period estimation ( how to do in time history analysis)

[hakimi]

Hi dear zaher, jae

I appreciate your discussion about period estimation. I think that you have to modify the analysis based period regarding nonstructural effects. This will affect design forces directly.

Ok! but for design of structures with energy dissipator devices, like friction dampers or viscous ones you have to apply nonlinear time-history analysis, then how can we consider the period shortening that we need to model the actual seismic effect on the structure?

I have a 6 story structure with sort of friction based bracing. The period I found is very long (around 2.0 sec) and nonlinear time history (with sap2000) analysis gives reduced result according to the structure's period. What do you think?

 

[Qshake]

I think that you should get a time history which includes the effects of the isolation devices. You should call the company whose bearings you are modelling and receive an accelogram from them.

You may have already accomplished this, but it was unclear in your post.

 

[hakimi]

dear qshake

the device i am trying to use is somewhat new and designed by myself and no company exists to help me.

 

[Qshake]

ok, You will need to test this device to provide information concerning its sustainability, durability, and performance. Engineers using this device need to be able to use the output time history for this element. In other words you will test this using a time history such as El Centro and based on the load applied to the bearing/isolator and stiffness parameters of the bearing/isolator or other proprietary information you will most like record the displacement of the bearing over time in response to the El Centro accelogram. That output is what engineers would use to input in the appropriate structural analysis program for a building or bridge.

For more information on what is required now, by the industry, check out FHWA's HiTech study on seismic isolation bearings.

http://www.fhwa.gov

 

[hakimi]

when you are to face with a device inside the structure, what is ur suggestion? suppose that you have to analyse and design an irregular structure (in plan, along the height) and you have to use time history analysis, how you will consider the period gap between codes and your model? thank you in advance!

 

[Qshake]

Unless you know the output of the isolation/dissapator device it will be useless to analyze the structure. Perhaps a more rudimentary strengthing approach is possible based on the information of the members.