Damper is more efficient at high speed then for high amplitude.

It will reduce the amplitude at the 4th stage and eigenfrequency of this mode should be enhanced. Probably the first mode.

It should not act on frequencies whose modes presents a node at top of building.

It all depends on the type of damper and the velocity of the movement.  Base isolation plus dampers will be much easier to incorporate in the basement, and should be effective at that point.  Dampers such as fluid filled reservoirs are best located at the top. 

Hi

I concur with Gordon - it all depends on the type of damper you apply.

Some types use relative displacement and then work best where you have the largest relative displacement between connection points that can grab into the major structural strength.

Other types of dampers leverage motion and then work best where you have the largest motion which, usually is at the top.

The amplitude dependence also depends on the damper type. Some types prefer small relative amplitude, e.g. viscoelastic shear layers while, other types, e.g. hydraulic viscous dampers, do not work at all at low relative displacement amplitude due to things like mechanical gaps, gas that is entrained in the viscous medium and so on.

Damping can be many other things on top of the above. You find some ramblings of mine on this subject here http://qringtech.com/2014/06/22/designed-damping-types-mechanisms-application-limitation/

SIncerely

Claes

Thank you all for your answers and replays;

Dear Jean-Francois Antoine, I'm using a MR damper, which need velocity and displacement on the floor where it is located, and my question was ! which velocity and displacement should I us, if my damper is located at the 5th floor ? absolut displacement and velocity ? relative displacement and velocity ?

Dear Gordon and dear Claes, what about MR damper ? I'm traying to use an algorithme to decide about the optimal damper location, and I was asking, if the MR damper needs displacement and velocity of the floor where it is fixed (to react or to work), would that change if we move the damper from ground floor to top floor ? means if the damper is at ground floor it is fixed at the base which is supposed not moving, but if it is located at 5th floor (top floor) it will be fixed at 4th floor which is moving ? should I use the absolut displacement and velocity of the top floor ? or what should I use as input for my damper model in MATLAB ?

Best regards.

Hi Mahdi

The maximum power transmission into a connecting element is always found whenre you have impedance matching, i.e. compute your MR input impedance (Force/Velocity) and you structural impedance. These should match as closely as possible.

Beware that correct calculation of impedance requires a matrix inversion of the mobility (Velocity/Force) matrix. See Figure 4 here for an example of the difference http://qringtech.com/2014/01/28/need-to-know-about-vibration-isolation/

Sincerely

Claes

Thank you dear Claes,

So using the absolut displacement and velocity of the top floor while the damper is located at the top floor and fixed to the 4th floor is wrong ? and induce wrong results ?

Best rgerads.

Hi Mahdi

You MR should work at the top, possibly at other locations as well.

I have no experience with MR dampers but, I am guessing that they want reasonably large vibration amplitudes to work well. I am guessing this as liquids are involved and most liquids dissolve gas which tends to flex at low amplitude and as most dampers of this kind need gaps for aligment and must overcome friction.

A MR damper,  dashpot damper or damper link only adds damping from relative motion. So, connecting one end to the structure top and letting the other damper end grab free air would provide poor damping as air is too weak to load the damper. However, it would work if you have a heavy seismic mass at the top that is free to move and you add the dashpot between tower and seismic mass.

Therefore, large amplitude vibration would be my bet, i.e. a tuned damper (free mass, spring and damper connected between tower and mass) placed at the top of the structure to increase relative motion such that the damper can take up and destroy vibration energy should be a good start.

It would work also at other positions in the tower where you find relative motion.How well depends on how much is the relative motion and how much relative motion your damper needs to work well (everything works well in simulation models though, not always in real life).

The damper link is better at low amplitude vibration and can be very stiff but does not take as large loads or as large relative motion amplitude as a dashpot. It depends on the application which is the better choice.

One more thing. A dashpot damper and damper link are nice design elements in the sense that if you for some reasone fail, all they do is not work. If you put a tuned resonator onto a structure and for some reason tune it wrong, you may actually make things vibrate more.

Hope this helps

Claes

As Claes said, an MR damper needs relative motion to work.  They have been used on bridges, both between the substructure and the deck and also to damp vibrations in cable systems.  If the top floor motion is sufficient, relative to some part of the structure you can fix to, an MR damper would work at the top floor.   But why use and MR damper?  The key with MR dampers is that the designer needs movement at very low velocity movements (e.g. thermal expansion) but damping for high velocities (wind, earthquake).  What is the need for movement at low velocities in a building?

Dear Claes, I ended by using a Random function in matlab to tray all the MR damper location  in my 5 story structure, the best location for MR damper is at the midell floor of the structure. MR damper needs velocity and displacement as data in the numeric simulation so fot the first floor we use only first floor displacement because the base is fixed (zero displacement and velocity), for other floors we use (x(i) - w(i-1)) and (x'(i)-x'(i-1)) where (i) is the floor number. this are the resultats I came with at the end of the study.

Dear Gordon, MR damper is giving an important displacement reduction for, earthquakes, you can see that on my conference paper, I've been using MR damper on scaled structures and now I'm doing that on real scale structures the peak displacement reduction is around 60% for Kobe and El Centro earthquakes.

Best regards and thank you.

Any damper with the required movement/damping characteristic would work, including an untuned liquid damper ('shock absorber') such as in motor cars would work.  I do not see the need for the added complexity of MR dampers.

Dear,

It depends on superstructure materials and kind of dampers . Actually  it is very complex of structure to study analytically to get responses and data. So ıt may be verified by experimental studies too

Cengiz Ipek

Dear Gordon,

The MR damper can be controlled, with less energy input then a active damper, this is the advantage of the MR damper it works like a active damper but with less energy.

and we are trying to introduce fuzzy logic control algorithm to optimize the damper behaviour.

Passive dampers can absorb only the first vibration mode, but the MR damper can absorb a large rang of vibration modes, this also an advantage compared to shock absorbers.

Dear Cengiz,

Right now we are limited to a numeric simulation, but we are looking forward for an experimental studies to confirm what we are getting from simulations.

Best regards.

Hello Mahdi

I think because of this fact that most part of earthquake energy apply in the first floor, damper in ground-floor is more effective.

Sincerely,

Azadeh

Dear Mehdi,

I think Mis. Azadeh Amiri is right, However The point he is looking for  comparing the dampers studying up and down location anyway

Regards

Cengiz

Miss Amiri,

the damper optimal location depends on several parameters, one of the most important parameters is the structures elevation, more the structure is elevated more the damper location at ground-floor is unuseful. A 5 storey building is considered as a mid-rise building, so according the the researcher I'm doing the best MR damper location is at the middle floor, I will shear the paper on Researchgate, once it will be accepted by the conference committee.

Best regards.

Hello Mahdi

I think your paper can be very interesting!

I hope that it be accepted soon.

Good Luck,

Azadeh

Thank you Miss Amiri, I will shear it one it will be accepted

Best regards and thank you for the interaction with the question.