Kim, Lee, Hu, 2023
The study introduces a novel energy dissipating friction damper aiming to reduce residual damage in structures caused by earthquakes. The device includes springs made of a new material, polyurethane, that contributes to its improved self-centering ability, steel wires, and magnetic cubes for additional energy dissipation. The device is to be connected to structural bracing frames and members and designed to absorb the load transmitted by the brace-frame structural elements. Different experiments were carried out on used materials and the final damper design to evaluate its seismic performance by determining its energy dissipation capacity, residual displacement, recentering force and maximum load. The results indicated that among the six specimens, the damper with both the precompressed polyurethane springs and permanent magnetic cubes provided best seismic performance with the highest dissipated energy, validating the design of the new energy dissipating system.
System Concept
The main components of the proposed elastic friction damper include four cylindrical-shaped polyurethane springs, four steel wires and eight permanent neodymium magnet cubes. The springs are precompressed and fixed to the compression plate and are designed to be further compressed when load is applied through the slider. In addition to its elasticity, the polyurethane material in the springs also has great fatigue and abrasion resistance. The applied precompressive force in the springs is a design variable and can be increased accordingly to provide higher recentering force for greater loads. The permanent magnets are also connected to the slider and dissipate energy as it moves along the slider by friction, due to great adhesion of neodymium material. These magnets are contained in an acrylic box to prevent interaction with other steel components in the damper. While the springs serve as compression members as well as self-centering members, the steel wires act as tension members given its high tensile strength and ductility. The steel wires run through brackets which are attached to the cover and end plates. Hence, the device is effectively designed to resist both tension and compression loads transmitted through the attached brace-frame members of the structure.
Experimental Study, Results and Discussion
Different analyses and experiments were carried out on the elements in the damper and the final prototype specimens. Compression tests on polyurethane springs with precompression values of 0%, 5%, 10% and 20% were conducted and it was observed that the 20% precompressed spring performed the best with a 100% recovery rate. Following that, steel wire elements of the damper were subjected to displacement load tests which resulted in maximum loads ranging between 5.57 kN and 6.15 kN. The proposed structural model was then tested with three precompression states: 0 %, 10% and 20% including specimens without permanent magnet cubes for comparison. Some residual displacements were observed for the specimen with 10% precompression and larger displacements in specimens without polyurethane springs. As for recentering force, it was denoted that the absence of frictional force by magnet cubes result in a higher self-centering capacity. Thus, it was denoted that a minimum of 10% precompression was required for specimens with magnet cubes. Larger dissipated energy was observed for dampers with permanent magnet tubes demonstrating hysteresis behavior, however, with a tendency to deteriorate due to frictional wear. In conclusion, the damper with 20% precompressed spring and magnet cube performed the best in terms of residual displacement and energy dissipation capacity while the model without magnet cube demonstrated best self-centering capability.
Reference
Kim, Y. C., Lee, H. W., & Hu, J. W. (2023). Experimental performance evaluation of elastic friction damper. Case Studies in Construction Materials, 18, e01823.