Advanced Materials Research Vol. 629

Abstract: In this study, Dialdehyde sweet potato starch (DASS) with various carbonyl contents had been prepared by sodium periodate in the neutral condition and applied to improve the comprehensive properties of thermoplastic starch. Thermoplastic dialdehyde sweet potato starches (TPDASS) was prepared by thermal press when glycerol was added as a plasticizer. The thermal properties, moisture adsorption, mechanical and biodegradable properties of TPDASS were investigated. The results illustrated that at higher carbonyl content, the moisture adsorption and biodegradable ratio decreased with the increasing Tg of TPDASS, which may attribute to the partial cross-linking of DASS. The highlight properties of TPDASS95 were that: its tensile strength could reach 12.9 MPa even water content was 13.5%.

Abstract: Catalysts of Ni/MgO-ZrO2 were synthesized by the impregnation method and co-precipitation. They were characterized by X-ray diffraction (XRD), Scanning electron microcopy (SEM). It was observed that the monoclinic ZrO2 turned to tetragonal ZrO2 with the Mg2+ mixed. The tetragonal phase ZrO2 is considered as the desired phase which exhibits both acidity and basicity, and active in many heterogeneous catalytic systems. The NiO-MgO solid solution is also discovered on the surface of catalysts. Since the formation of carbon deposit needs a certain size of metal Ni, so the solid solution inhibited the reduced state Ni agglomeration .

Abstract: Long span bridges, as cable-stayed and suspension bridges, have gained much popularity in recent decades for their structural shape, efficient use of materials and other optimal solution. A new phase is starting with main span lengths going over thousands of meter. As a matter of fact, small size substructures are required, the development of efficient construction techniques are growing on and faster progress in the FEM and design are evident. Ever since the dramatic collapse of the first examples of such long span structures, as the Tacoma Narrows Bridge in 1940, much attention has been given to the dynamic behavior of these structures. In this paper a moving load analysis performed on a cable stayed high speed railway bridge is presented together with a fatigue analysis of the cable stays, discussed according to the Italian code verification procedure.

Abstract: Moving loads analysis in bridges are currently undertaken as a result of code provisions. However, this relevant part of the structural analysis in bridges, could be implemented with a wide variety of instruments and analysis. This paper deals with the response of bridges to moving loads: in the first part, in order to take advantage of the high amount of works performed in the past, a review of the principle method for the dynamic response of bridges to moving loads are outlined; in the second part code provisions of Eurocode are presented. Current short and medium span bridge types are analyzed, including long span bridges, as cable-stayed and suspension bridges, having gained much popularity in recent decades for their aesthetic appearance, efficient utilization of structural materials and other notable advantages. A wide amount of references from the analyzed literature are included.

Abstract: In the present paper, the time-dependent behavior of a salt cavern was analyzed using finite element method. A viscoplastic model considering inelastic volume changes was utilized to describe the time-dependent mechanical behavior of rock salt. The model was then implemented in a finite element procedure to analyze the stress and deformation of rock salt around an underground cavern using an axisymmetric representation. Finally, finite element analyses results were compared with those obtained by a viscoplastic model neglecting inelastic volume changes.

Abstract: The rheological behavior of rocks has been more and more important to predict the long-term deformation of rock engineering. We select a typical medium-strength marble rock as a research object to study the long-term stability of large-scale underground caverns. Some dry and water-saturated rock specimens are used to perform the uniaxial compressive test and the uniaxial compressive creep test. Then a non-constant-parameter damage rheological constitutive model for this medium-strength marble rock is put forward based on the in-situ geological data and uniaxial compressive rheological test results. The least square method based on search mode is utilized to perform the identifications of the rheological parameters. According to the test curves, the related rheological parameters are obtained through inversion analysis on a basis of the non-constant-parameter damage rheological constitutive model, which can provide more accurate rheological parameters for long-term stability analysis of actual projects.

Abstract: In the decision making of tunnel excavation and support scheme, stability analysis of surrounding rock-support structure is an essential link. Especially in fractured weak zone under complex geological condition, accurately measuring the deformation of support structure has an important significance for fast and safe construction. Based on the application of convergence confinement principle in judging tunnel deformation, this paper presented a new idea of using the ultimate displacement of tunnel initial support to analyze the stability of tunnel surrounding rock-support structure. Then, with a full investigation on the deformation and failure characteristics of highway tunnel surrounding rock at fractured weak zone, the ultimate displacement was got by using methods of numerical calculation and site monitoring measurement. Finally, the stability analysis of support structure in Zhongxing Tunnel was done. It can be arrived that there is a certain gap between true value u and measured value um of surrounding rock deformation. If the measuring points are installed after three excavation cycle, u is approximately equal to 1.6 um. then, based on the analysis of numerical simulation results and monitoring data of Zhongxing Tunnel, the paper indicated that the top and spring of arch are risk regions, reserved deformation of fractured weak zone is not enough, it should be adjusted from 10cm to 20cm.

Abstract: A stochastic analysis that incorporates spatial variability of material parameter of clay i.e. undrained shear strength, c within the finite element analysis was done. A smoother change of c between two neighbouring soil elements is expected than two elements at a distance apart, thus a spatial correlation length is used within the random field to describe the distance over which random values tend to be correlated. When the correlation lengths in horizontal and vertical directions are same, the soil elements can be described ‘isotropic’. Most of the previous studies investigated the effect of variation of c in terms of coefficient of variation, COV (standard deviation/mean) and the isotropic correlation length on bearing capacity. However, the correlation length of soil may not be isotropic as they may be deposited in layers i.e. correlation length in horizontal direction may be higher than that in vertical direction. Thus, this study investigated the effect of isotropic as well as anisotropic (in terms of correlation length) conditions and their lengths over a range of COV of c on the bearing capacity. The result of this study would help to understand the effect of soil anisotropy on bearing capacity.

Abstract: In this paper,the functions and performances of filling layer of self-compacting concrete(SCC) in CRTS(China Railway Track System)-Ⅲ type track system were introduced. Developments of SCC including design methods and test method was described in detail. The influencing factors of workability of SCC was analysised. The trends of future development of mix proportion design methods,durability evaluation admixtures,applications were discussed.This paper also pointed that it's importance for SCC to studying the quality control methods and the application.

Abstract: This paper studies the influence of different urban coverings (green areas or dry cover) on the urban microclimate. Different urban structures in a small area show different microclimatic behavior, depending on the thermophysical properties of the surface materials, in particular on the presence and extent of green areas. The research has been developed in downtown Rome in the summer period. In order to evaluate the impact of different urban envelopes, a typical urban square has been considered and analyzed systematically with the microscale climate model ENVI-met. A number of simulations has been performed with various kinds of surface covers and of vegetation and their effect on the air and soil temperatures and on the surface heat fluxes has been determined.