Simple model of creep coefficient for expansive concrete filled steel tube

Through long-term test on the shrinkage and creep of eight concrete circular columns specimen for more than800 days in the indoor environment,and the comparison of time history of shrinkage and creep among different types of cylinders,including concrete cylinder,concrete filled steel tube and expansive concrete filled steel tube,the shrinkage and creep properties of expansive concrete filled steel tube were obtained. Results show that shrinkage strain of expansive concrete filled steel tube is small,and the early shrinkage deformation is almost zero due to the influence of expansive agent. The creep deformation of expansive concrete filled steel tube changes a lot within 100 d and is almost unchanged after 100 d. The time-varying regularity of creep coefficient is basically identical with concrete filled steel tube. Under a reasonable assumption of creep mechanism for expansive concrete filled steel tube,an estimation method of final creep coefficient of expansive concrete filled steel tube was proposed,based on elastic continuation and plastic flow theory and creep theory with multiaxial stress. This estimation method of expansive concrete filled steel tube can obtain the sum of three extremums of recoverable lag elastic deformation, the initial irreversible rapids plastic deformation and unrecoverable viscous flow,and can account for the time-varying regularity of the measured values of expansive concrete filled steel tube. The formula is simple and has reasonable accuracy after comparison with test results.