Theory of delayed concrete deformation and its application in progressive collapse analysis of reinforced concrete multi‐storey buildings

This study addresses the limitations of semi‐empirical formulas in describing the increase in the dynamic strength of concrete through the dynamic increase factor, particularly when the strain rate varies over time. Furthermore, previous experiments indicate that under dynamic loading exceeding its static strength capacity, concrete does not fail instantaneously but after a specific delay period. To overcome these issues, a simple rheological model is proposed, consisting of a nonlinear spring and a viscous dashpot connected in parallel. This model enables the analytical simulation and determination of the delayed failure time, as well as the evolution of strain and strain rate over time. Four cases of sudden dynamic loading are considered: (1) load below static strength, (2) load equal to static strength, (3) load greater than static strength, and (4) a specimen pre‐loaded statically before dynamic loading. The study provides a detailed analysis of the influence of input parameters—such as the viscous damping coefficient, concrete grade, and dynamic load intensity—on the delayed failure time. Finally, the paper proposes an application of this computational model for determining the delayed failure time in progressive collapse analyses of buildings and structures. This offers a novel perspective for assessing concrete failure under dynamic loading.