Experimental and numerical investigation on impact dynamic performance of steel fiber reinforced concrete beams at elevated temperatures

Building structures and members may suffer the action of blast or impact loads and fire during the service life. In some cases, they are applied to the building structures and members sequentially and this leads to the combined effect of high strain rate loads and elevated temperatures. In order to investigate the dynamic behaviors of steel fiber reinforced concrete beams (SFRCB) subjected to blast or impact loads after fire exposure, a series of drop-weight impact tests on SFRCB were carried out at elevated temperatures. An electric furnace was used to heat the specimens following the temperature time history expressed by the ISO834 standard temperature rising curve, and then drop weight impact loads were applied to the specimens immediately when the expected temperature was reached. The test results showed that the addition of steel fiber can improve the dynamic performance of specimen beams. For the specimen beam with the steel fiber volume content of 1% and 2%, the mid-span peak displacement at 600 degrees C has a decrease of about 8.9% and 19.6%, respectively, comparing to that of the specimen beam without the steel fiber. The peak impact force of the specimen beam with the steel fiber volume content of 2% is 8.5% higher than that of the specimen beam without the steel fiber at 400 degrees C. The peak impact force of the specimen beam with the steel fiber volume content of 1% and 2% is 17.5% and 10.3% higher than that of the specimen beam without the steel fiber at 600 degrees C, respectively. The elevated temperature can deteriorate the dynamic performance of specimen beams. A finite element simulating model was developed in LS-DYNA to predict the dynamic behaviors of the fire damaged SFRCB. The continuous surface cap (CSCM) constitutive model was adopted to describe the mechanical behaviors of SFRCB. The impact dynamic response of specimen beams at elevated temperatures was numerically simulated and compared with the corresponding test results. The numerical results reveal a generally good agreement with the test results. Experimental and numerical results show that the specimen beams suffer more serious impact-induced damage, including more cracks and larger mid-span displacement at elevated temperatures than that at normal temperature. This research will be of direct importance to both practitioners and researchers involved with protective design of buildings.