High strain rates testing and constitutive modeling of B500B reinforcing steel at elevated temperatures

摘要

Understanding the response of the building materials under extreme condition of loading (blast and impact events) and temperature (fire) is fundamental for civil engineers to design safe structures for civil or defense applications. In this paper an experimental investigation on the influence of the combined effects of high strain rate and elevated temperature on the mechanical properties of B500B reinforcing steel in tension is presented. The quasi-static tensile tests have been performed at temperatures of 20 degrees C, 200 degrees C, 400 degrees C and 600 degrees C under steady-state conditions at ETH Zurich, using a closed-loop strain rate control system. The mechanical characterization at high strain rate has been performed by means of a Split Hopkinson Tensile Bar installed at the DynaMat Laboratory (SUPSI). In order to evaluate the extreme combined effect of dynamic loadings and elevated temperatures a water-cooled induction heating system was used. The tensile stress-strain response of B500B steel is found to depend strongly on both the applied strain rate and the test temperature. Dynamic tests at room temperature highlight an increase of strength and strain capacities. At high strain rate the increase of the temperature causes a decrease of strength, strain and energy absorbed in the plastic deformation. The strain hardening rate of this material is analysed as a function of strain rate and temperature. Two widely used constitutive laws (Johnson-Cook and Cowper-Symonds) have been calibrated. Numerical and experimental results have been compared. This research provides new data that starts to cover the lack of information about this widely used reinforcing steel in reinforced concrete structures. The degradation factors of different mechanical properties of B500B steel can be used by the designer in case of multi-hazard scenario, such as fire followed by an explosion.