Advanced Materials Research Vols. 168-170

Abstract: An experimental study is conducted to simulate the thermal field in mass concrete. Accurate prediction of the thermal stress by analysis is quite difficult particularly at early ages, due to uncertain age-dependent properties of concrete. A series of tests was conducted in which the temperature was measured for a large number of observation points. The effect of aging and the amount of measuring points on thermal field development that can occur in realistic structures was evaluated. Numerical simulations of the thermal field setup were also performed using the finite element with ANSYS software to verify and extend the experimental interpretation and to determine the maximum temperature value which would occur under construction process. Mass concrete temperature field and stress field for specific projects were measured and analyzed. Numerical simulation of mass concrete temperature field for the actual project is compared with the measured results. The results show that the temperature field of numerical simulation results and measured curves result are of the same trend. And it is feasible that mass concrete temperature field is simulated based on ANSYS.

Abstract: The field of Nondestructive Evaluation (NDE) is a very broad, interdisciplinary field that plays a critical role in civil engineering for controlling new structures (quality control) as well as for assessing the internal grout condition of prestressed pipes in post-tensioned concrete structures. Because it allows voids in grouted tendon ducts to be inspected and measured without damaging them, impact-echo based NDE provides an excellent balance between quality control and cost-effectiveness. This paper focuses on the nondestructive evaluation of internal injection quality in post-tensioned bridge ducts, and the developments in civil engineering NDE in China are also introduced.

Abstract: For the soil is a very complex natural material, significant strain gradient effect exist in soil analysis. Based on the "gradient" phenomenon, we add the plastic strain gradient hardening item into the traditional Cambridge yield surface. By using the consistency conditions and associated flow rule, we get the explicit expression of plastic strain gradient stiffness matrix. And the finite element method of plastic strain gradient is also shown in this article. Plastic strain gradient is actually a phenomenological non-local model containing microstructure information of the material. It may overcome the difficulties in simulating the gradient phenomenon by traditional mechanical model.

Abstract: A three-dimensional thermo-mechanical coupled model of hot leveling and cooling processes of the steel plate has been conducted with MSC.Superform software. Four kinds of initial temperature distribution patterns have been determined according to literature. The effects of hot leveling and cooling processes on the transversal and longitudinal residual stresses of the steel plate have been analyzed. The results show that the initial temperature distribution patterns have significant influence on the residual stress of the plate. The more uniform temperature distribution patterns along the width of the plate, the smaller residual stress and also the smaller stress fluctuations. The cooling process has greater effect on the residual stress compared with the hot leveling process. The bigger the temperature gradient along the width of steel plate, the larger the residual stress and its fluctuation is. Through the FEM study, the value and direction of transversal and longitudinal residual stresses can be confirmed quantitatively at various positions along the width and length of plate, which can provide guidance to actual measurement of residual stress.

Abstract: It is difficult to determine the magnitude and distribution of permeability in gob areas, which are therefore treated as homogenous and isotropic generally. Another way to computer the distribution of permeability is based on the presupposed distribution of expanding coefficient of falling rocks. In view of the complex geological conditions of gob areas, the two methods are both subjective and arbitrary in a large degree. By importing the conception of boundary layer, the hypothesis of free deposited permeability of gob areas is put forward here. By setting the reasonable limit magnitude of permeability, namely the free deposited permeability as maximum whereas the sufficient compressed permeability as minimum, a more exact method is deduced to analyze and determine the distribution of permeability in gob areas. The application of this hypothesis in the numerical simulation of seeping flow filed in a gob area indicated that the distribution of permeability based on the hypothesis is more compliant to the fact.

Abstract: This paper presents three static load tests of composite foundation incorporating flexible piles, rigid piles and different cushion materials to clarify the load-displacement behavior of composite foundation. The results of static load tests indicate that the cushion made of stone and sand is not suitable because of a large pile penetration. As far as the influence of cushion material is concerned, the cushion made of sand, gravel and rubble with the maximum particle size of less than 20 mm and grouted with cement slurry can be used to fully mobilize the bearing capacity of each part of composite foundation, and modify the load transfer mechanism of the piles. Moreover, this type of cushion can reduce the overall settlement and ensure the uniform settlement of building.

Abstract: The paper investigates the effects of different concentrations of crumb rubber (CR) on the pavement performance of the conventional penetration-grade 80/100 bitumen and the dense-graded wearing course asphalt mixture (AC16). A wet process and 0.6mm size CR were used and the control variables included three types of CR of concentrations 5%,10% and 15% by total weight of binder. The evaluations were twofold. Firstly, a comparison of the basic and rheological properties of those modified and unmodified binders was conducted. Secondly, a comparison of the resistance to moisture damage, low temperature cracking and permanent deformation of the AC16 and CR modified AC16 was performed. The results show that all the CR modified binders and mixtures are found to have improved performance as evaluated by a series of laboratory tests. In addition, among three CR concentrations, AC16 modified with 10%CR by total weight of binder exhibits the most satisfactory performance properties with respect to the resistance to moisture damage, permanent deformation and low temperature cracking.

Abstract: The low velocity impact response of sandwich panels at different energy levels has been investigated by conducting drop-weight impact tests using an instrumented falling-weight impact tower. Impact parameters like maximum impact force and the extent of the damage were evaluated and compared for different types of sandwich panels. Finite elements simulations have been undertaken using the LS-DYNA software; the results of FE simulations have a good agreement with the experiments. It shows that, the impact force increased with thickness of face-sheets and foam core, the extent of the damage increased with the impact energy, sandwich panels with steel face sheet has a good impact resistance in comparison with sandwich panel with aluminum face sheets.

Abstract: Carbon fiber reinforced cement could sense its own temperature based on the temperature resistivity effect. In contrast with Portland cement, sulphoaluminate cement has much better freeze- resistance. As a result, carbon fiber sulphoaluminate cement composite (CFSC) has the superior potential to sense its own temperature than carbon fiber reinforced Portland cement in the negative and positive temperature, especially for the negative temperature range. The temperature resistivity effect of CFSC was discussed in the positive and negative temperature. And the lower and the upper temperature limit of temperature resistivity effect were investigated. The results indicated that temperature resistivity effect of CFSC was related to the hot expansion and the electric carrier activating. And the electric carrier activating was the primary influence factor. Temperature sensors could be made by CFSC based on its good temperature resistivity effect in positive and negative temperature range. Therefore CFSC has the advantage to sense positive and negative temperature by resistivity measurement.

Abstract: This paper firstly introduces a new general solution constructed by double trigonometric cosine series with supplementary terms for the bending and vibration analysis of orthotropic rectangular plates with four free edges on the Winkler foundation subjected to arbitrary vertical force. The general solution, which is fourth-order continuously differentiable with less undetermined coefficients, can be used to solve the bending and vibration problems of orthotropic rectangular plates on the Winkler foundation with various physical parameters requiring no classification and superposition. This makes the bending and vibration analysis of orthotropic rectangular plates with four free edges on the Winkler foundation more unified, simplified and regulated. This paper also gives a Series of analytical example to prove that the method is feasible.