EQUATION AND NUMERICAL SIMULATION ON MULTISCALE STRESS RESPONSE OF CONCRETE

Aiming at the multi-phase and multi-scale composition characteristics of concrete and its complicated mechanical response problem, firstly, according to the geometric characteristics of constituent material in concrete, C-S-H gel, hardened cement paste, cement mortar and meso-scale concrete were respectively regarded as composite materials at different scales of concrete, including the nanoscale, microscale, sub-mesoscale and mesoscale, and their simplified geometric models were reconstructed by using the particle space accumulation method. Secondly, based on the reconstructed simplified geometric model and equivalent inclusion theory, the transition relationship of stress response between composite materials at different scales of concrete was established by using upscaling calculation method of equivalent stiffness and downscaling calculation method of stress response, on this basis, the multiscale stress response equation of concrete under the loading was derived, and the corresponding computing program was compiled. Finally, taking the uniaxial compressive loading as an example, the stress response in composite materials at different scales of concrete under uniaxial compressive loading was numerically calculated, and the influence of spatial position and interaction of aggregate particles, as well as the stiffness, geometric shape and spatial orientation of cement hydration products on their stress response were analyzed. Results show that, the stress distribution in the meso-scale concrete is uneven under uniaxial compressive loading, which was affected by the distance between the aggregate particles, and the effective impact range is about 6 times the radius of aggregate particle. The stiffness, geometric shape and spatial orientation of cement hydration products are important factors affecting their stress distribution under loading, the greater the stiffness, the greater the stress in the hydration products, while the smaller the angle with the direction of loading, the greater the stress in the hydration products of prolate ellipsoids along this direction, however, the stress in the hydration products of oblate ellipsoids is the opposite.