Research On Residual Life Of RC Columns Of Coastal Substations In Fujian Province

According to the field investigations,on-site inspections,design papers and existing research,this article has conducted a disease investigation on the damage to the frame columns with the atmospheric environment in the coastal area in Fujian and the special stray current working environment of substations,and conducted a disease investigation on the reinforced concrete of the substations in service.The life of the frame column is analyzed,and the main research results are as follows:(1)The results show that the common diseases of substation frame columns can be summarized into three categories:concrete deterioration;steel reinforcement corrosion;and damage caused by process factors,such as formwork joints,steel ring joints,etc.(2)The corrosion characteristics of the frame column have obvious local differences in the members,and the corrosion of the root and the top of the member is more serious than that of the shaft.In the precast production process of reinforced concrete frame columns,the thickness of the concrete protective layer of different components is different,and the ratio of the protective layer to the diameter of the steel bar is different,and the damage modes that ultimately lead to concrete cracking are divided into two forms:along the bar crack and concrete spalling.The study also found that the damage and corrosion degree of substation frame columns in the coastal areas of Fujian gradually weakened with the increase of the distance from the coastline,showing roughly three grades.(3)Research shows that the corrosion deterioration of substation frame columns in the coastal areas in Fujian is affected by many corrosive media such as chloride,carbonization,acid rain,stray current,etc.At the same time,the high-temperature and high-humidity climatic environment in the coastal areas of Fujian accelerates the corrosion rate.Based on the actual engineering corrosion situation,combined with literature research,according to the distance between the substation and the coastline,the corrosion zoning of the frame column can be divided into three categories.(4)According to the existing literature research,it is proposed to adopt the "dual state" method of steel corrosion depth limit state and bearing capacity limit monitoring state to evaluate the remaining life of the structure.When the component exceeds the corrosion depth limit state of the steel bar,it means the life of the component ends.When entering the monitoring state of the bearing capacity limit,the damaged components should be repaired as soon as possible,and the reference formula for calculating the bearing capacity after the corrosion of the steel bar is given.(5)Based on the existing research models,the carbonation calculation model considering the influence factors of acid rain and the calculation model of chloride ion diffusion in concrete under the coupling effect of stray current and chloride salt were established,and actual engineering projects were selected for life calculation and analysis..The results show that acid rain has a greater impact on the overall life of the components.Taking into account the stray current,it will shorten the time for the steel to corrode in the chloride environment.The calculation results of the proposed model are in good agreement with the actual situation.As the shaft is prone to micro-cracks during the production process,the actual total life of the component will be shorter than the result of the theoretical calculation model.In addition,the difference in the thickness of the protective layer caused during the production process of the frame column will cause different forms of concrete cracking and damage,which will accelerate the overall deterioration of the structure,which is more significant than the deterioration of other structures in the substation.(6)The damage caused by environmental effects is identified through visual inspection into the following three states:there is material performance degradation,component damage occurs,and the structural performance of the component is seriously affected.It also puts forward suggestions for repairing damaged substation frame poles and assembled joints in the coastal areas of Fujian.