混凝土爆炸损伤的超声波速分析

在高强度混凝土爆炸前后,利用超声波检测技术,进行声波测试并重构波速分布,可得出混凝土损伤变化规律.试验结果表明,超声波速变化能有效的表征混凝土损伤,且波速降低率越大表示试件损伤度越高;混凝土试件经爆炸载荷作用下发生损伤,损伤区域主要集中在炮孔周围、下方及试件底部,其中炮孔下方损伤度最大.     

岩石损伤特性与强度的超声波速研究

借助于损伤力学的观点 ,用岩石在未受荷载条件下的超声波速定义岩石的初始损伤变量 ;然后基于岩石在受荷载条件下的声学特性模型 ,建立岩石的损伤演化方程 ,从而给出运用岩石超声波速估计岩石强度的方法     

Concrete compressive strength prediction using ultrasonic pulse velocity through artificial neural networks

Numerous attempts to use ultrasonic pulse velocity (UPV) as a measure of compressive strength of concrete has been made due to obvious advantages of non-destructive testing methods. The present study is conducted for prediction of compressive strength of concrete based on weight and UPV for two different concrete mixtures (namely M20 and M30) involving specimens of two different sizes and shapes as a result of need for rapid test method for predicting long-term compressive strength of concrete. The prediction is done using multiple regression analysis and artificial neural networks. A comparison between two methods depicts that artificial neural networks can be used to predict the compressive strength of concrete effectively. The results are plotted as experimentally evaluated compressive strength versus predicted strength through both methods of analysis.     

Evaluating residual compressive strength of concrete at elevated temperatures using ultrasonic pulse velocity

In this paper, the ultrasonic pulse velocity (UPV) is used to quantitatively evaluate the residual compressive strength of concrete subjected to elevated temperatures. A series of tests were performed to examine the relationship between the residual UPV and strength of concrete with different mixture proportions at elevated temperatures. Cylindrical specimens were made of concrete with water–cement ratios of 0.58 and 0.68, and heated in an electric furnace at temperatures ranging from 400 to 600 °C. After exposing to the elevated temperature, the concrete specimens were cooled down in the ambient air and tested on different days. For each test, the pulse velocity and compressive strength were measured. Experimental results show that change in mixture proportion of concrete does not have a significant effect on the residual strength and UPV ratios of concrete subjected to elevated temperatures. This important finding considerably enhances the feasibility of using UPV for quantitative evaluation of the residual strength of fire-damaged concrete structures. The relationship between the residual strength ratio and the residual UPV ratio was developed and a general equation was proposed for residual strength prediction. Finally, this paper verifies the suitability of the proposed equation for predicting the residual strength ratios of different concrete specimens with the measured residual UPV ratios.     

岩溶区利用地震速度成像研究地下地质结构及特征

在场地狭窄,电性干扰严重的浅覆盖岩溶区,不利于电探方法来探查地下地层的岩溶发育特征。推荐采用地震纵波速度成像、横波速度剖面来综合探查地下的基岩起伏、地质结构和岩溶发育特征。在野外采用同一个排列保持道距不变的情况下,很容易获得这两种方法的地震记录。两种方法研究结果表明,多道噪音记录的折射微动面波法在探测基岩起伏方面具有较高的分辨率但探测深度浅;多炮点纵波速度成像对基岩面有平滑作用但探测深度较深。钻探资料证实,纵波速度成像中的相对低速区反映基岩内岩溶裂隙发育,是寻找地下水的有利靶区。多道记录,炮点—检波点射线高密度覆盖,可保证获得可靠的速度资料。两种方法联合探测地下岩溶特征具有一定的优势。     

Experimental and numerical study on microcrack detection using contact nonlinear acoustics

This paper introduces a non-classical nonlinear acoustic theory for microcrack detection in materials, comparing contact nonlinearity with material nonlinearity. The paper’s main work concentrates on the experimental and numerical verification of the effectivity of contact nonlinear acoustic detection by using the contact nonlinear parameter β′, which can be represented by the ratio of the second-harmonic amplitude to the square of the first-harmonic amplitude. Both experiments and numerical tests are performed. The results show that β′ is sensitive to the initiation of microcracks and varies with the development of the microcracks. The numerical test illustrates the decline of β′ when microcracks penetrate each other. __________ Translated from Engineering Journal of Wuhan University, 2007, 40(6): 61–65 [译自: 武汉大学学报 (工学版)]     

In situ continuously monitoring the early age microstructure evolution of cementitious materials using ultrasonic measurement

The early age microstructure evolution was continuously monitored by using a specially improved ultrasonic monitoring apparatus. The influence of water-to-binder ratios, mineral admixtures, aggregates and temperature were systematically investigated. The experimental results show that concrete can be clearly classified into four stages, while only the three stages can be observed without coarse aggregates. In addition, pre-percolation threshold, percolation threshold and full connectivity of the solid phase were identified. The microstructure formation is promoted with the reduced water-to-binder ratios, increased temperature, silica fume and aggregates addition, while the reverse phenomenon is observed when fly ash and slag are incorporated.     

Three-dimensional time-lapse velocity tomography of an underground longwall panel

Three-dimensional velocity tomograms were generated to image the stress redistribution around an underground coal longwall panel to produce a better understanding of the mechanisms that lead to ground failure, especially rockbursts. Mining-induced microseismic events provided passive sources for the three-dimensional velocity tomography. Surface-mounted geophones monitored microseismic activity for 18 days. Eighteen tomograms were generated and high-velocity regions correlated with high abutment stresses predicted by numerical modeling. Additionally, the high-velocity regions were observed to redistribute as the longwall face retreated, indicating that velocity tomography may be an appropriate technology for monitoring stress redistribution in underground mines.     

