Mesoscopic discrete modeling of multiaxial load-induced thermal strain of concrete at high temperature

This work presents a mesoscopic discrete model of load-induced thermal strain (LITS) as part of the Lattice Discrete Particle Model at high temperature (LDPM-HT) that captures the experimentally observed deformations and mechanical responses of concrete heating up to 800 °C under multiaxial loads. In the proposed model, the LITS is decoupled into elastic strain increment due to thermal degradation, and thermo-mechanical strain at the mesoscale. As the most important component, the mesoscopic thermo-mechanical strain is decomposed into a normal and two shear components. The normal component in compression of the thermo-mechanical deformation at the mesoscale controls the macroscopic LITS in the load direction, while the mesoscopic thermo-mechanical strain components in normal tension and shear directions dominate the macroscopic LITS in the unloaded directions. The correctness and accuracy of the improved LDPM-HT are demonstrated by simulating two experimental investigations, namely a heating test up to 800 °C with uniaxial load and a heating test up to 250 °C with multiaxial loads.