Investigating high-temperature deformation evolution of concrete under sustained loading using DIC technology and a temperature-mechanical coupled damage constitutive model

Abstract

Based on digital image correlation (DIC) technology and uniaxial compression tests, the deformation evolution characteristics of concrete were analyzed in the heating process under a sustained load and in the failure process under uniaxial compression. The effect of the sustained load on the mechanical properties of concrete at high temperatures was explored. A damage constitutive model of concrete under the combined action of high temperature and the sustained load was established. The research results show that a sustained load can effectively restrain the vertical thermal expansion of concrete and compact loose and weak zones of concrete. However, when the load level or temperature is too high, excessive lateral deformation of concrete will cause local strain concentration and cracking failure. In the failure process under uniaxial compression, both high temperature and sustained load can make the macroscopic cracks more smeared and branched. When the temperature is 200 °C and 400 °C, the sustained load has only a little enhancement effect on the high-temperature mechanical properties of concrete. When the temperature is 600 °C and 800 °C, the sustained load can significantly enhance the mechanical properties of concrete at high temperatures. However, at higher temperatures, excessive sustained loads can cause premature failure of the specimen. Based on the Weibull distribution, a statistical damage constitutive model of concrete under the combined action of sustained load and high temperature is established, which is in good agreement with the test curve. The curve of the degree of damage of concrete Dm shows that the sustained load causes the damage Dm to start earlier, the damage rate to increase, and the degree of damage at the peak stress to increase in the failure stage under uniaxial compression.