Vision-Based Monitoring of Absolute and Relative Displacements in Multistory Buildings During Full-Scale Shake-Table Tests

Displacements are among the most important engineering response parameters to be monitored during shake-table testing, with experiments playing a key role in studying the seismic behavior of structures. However, their accurate measurement is not a trivial task when using contact sensors. Computer vision is an attractive alternative for monitoring absolute and relative displacements, and this study presents a new configuration to fully exploit its potential. The proposed solution combines internal and external video cameras. The former is installed on the roof and points downwards to simultaneously acquire the displacements of targets located throughout the height of the building. The latter was installed outside the shake-table platen and tracked the roof displacements to provide redundant measures for control and noise compensation. In this way, the movements of the buildings can be reconstructed with high robustness and precision using a limited number of video cameras. The proposed configuration was applied for the first time during shake-table testing of a full-scale six-story building on the outdoor shake table at the University of California, San Diego. The measurements obtained up to strong dynamic inputs showed the capacity of the proposed approach in real-world environmental conditions and were used for a critical comparison with conventional contact sensors.