Hi everyone, so I have been doing my Dissertation on Base Isolation system ( Lead Rubber Bearing ) on Etabs and want to compare my results with the Fixed Base system ( same building ). I have almost done it but wanted few clarifications about the results and procedure.
1) As i needed a maximum force for the design of Base Isolation system. I picked the Maximum force ( Design Reaction Table ) so does Design Reaction means force acting on the base of all the columns ? How is it different from Base Reaction Table in ETABS ?
2) I am getting more Time Period by using Base Isolator in Model Analysis in all Modes, Is that a positive impact ? How Time period of Mode effect Seismic forces ?
3) I am getting more displacements in Base Isolator Model as compared with Fixed base, Is it normal to expect more displacement is a Base Isolation Model ?
Please give your opinions about the results. ( Images attached )
Many Thanks,
1. It is correct to design the base isolation system under the maximum force if you consider the design level earthquake. If you are using spatial design model for your building, then Design Reaction Force (Base Shear Force) means the force acting on the base of all the columns. It should not be different from Base Reaction Table in ETABS.
2. Of course, it is positive result (impact), as one of the main features of base isolated buildings is that they have much longer period of vibrations than the fixed base buildings. And this makes base isolated buildings very reliable, as they will work in the range of earthquake spectra where spectral accelerations are very small. Also, the period of vibrations of base isolated buildings is much longer than the predominant period of the ground motion. All this will make the seismic forces in base isolated buildings smaller by about 3 times in comparison with the fixed base buildings.
3. For sure the displacement at the level of seismic isolation system must be very big, otherwise your system will not be effective. But from the other side, the inter-story drifts in the superstructures (parts of the buildings above the seismic isolation plane) of base isolated buildings must be much smaller than in fixed base buildings.
From your questions I understood that you have very little knowledge and experience in seismic isolation. Therefore you have to read many papers and books published in this field. I can recommend you to read my book "New Solutions in Seismic Isolation" where many examples on analysis and design of base isolated buildings are given together with their comparison with fixed base buildings.
I wish you success in your work and research!
Best regards,
Prof. Dr. Mikayel Melkumyan
I think, better, you can create script based solution for covering various types problems.
Technical Report Parametric Design and Investigation of Base Isolators Using ...
- Badges
- Science topic
- Similar topics
- Force