Advanced Materials Research Vols. 250-253

Abstract: Urbanization can not be avoided in the phase of human civilization. Urbanization in developed countries such us Europe, America has experienced the course of agricultural revolution, industrial revolution and the commercial revolution, and from this we can learn a lot. Through this article, we can analyze the development history of urbanization in developed countries, learn from their good experiences, and summarize the problems and disadvantages brought in the process of urbanization. According to the urbanization development in western Hubei, urbanization in mountainous area should be on the way of ecological development and it can be done by focusing on the cultivation character, making full use of the natural resources so that we can promote urbanization in a healthy, scientific and sustainable fashion.

Abstract: A finite element analysis (FEA) model was proposed to predict the behavior of concrete-filled steel tubular (CFST) columns at overall stage of fire combined load based on ABAQUS. The whole stage includes initial loading, heating, cooling and post-fire phases. Accurate thermal and material model, element type, and solution method were chosen reasonably in the model considering the temperature and combined load. Due to lacking of test data about multi-phase of fires, the FEA model was verified with tests at different stages respectively. Some experimental specimens under different thermal and mechanical conditions were modeled using the FEA model, and the results obtained have good agreement with the experimental results. The mechanism of the CFST columns after exposure to overall stage of fire was also investigated based on the model.

Abstract: Urbanization is a necessary phase of development of human being's civilization,which is a combination of social, economic, science, resources and technology.Therefore, the healthy development of urbanization should be based on Sciences of Human Settlements,controlling city size, developing conurbation, optimizing city layout, belancing environmental carrying capacity and the intensity of urban development, highlighting the characteristics of regional resources and industrial structure, protecting regional characteristic.Urbanization has strong complexity and various constraints. The key to development is the coordination of various influencing factors scientificly and rationally, so as to ensure healthy and sustainable development of urban system.

Abstract: In order to make sure the structures have well seismic performance, the designer adopt dynamic time-history analysis method .But there is a problem to calculate the dynamic response of the structures which is how to find a scientific and reasonable criterion to select seismic wave records. In order to solve this problem and find a scientific and proper criterion to select seismic wave records, this paper referred to the standards ruled by the new Chinese Seismic Design Code for hydraulic structures and used the numerical analysis and scientific computation, conducted a well meticulous analysis, then put forward one way to select seismic records for time-history analysis method of hydro-structure. Except for taking the site condition, the fortified intensity, the duration into consideration, the author also give more emphasis on the fitting degree between the response spectra of seismic records with the new code to provide better fitting degree.

Abstract: Experiments on reinforced concrete frame spatial joints are conducted under low level cyclic loadings.The seismic performance of the spatial joints is investigated,including failure mode,hysterisis curve, stiffness degradation,energy dissipation and displacement ductility.The experiment result shows that the column-hinge damage mechanism had happened and the bearing capactity ,energy dissipation character and displacement ductility had decreased under the oblique direction earthquake effect.The aseismic designing method should consider the oblique direction earthquake effect.

Abstract: The study on the hysteretic characteristics of steel reinforced concrete (SRC) members is the basis of nonlinear seismic analysis of such structures. So in this paper, by summarizing the hysteretic features of SRC members, a quadrant-linear restoring-force model is suggested. Then the model is verified with available experimental results and proved to be effective and reliable.

Abstract: Based on extended finite element coupled with field variable method, fatigue damage numerical test of three point-bending beam with initial notch has been made to predict crack propagation path, numerical results showed : under the fatigue loading with 200Hz, and amplitude is 20KN, length of crack expanding was the biggest and crack grew as some angles with the initial crack during the first loading, crack propagated parallel to the initial angle during the other loading cycle. These results can fit the experiment very well. Using Fortran, A new user subroutine named USDFILD (User subroutine to redefine field variables at a material point) was also provided on the platform of ABAQUS, which can modal the change of physic material with time. This user subroutine can also import fatigue characterize of material into the model.

Abstract: Aiming at the problems of the applied technology of ground penetrating radar(GPR), the rationality and applicability of some common existed dielectric constant models to asphalt concrete material are verified and modified based on experiment, and then the new dielectric constant model models suitable for asphalt concrete material are established. The new models are applied to the real project, the results show that the new models can explain the characteristics of asphalt concrete material more accurately, and the calculated error of the compaction of pavement structures based on the modified models is significantly reduced compared to that based on the existed models.

Abstract: Two-dimension finite difference time domain (FDTD) update equations are established, and the GPR electromagnetic wave propagation in rigid pavement with voids beneath slabs is numerical simulated by using effective CPML boundary conditions, and then the two-Dimension GPR images for voids beneath slab are obtained. Moreover, the relationship between characteristics of voids beneath rigid slabs and GPR data is analyzed. The achievements of this paper will provide a theoretical basis for the use of GPR to rapidly detect voids beneath rigid slab.

Abstract: Aiming at the problem that the asphalt pavement is prone to early crack and reduces its service life, the response of transverse and longitudinal surface vertical cracks under moving loads is studied based on fracture mechanics theory. By means of 3D numerical simulation with the general finite element software package ABAQUS, the change law of stress intensity factor kⅡ of transverse and longitudinal surface crack under moving vehicle load are deeply analyzed and some conclusions are drawn, which contribute to further research on the propagation behavior of asphalt pavement surface crack in service condition, and will provide some guidance for the maintenance and rehabilitation of asphalt pavement.