基于声波技术混凝土梁损伤特性的试验研究

利用超声波技术对不同水灰比的混凝土立方体试块和棱柱体试块的损伤特性进行了试验研究,讨论了加载过程中声学参数变化与混凝土损伤演化规律之间的关系.试验研究表明,超声法能够比较全面反映混凝土内部裂缝的扩展规律,有利于进一步研究混凝土的损伤力学机理.     

Assessing fire damage to r.c. elements

An original method is illustrated for assessing the fire damage to reinforced-concrete buildings. The basic idea underlying the method is to reconstruct the thermal history and the evolution of stress fields in the building during the fire by utilising the irreversible thermo-chemical reactions of the concrete aggregates as temperature indicators. By way of example, the method is applied to real cases to demonstrate its validity and effectiveness.     

混凝土损伤的超声波检测技术实验研究

采用超声波检测仪对SHPB杆累积冲击下的混凝土进行损伤检测,将定义出的损伤值D与混凝土宏观状态对比,从而客观地反映出在动态冲击下的混凝土损伤演化规律,以推广超声波检测方法。     

骨料级配对透水性混凝土强度及超声波速度的影响

透水性混凝土与普通混凝土不同,由于含有大量的连通孔隙使强度变得很低.所以,如何提高强度是透水性混凝土的关键技术之一.本文用改变骨料级配的方法研究了透水性混凝土的强度、超声波速度与孔隙率之间的关系.     

Evaluation of rubbercrete based on ultrasonic pulse velocity and rebound hammer tests

Several research works have been carried out to study the fresh and hardened properties of concrete containing crumb rubber (rubbercrete) as a replacement of fine aggregate. The outcomes of these studies have highlighted the advantages and disadvantages of rubbercrete compared with conventional concrete mixtures. In view of the fact that rubbercrete is being used in the construction industry for a variety of purposes, evaluations of the rubbercrete mixtures using non-destructive tests such as rebound hammer (RH) and ultrasonic pulse velocity (UPV) to establish valid relationships is worthwhile. Fifteen mixtures with different w/c ratios (ratios of weight of water to weight of cement) and crumb rubber content percentages were prepared, cast and tested using RH and UPV at different curing ages. Models were proposed and statistically validated to predict the relationship between compressive strength with UPV and rebound number (RN) for rubbercrete mixtures at 3, 7 and 28 days.     

冻结哈尔滨粉质黏土超声波速测定试验研究

采用超声波技术测定冻土动弹性力学指标正是目前冻土学术界及工程领域致力研究的一个热点。本文将基于日产UVM -2型声速仪对冻结哈尔滨粉质黏土超声波速测定结果 ,主要考察负温和含水率对超声波在冻土中传播速度及冻土动弹性力学指标的影响     

A data analysis method for detecting wall thermal resistance considering wind velocity in situ

To improve the accuracy of data analysis methods for the field measurement of wall thermal resistance, a method considering wind velocity is presented through an analysis of both surface heat flux and temperature samples. This analysis method takes the wall heat transfer of linear system into account, simplifying the first order differential equation of wall transient response based on the nodes of the interior and exterior wall surfaces. An approximate solution has been proposed in the form of time domain interpolation. By applying the weighted residual method for the approximate solution, the data analysis method about temperature, heat flux, and wind velocity can be achieved.A transient heat transfer model of a wall was established applying the infinite difference method, by which the proposed analysis method was validated in this paper. Additionally, the heat flow meter experiment platform considering wind velocity was built, on which the proposed method, the mean method and the dynamic analysis method suggested by the international standard ISO 9869 were applied to the test wall under different wind velocities. The wall thermal resistance value obtained in our proposed method has proven to be in better agreement with that obtained for a steady state.     

Evaluation of concrete made with crushed limestone aggregate based on ultrasonic pulse velocity

Ultrasonic pulse velocity is one of the non-destructive tests to assess construction materials that have more advantages. It has been used to determine concrete quality by using regression analysis models between compressive strength and ultrasonic pulse velocity values. However, it is not reliable without a calibration curve. For this study, 100 concrete mixtures were prepared with crushed limestone aggregate obtained in the Yucatan Peninsula. The results from the compressive strength and the ultrasonic pulse velocity tests allowed the proposal of a criterion to qualify the concrete quality, without the use of calibration curves, based on the quality of the aggregate employed.     

Empirical estimation of shear wave velocity from in situ tests on soil formations in Greece

Shear wave velocity is an important input parameter for dynamic ground analysis. Standard penetration test blow counts, static cone penetration tip resistance and shear wave velocity (V_S) obtained by the cross-hole technique have been collected from a large number of projects in Greece over the last 10 years and regression analysis used to develop empirical relationships. The paper discusses the factors which influence the derived equations, in particular the relevance of the soil type.     

Identification and correction of water velocity measurement errors associated with ultrasonic Doppler flow monitoring

Ultrasonic Doppler flow monitoring (UDFM) is used to measure water flow in pipes and channels. However, a lack of scattering particles and signal noise can cause velocity errors, particularly for smaller discharges and surface water ('clean') flows. A postprocessing methodology is presented that identifies and corrects these errors, maximising the value of existing data. Test criteria are used to identify errors. The error correction procedure defines depth–velocity relationships from cleaned 'training data' representing the range of flow conditions (including backed up) and uses these relationships to replace erroneous velocities automatically. UDFM velocity errors have been successfully identified and corrected in example applications. Routine use allows early identification of changes in instrument or site behaviour. The methodology is practical, consistent and updateable. This is a significant advancement over previous methods for correcting velocity errors, improving the applicability of UDFM.