Papers by Author: Yuan Hua

Abstract: The wet sprayed concrete technique has good virtue of improving the working condition within the tunnel, fewer reflective concrete loss and higher sprayed concrete quality. The concrete mixed with polypropylene fiber could improve the concrete inner structure, the flexural strength, tensile strength and anti-penetrating ability. The application of the wet sprayed polypropylene fiber reinforced concrete in the construction of tunnel lining structure could improve the stability of tunnel rock mass. The nonlinear finite element analysis is performed on rock mass stability of the railway tunnel lining structure and the rock mass stability is analyzed both for the un-lining tunnel and the lining tunnel. The computation result shows that the rock mass plasticity zone distribution with the lining structure is fewer than that without lining structure. To measure the deformation behavior, tunnel deformation measurement sensors are installed in the railway tunnel transverse section. The measured railway tunnel deformation result also shows that the lining structure deforms little and the rockmass is in stable state.

Abstract: Different kinds of fiber are used to reinforce the concrete to improve the concrete mechanical properties. The high modulus and high flexibility fibers are often used to reinforce in the cement base, which leads to the higher performance compound cement based materials. In the paper, the carbon fiber and glass fiber material are used as flexibility reinforced materials. The polypropylene fiber and the polyethylene fiber are used as strength reinforced materials. The combinations of the flexibility reinforced fiber and strength reinforced fiber are chosen as C-P HF (Carbon and Polypropylene Hybrid Fiber) and G-Pe HF (Glass and Polyethylene Hybrid Fiber). The concrete mixture ratio and the fiber-reinforced amount are determined to the author’s previous study. The relationship between compressive strength, flexural strength and length/diameter aspect ratio of fiber for the carbon and polypropylene hybrid fiber reinforced concrete (C-P HFRC), and for the glass and polyethylene hybrid fiber reinforced concrete (G--Pe HFRC) was tested and discussed. The testing results show that length/diameter aspect ratio of fiber obviously affects the flexural strength of C-P HFRC and G-Pe HFRC, though the compressive strength is slightly affected by the length-diameter aspect ratio.

Abstract: The parametric variational principle adopts the extreme variational idea in the modern control theory and uses state equations deduced from the constitutive law to control the functional variation, which is an effective solution to the nonlinear equations. Based on the fundamental equations of elasto-plasticity coupled damage problem, the potential functional of elasto-plasticity is constructed. Also the state equations with approximation of damage evolution equation and load functions are constructed in the paper. The solution of elasto-plasticity damage problem can be deduced to solve problem of the minimum potential energy function under the restriction of state equations. Thus the parametric variational principle for coupled damage is proposed. The variational principle has the virtue of definite physical meaning and the finite element equations are presented in the article to facilitate the application of parametric variatioal principle, which is easy to program on computer. Using the method mentioned in the article, a numerical calculation is carried out and the calculation result shows that the method is efficient for solving elasto-plasticity damage problem.

Abstract: The finite element analysis fully coupled fatigue damage evolution is implemented on the user subroutine UMAT of the finite element software ABAQUS. The fully coupled method developed with damage mechanics and the finite element analysis is performed on calculation of fatigue damage accumulation of the critical welded member in the Tsing Ma Bridge. The calculated result shows that the fatigue damage in the critical welded member is accumulated in the region of toe of welding. The value of faitgue life calculated by the fully coupled method is smaller than that by the uncoupled method, which suggests that there exists interaction between the fatigue damage evolution and the structural response. The linear Miner’s Law is widely used however conservative for the evaluation of fatigue life of bridge on service. The above results provide feasible method for accurate evaluation of fatigue damage in bridge components based on the hot spot stress analysis and the damage mechanics theory.

Abstract: The twin shear strength criterion has been proposed to consider the intermediate principal stress effect on the rock mass strength. The unified rock mass strength criterion could consider the intermediate principal stress effect on the rock mass strength. The unified rock mass elasto-plastic material model is implemented in ABAQUS user interface. As a case for study, the stability analysis of Dongjusi railway tunnel within hard rock mass is studied using the unified rock mass strength material. For comparison, the Hoek-Brown empirical strength criterion is also chosen for the rock mass material modeling. The computation results show that the plastic zone calculated using the unified rock mass strength criterion is smaller than that using the Hoek-Brown empirical strength criterion. The railway tunnel lining structure is designed according to the unified rock mass strength criterion and greatly makes use of the rock mass potential strength, which decreases engineering cost.

