Abstract:After operation of the metro, there has been increasing longitudinal nonuniform settlements of shield tunnel due to various interior and exterior factors, and then some expansion of shield tunnel segment joint develops to varying degrees, which seriously impacts on the safety of the train. Taking geometric dimension of segment, curvature radius, stiffness ratio in longitudinal, uncertainty and epistemic uncertainty into consideration, an interval Monte Carlo method has been developed which combines simulation process with the interval analysis to estimate the probability of shield tunnel segment joint failure. Finally, the interval of the failure probability is obtained. Case studies are presented to discuss the effect of different curvature radius and stiffness ratio in longitudinal on the failure probability. Herce, the control sphere of the two factors is obtained under the certain interval of the failure probability. The results provide the guidance for tunnel protection，waterproof design and construction technique of shield tunnel.

Abstract:In order to study the creep-degradation settlement properties of municipal solid waste, the change of static-creep-settlement for fresh municipal solid wastes which collected from the Chongqing landfill was observed elaborately during the 330 days Laboratory test, and the PTH Model which would fit the settlement properties better was funded. By analyzing leachate-degradation-strain-time relational curves, the number of total creep settlement caused by external load and inner degradation in the waste can reach 33.2% of the sample height. The leachate production can be controlled by the external load and organic content. The tests results indicate that the degradation rule of MSW can be expressed as the Richards model，and the relation of cumulative sellenment with cumulative leachate fit the Exponential function model. The corresponding section for organic content that suit for the initial compression deformation and the creep-degradation settlement could be ranged from 29.1% to 36.47%. During the monitoring for settlement and internal temperature field in the anaerobic reaction stage, an optimum temperature zones that varied from 20℃ to 41℃ are found, which could accelerate degradation speed of organic matters in the waste. Moreover, degradation speed of organic matters becomes maximum when the temperature reaches 41℃.

Abstract:Aimed to analyze the influence of rainfall on slope stability. The finite element method (FEM) is used for the calculation of 2-D transient seepage in the unsaturated slope, while the method of limit equilibrium is used for computing its safety factor. The change of pore water pressure, slip surface and safety factor are investigated through numerical calculations with consideration of various intensity and duration of rainfall. Special attention has been paid to slope stability after rainfall. It is found that sometimes the minimum safety factor may occur several hours or several days after the rainfall, instead of the time during the rainfall or when the rain just stops.

Abstract:In order to investigate the creep behavior of warm and ice-rich frozen soils, a number of pressuremeter tests were carried out in permafrost regions on the Qinghai-Tibetan Plateau with Menard pressuremeter. Then, the regression analysis results of the creep curves generated by Merchant model and relevant parameters were obtained. The test results indicate that the temperature plays a more important role than the water content in affecting the mechanical behavior of warm frozen soils. As pressure increases, the proportion of instantaneous strain in the total strain under each pressure decreases gradually. The regression results show that the instantaneous shear modulus increases linearly with decreasing temperature, but the delayed shear modulus as well as the viscous coefficient present a power function trend. Their peak values appear at the water content of 46%, which is rather different from the test result on lower temperature frozen soils.

Abstract:Based on complex variable theory in plane elasticity, the equivalent spring stiffness is derived from the analytical solution by means of simplifying shallow shield tunneling to semi-infinite plane with hole, which is applied to response displacement method. The performances of the analytical solution are evaluated and compared with that of the deep shield tunneling through a series of selected various tunnel depths and soil Poisson's ratios. The relation of compression and shear spring stiffness is discussed. Meanwhile, two factors affected soil spring stiffness, tunnel depth and soil Poisson's ratio, are also analyzed. It is shown that soil spring stiffness of shallow shield tunneling is different from that of deep shield tunneling, and the ratio of compression and shear spring stiffness varies along shallow shield tunneling. It is also found that the value and distribution law of soil spring stiffness of shallow shield tunneling greatly depend on tunnel depth and soil Poisson's ratio.

