Study On Effect Of Steel Corrosion On Seismic Capacity Of Concrete Bridge Piers

Piers are important components of bridge structures which are mostly constructed with reinforced concrete.Owing to weak crack resistance of concrete,it is usually unavoidable that the reinforcements of piers get rusty in their service period.China is one of countries with the most intense seismic activities and rusty reinforced concrete piers must withstand tests of earthquake in seismic zones,so it is necessary to investigate seismic capacity of rusty reinforced concrete piers.This paper takes the single-column pier as the research object,the impacts of reinforcement corrosion upon seismic capacity of concrete piers were studied,the research work are mainly as follows:(1)After consulting lots of related literature,the ways for considering rusty reinforced concrete structures were investigated and a method for numerically modelling rusty reinforced concrete piers was put forward.Besides,this method was verified to be reliable by simulating existing cyclic loading tests of rusty reinforced concrete piers.(2)Seismic capacity of piers was studied by pushover method in three cases,only longitudinal reinforcements corrosion,only stirrups corrosion,both longitudinal reinforcements and stirrups corrosion.The results suggest that the corrosion of longitudinal reinforcements mainly impacts ultimate bearing capacity of piers;corrosion of stirrups is a major factor affecting displacement ductility;when both longitudinal reinforcements and stirrups corrode,the ultimate bearing capacity and displacement ductility of piers decline with the increase of reinforcement corrosion rate;in particular,the ultimate bearing capacity declines rather significantly,and its decrease is as high as 38.9% for a corrosion rate of 50%.(3)Seismic capacity of piers with both corroded longitudinal reinforcements and stirrups was corroded in the seismic intensity level 7,8 and 9 zone respectively.The evaluation results indicate that under the seismic impacts,the pier damages deteriorate a lot with the increase in the corrosion rate of reinforcements.For piers with a seismic intensity of 7(E2),they will be only slightly damaged when reinforcements are not corroded and they will be severely damaged in case that the corrosion rate is 50%.The damages differ a lot among piers with the same corrosion rate under the impacts of varying seismic intensity.The piers with a seismic intensity of 7,8 and 9(E2)will be subject to moderate,severe and collapse damages provided that the corrosion rate is 40%.(4)The seismic capacity of corroded reinforced concrete piers in a single seismic record was examined by IDA method.The results suggest that the seismic capacity of piers declines with the increase in corrosion rate of reinforcements.Impacted by near-field non-pulse,far-field,far-field pulse type earthquakes,the seismic capacity of piers is less and less sensitive to the corrosion rate of reinforcements.When the corrosion rate is the same,the seismic capacity is the highest under the impacts of the near-field non-pulse type earthquake,followed by far-field and near-field pulse type earthquakes successively.(5)IDA method was applied to study the seismic capability of the pier with corroded steel bar under the effect of multiple seismic records,the result shows that the seismic capability of the pier with corroded steel bar decreases significantly with the increase of steel bar corrosion rate under the effect of pulse ground motion and non pulse ground motion in multiple seismic records,among which the seismic capability of the pier with a steel bar corrosion rate of 40% decreases by 31.91% under the effect of pulse ground motion and declines by 30.87% under the effect of non pulse ground motion.Furthermore,the seismic capability of the pier under the effect of non pulse ground motion is basically three times more than that under the effect of pulse ground motion on the condition of the same steel bar corrosion rate.(6)Seismic vulnerability analysis is made on the pier with corroded steel bar,the result shows that the seismic vulnerability of the pier with corroded steel bar increases significantly with the increase of steel bar corrosion rate under the effect of pulse ground motion and non pulse ground motion,and the speed of seismic vulnerability increasing with the increase of PGA of the pier under the effect of pulse ground motion is much faster than that of under the effect of non pulse ground motion on the condition of the same steel bar corrosion rate.Taking the pier with a steel bar corrosion rate of 40% under the effect of 0.4g pulse ground motion as an example,the probability of destruction of the pier under the pulse ground motion is 99.09%,while under the non pulse ground motion is 18.67% only.