Numerical Methods Of Shakedown Analysis With Its Appliction

Shakedown analyses the plastic behavior of structures subjected to variable loads and provides a rational tool for prediction of structural response. However, existing numerical methods are basically based on mathematical programming, which has deficiency of high computational costs and low efficiency solution and are difficult to apply to practical engineering. To solve the problems in research field of shakedown, a numerical method for shakedown analysis of structures had been established using plastic strain energy as shakedown criteria based on the lower bound theorem. The proposed method has more effective to solve the shakedown problem that using mathematical programming method. The proposed method had applied to different field in practical projects and shakedown theorem was extensively used. The gist and primary new findings of this dissertation includes:(1) The shakedown behavior of DH36 steel was experimentally investigated under uniaxial cyclic loading at room temperature. The effects of loading rates, loading wave forms, mean stress, stress ratio, stress amplitude and their histories on strain cyclic characteristics were studied. Based on the experimental data, the flow plastic properties of DH36 steel under cyclic loading were analysed. These conclusions are very useful to implement the numerical method.(2) According to test results of DH36 steel, solution based on energy principle was extended from beam structure to continuous structure. A numerical method for lower bound shakedown analysis of continuous structure had been developed. The method used plastic strain energy as shakedown criteria via a special load path and the just residual stress field was obtained. It avoids the operation of mathematical programming in traditional methods of shakedown analysis and therefore obstruction due to large scale mathematical programming is overcome.(3) The proposed numerical method of shakedown analysis was introduced to ultimate bearing capacity analysis of the brace of semisubmersible considering cyclic wave load. Based on the overall three-dimensional model, local model of brace was obtained. By applying the method to shakedown analysis of brace, influence of load angle, shell thickness, stiffener thickness and stiffener spacing on shakedown limit were studied. Numerical results show that shakedown limit increases with the increase of shell thickness and stiffener thickness, while decreases with the increase of stiffener spacing. In general, comparing with ?=90°, ?=0°is more dangerous.(4) The proposed numerical method of shakedown analysis was applied to evaluate bearing capacity of engineering structures under cyclic traffic load and effects of some parameters were investigated. The results reveal that shakedown limit between plastic limit and elastic limit is a rational evaluation parameter which can release the potential of materials on the premise of ensuring safety of structures.(5) Field monitoring and theoretical analysis were performed to study disturbance of the soil behind the reaction wall of open caisson induced by pipe jacking construction. Then, solution procedures for displacement prediction of the soil behind the reaction wall of open caisson were given on the basis of proposed numerical method. After the validity of the present procedures was illustrated by the monitoring data, the dependence of displacement on important parameters, including value and position change of reactive force, stiffness of soil, thickness of reaction wall, were investigated in details. It is shown that displacement increases with the raise of position of reactive force and increase of value of reactive force, decreases with the increase of stiffness, increases with the decrease of thickness of reaction wall.