Can anyone explain masonry plate? 1

[koo]

I saw bearing details for elastomeric pad sitting on top of a masonry plate, and some sitting directly on abutment seating or an elevated concrete pedestal. Why do you need a masonry plate? in what situation? Can anyone answer? Thanks.

Koo

 

[VoyageofDiscovery]

Hi koo,

Base plates (masonry plates) are used for pintles when elastomeric bearing pressures are not high enough.

A larger base plate also spreads the load to the supporting structure if required.

Regards

VOD

 

[koo]

VOD,
Thank you for replying. But can you elaborate on "used for pintles when elastomeric bearing pressures are not high enough", I don't quite get it.

As of spreading load, is there a analitical procedure to follow? What determines when to use a masonry plate, analysis or more of customary in some area?

I have a concrete pedestal 6"-14" high underneath the elasto. pad. Does a masonry plate help protect the elsto. pad?

Koo

 

[VoyageofDiscovery]

Hi koo,

You have to design the bearing and interface for the applied loads.

For example if you cannot overcome the shear force through friction of the pad and concrete then you need to make some mechanical mechanism, thus the pintles.

Depending on your code, another criteria is the minimum average vertical pressure on the bearing at around 200 psi, any lower you will need positive attachment (pintles).

Regards

VOD

 

[VoyageofDiscovery]

Hi koo,

With regard to spreading the load. It depends on the substructure. For example if your bearing sits on a log crib, then chances are you would use a bearing plate under the elastomeric pad to reduce the bearing stress on the notched log. The check should be made for the strength of the material supporting the bearing, wood, stone masonry, etc..

Regards

VOD

 

[koo]

VOD,

I designed the elsto pad according to AASHTO 16th Chap 14 Method B that checks compression and uplifting. I heard that it is much more complex and thorough than old codes. I have compressive stress in the range of 700psi.

If I get you correctly, the masonry pad is mostly for providing a positive link for uplifting and spreading load in some cases. Do you know of any problem with putting elato. pad directly on concrete seating, like smoothness, protection...?

Regards,
Koo

 

[VoyageofDiscovery]

koo,

The pintles are used to transfer the horizontal loading, when friction of concrete to pad are not enough or used to counter the possibility of slippage when elastomeric bearing stress is not high enough.

Any uplift is resisted by anchor bolts.

Regards

VOD

 

[VoyageofDiscovery]

koo,

These pintles are welded on top of the base plate around the bearing (sometimes at the corners) or are small vertical dowels attached to the base plate engaging through the bottom shim within the elastomeric bearing.

Regards

VOD

 

[koo]

VOD,

It's interesting to know this. I've never seen any detail like it yet. I know they sometimes put an anchor/dowel bar thru a plain elasto pad and sole plate, or put a guide bar/angle along the pad.

Is there a guideline on when and how to use the pintle design? a book or code? AASHTO seems to have no mension of the friction btw conc. and elsto. pad.

Regards,

Koo

 

[VoyageofDiscovery]

Hi koo,

I have mentioned the requirements already. However, in Canada we design according to CSA-S6 Section 11. This section will help you with the design of bearings. Pintles are covered under Positive Attachment (Section 11.6.6.6).

This detail is not uncommon in Canada for steel highway bridges, particularly for logging road bridges.

I am a bit surprised that AASHTO doesn't have a requirement for this, check CALTRANS. We typically use the same US manufacturers when we spec bearings in Canada.

Regards

VOD