Applied Mechanics and Materials Vols. 351-352

Abstract: The space truss structure is difficult to avoid damage in service. There are so many nodes and bars in the structure that damage identification could not be achieved, if sensors are putted on all nodes to obtain response of the structure. Therefore, wavelet analysis method is proposed in the paper, which uses limited information of measuring points to measure acceleration response of the nodes. Damage of a bar will lead to the singularity of the acceleration high-frequency signals by wavelet transformation. According to singularity value, the range of influence of damaged structural bar is determined, then structural sub regions are divided and accelerators are distributed. The first step damage detection methods is identifying damaged bar occurrence region; the second step damage detection methods is locating damaged bar in the region using strain mode method. At last, taking the space truss structure as numerical example, it shows the method has the capability to detect the fracture damage of bars successfully.

Abstract: To confirm precision of acoustic emission source localization technique and validate rationality of acoustic emission parameters setting in concrete detection, defects location in pull-out specimens during bond failure were monitored by the method of 3D localization technique. In the monitoring,formation and propagation of cracks calculated by localization algorithm agrees with the real situation. AE parameters proposed in the paper help to identify source location with high accuracy.

Abstract: Based on a box girder bridge in an actual highway project, in-situ tests are carried out to understand the real stress state of vertical prestressed tendon. Researches of vertical prestressed losses during construction have been made in this paper. What is more, the regular pattern between the effective stress and time is proposed. Meanwhile, an efficient method which could control the prestressed losses is introduced. Eventually, it is aimed to conduct the construction of vertical prestressed tendons and improve the quality of tensioning. It also could provide a reference for design and quality control of vertical prestressed tendons in the similar type of bridges.

Abstract: In this paper, firstly, a new nonlinear Bingham hysteretic model is established by studying on the Test results of damping force characteristics of the magneto rheological fluid. The model not only can simulate the damping characteristics of the magneto rheological damper very well, but also can well describe the relationship between damping and velocity with the small velocity, and has fewer parameters by compared with other magneto rheological damper model. Secondly, based on nonlinear least square method, the parameters with different current are recognized and the relationship between the parameters and current is defined, then the mechanical model is theoretically verified. Furthermore, the mechanical model is simulated by ANSYS, the data obtained agree well with the calculated value.

Abstract: Lanzhou-Xinjiang passenger dedicated line is the first high speed railway on chinas northwestern Gobi where the temperature range is large and the wind is huge. Most road section of Lan-Xin passenger dedicated line is subgrade. This paper researches the ballastless track subgrade settlement observation scheme and assessment method on area where climatic conditions is harsh and geologic conditions is complex. The result shows that: the observation accuracy of subgrade settlement tests satisfies the requirement by using Layered settlement instrument, intelligent static force level and high-accuracy Hydraulic settlement instrument; Subgrade lies upon bedrock or Gobi soil with great bearing capacity in gale area, and distance between observation sections could be increased seemly. The space between observation sections generally should be less than 100m in areas where bedrock exposed, thick gravel soil distribute commonly; the distance between observation sections should be less than 50m in pre-mountain Alluvial-pluvial plain areas; hyperbolic method adapt the estimate of subgrade settlement on Gobi area, and the correlation coefficient is 0.97; Subgrade settlement deformation curve converges quickly and the settlement value after 40 days reaches 85% of ultimate settlement.

Abstract: In this paper, FBG temperature sensor and strain sensor have been used to monitor shrinkage and temperature of concrete retaining wall in construction site within its casting early age. As FBG senses both strain and temperature simultaneously, thermal shift of FBG strain senor is compensated by FBG temperature sensor. The test results indicate that this FBG monitoring system is feasible for monitoring concrete properties at its early age. The dual FBG monitoring technique applied in this research could be extended to monitor shrinkage and temperature for other concrete structures.

Abstract: Combined with a repaired project, an old twin decks bridge by simply supported the fabricated prestressed concrete hollow slabs with 16m span was detected in-site. The two decks were built separately in 1987 and 1997 because of economic reasons and demands of traffic flow. The aim of test was to decide whether the bridge can be further used or should be strengthened to meet the demands according to the current design code. Firstly, the damaged and corroded situations of whole bridge were investigated. Then the nondestructive testing methods were adopted to detect the concrete strength and carbonation depth of slabs and piers. The static loading test was conducted to make sure the service behaviors such as crack and mid-span deflection of the whole bridge. Finally, whole bridge was detected by dynamic loading test. The results show that the bridge has enough flexural stiffness to prevent larger deflection and most of slabs are in good service performance. But attacked by the environmental factor such as acid rain, CO₂ and winds erosion etc., part of slabs, all railings and sidewalk flats should be replaced. Based on service conditions, the suggestions are given to recover the strength and durability of the bridge. The conclusions would serve as a reference for similar engineering structures.

Abstract: In this paper, we propose a multi-sensor based incline measuring system. The systems include: g-sensor, e-compass sensor, and image-based incline measuring system install in a same structure, the solar cell system and wireless transmission system (zig-bee) also install in the same structure. The g-sensor and image-based incline measuring system use to measure the incline angle and the micro-vibration, and the e-compass sensor to measure the angle of rotation. The image-based incline measuring system include: a laser projector, a measuring board and a camera, and the system use the characteristic of laser, and the laser projector hanging on structure project a laser beam on the measuring board vertically. The camera captures an image to identify the coordinate of laser spot, and use the coordinate of laser spot to calculate the actual incline angle. The results of incline angle combine two different sensors to increase the accuracy of measurement result.

Abstract: During the period of tunnel excavation, shoring, forming and long-term operation, stress changes of tunnel surrounding rock are complex, the real-time monitoring of surrounding rock pressure is the key factor in ensuring long-term stability in tunnel. Fiber Bragg grating earth pressure sensors apply in surrounding rock pressure of tunnel which can change the pressure of the surrounding rock into fiber Bragg grating wavelength shift. According to the feature of pressure and temperature in Tian Xin Tunnel, 40 earth pressure sensors are embedded in 20 representative sections and one earth pressure sensor is embedded in each arch shoulder. In addition, one temperature compensation sensor is embedded in each arch crown. During the 235 monitoring days, the biggest daily change of surrounding rock pressure reaches 800 KPa. In 3 months of the sensor installation, the average monthly variation is within 50 KPa. The long-term measurement results indicate that the changes of surrounding rock pressure are different in different locations. When the surrounding rock is close to the excavated and blasted surface the surrounding rock pressure changes largely.

Abstract: Whether the leakage taking place is an important basis for the safety evaluation of the hydraulic tunnels that the concrete liner was pre-stressed with tendons. Based on the long-term monitoring data of piezometers in Xiao Langdi pre-stressed sediment tunnels over operation period, the influence factors on the monitoring data of piezometer and the development of measured water pressure were analyzed. The results show that the variation of water level in the tunnel has no impact on the monitoring data of piezometers when the sediment tunnels were in service state; The variation of piezometers monitoring data closely related to the seasonal variation,it increased in rainy season and returned to normal in the dry season. The main reason resulting in the increase of water pressure measured by piezometer is the arising of external water level in rainy season. No leakage phenomenon was observed in Xiao Langdi sediment tunnels over operation period. Based on the monitoring results a conclusion can be made that the design requirements of anti-cracking and anti-leakage were satisfied in Xiao Langdi sediment tunnels.