Elastomeric pad plus dowels

[lprogers]

Does anyone know what the best way to model this type of bearing is? It is a elasomeric pad with 2 steel dowels to prevent 'walking'. Figure 1 shows what I need to define. I have tried multilinear plastic link but did not get good results, my link definition is figure 2.
Figure 1
Figure 2

 

[stressed]

I would think that you need to define separate links for the pad and dowels if the elastomer is acting in the same direction as the dowels. The dowels may have some "play" gap/hook type behavior.

Your force-deformation input for your link includes 2 different displacements for the same force in the same direction. Was that an error?

Since you mentioned in an earlier thread that this was for your thesis, do you have a professor to ask these questions? It would be interesting to know the recommended modeling approach for this problem

 

[lprogers]

Stressed,

thanks for the input. Yes I did end up modeling the bearing as 2 separate links, one for the pad another for the dowels and it seems to be working. I was hoping that I would be able to combine them into one link due to the number of bridges I need to analyse. I am looking for any way to expedite the process.

My professor and I are the only ones using this program at this university and its the first time using it for both of us.

On another note, I am applying vertical ground motions as well to the models. the bearings need to be able to release the girders if the girder wants to separate vertically from the bearing pad but yet the pad needs to support the girder when the girder makes contact with the pad. This will simulate vertical pounding between the bearing pad and girder bottom. Generally with this type of bridge and bearing type there is no vertical restraint preventing pad/girder separation under vertical ground motions.

I have added separate links at the bearing location to try and model this behavior. I tried both multilinear(high stiffness for negative deformation, low stiffness for positive deformation) and gap links with no success. the result after using the multilinear link is excessive vertical deformation, and the gap element seems to restrict vertical separation when it shouldn't.

What is your opinion on this?

 

[stressed]

Compression-only gap links should work if you have the correct orientation, input stiffness roughly equivalent to bearing stiffness, and analyze as nonlinear. Draw 2 point link from girder to bearing. I've found that use of the Edit>Interactive database tables and exporting/importing with Excel is sometimes faster than working with SAP's graphical user interface.

If you still have problems, have your professor attach your SAP .sdb model and send to CSI technical support email with your questions, and share what you learn.

 

[lprogers]

It seems I have resolved this issue. Since I am running Non-linear Modal time history analysis each link element needs an appropriate linear stiffness defined in addition to the nonlinear stiffness value. By trial and error I arrived at a stiffness which gave realistic results for vertical displacement. It would be more desirable to run direct integration since the linear stiffness would not be needed but our computer cannot finish the analysis in a reasonable time.