Papers by Author: Sheng Qiang

Abstract: The penetration cracks in sluice concrete structure have more disadvantage influence on the structure integrity. On the condition of earthquake, it may cause structure collapse. For a typical sluice structure found penetration crack in construction, the finite element model is created and the structure dynamic computation is applied with response spectrum method. The calculation results show if the reinforced steel bar cross the crack is not rusted and destroyed, the tension stress in the sluice and the general safety factor against sliding will meet the corresponding standard. As for the existing cracks, seepage prevention is suggested to avoid steel bar against rust.

Abstract: Concrete is a typical heterogeneous porous media material, but the influence of the heterogeneity of concrete on coupled temperature and moisture transfer is rarely involved in the present numerical methods. Thus, the research direction on the coupled temperature and moisture transfer with damage evolution of the heterogeneous material will be greatly helpful to understand the coupling mechanism. This paper firstly presented the purpose of the study on the coupled temperature and moisture transfer in concrete, and then offered a literature review of the development of this theory. To launch the elaboration of this topic, three relative important parts were presented separately in this paper. (1)The comprehensive theory of porous media heat and mass transfer. (2)The development of the coupled temperature and moisture transfer on mesoscopic scale. (3) The numerical simulation methods of the coupled temperature and moisture transfer. And then the influence of damage on the parameters of temperature field and humidity field was pointed out, which would be a valuable research field.

Abstract: In the summer of southern cities of China, the duration of high temperature becomes longer which requires stricter temperature control and crack prevention measures for mass concrete in construction. By using finite element method for unsteady temperature field and stress field a simulation is made for a pump station built in summer. The cement hydration velocity of this engineering is so high that makes the temperature control very difficulty. Through result analysis of different cases, some optimized measures which include surface preservation and water cooling are proposed. It has an important significance for concrete structure in the same area.

Abstract: Lining of water transportation channel needs high requirements of crack prevention. The tension stress which results from temperature and other factors during construction is an important reason that causes concrete cracks. Through the simulation of concrete lining during construction period with a section of the middle route of South-to-North Water Transfer Project, it is found that concrete pouring temperature, joint space, cutting joint time always make great contributions to lining crack. Based on calculation results some pertinence measures for temperature control and crack prevention are put forward. Engineering practice shows that effects of these measures are remarkable, which means these measures have significant reference to the concrete lining construction of the same type channels.

Abstract: The real thermal parameters always have inevitable influence on the simulation results of the structure thermal field and stress field in the construction of mass concrete. A new measuring and calculation method for concrete thermal conductivity was put forward. Eight or six sensor points measuring method and calculation formula are present, and the latter is the simplification of the former. Comparing the real thermal conductivity with the calculation result by the new method, it can be seen that the thermal conductivity can be obtained within about 6 day’s age at site and with the accurate degree of 98%. The new method will provide an efficient way for the concrete structure researcher and designer.

Abstract: Before and after pouring the concrete for a dam, how to predict and obtain the accurate temperature and stress of the various parts of the dam, is the key to prevent cracks in concrete. The stresses calculated from the parameters of the laboratory under the ideal conditions have obvious difference with the value calculated from site measured strain. As for such problem, based on the measured temperature and strain data of rolled compact concrete gravity dam engineering, the thermal and mechanics parameters of the concrete materials are inversed. The dam stress of construction period is simulated and analyzed separately based on the site parameters and lab parameters. The results show that although the stress development law from different ways is near, their values are different obviously because of three aspects. The site measured values should be more real. So it is necessary to inverse the thermal and mechanics parameters according to the site measured data.

Abstract: The water passageway structure of pumping station is both mass concrete structure and complicated structure. Cracks always appear in these areas during construction period. It will shorten the building life, and endanger the safety of pumping station. Three dimensional finite element method is adopted to simulate the temperature field and stress field of pump station in construction. The considering loads include gravity, temperature, autogenous volume deformation, and creep. The temperature and the first principle stress duration curves of easily cracking area are analyzed in different cases. After optimization of different temperature control measure, the tensile stress of different areas in early age or later age can be controlled lower than tension strength, and the cracking prevention safety factor can be raised. It is found that pipe cooling, surface insulation, pouring intermission, structure constrains can change the tensile stress obviously for pumping station. The influence of these factors is separately concluded.

Abstract: Cracking is a common phenomenon in long concrete structure. But for hydraulic structure it is not permitted because crack will cause heavily seepage and other disaster. Temperature control is an important way to prevent cracking. As for a long deck which has to be constructed in summer, temperature control and crack prevention is a hard work. With the aid of finite element method for temperature field and stress field simulation, research is carried out for a long deck of a pump station. Different measures, such as pipe cooling, surface preservation and pouring temperature control, are tried to control the temperature and stress. The simulation results of different measures composite schemes are analyzed. At last the optimized measures are proposed and its application at site shows it’s successful.

Abstract: Using low placement temperature and proper water pipe cooling water, the cracks are rarely appears in the interior of the dam, but the surface of the dam is prone to cracking. During the construction, the surface of the dam may be wet due to several factors such as creep, maintenance and so on, so the effect of the heat preservation is always been over-estimated. For those concrete blocks constructed in cold season, without proper heat preservation, the cracks are easy to appear soon after construction. For those concrete blocks constructed in hot period, under the influence of air temperature, the temperature of those concrete within about 5.0m of the dam surface are hard to control. So the key point to prevent the dam surface constructed in cold period is to take heat preservation measure suiting the on-the-spot situation. And for those dam blocks constructed in hot period, water cure on the surface of the dam can greatly reduce the risk of dam surface cracking.

Abstract: Pier concrete is vulnerable to cracking when using concrete rapid construction after long off period. In order to solve this problem, crack mechanism and effects of several temperature control measures of thin-walled structure concrete is analyzed. Through analyzing the temperature and stress time-space variation using 3D finite element method, it can be found that stress is more sensitive to controlling concrete placing temperature than other measures. It also shows that under the condition of taking other proper temperature control measures, low placing temperature can not be spared.