Elastic Modulus Reduction Method Based Integral Safety And Fatigue Evaluation For Engineering Structures

Integral plastic collapse and fatigue damage are the two main failure modes of engineering structures. Its corresponding analysis theory and methods are important research subjects in structural safety assessment. The selection of the assessment index and its solution method are the key problems. In this paper, research works are performed on integral safety and fatigue evaluation methods for the failure modes mentioned, which is based on the elastic modulus reduction method (EMRM) proposed by our research group. The main contents are as follows:(1) An EMRM based integral safety evaluation method which incorporating strain hardening effect is presented. The safety evaluation method using ultimate bearing capacity as evaluation index is introduced. By equating the strain energy of elastoplastic constitutive considering strain hardening with that of the ideal elastic-plastic constitutive, the equivalent yield strengths for bilinear hardening, power hardening and Ramberg-Osgood models are obtained. The calculation method for ultimate bearing capacity considering strain hardening is put forward combining the elastic modulus adjustment strategy and limit load solution technique of the EMRM. Then a concise and efficient structural integral safety evaluation method is presented.(2) The EMRM based local strain and structural strain analyses are proposed. The definition of modified yield strength is introduced from the generalized local stress strain method into defining the element bearing ratio and reference element bearing ratio for elastic-plastic strain analysis. The elastic modulus adjustment strategy of EMRM for the plastic strain analysis is established, then a calculation method is given by two linear elastic iterative finite element analyses. Then the structural strain is provided by linearization of local strain along the control section. The EMRM based structural strain can overcome the problem of low precision of strain solution by Neuber rule in the ASME Boiler&Pressure Vessel code.(3) An EMRM based fatigue evaluation method for welded structures is presented. The structural stress based Master S-N method of ASME Boiler&Pressure Vessel code is adopted and verified on its applicability for high-cycle fatigue evaluation. The low-cycle fatigue evaluation method combined with the Master S-N and structural strain is also validated. Then the fatigue evaluation method using the Master S-N and structural strain obtained from the EMRM is proposed and verified, which can be used as a unified and effective fatigue evaluation method of welded structures for high-cycle and low-cycle fatigue.