Dynamic Increase Factors for Concrete

Abstract : For reinforced concrete structures subjected to blast effects, response at very high strain rates (up to 1000 s(-1)) is often sought. At these high strain rates, the apparent strength of concrete can increase significantly. The dynamic increase factor (DIF), i.e. the ratio of the dynamic to static strength, is normally reported as function of strain rate. For concrete, the DIF can be more than 2 in compression, and more than 6 in tension. Knowledge of the DIF is of significant importance in the design and analysis of structures for explosives safety. DIF curves for concrete have been published in manuals by the Tri-Services, the Defense Special Weapons Agency, the Air Force, and the Department of Energy. However, these curves are typically based on limited data. A literature review was conducted to determine the extant data to characterize the effects of strain rate on the compressive and tensile strengths of concrete. This data support the dynamic increase factor (DIF) being a bilinear function of the strain rate in a log-log plot. The DIF formulation recommended by the European CEB was described, together with its origins. For tension, it was found that the data differed somewhat from the CEB recommendations, mostly for strain rates beyond 1 s(-1), and an alternate formulation was proposed based on the experimental data.