I am doing a comparative study of 20 storey structure with and without viscoelastic damper in etabs. So I need to get how these parameters which is to be entered while selecting damper properties in etabs? Also i want to know how can we find number of dampers required in a building?
Hi
There are many ways to do this. Perhaps the simplest is to introduce a bunch of dampers and look at their energy as % part of the total modal strain energy. Damping is added when the dampers you introduce start to take up a significant portion of the modal energy.
The total loss factor can be estimated using the Modal Strain Energy (MSE) approach, i.e. etatotal = sum(eta_k*%SE_k), where eta_k is the local loss factor for part/area k and %SE_k is the part of the total modal strain energy for area k.
The viscoelastic dampers can be modelled as complex springs K = K0*(1+j*eta), where eta is the structural loss factor.
With MSE, you can see which dampers truly add damping.
However, to judge their practical effect, you will need to know also the current lavel of damping, i.e. if ambient damping (damping without the dampers is, say 1%), and your analysis shows that you get 2%, you will end up with a total damping loss factor of 1+2 = 3% and a 3/1 = 3x resonant amplitude reduction.
About positioning. Dampers have effect only where there is a relative displacement.
Perhaps you find some of these ramblings to be of interest? http://qringtech.com/2014/06/22/designed-damping-types-mechanisms-application-limitation/
Sincerely
Claes
1. Do a modal analysis assuming zero damping.
2. Look at the type of structure you have - rigidity of connections, material, form of structure - and based on this assign a level of self damping (0.1 to 1%)
3. Look for the points of maximum movement in the first few modes, and add damping there. If this introduces physical problems (access, inability to support the damper, etc.) look carefully at connections and supports to see if damping can be introduced there. See the Thesis by Eric Ancich https://www.researchgate.net/publication/259572229_Structural_Dynamics_of_Modular_Bridge_Expansion_Joints_Resulting_in_Environmental_Noise_Emissions_and_Fatigue?ev=pubfeed_top&trpid=5544a431f15bc720598b4588_1
I proposed the use of high damping elastomeric bearings bearings and compression springs specifically to introduce damping into the system. The same idea is used in car suspensions and engine mounts.
Thesis Structural Dynamics of Modular Bridge Expansion Joints Resul...
How can we obtain modal strain energy for each story in etabs.Is there any option for it in the software?
Hi
I advice you to see these documents. You will find what you need.
Best regards
http://www.scielo.br/scielo.php?pid=S1678-58782011000300006&script=sci_arttext
http://www.iitk.ac.in/nicee/wcee/article/WCEE2012_0508.pdf
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