Will the method to find horizontal stiffness of an isloator for an SDOF system ie. T=2*pi*sqrt(m/k) give nearby results in SAP for a 3D bridge model?

Question

Data:

• Isolation Time Period T= 2 sec
• Bridge is horizontally curved 3 spans box girder 88 m length
• 8 isolators - 2 under each pier and 2 at each abutment

And will the results be nearby if I use area, spline or solid model?

Answer 1

Creating a building seismic profile requires in most of the times a SDoF model. For a bridge, it's necessary to have 6 DoF comprise of:

• 3 x translations
• 3 x rotations in 3D

If you don't have that many directions, the longitudinal axis should be used therefore the calculation you've posted above should match your needs