Applied Mechanics and Materials Vols. 256-259

Abstract: The optimization of second isolation period for parallel base isolation system is investigated systematically. The maximum dissipative energy scale factor is used as the objective function, the maximum sliding displacement of base-isolated layer, the residual displacement and the maximum base shear coefficient are considered as the constraining factors. For first to fourth category site, under the low amplitude severe earthquake, the variation rule of the four seismic response indicators for the second isolation period is approximately same, the second isolation period is proposed to be in the range of 4s to 6s.

Abstract: We found through the statistics of disease that the void is one of the major problems of the CFST in recent decades. In fact, the void is inevitable with the current state of materials and construction method. This paper describes detailedly many methods of repairing void from the two aspects of the existing bridge and the under-construction bridge, including secondary grouting method, longitudinal stiffening rib, inner flange, bell-shaped anchoring box, etc.

Abstract: Combined with the dynamic compaction example of a nuclear power plant, a fully field tests was conducted to get the permeability and integrality of the impervious wall in real time. The dynamic compaction vibration impact on impervious wall was researched based on the test results. The relationships between damage characteristic and peak particle velocity of impervious wall are suggested also. The safety control standards which used vibration safety threshold to control the potential damage for impervious wall under long-term dynamic compaction were presented. When the PPV of impervious wall is not exceeding the safety threshold, the impervious wall will in its secured state. According to the damage detection method and the presented safety threshold of vibration velocity, the protected structure can be simply and protected during dynamic compaction. The research methods reflects the damage of protected structure directly, and more accurate and safety than traditional methods.

Abstract: Considering characteristics of gird truss structure, the suitable two-step damage detection method for these structures is proposed in the paper. The acceleration power spectral density sensibility of structural nodes is obtained by analyzing their acceleration power spectral density value caused every damaged structural bar. According to sensibility value, the range of influence of damaged structural bar is determined, then structural sub regions are divided and accelerators are distributed. The first step damage detection methods is identifying damaged bar occurrence region, it is extracting damage index to identify the damage occurrence region based on changes of acceleration response power spectral density of structure damaged after and before. The second step damage detection methods is located damaged bar in the region, it is completed by finding the damaged bar based on the theory of dissipation ratio of modal strain energy damage detection method. At last, taking the gird truss structure as numerical example, it shows the method has the capability to detect the damage of complex gird truss structures successfully.

Abstract: This paper through the test results and theoretical calculation of the batter pile static load, analysis of the actual stress state of cables, and according to the test results to determine the level of the foundation soil resistance coefficient ratio and allow level a transplant.

Abstract: It is quite difficult to estimate system reliability of complex structures which involve lots of potential failure modes. A novel method for system reliability analysis of frame structure was proposed based on stochastic limit analysis. Stochastic limit load was firstly calculated based on the elastic modulus reduction method (EMRM) by taking the uncertainty of structural resistance into account. Once the limit state equation was established by the stochastic limit load, the system reliability index can be calculated by the first-order reliability method (FORM) efficiently. Numerical example illustrates the efficiency and accuracy of the proposed method by comparing with the traditional failure mode analysis approaches.

Abstract: This paper presents the results of reinforced concrete (RC) beams strengthened in shear by external reinforcement with RC or epoxy resin mortar. The test specimen was 2000mm long with a cross section of 150mm×200mm and after section enlargement the cross section was increased to 250mm×300mm, in addition, shear span to beam depth ratio of a/h0 was 2.35. All specimens had the same geometry and were distinguished by the configurations of stirrup which was the primary test variable. No shear reinforcement was provided in the first phase of test, while in the second phase external RC or epoxy resin mortar was provided to enable failure due to shear. Experiments are undertaken to investigate the influence of preexisting damage, configurations of stirrup and different methods on the strengthened behavior and mode of failure. A group unstrengthened control beams were tested and failed in shear. In contrast to the control beam, all of the strengthened beams showed a significant improvement in their ultimate load capacity when they were failing in shear. The enlarged section with reinforced concrete can significantly increase the ductility and ultimate shear strength of a concrete beam. The method of section enlargement with RC is a high effective technique to enhance shear ability. An analysis for shear strengthening of beams using external reinforcement with RC has also been carried out as well.

Abstract: GA-Bp network model was proposed. GA was used to optimize the initial real values population of Bp network, and optimizing crossover fraction was fulfilled. In addition, the modified GA-Bp was applied to predict the deformation of the surrounding rock around tunnels.

Abstract: Based on the research of rock burst in underground engineering at home and abroad， definition，type, intensity grading，influencing factors，the failure mechanism，the empirical criterion and on-site forecasting and control methods of rock burst are summarized systematically. The current main problems in rock burst research are pointed out and the idea of rock burst comprehensive prediction are put forward. We recommend that the rock burst prediction should be divided into three steps, i.e. tendentiousness prediction，trend prediction and field prediction and forecasting.

Abstract: In order to diagnose the disease degree of operation tunnels and to estimate tunnel's security condition, this paper analyzes the causes of bugs existing behind the tunnel lining, expounds the theory and method of making non-destructive test on tunnel lining quality by using Geological Radar. By processing and analyzing field data, the following functions can be performed, such as detecting the thickness of concrete lining accurately, determining the distribution position and quantities of rebar and grid steel, searching existed cavity and uncompacted area behind the lining especially lining arch top. We also apply the method of morphology to the extraction of liner image feature. We get the liner boundary line and waterlogging area more intuitively by wavelet analysis, and find the anomalous point in the liner. It has been proved that Geologic Radar is a feasible method to inspect the structure of tunnel concrete lining. A dopting hole-drilling method to make verifications with detecting results of geological radar, the results of the two kinds of methods have not big difference.