Applied Mechanics and Materials Vols. 212-213

Abstract: A three-phase mesomechanics model was established to simulate the aggregate, cement mortar and the interface between them. In order to reflect the meso characters and heterogeneity of concrete, the parameters were randomly valued on the Weibull distribution. Then, by using this model the complete process of concrete crack propagation was analyzed based on the elastic brittle damage theory. This method was verified by simulation of uniaxial tension and three-point bend beam test. Finally, concrete structure cracking at early age during a cold snap was simulated under different surface insulation conditions. The results show that this method can simulate the crack initiation and propagation effectively and reflect the whole process of concrete crack under temperature load.

Abstract: Taking the properties of aqueduct in the middle line of the South-North Water Diversion Project, such as high flow, long span, large load and cross section and so on, two schemes about layout of prestressed steel strands are put forward. In order to guarantee safety of the project and structural optimization, 3-D FEM is adopted to study the regularity of distribution of stress and strain on control section under each condition of the two schemes. The results show that the design of steel strands in the first scheme (wavy steel strands) is much more reasonable and meets the requirements for anti-crack and deflection of the aqueduct body.

Abstract: In practical projects, GFRP anchor bolts are in complex geological conditions with corrosive factors such as acid, alkalis, salt and freeze-thaw circle. In corrosive conditions, the bonding strength of GFRP anchor bolts are in direct relation to safety of anchoring works. Based on comparative tests on bonding strength between GFRP anchor bolt and concrete, failure modes in pull-out tests of GFRP anchor bolt and concrete are mainly pull-out failure and splitting failure. Pull-out failure is a chemical and mechanical interlocking failure between GFRP anchor bolts and concrete cubes, which can actually reflect the bonding status of bolts and concrete cubes. Splitting failure is a failure that the radial expansion force caused when the GFRP anchor bolt are bearing forces damages the concrete if it is of low strength or insufficient in thickness of protection layer and thus leads to boding failure. From the analysis on test results of bond-slip performance, the bonding strength decline the most in alkalis conditions: the bonding strength decreases by 23% after 1500 hours of corrosion and the slip displacement increases by 2.4mm; in acid and salt conditions, after 1500 hours of corrosion the bonding strength decreases by 19% and 17% and slip displacement increase by 1.6mm and 1.8mm, respectively. Based on analysis of nonlinear curve fitting on test data of bonding strength in three corrosive conditions, three empirical equations of degradation of bonding strength are fitted for GFRP anchor bolts in three corrosive conditions. Compared with data from reference [13], the bonding strength of GFRP anchor bolts working in acid, alkalis and salt geological conditions for 50 years decrease by 19.5%, 25% and 19.2%, respectively. These research results supply a test basis for GFRP anchor bolts used in complex geological conditions.

Abstract: In order to guide temperature control design and construction and to guarantee the construction quality of roller compacted concrete (RCC) gravity dams in severe cold area, it is of great significance to carry out the simulation analysis of temperature and stress. The whole progress of construction and operation of Longlin RCC gravity dam in harsh climate region were simulated by using the heat of hydration analysis control function, construction stag analysis control function and the time-dependent material link of MIDAS.civil.2006. According to the construction process, the curves of temperature and the curves of stress were obtained. The locations where the crack ratio may exceed 20 were also obtained and the correct temperature control measures and the rational construction progress control system were pointed out.

Abstract: The spiral case with combinatorial embedding manner is a novel design and inherits the advantage of the general types of embedding manners of embedded with cushion layers and embedded directly, which is progressively used in hydro projects. In the present paper, the mechanical behavior of a larger spiral case with combinatorial embedding manner is analyzed by using 3-D non-linear finite element method. The deformation of the spiral case structure and crack analysis of outer reinforced concrete structure are carried out. The strengthening measures under the engineering control criterion are also discussed. The results show that the penetrating crack will appear in the concrete and the relative rising displacement of generator pedestal structure is out of the control criterion if no strengthening measures implemented. Increasing the quantity of reinforcement only is not able to hold back the penetrating cracks. The enhancement of the tensile strength of concrete is an effective way to decrease the range of crack propagation, resist the penetrating and decrease the rising displacement of generator pedestal structure. It also indicated that extending the laying length of cushion is another effective way to decrease the rising displacement of generator pedestal structure

Abstract: Slope stability of high rockfill cofferdam is related not only to the structure and shape, material characterization, working characteristics of the cofferdam body, but also to the construction process. The influences of rock mechanics parameters are analyzed, which caused by the changes of structural stress state and transfusion equivalent stress in cofferdam construction process. Based on the slope stability strength reduction method, the slope stability analysis model of high rockfill cofferdam mirroring the construction process is established. At the same time, the parameter calculation methods are submitted and the correctness is proved. By the slope stability analysis of construction-running process, the results show that the most dangerous condition of cofferdam slope appears in the period of water level falling after pit excavation finished. With the increase of level falling speed, the position of the cofferdam dangerous sliding surface shifted from downstream slope to upstream slope. When the front weir level falling speed is determinate, the slope safety factor is appearing downward trend firstly and then upward trend, the minimum slope safety factor and the critical time is related with the level felling speed.

Abstract: Some high CFRDs had the problems of face slab crack and large leakage. And it was found out after deep analysis that the basic reason was the big inhomogeneous deformation in the rock-fill zone, mainly the vertical displacement. So it was of great significance to master their deformation behaviors so as not only to monitor the dam safety but also to supply the suggestions to repair the defect and reinforce the dam. The special features of dam displacement in the initial impounding period should be considered in the quantitative analysis of dam displacement study. Taking a certain dam as an example, some displacement models with impoundment factors were adopted to study the deformation features of high CFRD in this paper. After comparing and testing, the models were verified and could be used to monitor and forecast the deformation of the certain dam.

Abstract: Based on the theories of Fuzzy Math and Analytic Hierarchy Process(AHP), combining the natural, social and economic characteristics of earthfill dam and adequately considering different factors or indexes imposed on the safe operation of earthfill dam, the comprehensive safety assessment of earthfill dam through using multi-stratum fuzzy evaluation has been established. Furthermore, the safety assessment indexes, the theory of assessment, comprehensive weighting coefficient matrix and resolution methods are also established. From the practical measurement of Xixia reservoir earthfill dam, multi-stratum fuzzy evaluation method which is used to assess the comprehensive safety is reasonable and practical.

Abstract: Prototype observation of the concrete dam is an important and effective measure to master the operating condition of dams. Analysis of changes of concrete temperature for dams is the basis of studying the safety of dam operation. By analyzing the raw monitoring data of temperature of a RCC dam, this paper researches the changing process of concrete temperature and internal concrete partitions temperature variation of dams. It also draws the temperature field of the dam concrete. The results show that the isothermals of downstream side parallel with the surface of the downstream dam, and the isothermals of upstream side intersect with the dam. Isothermals which are near to the dam’s surface are close. This suggests that temperature gradient there is large. There is a high temperature nucleus and two low temperature nucleuses in the temperature field of the dam in summer, while in winter there is only one high temperature nucleus. So it suggests that the temperature field in summer is more complex.

Abstract: The weight loss measurements and potentiodynamic polarization techniques are used to assess the inhibitive and adsorption behaviour of 2-Benzothiazolethiol (BTT) for Q235 steel in hydrochloric acid solution. The inhibition efficiency is found to increase with increase in BTT concentration but decrease with rise in temperature and hydrochloric acid concentration. The results show that BTT acts as a good corrosion inhibitor in hydrochloric acid solution. Adsorption of BTT is found to obey Langmuir isotherm. Polarization curves indicate BTT is a mixed-type inhibitor.