Purpose of masonry plate (bridge bearing)

[sil3ntsid3]

I am working on the design of a bearing pad assembly as per AASHTO LRFD standards.

Can anyone explain me the purpose of the masonry plate as an interface between the bearing pad (rubber) and the concrete plinth. Is it a mandatory functional component ?

I have seen projects that use the masonry plate and ones in which they aren't used. But I don't have any technical justification for their use.

Can anyone help me out with this.

If you require any inputs for your inference, I shall provide it.

Thanks!

[Kelly_Bramble]

The masonry plates are used for pintles when the elastomeric bearing pressure is not high enough. A larger base plate also spreads the load to the supporting structure if required.

If your design cannot overcome the shear force through friction of the pad and concrete then you need to make some mechanical mechanism, thus the pintles.

[sil3ntsid3]

Thanks a lot Kelly. Much appreciated.
I understand your explanation. Found the relevant AASHTO reference stating the clause you mentioned.
In one of our previous projects, we had designed without a masonry plate and the rubber bearing pad was resting on the mortar above the plinth. In that case, friction of pad outwent the shear force and hence it was safe.

In one of the running projects which I'm currently working, the friction of the pad still overcomes the shear force, but a masonry plate is shown in the input drawings from the client. As evident, this would be uneconomical.
And keeper plates are provided around the bearing which are bolted to the concrete to prevent walking off of the bearing.

So, if we examine the above scenario, the two purposes of the masonry plate are taken care with alternate arrangements. In such a case, is the masonry plate mandatory ?

Because this is one of the important factors affecting the cost of the assembly.

Thanks a lot for the help!

The masonry plates are used for pintles when the elastomeric bearing pressure is not high enough. A larger base plate also spreads the load to the supporting structure if required.

If your design cannot overcome the shear force through friction of the pad and concrete then you need to make some mechanical mechanism, thus the pintles.