# Seismic Performance Evaluation of Highway Bridges under Scour and Chloride Ion Corrosion
## 4 Conclusions  
For the joint action of scour and earthquake, the analysis method to obtain sub-factors of the action with reasonable consideration of joint hazards was proposed. Furthermore, the effect of Cl\({}^{-}\) corrosion on seismic performance of bridge columns was investigated by conducting pseudo-static tests on three groups of reinforced concrete columns. The specific conclusions are as follows:  
1. The restraining effect of soil on the pile foundation was weakened due to scour action. It was found that the fragility of bridge columns decreased while the fragility of pile foundation increased with the increase of scour depth. The non-linear relationship between scour depth and failure probability of pile foundation could be determined by vulnerability analysis under the combined action of scour and earthquake. 2. The distribution of PGA corresponding to basic intensity of earthquake in the bridge site area was studied, according to which the distribution of seismic effect could finally be determined. The IDA curve of the seismic effect was established. Both a quantitative description of seismic input and a definite functional expression for the output of the seismic effect could be achieved. 3. The joint distribution of scour depth and seismic failure probability was established to determine the reasonable scour depth. The sub-factor considering the combination of scour action was calculated so that the combined expression for the joint action could be obtained as shown in Equation (16). 4. Strength and bulk stability of the concrete were affected by Cl\({}^{-}\) corrosion as the result of severe corrosion of the reinforcement, which had a serious impact on the performance and durability of the reinforced concrete columns. 5. Cl\({}^{-}\) corrosion caused a remarkable reduction in yield resistance, peak resistance, and ultimate resistance of columns. A decrease of 56.35%, 88.01%, and 75.2% in cumulative hysteretic energy dissipation of columns at ultimate displacement occurred, respectively, due to Cl\({}^{-}\) corrosion. The equivalent viscous damping coefficient of corroded columns was always greater than the corresponding un-corroded columns before ultimate displacement. At the same stage, plasticity development of the corroded columns was larger, which indicates that corroded columns were more prone to damage. 6. Ductility properties of medium-high columns with medium and high reinforcement ratios could be significantly weakened by Cl\({}^{-}\) corrosion, whose displacement ductility coefficients dropped by 41.56% and 46.85%, respectively. For columns with low reinforcement ratios and low heights, the displacement ductility coefficient increased by 3.91% while the hysteresis loop area shrunk by 56.35%, which indicated that there is a limitation in judging seismic performance of columns by ductility coefficient only. * 7 Through the two-parameter model, it was found that the aggravation degree of seismic damage on columns caused by Cl\({}^{-}\) corrosion rose linearly with the increase of displacement, which eventually resulted in the damage index of corroded columns growing to twice that of the uncorroded columns at ultimate displacement. Indexes of displacement and energy dissipation should be taken into account in selecting reinforcement ratio for ductile columns simultaneously. The bridge type in the project on which this paper is based is relatively homogeneous, which limits the investigation to summarizing the influence of the combination of subfactors on the seismic design condition effects of different bridge types. The quantitative analysis of the coupling between scour and erosion, for instance, the effect of the increased eroded area due to scour on the seismic performance of the bridge substructure, is one of the areas to be further investigated in future studies. Conceptualization, M.Z. and S.Y. ; methodology, G.Z. ; software, J.F. ; validation, M.Z., S.Y., G.Z. and J.F. ; formal analysis, M.Z. and S.Y. ; investigation, M.Z., S.Y., G.Z. and J.F. ; resources, M.Z. ; data curation, G.Z.