Advanced Materials Research Vols. 250-253

Abstract: Numerical substructures adopt predetermined hysteretic models for conventional substructure testing (CST). It is difficult to achieve accurate results in CST due to errors from modelling of numerial substructures. To diminish the negative effect caused by the assumed restoring model, online identification with least square method using experimental data was adopted to update the model of numerical substructure. The effectiveness of least square method are verified with pseudo-dynamic substructure testing for single story frame with a buckling-restrained brace. The results indicate that the on-line identification algorithm based least square method has good accuracy, stability, and efficiency.

Abstract: Joints between segments in cantilever casting concrete bridges require special attention in design and construction. These joints introduce discontinuity in the bridge; furthermore weaken the connection stiffness and strength of corresponding section, which may lead to excessive downwarping of bridge. Experiments were conducted to assess the shear stiffness of segmental joints section. The parameters studied included monolithic non-joints, joints roughened, joints roughened with shear-key. It was found that the shear stiffness of jointed section is largely lower than that of non-jointed section; however, the shear-key can effectively enhance the shear strength and especially shear stiffness of the joints section. Measures are proposed for shear-key design, and may provide a rational basis for the design of cantilever casting concrete bridges.

Abstract: Pitted courtyard cave dwellings were used as a long-term living form in Baishe village. After field measurements, the size of local pitted courtyards and cave dwellings had been mastered, and the variation of average annual rainfall and monthly rainfall had been analyzed. By the experiment, the changes of physical and mechanical indexes could be showed with different water contents. At the same time, based on the literature, the relationship could be established between rainfall and water content. Basis in the expression of room rock stress and the Mohr-Coulomb strength criterion, the stability of the cave dwellings could be analyzed under different water contents, and the definition could be found of safety factor of loess cave. Then, the stability variation of loess cave dwelling could be obtained in different rainfall, and the evaluation results are given.

Abstract: Regarding the multi-degree of freedom as the research object, we study vibration theory and engineering application of the multi-degree of freedom. Main content as follows: When establishing vibration system model, we deal with the structure’s discretization and the motion simulation, as well as simplify the foundation model and other issues. The establishment of vibration motion equation must combine with the specific situation and ensure the accuracy of equation, so that we can achieve the best equation of engineering fitting. Harm treatment of engineering vibration is the key to enhance structure durability.

Abstract: An experimental study on the fire performance of reinforcing concrete beam-column joints under ISO834 standard temperature-time curve was carried out, and the main parameters including the load ratio of the beams and axial compression ratio of the columns were chosen to study the performance of the joints. The deformation, the explosive spalling of concrete, the fire resistance and the collapse mechanism of the joints in fire are observed carefully, and several conclusions are drawn in the end.

Abstract: The criterion to judge the ultimate state of the scooted head pile bearing uplift load in soil foundation is insufficient at present. According to this problem, a numerical simulation method based on Failure Approach Index considering Mohr-Coulomb yield criterion is adopt to study a quantitative and sufficient criterion for the ultimate state of the scooted head pile bearing uplift load in soil foundation. A scooted head pile in homogenized soil foundation is taken as an example, the ultimate uplift load of the pile is obtained by test, at the same time the ultimate uplift load of the pile is obtained by numerical simulation method based on Failure Approach Index considering Mohr-Coulomb yield criterion. The research results indicate that the two values of ultimate uplift load of the pile obtained by test and the numerical simulation method are very close, which give the sufficient evidence that the criterion for the ultimate state of the scooted head pile bearing uplift load in soil foundation based on Failure Approach Index is sufficient and reasonable.

Abstract: Because our country is a mountainous country, in engineering construction process, inevitably involve a lot of high cutting slopes. Summarized the relevant research achievements of predecessors, we put forward the type optimization scheme based on the current problems of smaller longitudinal slope degrees at bottom interface of high cutting slopes. Setting some slower longitudinal slope degrees at the bottom interface of high cutting slopes, which will reduce excavation volume to a certain degree, thus reduce energy consumption, reduce the influence of excavation on the surrounding environment, and reduce relevant expenses to restore the slope environment. After setting some slower longitudinal slope degrees, the slope toe drainage will be more unobstructed, the slope height will be reduced, and the slope will be more stable, thus reduce the work amount of slope retaining. For each year, thousands of kilometers mountainous highway will be built, bottom interface type optimization of high cutting slopes will have very big economic value. Therefore, which is worth to recommend in construction and designing of high cutting slopes.

Abstract: The minimum rock cover is one of the most important factors determining the safety and cost of subsea tunnels .There are seven main influence factors and four methods determining the rock covers of subsea tunnels. Unfortunately, whether in Norwegian experience method (NEM), Numerical method (NM), Japanese experience method (JEM) or in mining under water experience method (MUWEM), these factors are considered separately in the study. The synergies reflecting the preferred primary or minor importance between the factors are not fully considered. The group AHP method (GAHPM) was put forward to solve the problem. GAHP is an optimization technology, where choosing suitable weights are the most importance. Adopting the advantage of AHP and avoiding the disadvantage at the same time, it can fully reflect the importance of each factor in determining the ultimately thickness of rock covers. In this paper, firstly, we construct the hierarchy and pair-wise comparison matrix. Secondly, determine weights of the experts. Thirdly, check the consistency of the judgment matrix. Ultimately, we obtain the ultimate minimum rock cover of the subsea tunnel by the product of initial selectable thicknesses and weights.

Abstract: In the area where hard formation buries deeply, large-diameter and extra-long cast-in-place piles set into soft fragmental rock with high pressure grouting technique may raise the bearing capacity and reduce settlement apparently. This article approaches and analyses the subject through testing data of comparing two groups of piles experiments with two different ways of construction in the same project. The research enhanced original designing arrangement, shortened construction period, reduced cost of the project and drew some valuable conclusions. As a result, it also proposed that it’s not necessary to elevate the length of piles worthlessly and set too deep into hard formation unrealistically to avoid wasting in the later similar engineering.

Abstract: In consideration of the excessive mid-span deflection and box girder cracks of continuous rigid-frame bridges, this paper analyzes the maximum first principal stress and mid-span deflection increment of a continuous rigid-frame bridge with density gradient concrete under shrinkage and creep effect. The maximum first principal stress increment at main span is 0.084MPa and mid-span deflection increment is 73mm after 10 years for continuous rigid-frame bridge with density gradient concrete, which are smaller than a continuous rigid-frame bridge with normal concrete. All of that show that continuous rigid-frame bridge with density gradient concrete reduces effect of shrinkage and creep. The research provides a theoretical basis for the successful application of continuous rigid-frame bridge with density gradient concrete.