Dynamic Increase Factors for Steel Reinforcing Bars

摘要

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 reinforcing bars yield stress can increase by 100%, or more, depending on the grade of steel used. The dynamic increase factor (DIF), i.e. the ratio of the dynamic to static value, is normally reported as function of strain rate. Knowledge of the DIF is of significant importance in the design and analysis of structures for explosives safety. DIF curves for both yield and ultimate strengths have been derived and 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, and even on data from steel bars of a different grade. A literature review of the effects of high strain rates on the properties of steel reinforcing bars (rebars) was conducted. Static and dynamic properties were gathered for bars satisfying ASTM A615, A15, A432, A431, and A706, with yield stresses ranging from 42 to 103 ksi (290 to 710 MPa). The data indicates that the DIF decreases for higher rebar yield stress, and that the DIF is higher for yield stress than for ultimate stress. A simple relationship is proposed that gives the DIF (for both yield and ultimate stress) as a function of strain rate and yield stress.