Applied Mechanics and Materials Vols. 578-579

Abstract: For the application into country point highway of Xiamen to Kunming, a series of the C40 concrete with fly ash and slag have been studied by rebound detection and compression strength, the detecting wave of rebound value and compression strength is set up by regression analysis of the testing data. It is shown from the example that the compression strength and rebound value have good relativity, this rebound detection method used in steel fiber concrete is simple and practical.

Abstract: Base on the structural modal parameters, the linear regression models of physical parameters are derived from the dynamic equations. The posterior joint Probability Density Function (PDF) of physical parameters is obtained by using Bayesian statistics theory. Then the Markov Chain Monte Carlo (MCMC) sample method is adopted to get the marginal PDF and optimal estimation of structural physical parameters. A numerical simulation of a 5-stroy structure under the excitation of white noise with different noise level is used to identify the physical parameters by the presented method. It is shown that the method can not only determine the optimal estimate but also get the probability distribution of the structural physical parameters from the known modal parameters of the primary modes. The method is with higher validity, robustness and efficiency, and can be applied to the structural health monitoring, damage evaluation, and so on.

Abstract: The wave speed of acoustic emission in the medium is uncertain, which is influenced by the source characteristics and the relative position between the acoustic emission source and the sensors. Due to this difference, the results of TDOA location method determination of wave speed in advance are very discrete. As to liner location ,the more farther the distance between two acoustic emission source sensor are, the more serious the discrete error are. Any of the two sensors, a location line can be obtained by setting the wave speed as a horizontal coordinate and the location as the vertical coordinate. The horizontal coordinate of location line of the different sensors is the real wave speed of acoustic emission events. This method has lower computational complexity, which can overcome the influence on acoustic emission location which wave speed setting error brings, having some practical value in Engineering.

Abstract: Based on mode shape, a new parameter was put forward—mode shape curvature ratio, for detecting structure damages. And it was also the input vector of the RBF neural network. Then through finite element analysis and calculating, the training and forecasting samples were got for the network. The trained neural network can identify the damage location and degree of the frame structure. It proved that this method is simple and valid.

Abstract: For the application into country point highway of Xiamen to Kunming, a series of the C40 concrete with fly ash and slag have been studied by ultrasonic detection 、rebound detection and compression strength, analyzed the influence of ultrasonic velocity 、rebound value and compression strength with steel fiber content, fly ash and slag, the ultrasonic strength detecting wave of ultrasonic velocity、rebound value and compression strength is set up by regression analysis of the experimental data. The results show that the compression strength 、ultrasonic velocity and rebound value have good relativity, this ultrasonic-rebound detection method used in steel fiber concrete is simple and practical.

Abstract: A method for monitoring the crack damage of concrete structure based on piezoceramics transducers was introduced in the paper. The PZT patches were packaged as smart aggregates which buried into concrete structures in pair. One is as actuator to transmit monitoring signals, and the other is as sensor to receive the monitoring signals. Sine sweep frequency wave was used as monitoring signal type, and its energy value was used as damage identification parameter. At last, a test was conducted to prove the effectiveness of monitoring method. The crack damage of a reinforced concrete beam under the load was monitored during the whole test process. The develop trend of damage identification parameter could reflect the develop trend of damage. The method proposed in the paper is feasible for crack damage monitoring of concrete structure.

Abstract: Researches on health monitoring technology of concrete structures by using piezoelectric smart aggregates have achieved a great development. However, the technique is not widely used so far in practical engineering.   Because when constructing large-scale structural health monitoring (SHM) system using wire-based sensors, it requires a lot of cables to form a monitoring network, resulting in huge cost of abundant material of wires and labor for wire placement, and the relatively heavy maintenance work in case of failure of the SHM system. A kind of wireless sensor network based on the protocol for Zigbee802.15.4 and the passive piezoelectric smart health monitoring technology is developed in the paper. Through internal load monitoring tests of a concrete bridge model under impact loading, the developed wireless smart aggregate (WSA) health monitoring system is experimentally validated. The finite element method (FEM) is used to simulate the process as the same as the bridge model test, and the numerical results are consistent with those of the experiment. The experimental results show that the developed wireless system is stable and reliable, and can be applied in concrete bridge structure health monitoring under impact loading.

Abstract: In dry-wet cycle chloride environment, the corrosion potential of the SFRC specimens is stable between-300mV to-400mV. And the common concrete specimens were about-500mV, adding steel fibers is higher corrosion potential and lower the corrosion possibility. Steel fiber has effective action on the controlling rebar corrosion and concrete crack. There were no cracks on all the surface of the SFRC specimens. Adding Steel fiber in concrete composed to be a corrosion cell as sacrificial anodes to protected steel rebar as cathode, in some degree to postpone rebar corrosion beginning time and increasing the structure services life.

Abstract: Concrete is a composite construction material frequently used in civil engineering. We know that concrete is as a man – when concrete is made it is as a baby, then it ages and its properties change in accordance to its baby life. That means it is better to monitor and change its properties when it is young as soon as possible. However, using the methods immediately after concrete birth (making the mixture) is difficult. Article describes monitoring concrete structure during the first 24 hours from their making. Acoustic Emission Method and the measurement temperature were used for monitoring both samples.

Abstract: In order to verify the feasibility and validity of frequency ratio as diagnostic parameter in structural damage detection proposed in the Musical Tone Law Method (MTLM), steel pipes and three-story steel frame structure model tests are carried out. According to the experiment results, it is clear that the diagnostic parameter is effective for symmetrical structure in structural damage detection, such as cable structure, framed structure, and so on. Model tests prove that the frequency ratio is effective in detecting the 3mm width crack damage of steel pipe. In the damage detection test of three-story steel frame structure, the parameter also successfully diagnosed the damage caused by bolts loosening at the node of model.