CREEP CALCULATION AND BEHAVIOR ANALYSIS OF CONCRETE-FILLED STEEL TUBULAR MEMBER UNDER AXIAL COMPRESSION

In order to analyze the effect of concrete creep on long-term behavior of concrete-filled steel tubular member under axial compression, the theoretical model of stress and strain at a member cross-section which changes with concrete age was deduced by taking the internal force redistribution into account. Based on the comparison between the experimental results and the calculated ones, the new model was verified and model Huo is selected as the most suitable model among the existed 12 types of creep coefficient calculation model. The stress and strain at the cross-section of a concrete-filled steel tubular member under axial compression were analyzed until the age of 10000 days, and the factors affecting the creep behavior were discussed, including concrete strength, environmental relative humidity, loading age, steel ratio, member length and cross-section stress level. The results show that, as the age grows, the stress of the steel pipe increases gradually with the maximum increment being 61.4% of the initial stress, and the concrete stress decreases with the maximum stress reduction being 26.2% when the axial force is less than 60% of its ultimate bearing capacity; the creep strain of the concrete-filled steel tubular member increases quickly at the beginning, and slows down after 1000 days, and the ultimate strain is about 1.60 times of the initial one. With the same axial compression ratio, the creep strain of the concrete-filled steel tubular member increases gradually with the core concrete strength grade improving; the creep strain of the concrete-filled steel tubular member decreases significantly with the increasing of steel ratio; with the increases of environmental relative humidity, loading age and member length, the creep strain of the concrete-filled steel tubular member increases. Axial compression ratio has the most significant influence on the creep of concrete-filled steel tubular member under axial compression. The creep strain increases with the increasing of axial compression ratio when the compression ratio is less than 0.6. The study provides useful references for the creep calculation and creep control of concrete-filled steel tubular members under axial compression.