An experimental verification on inducing instability in a tall structure under seismic load using a single axis shake table

Instability of structures, such as large vertical pressure vessel, is always an issue under the seismic load. In the current work, a lab setup has been created to experimentally verify the critical acceleration/deceleration level that would trigger the instability in the structure. An educational R-191 single axis shake table with maximum displacement of ±15 cm is used for this purpose. This shake table is programmed to simulate sinusoidal waves at different frequencies using FOXTROT program. Different frequencies in sinusoidal waves generate different levels of maximum accelerations and minimum decelerations. A 3D printed 1:50 scaled down model is used for vertical pressure vessel which is supported by its three legs at the ground. Forces transmitted through these supports are measured using loadcells and recorded. The critical levels of accelerations (and decelerations) are estimated at the instants when the transmitted load though the joints are measured zero or “negative”. This situation triggers instability in the structure. The experimental results are compared with the theoretical calculation. The future work will involve the prediction of level of acceleration/deceleration that will initiate the failure of the actual structure in the field. It is also important to verify from the available earthquake data whether that level of acceleration is generated in a particular earthquake event.