Abstract:The critical reliability slip surface with minimum value of reliability index is difficult to be obtained by the Monte-Carlo method. The simplified Bishop method was adopted to calculate the factor of safety for given circular slip surface thereby defining the performance function in reliability analysis. Six variance values of random variables were designed and four sample ranges were assumed. A quasi-Monte Carlo method was defined with fow samples. One hundred and thirty-two potential slip surfaces were randomly generated. The reliability indexes regarding those slip surfaces were calculated by Monte-Carlo method and quasi-Monte Carlo method, respectively. The comparative results show that in the case of one random variable, the reliability index from Monte Carlo method is found to be linear with that from quasi-Monte Carlo method. In the similar conditions, the wider the sample range, the smaller the tangent value of line, and Vice versa. In addition, the bigger the sample number, the bigger the tangent value of line. The Quasi-Monte Carlo method is approved to be practicable for the determination of critical reliability slip surface for homogeneous slope.

Abstract:The climate has a great impact on highway bridge rubber bearings than on building rubber bearings. In order to study the change of the mechanical properties during the life of the plain chloroprene rubber bearings of highway bridge under freeze-thaw cycle condition, the plain chloroprene rubber bearings were processed 25, 50, 75, 100 times by freeze-thaw cycle in the standard freeze-thaw chamber, then the axial compression tests were carried. The changes of the performance indicators in the bearing capacity , the ultimate compressive strength, vertical stiffness, elastic modulus under different freeze-thaw cycles were analyzed comparatively. The results show that the plain chloroprene rubber bearings are more prone to brittle failure after the freeze-thaw cycle, and the failure phenomena of steel plate exposing or cracks is more serious than the phenomena of the standard specimen. With the increase of the number of freeze-thaw cycle, the ultimate bearing capacity, ultimate compressive strength and compressive elastic modulus of the plain chloroprene rubber bearings decrease. The attenuation formula and decay curve in 50 years of ultimate compressive strength and elastic modulus of compression are analyzed by least square method, the trends of change are both in line with the exponential function. The mechanical properties of plain chloroprene rubber bearings of highway bridge significantly decreased under freeze-thaw cycle condition. therefore, the temperature ranges of plain chloroprene rubber bearings of highway bridge should be strictly controlled, and some suggestions, such as increasing its minimum applicable temperature, usng the natural rubber bearings as much as possible in cold regions, have been given.

Abstract:Based on the yield criteria of second-order parabola, a refined translational model for punching failure has been developed, assuming that the critical ultimate state is characterized by cracking of the compression concrete on the punching cone and simultaneous splitting of the tension concrete at longitudinal-rebar level. An upper-bound solution was obtained and a general one was developed under arbitrary-order parabola yield criteria. Moreover, the deduced complex model was simplified for better practice. The statistical results, with a collection of 231 specimens, show that for the proposed curved-generatrix model, the coefficient of variation for the prediction-to-observation ratios(i.e.,0.201) is much less than that for the straight-generatrix model previously proposed(i.e.,0.250). In addition, it is slightly lower than that for the current GB code(i.e.,0.202), and its mean(i.e.,0.940) is obviously superior over the latter(0.799).

Abstract:A robust method for determining the component safety factor and structural safety factor of steel truss bridge is developed based on elastic modulus reduction method (EMRM). A procedure of two-level safety analysis and structural optimization is presented by means of the linear FEA iteration and the generalized yield criterion to take multiple internal forces into consideration. The strategy of elastic modulus adjustment is derived according to the principle of conversation of energy. The element bearing ratio (EBR) in every step can be obtained, and the first and last EBRs are employed to determine component safety factor and the structural safety factor for two-level structural safety evaluation of steel truss bridge. Those components with higher or lower EBR than the referenced EBR can be identified. By taking the quantitative relationship of the two level safety factors, a structural optimization scheme with better distribution of the EBR and saving material consumption can be achieved by adjusting the sectional strength of components with higher and lower EBR. Numerical examples show that the proposed method is promising with satisfying accuracy. The analysis of structural safety and optimization can be implemented by using the linear iteration while complicated nonlinear analysis in classical scheme is avoided.

Abstract:Based on the strain energy considering the effect of dead loads, the general form static equilibrium differential equations were formulated by means of the potential energy principle. The approximate solutions of live load or later load displacement including the effect of dead loads for the clamped rectangular plate and the simply supported rectangular plate were generated by the Galerkin method. These formulas are simple and clear, and their physical concepts are explicit. The correctness of these formulas was verified by the finite element method. The dead loads and other factors that influence the effect of dead loads are shown by these formulas. The effect of dead loads on the two different boundary condition rectangular plate were analyzed by these approximate solutions. The effect of dead loads improves the bending stiffness of plate and minimizes the displacement of live loads or later loads. The key physical factors governing the effects of dead loads on plates are the dead load, the ration of span to thickness and boundary condition etc. This effect of dead loads is not negligible, especial in thinner plates or plates with smaller stiffness, more attention should be paid to the effect of dead load in the calculation and analysis for plates.

