Experiment and meso-scale modelling on combined effects of strain rate and specimen size on uniaxial-compressive failures of concrete

This paper presents experimental and meso-scale modelling studies on the combined effects of strain-rate and specimen size on uniaxial compressive failure behaviour of concrete. A series of uniaxial compressive tests and meso-scale simulations were conducted on concrete with various specimen sizes under different strain-rates covering the strain-rate range of seismic load, with special focus on the quantitative contribution of end-friction to compressive strength and its corresponding strain-rate effect as well as size effect. Results indicate that the uniaxial compressive failure with end-friction follows an hourglass failure pattern while that without end-friction exhibits a columnar failure pattern. The end-friction effect can form different confined zone distributions for various sized specimens, which can cause the contribution of end-friction to compressive strength is size dependent as well as enhance the influence of specimen size on static and dynamic strength. The contribution proportion of end-friction to compressive strength is around 20∼25%. Moreover, larger-sized specimen performs a stronger strain-rate effect and the increasing strain-rate can weaken the influence of specimen size on the real compressive strength. The proposed real DIF empirical formula considering the size-dependency (covering the low strain-rate range) can well estimate the strain-rate effect for concrete with different sizes, which can provide a valuable reference for the numerical calculation of dynamic mechanical response and the safety design of concrete structures.