Abstract: Variability in the physical properties of rock mass is a major source of uncertainty encountered in railway tunnel stability analysis. The conventional safety factor method on stability assessment of railway tunnel within soft and weak rock mass can not represent the variability of rock mass. A formulation to compute the reliability of soft and weak rock mass, in which physical non-linearity is taken into account, is proposed. To consider the intermediate principal stress effect on the rock mass strength, the unified elasto-plastic strength criterion is proposed in the nonlinear finite element analysis. The unified rock mass elasto-plastic material model is implemented in ABAQUS user interface. The reliability analysis is performed in two steps. Firstly, the failure response is obtained by fitting the limit state function of the rock mass using the quadratic polynomial based on the nonlinear finite element analysis of the rock mass. Secondly, the JC method is proposed to obtain the design point and the reliability index of rock mass. As a case for study, the reliability analysis of Jinhuashan railway tunnel within soft and weak rock mass is studied using the proposed method. The two dimensional analysis is performed to consider the excavation stage effect and the unloading effect on the rock mass. Computation result shows that the rock mass is in stability.

Abstract: The fracture toughness and the fracture energy are obtained on the notched beams in three-point bending according to the RILEM draft recommendation. An experiment is designed to obtain the law on the alteration of the PPFRC’s (Polypropylene Fiber Reinforced Concrete) fatigue life and fatigue strength caused by the fibers. S-lgN curve is plotted according to the experimental data and fatigue is obtained through the Linear Regression. Theoretical analysis of the PPFRC’s bending fatigue characteristic is carried out. The fiber’s influence on the PPFRC’s fatigue behavior is stated and the fiber reinforcement mechanism is discussed. The result shows that the fiber can improve the PPFRC’s fatigue life and fatigue strength. The composition and development of the fatigue strain under the cyclic load are analyzed using experimental data. The law of the fatigue damage accumulation and evolution under cyclic load is studied. A fatigue damage mode, which can be used to predict the fatigue life of the PPFRC, is established.

Abstract: The behavior of crack growth with a view to fatigue damage accumulation on the tip of cracks is discussed. Fatigue life of welded components with initial crack in bridges under traffic loading is investigated. The study is presented in two parts. Firstly, a new model of fatigue crack growth for welded bridge member under traffic loading is presented. And the calculate method of the stress intensity factor necessary for evaluation of the fatigue life of welded bridge members with cracks is discussed. Based on the concept of continuum damage accumulated on the tip of fatigue cracks, the fatigue damage law suitable for steel bridge member under traffic loading is modified to consider the crack growth. The proposed fatigue crack growth can describe the relationship between the cracking count rate and the effective stress intensity factor. The proposed fatigue crack growth model is then applied to calculate the crack growth and the fatigue life of two types of welded components with fatigue experimental results. The stress intensity factors are modified by the factor of geometric shape for the welded components in order to reflect the influence of the welding type and geometry on the stress intensity factor. The calculated and measured fatigue lives are generally in good agreement, at some of the initial conditions of cracking, for a welded component widely used in steel bridges.

Abstract: Because there were many random factors, the failure analysis and reliability analysis of stochastic structural system was very difficult. In this paper, failure procedure and reliability analysis flow chart of stochastic structural system based on stochastic finite element were present. Establishment of the safety margin, reduced member stiffness matrix and opposite sign of the equivalent nodal force was analyzed in the failure process. Stochastic finite element method was adopt to solve the structures’ stochastic, and the reliability of structural system is evaluated by PNET method. According to probabilities of the failure paths redound to probability of failure of the structural system, the most significant failure paths was determined on the basis of the branch-and-bound method. Then, a classical 48-bar space truss problem is made as an example to illustrate the predominance of this algorithm, the calculation shows that the analysis of the failure process is justified; this methodology is efficient and useful for reliability analysis of large stochastic structural system.