Study on Long-Term Behavior and Ultimate Strength of CFST ColumnsQ

摘要

Long-term tests (864 days) were conducted on three types of columns,rnincluding plain concrete (PC) columns, reinforced concrete (RC) columns andrnconcrete-filled steel tube (CFST) columns. The shrinkage and creeprnperformance and the ultimate strength of the columns were tested andrnanalyzed. The results show that the shrinkage strain of RC columns is aboutrn87.6% of that of PC columns, the shrinkage strain of the CFST columns isrnabout 34.8% of that of PC columns, and that the effect of expansion agent onrnshrinkage strain is about 2% for the PC columns. It was also found that thernsmaller the loading age, the greater the creep coefficient. Reinforcement canrnsignificantly reduce the creep deformation of PC columns. The creeprncoefficient of steel pipe surface is larger than that of inner concrete for CFSTrncolumns, leading to a longer life due to the creep of inner concrete to achievernstability. The loading age and the reinforcement have great impact on extremerncompressive strain and ultimate strength. The hoop effect of RC columns isrnobvious. Loading rate influences the stress redistribution of CFST columns.rnThe stress redistribution effect is relatively small for columns with loadingrncourse. However, the effect on the ultimate strength is very small for columnsrnwith or without loading courses. The difference of two is only 2.4%.