Limit And Shakedown Analysis And Its Application Research In Bearing Capacity Safety Assessment Of Penstocks

In bearing capacity analysis and safety assessment of engineering structure, the numerical method for limit and shakedown analysis is a key problem, and is also a popular research subject in hydraulic and civil engineering recently. Based on the elastic modulus reduction method proposed by our research group, some innovation work on numerical method for limit and shakedown analysis is carried out, and is applied to safety assessment of penstocks. The main contents include:(1) Two kinds of high efficient element bearing ratio based limit load multiplier are presented on the basis of elastic modulus reduction method (EMRM). According to the existing elastic modulus adjustment strategies of EMRM, the stress based upper and lower bound limit load multipliers are investigated, and then two kinds of high efficient element bearing ratio based limit load multipliers are proposed, and then applied to the ultimate bearing capacity analysis and safety assessment of penstocks.(2) EMRM based shakedown analysis method is presented for proportional loading. According to the lower bound shakedown theorem, the elastic iteration process of EMRM is adopted to simulate of the structural damage evolution process, the self-equilibrium field is obtained by removing elastic stress field from iterative stress field, and then shakedown load multiplier under proportional loading is gained by making self-equilibrium field and iterative stress field both not violate yield condition. At the same time, the efficient approach of element bearing ratio based shakedown load multiplier is determined and applied to the shakedown analysis of penstocks. (3) Element bearing ratio based path tracking method of shakedown analysis is proposed. Element bearing ratio, expressing bearing condition of element, is introduced to path tracking method of shakedown analysis. The damage evolution process is simulated by elasto-plastic incremental analysis, the self-equilibrium field is obtained by removing corresponding elastic stress field from elasto-plastic stress field, and then shakedown load multiplier under proportional loading is gained by making self-equilibrium field and elasto-plastic stress field both not violate yield condition. Meanwhile, the approach is applied to the shakedown analysis of penstocks.