楼板四等分点处的竖向变形。结果表明:未进行防火保护的钢梁温度与烟气温度基本一致;升温阶段混凝土板温度滞后于钢梁的温度,停止升温后钢梁温度迅速降低,混凝土板温度仍会升高直至两者温度趋于一致。在整个试验过程中,沿混凝土板截面高度存在较大温度梯度;整体结构中未进行防火保护的钢梁具有很好的变形性能,可以考虑减少防火保护;不同位置的构件由于受到相临构件的约束程度不同,在火灾中的变形性能不同,在抗火设计时应进行区别对待;钢柱虽不受火,在整个试验过程中产生轴向膨胀。     

A Methodology Based on Pulse-Velocity Measurements to Quantify the Chemical Degradation Levels in Thin Mortar Specimens

In this research, ultrasonic pulse echo measurements are used to quantify through thickness chemical degradation in thin mortar specimens. The degradation level is predicted using the time of travel of the acoustic wave through the thickness of the structure. The front and back wall interaction reflections are used to obtain additional information from very early stage degradation. The pulse-velocity of sound waves as a function of the thickness of the layers within the structure is described. With knowledge of the pulse-velocity in pristine and fully degraded conditions, it is possible to determine the complete range of degradation length over the layer thickness. The method is applicable for leaching of calcium and acidic attack. The acoustic measurements were verified with destructive testing. The correlation between the acoustic and non-acoustic experiments agree with the described pulse-velocity and degraded depth function. The method based on ultrasonic measurements can be implemented in other thin-layered structures.     

基于多尺度排列熵的波纹管压浆超声检测

将多尺度排列熵引入波纹管压浆质量检测中,对不同注浆密实程度的波纹管进行超声检测,对回波信号进行分析。为了检测信号在不同尺度下的动力学特征,提出了一种基于多尺度排列熵偏均值的波纹管压浆质量检测方法,利用有限元进行仿真,仿真结果表明,波纹管压浆质量越差,回波信号对应的排列熵偏均值越小。实际模型的处理结果表明该指标能够有效地判断波纹管压浆质量。     

多排预应力波形钢腹板组合挑梁承载能力试验研究

波形钢板由于其独特的力学性能,在组合结构中得到广泛的应用。该文对脊骨梁中多排波形腹板钢挑梁支撑的预应力混凝土板的这种新型组合挑梁进行了承载力的对比试验研究,根据波形钢腹板特性及组合梁的基本理论,推导了其极限承载力的计算公式,并与试验结果对比,验证了理论公式的正确性。采用有限元方法进行了几何参数分析,总结出该结构的优化设计参数,以供工程实际参考。     

Experimental and analytical study on grouted duct connections in precast concrete construction

Owing to its forgiving tolerances and eliminating the need for welding, grouted dowel in-conduit connections are widely used for connecting various precast concrete elements, for instance in precast wall construction and bridge bent cap systems. Current design recommendations for such a connection treat it similar to a conventional reinforcing bar-in-concrete and do not account for the restraining effect of the duct. In the present study, a series of experimental and analytical approaches have been adopted to explore the disparity between grouted dowel connections and bar-in-concrete. The experimental program consisted of testing twenty-four pull-out specimens under monotonic loads. The main parameters investigated included the embedment length, concrete compressive strength and corrugated duct. Results from the experimental and analytical procedures showed that grouted dowel in-conduit connections behave markedly different from bars in concrete. Different failure mechanisms occurred in the grouted connections due to the confinement effect of the duct. Moreover, an increase in load carrying capacity and ductility of the connections was observed at all embedment lengths, regardless of the concrete compressive strength. Based on the experimental findings, an analytical model for predicting the embedment length of the connection was derived, calibrated and proven to be more accurate than state-of-the-art design procedures.     

Ultrasonic Imaging Methods for Investigation of Post-tensioned Concrete Structures: A Study of Interfaces at Artificial Grouting Faults and Its Verification

This paper presents the progress of successful location of grouting faults in tendon ducts with ultrasonic imaging. The examples were obtained in the research group FOR 384 funded by DFG (German Research Foundation). The co-operation of experimental research and modeling allowed imaging and identification of grouted and ungrouted areas of tendon ducts (including strands) in a large test specimen (40 m²). In addition to the criteria for indicating grouting faults in post-tensioned ducts known until now the phase evaluation of reflected ultrasonic pulses is described. Experiments and modeling of wave propagation are presented for reflections at metal plates in concrete (thickness range 0.5 mm to 40 mm) and for tendon ducts including strands. The main part of the progress was achieved by automated measurements using dry contact transducers, 3D-SAFT reconstruction including phase evaluation and modeling considering wave propagation for typical elastic parameters and exact experimental site conditions. The results for shear waves as well as for pressure waves are compared in the frequency range from 50 kHz to 120 kHz.     

ANN Model to Predict Fracture Characteristics of High Strength and Ultra High Strength Concrete Beams

This paper presents fracture mechanics based Artificial Neural Network (ANN) model to predict the fracture characteristics of high strength and ultra high strength concrete beams. Fracture characteristics include fracture energy (Gf), critical stress intensity factor (KIC) and critical crack tip opening displacement (CTODc). Failure load of the beam (Pmax) is also predicated by using ANN model. Characterization of mix and testing of beams of high strength and ultra strength concrete have been described. Methodologies for evaluation of fracture energy, critical stress intensity factor and critical crack tip opening displacement have been outlined. Back-propagation training technique has been employed for updating the weights of each layer based on the error in the network output. Levenberg- Marquardt algorithm has been used for feed-forward back-propagation. Four ANN models have been developed by using MATLAB software for training and prediction of fracture parameters and failure load. ANN has been trained with about 70% of the total 87 data sets and tested with about 30% of the total data sets. It is observed from the studies that the predicted values of Pmax, Gf, failure load, KIc and CTODc are in good agreement with those of the experimental values.