Behavior of bidirectional spring unit in isolated floor systems

To investigate the mechanical behavior of bidirectional spring units used as isolators in a kind of isolated floor system, three types of characterization tests were conducted-from spring components alone to the complete spring unit in its implemented configuration. The test results show that the behavior of the springs and spring units is stable when subjected to cyclic repeated motions, and is not sensitive to the velocity of motion. The hysteretic behavior of the spring units was found to be unconventional, with bilinear and different ascending (loading) and descending (unloading) branches. Based on the experimental behavior, a physical model was developed to replicate the unique behavior of such bidirectional spring units. Good agreement was found from the comparison between the results from the physical model and the corresponding tests. Finally, a sensitivity study, with respect to the model's four primary defining parameters, shows that this physical model is more sensitive to the sliding friction coefficient between the spring cable and the bushing in the spring unit than to the other three parameters.