| The RC structure located in northern China is often affected by freeze-thaw,especially the bridge substructure in rivers.Due to the effect of alternating dry and wet conditions,it is easy to cause freeze-thaw damage in areas with fluctuating water levels.After many freeze-thaw cycles The mechanical properties of materials and components will be reduced,which will affect the seismic performance of the bridge to a certain extent.As the bridge pier is an important part of the bridge structure,it is also a part that should be studied in the seismic response analysis.This article takes the pier column as the object to study its seismic performance after freeze-thaw damage.The main work is as follows:1.On the basis of referring to the existing literature,the previous research on the bonding mechanism of steel and concrete under freeze-thaw damage was collected,and an analysis and summary was made to this.It is due to two factors: one is the reduction of the protective effect of the protective layer;the second is the reduction of the strength of the concrete.Based on the existing bond-slip constitutive model and the existing freeze-thaw bond-slip test,the Wu model was modified to establish a bond-slip constitutive model suitable for freeze-thaw damaged concrete.2.Based on the collected freeze-thaw bond slip test(pull test)data,the bond slip constitutive model under the freeze-thaw damage proposed in the first part is verified,and on the basis of the new model,combined with the micro The meta-algorithm derives the longitudinal steel slip model suitable for freeze-thaw damaged concrete,and applies it to zero-length section elements,and constructs a zero-length fiber model of reinforced concrete members considering the effects of bond slip under freeze-thaw damage.Based on the low-cycle repeated loading test of the existing freeze-thaw RC column,the rationality and accuracy of the zero-length fiber model established in this paper were verified from a qualitative and quantitative point of view,and the freeze-thaw damage considering only the degradation of concrete strength Compared with the model,the model in this paper is in good agreement with the experimental data,that is,it can more accurately simulate the seismic response of reinforced concrete columns after different degrees of freeze-thaw damage.3.With reference to the ATC-63 report,36 ground motion records were selected from the strong earthquake database of the Pacific Earthquake Engineering Research Center(PEER).Based on the previous zero-length fiber model,the destruction of the bonding performance by freeze-thaw and the cross-section concrete caused by freezethaw were also considered.For non-uniform damage,the elasto-plastic finite element dynamic analysis model of pier columns with standard freeze-thaw cycles of 0,200 and 300 times was constructed using OpenSees finite element software.The peak acceleration of the ground was used as the ground motion strength parameter,and the pier top was shifted laterally.Angle is used as the damage index.Incremental dynamic analysis of RC piers under different freezing and thawing conditions was carried out to study the response of the pier columns under three types of earthquakes and the effect of freezing and thawing on the seismic response of the structure.The results of numerical simulation analysis show that under the action of three types of ground motions,as the number of freeze-thaw cycles increases,the seismic performance of the pier columns will decrease to varying degrees,especially under the action of near-field pulse earthquakes.The impact of seismic performance is the most significant,and attention should be paid to the seismic design of the structure.At the end of this paper,the factors other than freezing and thawing that affect the seismic response of the pier column are expanded,and the seismic response of the bridge with different characteristic parameters(concrete strength,shear-span ratio,axial compression ratio,stirrup ratio)is analyzed. |
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