Seismic Risk Assessment Of RC Frame Structures Considering Aging Effects

For structures in harsh environments,reinforcement corrosion and concrete cracking are manifestations of aging of concrete structures.The aging of concrete structures degrades the seismic performance of structures,and if the aging process is ignored,its seismic risk may be underestimated.Therefore,this paper studies the impact of steel corrosion and concrete carbonization on the performance of each limit state of a frame structure.The mean value of the structural deformation capacity corresponding to each limit state of the structure is defined as a function of time,and the probability of each limit state of the structure considering the aging effect is obtained by considering the annual average failure probability integral of the aging time on each limit state of the structure.Firstly,a seismic risk assessment method considering structural aging effects is proposed,and then this method is applied to aged RC frame structures with different fortification intensities,heights,and periodic reductions to study the impact of structural aging effects on seismic risk at various limit states.The main content of this article is as follows:(1)The causes of reinforcement corrosion and concrete carbonation are introduced,and the degradation models of reinforcement elongation,reinforcement yield strength,tensile strength,wrapped concrete strength,bond strength,and bond slip amount affected by reinforcement corrosion and concrete carbonation are summarized and compared.(2)Design 9 RC frame structures and aging structural models corresponding to each aging time point according to Chinese standards,and verify the rationality of the finite element model.The establishment of an aging structural model is to approximately simulate structural aging by selecting a degradation model for the performance of reinforced concrete materials to degrade the structure.(3)The effect of material degradation on the vulnerability of aged RC frame structures is studied to lay the foundation for seismic risk analysis of aged RC frame structures.(4)A seismic risk assessment method considering structural aging effects is proposed and used to assess the seismic risk of aging RC frame structures in various limit states in different intensity regions,different heights,and different period reduction coefficients.Finally,the seismic risk of RC frame structures in different intensity regions,different heights,different period reduction coefficients,and different aging times is compared.The research results indicate that the seismic risk of the nine RC frame structures designed in this paper with different fortification intensities,heights,and periods considering aging effects is greater than that of structures without aging effects.Among them,the RC frame structures with 6,7(0.1g),7(0.15g),8(0.2g),and 8(0.3g)degree fortifications have an average annual probability of collapse exceeding 100 years of aging,which is 34.84%,48.24%,51.77%,27.76%,and 29.08% higher than the probability of structures without aging effects,respectively;The average annual probability of collapse exceeding for three story,five story,and eight story RC frame structures considering aging for 100 years is 35.62%,48.4%,and 34.15% higher than that of structures without aging effects,respectively;RC frame structures with a period reduction of 0.7,0.85,and 0.9 have an average annual probability of collapse exceeding 100 years of aging,which is 15.18%,48.24%,and 27.80% higher than structures without aging effects,respectively.