How effective is soil damping in pile response to seismic event 3

[IJR]

This is an extension of my thread posted in Foundation Engineering forum. I would like to post it here, in case no one extends my previous discussion.

4July greeting to all our pals in States

In modelling superstructure with pile included where deemed necessary, pile flexibility is taken advantage of in attempt to cut down seismic energy absorption. There have been suggestions to employ spring elements in pile modelling.

My opinion is that large damping is built in even poor(mud) soils, and large energy absorption is already built in.

As far as piles are concerned little vibration exists, and should behave almost rigidly. And the superstructure should vibrate as if the base is fixed.

I am talking about an extreme condition to stimulate the discussion

Anyone interested please join in.

regards
IJR

 

[Qshake]

In most cases, the soil-pile interaction is considered on the basis of determining what larger displacement repsonses can be expected for the structure as a whole. This response can't be predicted using the fixed foundation scenario. Fixed foundations will give maximum moment and shear response but are often considered too conservative.

You're assumption that the soil will asorb energy is correct, but by absorbing energy the soil has to yield and this is what leads to displacements. The other important item is for soils that will liquify.

 

[IJR]

Thanks Qshake

Your comments brought in some light as usual. But if you visit here again please comment on the role of soil damping in cutting down the displacements.

Respects
IJR

 

[dimitrios]

Hello IJR.

I am not sure if it can be of any help, but French regulations (Fascicule No 62 - Titre V) for example multiply the spring constant simulating elastic soil behavior, based on pressuremeter measurements, by a factor of 2 when dealing with seismic loads. I think this will lead to smaller displacements induced in the superstructure.
As Greek regulations provide with design values for seismic acceleration at the soil surface, there is propably another effect that interferes based on the assumed distribution of seismic acceleration with depth, but I think this depends on the model assumed. In that case in order to consider dumping one should use the real or design accelerograph curve as forced vibration.

If my comment is very well known or of doubtful value please consider it with caution as I am not an expert.

Regards