The Research On Safety Mechanics Of Bridge Structure Impacted By Sea Ice And Its Application Under Condition Of Frost And Thaw

Along with the development and utilization of marine space, Cross-sea bridge are springing up like bamboo shoots after a spring rain everywhere, based on its incomparable economic and social benefits, with distinctive architectural concept and endless innovative techniques. Alien from the other bridge structure, the lower support structure of Cross-sea Bridge is in the complex environment of the ocea. Its design, construction and operation will be many more competitive and difficulty. Especially for the bridge structure in the frozen waters, the multiple corrosion environment such as salt, freezing and thawing, sea ice, wave, current and so on seriously impact the safety and reliability of the units.The ice-induced vibration of structure, which impact by mass of ice sheet, can not only cause fatigue damage of structure, but also may lead the upper structure or equipment to damage and failure rupture.In addition, the long-term damage of freeze-thaw cycle to concrete structure will also affect the durability and security of bridge structure.At present, the sea ice has been one of the main environment factors and control loads that can not be ignored in the design prograss of bridge and offshore engineering structures.To ensure the security and stability of the sea-crossing bridge in frozen water, extensive efforts were made to improve the mechanism of interaction between ice and structure,which will provides scientific designing parameters and offer the important theoretical basis to the design, construction and operation of similar bridge works. At present, this research is also growing concern by the engineering community, who put forward more and more detail standards and feasible requirements on maritime engineering. So.the more pressing needs and strict requirements are put forward to the research on the mechanism of ice-structure interaction, safety evaluation and so on.In this paper, considering the decay of concrete freeze-thaw damage, the ice-induced vibration and other factors.A series of comprehensive and systematic studys were carried out on the characteristics of the structural dynamic responses influced by ice thickness, ice velocity, structural shapes, concentrated mass on the structur tops respectively by using nonlinear dynamic analysis software ANSYS/LS-DYNA.Based on the cohesive material coupling ice model was set up,the structural dynamical responses subjected to the pile spacing, aspect ratio and the stiffness of the structure respectively were numerically simulated. Based the engineering background of Qingdao Bay Bridge, the ice-induced respects of the bridge structure during different service period were analysed. This work are following:1. Development of the constitutive relationship for concrete suffered freeze-thaw damage.According to analyzing the results of indoor test, the mechanical properties of concrete suffered freeze-thaw damage with different cycles were studied. The constitutive relationship for concrete suffered freeze-thaw damage was suggested in the basis of the theory of fracture mechanics.It can be seen through the constitutive relations, with the increase of concrete freeze-thaw cycles, the stress-strain relationship curves tend to be flat, and peak stress was significantly reduced, the stress peak value corresponding to the strain value would increase gradually. The area under the curve was reduced; it was shown that energy dissipation capacity of material decreased gradually.2. Research on the structural dynamic responses induced by ice sheet and influencing factors.On the base of the theoty analysis, a series of finite element model of interaction between ice and structure was established on the basis of ANSYS. By calculating the models and showing the courses of the rock blasting process with nonlinear explicit dynamic finite-element program LS-DYNA, the characteristics of the structural dynamic responses influced by ice thickness, ice velocity, structural shapes and concentrated mass on the structur tops respectively were presented. The results showed that the above factors have different effect on the mode of ice sheet failure and the the characteristics of the structural dynamic responses.From the analysis of physical process and the influence degree of the different variables, the dynamic mechanism of interaction between ice and structure was explored.3. Establishment of the cohesive material coupling ice model and its application in numerical simulation.According to the mode of ice failure with a wedge-shaped edge during ice-vertical structure interaction and the material mesoscopic structure of ice, based on the cohesion theory of crack nucleation and extended, the cohesive material coupling ice model was established.By use of integrated and huge range of material modelbase systems of LS-DYNA, the finite element model of ice forming of several sorts of materials was achieved. By using nonlinear explicit dynamic finite-element program LS-DYNA, which can deal with fluid-solid coupling algorithm, the structural dynamical responses subjected to the pile spacing, aspect ratio and the structure stiffness respectively were numerically simulated. Some useful conclusions are obtained from the computational results. The results are useful to the construction and design of the similar bridge to a certain extent.4. Research on the ice-induced dynamic responses of substructure of bridge suffered freeze-thaw damage in different term of military service.Based the engineering background of Qingdao Bay Bridge, two kinds of the most unfavorable structure were selected. To take the adverse effect of freezing-thawing of concrete on bearing capacity into account, the finite element models of interaction between ice and structure were established by using of the cohesive material coupling ice model. With fluid-solid coupling algorithm of LS-DYNA, the physical process of interaction between ice and structure were simulated with the most unfavorable twelve combined operating conditions.It can be concluded from simulation results that with the dying out of the mechanics properties of concrete and the decline of structure rigidity, the relative ice force peak, max structure displacement and acceleration were increased. In addition.under the high-designed water level work condition, the max structure displacement increased more.That is to say the larger max structure displacement and acceleration would be occurred under the same external forces as service time prolonging, and the ice-induced vibration was more likely to suffer.so,to ensure the security of sea-crossing bridge in the whole process of design, construction and operation, more attentions should be paid to the serious effect caused by ice-induced vibrationthe with the years.