Ultimate Load-bearing Capacity Evaluation Of Steel Penstock Considering Materiil Strain-hardening Effect

Ultimate load-bearing capacity is an important indicator of safety evaluation and engineering design.At present,most methods for estimating ultimate load-bearing capacity of steel penstock are often based on the assumption of ideal elastic-plastic material model without considering the influence of materia strain-hardening.However,influence of strain-hardening on the ultimate load-bearing capacity of steel penstock is significant.To make full use of material,consideration of strain-hardening to evaluate ultimate load-bearing capacity is needed.In this paper,research is performed to evaluate the ultimate load-bearing capacity of steel penstock consideration of strain-hardening effect.The main contents are as follows:(1)The material models--bilinear hardening,power hardening,ASME and Ramberg-Osgood models,were built based on theoretical analysis and experimental date and based on these material models,we put our research on the effect of material model on estimating ultimate load-bearing capacity and failure evolution.Comparative analyses based on goodness-of-fit show that these material models could reflect the authentic mechanical function of material.It can be concluded that,the ultimate load-bearing capacity of steel penstock considering the strain-hardening effect could be increased by 20%or more as compared with that considering ideal elastic-plastic constitutive.Four chosen material models did not much affect the ultimate load-bearing capacity of steel penstock and the error between them was within 8 percent.(2)A method for estimating ultimate load-bearing capacity considering strain hardening was proposed.By equating the strain energy of elastoplastic constitutive considering strain hardening with that of the ideal elastic-plastic constitutive,this article proposed two methods to calculate equivalent yield strengths based on stress-strain curve or yield strength and tensile strength.It can be concluded that the equivalent yield strength based on yield strength and tensile strength could be employed for estimating ultimate load-bearing capacity of steel penstock conveniently,and the error from the experimental value was less than 10 percent.(3)An elastic modulus reduction method(EMRM)for ultimate load-bearing capacity of steel penstock considering strain hardening effect is presented.Based on above-mentioned the equivalent elastic perfectly-plastic material model,the element bearing ratio(EBR)was defined,and the reference EBR was given and used to dynamically identify certain high elements under high load.The elastic modulus adjustment strategy was proposed according to the principle of conservation of deformation energy,and the EMRM considering material strain hardening effect was presented.This efficient and convenient method provided a new approach to estimating ultimate load-bearing capacity of steel penstock.