Mechanical behavior of lightweight concrete structures subjected to 3D coupled static-dynamic loads

It is of great significance in the design and evaluation of anti-impact protective structures to investigate the dynamic mechanical properties of lightweight concrete structures. The present work aims to address this challenging task by the development of an improved large-diameter split Hopkinson pressure bar that can accurately predict the dynamic compressive strength and impact failure characteristics of lightweight concrete under different stress states. Our findings exposed that the impact resistance of lightweight concrete is substantially improved and the failure modes of it have altered under the 3D coupled static-dynamic loads. When the confining pressure remains at the same level and the loading strain rate is low, the unloading curve of lightweight concrete shows a significant hysteresis phenomenon. We have further found that for a higher strain rate the stress-strain curve can be divided into five stages: (i) the inertial-effect-enhanced stage, (ii) the nonlinear elastic deformation stage, (iii) the elastoplastic deformation stage, (iv) the strain-softening stage, and (v) the plastic flow stage. Based on the linear relationships among the logarithm of the strain rate, the dynamic increase factor (DIF), and the confining pressure conditions, we have constructed a two-factor equation for the DIF of lightweight concrete that depends on the confining pressure and the strain rate.