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Steel Bearing Plate on Concrete Masonry

Steel Bearing Plate on Concrete Masonry

Steel Bearing Plate on Concrete Masonry

(OP)
I've never been mentored on this one!

I checked a previous thread where it was stated "Even though ACI 530 allows 0.25 F'm for bearing (375 psi for F'm =1,500), I have always use 250 psi bearing to design beam bearing plates on masonry... I wouldn't be surprised if many others also follow this practice."

For years i've used the max 0.25f'm=375 (or other based on R & h'/r and so on...) for my bearing plates. But that never takes into consideration the vertical steel. I can design a CMU column to support a large beam reaction, but the bearing plate, even when using 375 psi, for a large enough reaction, in some cases will exceed the required size of the CMU column. Therefore, in many cases, if the bearing plate exceeds, i will design a steel column to be placed inside of the hollow CMU.

Can we consider the vertical steel when designing bearing plates on CMU? I've not seen a bearing plate design or example that allows this.

Can i subtract the allowable bearing on the vertical steel from the total reaction and THEN apply the difference ONLY to the grouted CMU, and THEN divide by the 375?

I tend to think that the perimeter stress of the plate would cause the CMU to fail or at elast crack, but, i want other opinions.

Thank you!





RE: Steel Bearing Plate on Concrete Masonry

Quote (BSVBD)

Can we consider the vertical steel when designing bearing plates on CMU? I've not seen a bearing plate design or example that allows this.

Only if the bearing plate is in direct contact with the CMU reinforcing. I've used similar principles with deformed bar anchors welded to embed plates. Otherwise the load has to pass through the CMU/grout before it gets to the vertical reinforcing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Steel Bearing Plate on Concrete Masonry

The allowable bearing on CMU is crazy low. Put it on a flat Southern Pine plate, and you get 565 psi.

Could you fill the cells with concrete and design it assuming ACI 318 ?

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Steel Bearing Plate on Concrete Masonry

The allowable bearing has been increased to f'm/3 in the 2011 masonry code. Maybe that solves your problem without resorting to the rebar.

RE: Steel Bearing Plate on Concrete Masonry

While it depends somewhat on regional bias, it's probably a no-brainer to spec at least 2000 psi for f'm.

I think the traditional use of 1500 psi was borne out of bare-bones 1900 psi C90 block, but most units I come across are actually much higher, > 4000 psi.

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