Creep Behavior Of Axially Loaded Reinforced-Concrete Stub Columns Constrained By Steel Tubes Under Sustained Loading

Compared with the traditional concrete filled steel tubular(CFST)column,the tubed reinforced-concrete columns(TRC)improve the concrete filled steel tubular(CFST)columns in the many aspects that exist in the actual engineering application.TRC has the characteristics of simple joint connection,high bearing capacity,good ductility and excellent fire resistance,etc.In recent years,TRC has been widely applied in many new priority projects in China.At present,some studies have shown that designers pay more attention to the creep behavior of CFSTs in structural design.Therefore,the creep performance of TRCs shall also be studied in practical engineering design.However,the research on the creep behavior of TRCs is still in its infancy.Therefore,this thesis intends to provide a further understanding of the linear creep behavior of axially loaded reinforced-concrete stub columns constrained by steel tubes under the sustained low stress level.The main work is presented as follows:The linear creep prediction model of concrete under uniaxial compression and the linear creep prediction model of concrete under multiaxial compression were studied.On this basis,the calculation procedure and formula for calculating the long-term deformation of TRC members was derived considering the interaction between concrete,reinforcement and steel tube.Case study was done to calculate the creep deformation of TRCs by using different plain concrete creep prediction models.Considering the influence of concrete strength and loading age,the long-term tests of 8 TRC specimens were carried out.The long-term deformation-time curve of the specimens were obtained after 480 days of data collection.The axial compression tests of 2 steel tube confined concrete columns were carried out,and the stress ratio range which makes the creep of confined concrete meet the multi-axial creep theory of concrete was studied.Five kinds of plain concrete creep prediction models were introduced into the creep prediction model for TRCs under axial compression.And the calculated results were compared with the test results to selecte the creep prediction model suitable for long term deformation calculation of TRCs.The creep deformation of three kinds of members was calculated so that the influence of the constraint action on the creep deformation of core concrete was studied.Different algebraic methods were applied to the creep modelling of TRCs and their applicable scope was investigated.The influences of the concrete strength and the concrete age at first loading on the creep behaviour were discussed based on the measured long-term deformation.