Seismic Damage Analysis Of Heightened Concrete Gravity Dams Considering Material Aging

Due to the increasing demand for water resources,sediment deposition and changes in operating conditions,a number of existing concrete dams need to be heightened.The dynamic response of concrete dam will change significantly with the increase of concrete age and degradation of concrete performance,and the influence of new and old concrete materials is also faced with the heightened gravity dam.Research on this issue is scarce at home and abroad.In this paper,on the basis of existing research,considering the material aging during operation and differences between new and old concrete materials,a non-overflow section of Danjiangkou heightened gravity dam was taken as an example of seismic dynamic response analysis.The displacement of dam crest,stress and damage are compared with that of demolishing and rebuilding(new material condition)and assuming that the dam is built at the beginning of design according to the height after elevation(old material condition).Specifically,this paper has carried out research in the following aspects:(1)Material aging is incorporated into the dynamic damage constitutive model of concrete.Based on the fitted degradation model of aged concrete,the relationship between elastic modulus,tensile strength,compressive strength of concrete at different ages was obtained,and the Concrete Damaged Plasticity(CDP),which is commonly used for dynamic response analysis of Concrete structures,was improved.It provides a constitutive model basis for subsequent dynamic analysis of the gravity dam.(2)Analyze the response of natural vibration frequency,crest displacement,key point stress and plastic damage of gravity dam with the aging of concrete material under seismic force.(3)Analysis of crest displacement,stress at key points and plastic damage of heightened gravity dam with concrete aging under oblique incidence of P wave and SV wave.The numerical simulation results show that the seismic dynamic response of the heightened gravity dam is obviously different from those of the new material condition and the old material condition.As the aging degree of concrete material increases,the earthquake damage of the heightened gravity dam passes through the neck of the old dam and tends to extend downward toward the combination of new and old concrete.However,the damage of the material in the whole new condition is small,and the main crack and secondary crack of the material in the whole old condition are nearly parallel.In addition,the impact of incident angle of ground motion on gravity dam is also significant.P wave is more likely to cause damage extending to the joint surface of new and old concrete than SV wave.