| Description |
A drop hammer facility, which allows steel weights to be dropped from a height of 16 ft, was built at The University of Utah Structures Laboratory. The drop hammer facility was used to perform a series of dynamic tests on concrete cylinders with and without fiber reinforcement from heights of 16 ft and 8 ft. In July 2011 strain gauges, load cells and high speed cameras were used to collect data from dynamic splitting tension (tension) and compression tests performed on cylinders at room temperature. Additional cylinders were heated to 400 0F before they were tested in April 2012. After testing, various methods were considered to determine the strain rate of the concrete. The dynamic impact factor (DIF), a ratio of peak dynamic load to quasi-static strength was also determined. Concrete has been known to have higher capacities when loaded dynamically. Thus, it is of interest to determine a factor that can be applied during design to account for this increase in strength. Models that have been produced to determine the DIF based on the strain rate were reviewed and compared with the test results. As predicted by these models, the DIF results for both the compression and tension tests increased as the strain rate increased. The tension results were comparable with the model, whereas, the compression model was much more conservative than the results. When compared to the tension model, compression specimens require much higher strain rates to produce similar DIFs. For tension specimens, DIFs were recorded as high as 4.1 at a strain rate of 1.2 in./in./sec. For compression specimens, the highest DIF was 3.2 at a strain rate of 12.1 in./in./sec. For compression tests at room temperature, fiber reinforce concrete (FRC) specimens did not perform as well as normal weight concrete (NWC) specimens when tested dynamically. For compression and tension tests on NWC, heated specimens had lower DIFs than room temperature specimens at higher strain rates. However, when tested at lower strain rates, there was no significant decrease. FRC specimens tested in tension at elevated temperatures exhibited a decrease in DIF when compared to room temperature. |
