Drop-weight impact tests on reinforced concrete beams

Sammanfattning: This master's thesis aimed to investigate the behaviour of reinforced concrete beams under dynamic loading conditions, specifically focusing on understanding shear failure. The study was conducted with KTH Royal Institute of Technology, the Swedish Fortifications Agency, and Tyréns. The research built upon previous studies and aimed to contribute to understanding dynamically loaded concrete structures.The thesis included a literature study to explore the fundamental concepts of dynamics, impulse loading, and the response of RC structures under dynamic and static loading. The experimental part involved manufacturing and testing 27 reinforced concrete (RC) beams with varying amounts of transverse reinforcement and load positions, where 18 were tested dynamically, and the rest were tested statically. The findings contribute to understanding structural response and failure mechanisms in such beams, considering three main factors: load position, shear reinforcement, and loading characteristics. In addition, essential data, such as reaction forces, beam displacements, and crack patterns, were measured using load cells, accelerometers, and high-speed cameras.The findings of the study revealed several important insights. The load's position significantly affected the beams' acceleration, with further load positions activating both shear and flexural modes simultaneously. Beams with different shear reinforcement configurations exhibited similar behaviour and the presence of weaker cross-sections due to insufficient bonding between steel and concrete. The study also demonstrated that dynamic loading increased the beams' load capacity compared to static loading, attributed to the strain rate effect and inertia forces. The crack patterns and residual eigenfrequency differed between dynamic and static loading conditions, with dynamic loading resulting in less extensive cracking and reduced residual stiffness.The use of a fiberboard provided cushioning effects, as its removal during testing resulted in a shorted load duration and the formation of the cracks in the beams. In addition, anchoring the flexural reinforcement significantly increased the stiffness of the beams, leading to an earlier rebound and a more robust impact response.