Abstract:Based on the probability conservation principle, a joint probability density evolution equation of random parameters and fatigue damage is derived. Probability density evolution surface and cumulative probability isoline of fatigue damage in term of the evolution equation can be used to predict the probability distribution of fatigue damage and fatigue reliability with a given damage threshold. The numerical solution of fatigue reliability for a constant-amplitude test has a good agreement with the experimental result. For a variable-amplitude fatigue test, the computation results, which are calculated according to probability parameters of two constant-amplitude fatigue life tests and Miner's rule, are also in good agreement with the experimental results.

Abstract:To investigate mechanical behavior and seismic behavior of concrete filled steel tubular column node (CFSTCN) in space truss structure, both full-scale test and Finite Element Method (FEM) were employed. The test load was 1.6 times of design load and by incremental step loading. Meanwhile, stress and deformation in CFSTCN were observed to monitor bearing capacity of the node. The results show that steel tubular works in elastic state and a small part of concrete beyond of compressive stress limits; steel tube and concrete adhesive well. The hysteretic energy dissipation capacity and failure mode under cyclic loading were revealed by nonlinear FEM. weakest position and ultimate bearing capacity of the node were obtained from FEM results. The method of combining full-scale test and FEM can well reveal the mechanical behavior and the seismic behavior of the node.

Abstract:According to the analysis of existing test data, the stress influence coefficient and water-cement ratio influence coefficient in the existing concrete carbonation depth forecasting models are modified and improved. Based on the reliability analysis, the rule of deterioration life is presented. The analysis shows that the rate of carbonation of concrete is accelerated or restricted at the status of tensile or compressive stress, respectively. Especially with the increase of the level of tensile stress, the carbonation rate of concrete will become faster and faster. According to the results of reliability analysis, the relation between probability and reliability of the concrete deterioration is one-to-one corresponsive, meanwhile, the concrete cover thicknesses and stress levels have great influences on the durability life of concrete structures. And with the same reliability, the time of deterioration of concrete decreases with a higher stress levels and a less cover thickness.

Abstract:The P-Δ effect is one of crucial reasons causing the structure to collapse under the excitation of strong earthquakes. Under the interaction of the geometric nonlinearity and the material nonlinearity, the backbone curve of structure behaves a negative post-yield slope. In order to calculate the structural response function rapidly, the proportion rule between the seismic intensity and the normalized yield strength for the similar inelastic systems under the same ground motion is revealed. Based on this rule, the relationship curve between the normalized yield strength η and the ductility factor μ of the equivalent single-degree-of-freedom system is established, and the simplified procedure to calculate the seismic intensity of each point in the pushover curve is derived, which generates the structural response curve. A numerical example of six-storey steel building is conducted, calculating using the proposed procedure and the exact incremental dynamic analysis method respectively for an ensemble of 20 ground motions to obtain the 16%, 50% and 84% fractile response curves of the roof drift ratio, which demonstrates the simplified method agrees with the IDA from elastic, inelastic to collapse.

Abstract:Lightweight foamed concrete is a new arresting material for arresting overrun aircraft. To reveal its compression properties and mechanism of deformation and destruction, a study on lightweight foamed concrete with different density, 0.21 and 0.31 g/cm 3 respectively, has been carried out. Experiment system include CSS4410 electronic universal testing machine and Dynatup9250 drop-hammer testing machine and VHS8800 high strain rate system. Then, extrusion strength under different indenter area is predicted with a theoretical model, and a crushing flow stress constitutive equation is proposed. The results show that it is characterized by the movement of crushing driving interface during the process of deformation, crush to compaction of the material, and the deformation is notably in local. The compression strength is relevant to density and impact velocity. Moreover, theoretical model can predict the extrusion strength under different indenter area exactly, and the crushing flow stress equation can describe mechanic properties of compression well.

