Abstract Summary
Vibration based damage detection is a particularly challenging problem for reinforced concrete beams and frames for which evolution of natural frequencies with damage often do not properly reflect local distributions of stiffness losses, even when they are large. With the recent development of MEMS rotation rate sensors, it is now possible to measure angle variations along the bar axis during vibrations of the structures. This way, for flexural elements, it is possible to directly obtain translational natural modes of the structure and their spatial derivatives (so called rotational natural modes). Having a rotational natural mode, one can obtain more easily a curvature natural mode which is directly related to flexural stiffness of the element. Early numerical simulations and experiments demonstrated many potential advantages for these new, angular measurements of axes of beams and rods of frames. The purpose of the planned presentation during the EURODYN2022 Conference is to report results of the experiment carried out on 6 m reinforced concrete (r/c) and ultrahigh performance concrete (UHPC) beams. The beams have been damaged using static actuator in a number of stages: from the moment when only 1-2 cracks where barely visible to the yielding of reinforcing steel bars. After each stage the beams were hanged in free-free conditions and their translational and rotational vibrations induced by a modal hammer have been measured with translational accelerometers and rotation rate sensors respectively. Measurements were later used to find average stiffness losses of the beams with model-updating technique. To help finding optimal solution, genetic algorithms were used. Our results show that by using rotation rate sensors one can improve determination of flexural stiffness losses in ordinary r/c or UHPC beams. Selected early results of the modal analysis of the UHPC beam specimens were recently published: https://www.mdpi.com/1424-8220/20/17/4711/htm
