Advanced Materials Research Vols. 1049-1050

Abstract: In order to research into the dynamic response of a steel box-girder continuous beam footbridge excited by a synchronised human stance excitation, a in-situ test and a code comparison were conducted. Sixteen model 891-B accelerometers of vertical, horizontal and lateral directions were instrumented on the bridge and the vibration signals were aqcuired at a sampling frequency of 512 Hz. The acceleration data were transformed into frequency domain to find out the fundamental frequency of the bridge, and the frequency weighted root-mean-square acceleration data were analysed to evaluate the bridge’s vibration serviceability under synchronised human excitation. Further more, the international standard of BSI5400, Bro2004, EN1990, and ISO10137 were applied to the aquired acceleration data to compare their applicability. The results indicate that the dynamic response of the footbridge will not invite uncomfortableness of the pedestrians.

Abstract: Making field test and finite element simulation on East Third Ring Road Xiaobawang footbridge in Beijing, considering the effect of the deck loads of the bridge on the model calculation results, we can find the effect of the secondary dead load on vibration characteristics of the footbridge model. Comparison of the frequencies of model before and after applying the secondary dead load make us know that applying dead load will lead to the lower frequency of bridge. In the process of the bridge finite element analysis, factors to consider should be more comprehensive and the way to simulation should be more realistic so that the results of finite element simulation can be closer to the actual.

Abstract: The measurement and finite element simulation was used to research the effect of bearing on vibration frequency of bridge. Sixteen models accelerometer was instrumented on the bridge and the vibration signals were acquired at a sampling frequency of 512 Hz. The finite element software is adopted to establish the model of the bridge. In this paper, beam element simulation and elastic connection simulation are two ways to calculate the vibrational frequencies. Through comparison, the characteristics of the two simulation methods can be known. By this study, the bridge bearing simulation model of the bridge has an obvious impact on the frequency of bridge model. At the same time, the simulation of bridge should be as close to the reality as possible to obtain more accurate data.

Abstract: Because of the inherent conflict between visual area and resolution in rock microscope structure, during the study of the RCTS (Rock Core Thin Section) microstructure, we cannot focus on the multi-scale structure characteristics of the particles, pores and throats, and it is fail to satisfy the demands of a more comprehensive study. In order to solve this problem, a microscopic image stitching method in RCTS is proposed by applying SIFT (Scale Invariant Feature Transform) detection algorithm. This method can successfully solve the conflict between the visual area and resolution, overcoming the problem of inclining and deformation in images acquisition under the microscope and finally, achieving the seamless stitching of RCTS microscopic image for big visual area. The experimental results show that this method can improve the accuracy of rock analysis in microstructure and has important practical and theoretical significance for the development of tight sandstone reservoir.

Abstract: Advantages, disadvantages, and drilling adaptability of several rigs earlier used in domestic coal mine are analyzed. CMS1-800/30 crawler jumbo is reconstructed from standing pillar rig according to specific condition of long bedding borehole at coal face which possesses rockburst trend. Wide blade spiral drill pipe and Φ65mm diamond compact bit are used to drill long bedding borehole at headentry and tailentry. Drilling efficiency of long bedding borehole is greatly improved, and effect of relieving stress is very good. Safe and quick mining is ensured, and economic benefit is remarkable.

Abstract: Negative Poisson's ratio honeycomb structure has unique mechanical properties. It has very good prospects for development. A mechanical model of star-shaped honeycomb structure is proposed and the mechanical properties of the model are derived. It can provide theoretical reference for engineering design of this kind of new structure.

Abstract: By introducing the basic theory of finite element method and commercial software ANSYS, the coupling field modeling theory, according to the structure of three point bending test to establish the finite element model for the electric and mechanical coupling field simulation test structure. At the same time, with the change of load structure deformation, due to smart layer piezoresistive effect, its potential changes, which can be implemented using intelligent layer resistivity changes of structural damage detection and monitoring.

Abstract: The orthogonal experiment method is utilized in this paper to get a comprehensive analysis of the compressive strength of magnesium phosphate cement (MPC) to prepare the cement with the best performance. What’s more, a further study is conducted on the compressive strength of paste and the compressive strength and the flexural strength of mortar, and the last is the adhesive properties. The results showed that the optimal ratio was obtained; the setting time of the optimum mix ratio of cement is 13min, which meets the requirements of rapid repair; the development of the strength of the paste and mortar all have the characteristics of early strength and fast hardening. Generally, the strength at 7d can reach the 90% of the strength at 28d, and the compressive strength of the paste at 28d can reach to 79.8MPa. The compressive strength and flexural strength of mortar at 28d are 53.2MPa and 11.3MPa, respectively.

Abstract: Effect of a chloride deicing additive (Cl^-DIA) on the performance of asphalt mixture was investigated by evaluating the moisture, cracking and rutting resistance. Freeze-thaw splitting test result showed that asphalt mixture containing Cl^-DIA weakened moisture resistance to some extent but it was still applicable for asphalt pavement. Wheel-tracking test indicated that Cl^-DIA evidently improved the rutting resistance of the asphalt mixture and the weight concentration of Cl^-DIA in asphalt mixture had to exceed 3%. Beam bending test implied that Cl^-DIA did not help for the cracking of the asphalt mixture.

Abstract: Freeze-thaw action in fractured rock mass is discussed. Moist rock exposed to subfreezing temperature would suffer from freeze-thaw deterioration, which would pose serious threat to the stability of geotechnical engineering. Some key factors influencing freeze-thaw action in rock mass is analyzed, such as temperature, freezing rate, freeze-thaw cycles and porosity of the rock. Further more, using the theory of physical chemistry, the freezing point and frozen ratio were derived. Finally, the model of frost crack was built by ANSYS and then imported into FLAC3D by converting procedure. The stress field, temperature filed as well as the normal and shear stress on surface of the cracks were demonstrated. The effect of freezing pressure is reflected in the results.