Abstract:The aim is to evaluate the seismic properties of ancient timber structure after strengthening and analyze the failure process and corresponding failure state. Based on the hysteretic behavior and energy dissipation principle of the dovetail column-frame strengthened with CFRP and Arches Brackets under the low reversed cyclic loading, the “potential of destruction-resisting” of the two energy-consuming components is obtained. The dissipated energy of each energy-consuming component under the various earthquake conditions is calculated combining with the shaking table test of ancient timber structure. The model of seismic damage evaluation of the two energy-consuming components is established on the basis of the “potential of destruction-resisting” and the dissipated energy. By means of the energy distribution coefficient, the relationship of the failure state between energy-consuming components and overall strengthened structure is discovered, and the model of seismic damage evaluation of the overall structure under the various earthquake conditions is presented. With the derived model of seismic damage evaluation, the failure coefficient of the energy-consuming components and the overall strengthened structure is quantitatively calculated. According to the failure state, the corresponding damage grade of overall strengthened structure is obtained. The results can provide a reliable theoretical basis for predicting the destruction before earthquake and re-reinforcement to the strengthened ancient timber structures after earthquake.

Abstract:Aimed at the limitations of total fluctuating wind-induced response with combination of background and resonant components using Square Root of the Sum of Squares (SRSS) method, the theoretical combination formulas of fluctuating wind-induced responses and ESWLs are derived based on structural dynamics and random vibration theory. Meanwhile, the refined analysis method is firstly presented by four components formula to compensate the coupling component between background and resonant modes. The proposed procedure avoids the integration process of calculating elastic restoring force and completely considers the modal coupling effects, which can be used to calculate the ESWL for any complex structures. Taking the steel grid roof structure of a large museum as an example, the new method was used to calculate its wind-induced response. Compared with results of complete quadratic combination (CQC), the effectiveness and accuracy of the present approach has been revealed.

Abstract:The stochastic fluctuating wind pressure field acting on a large-span membrane roof consists of Gaussian and non-Gaussian regions in the sense of statistics. Simulation of this stochastic field is presented based on the zero memory nonlinearity (ZMNL) transformation method. A case study is then given to show that the stochastic wind pressure field samples generated by the proposed method can well represent the specified statistical characteristics of data from the wind tunnel experiment. After that, the wind-induced response analysis is conducted on a membrane roof structure using the Gaussian/non-Gaussian composed wind pressure field samples generated by the proposed method and the Gaussian samples by the traditional method, respectively. Results indicate that response values of some components of the structure induced by the Gaussian samples are lower than those by the Gaussian/non-Gaussian composed wind pressure samples, which means the non-Gaussian characteristics of the stochastic wind pressure should not be ignored. Meanwhile, the total gust response factors of the components caused by the wind excitation are given to meet with the requirement of the designers.

Abstract:The mechanism for chloride penetration in cracked concrete and its major impact factors were analyzed. As a result, a revised chloride diffusion model based on Fick's Law was built by dual porous medium model. Then several cracked reinforced concrete beams self-anchored with sustained flexural loads were immersed in the 5% NaCl solution with the condition of dry-wet cycles. After 15 times of dry-wet cycles, the rapid chloride testing (RCT) was used for the determination of chloride ion content of the powder at each cracked sections. The test results show that: 1) with the condition of dry-wet cycles, the chloride content will occur a peak in the surface 20mm concrete, so the depth for surface convection zone can be assumed to be 15~20 mm; 2) when the crack width is less than 0.3mm, the equivalent chloride diffusion coefficient increases steadily, which agrees well with model's prediction; when the crack width is larger than 0.3mm, the equivalent chloride diffusion coefficient augments rapidly and influence of convection on chloride penetration becomes more significant; 3) the deterioration factor for equivalent chloride diffusion coefficient in flexural cracked concrete is directly correlative with crack width, which can be expressed by second order power function or separate function.

Abstract:With regard to the long span continuous composite beams, the early composite shear stud strength at the joint surface between the steel girder and concrete slab at different concrete ages should be considered while the concrete slabs are casted by phases in construction stage. In this study, the push-out test of stud shear connectors were conduced at different concrete ages. Meanwhile, the change law of the ultimate shear strength, ultimate slip deformation, design shear strength, and shear stiffness of the stud shear connectors with concrete ages were analyzed, and the corresponding time-dependent calculation equations were presented. The results include that the main failure modes of stud shear connectors are the concrete slab splitting failure before 3-days concrete age. The load-slip laws of stud shear connectors at different concrete ages are basically the same, however, the shear strength and stiffness all increase with the concrete ages prolonging, and the increase degree is faster at early ages, but slower at later ages, which indicates that the early composite shear stud strength at the joint surface of composite beams should not be neglected.