Return to index: [Subject] [Thread] [Date] [Author]

Re: Concrete bearing Edge Distance

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Bill,

I would not let a beam bear directly on a wall (or a column for that 
matter).  A beam will deflect and you will end up with edge bearing and that 
will cause trouble.

Without looking in the code (since it is at the office), I typically use a 
minimum of 1" (more for heavily loaded beams) between the edge of the wall 
and the edge of the bearing plate/pad.  The bearing area is, of course, 
determined by the allowable bearing stress per ACI Code.  (Beware of random 
oriented fiber [ROF] neoprene bearing pads as the allowable bearing stress on 
these can be higher than the allowable bearing stress on concrete.)  Also, I 
will rarely use the allowable increase in bearing stress permitted by the 
code based on the area ratios of the bearing plate and truncated pyramid 
below the bearing plate.

The beam should bear full length on the bearing plate/pad so that the 
assumption of uniform stress under the bearing plate is not too far from 
wrong.  Oversize bearing plates/pads are worse than undersize as the concrete 
doesn't know that the plate/pad isn't supposed to be so close to the edge of 
the concrete.  (I have some dramatic photos of concrete spalling off of 
columns because the bearing pad was larger than specified, the beams 
deflected [together with other factors], causing high edge loading, resulting 
in the spalling.)

I don't know if this answers your question.  The 1-1/2 inch bearing of the 
beam is very small and appears to be the result of arithmetic dictating a 
wrong answer and no one visualizing what is happening.  It seems like a beam 
stretcher is needed on this one!

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Bill King wrote:

>>The info in PCI is very close to the info in ACI318 section 10.17 so I will 
give some more detail as to my question.
The question comes from a residential building where there is a steel beam 
bearing on a concrete wall.  The problem is that the beam only bears ~1.5" on 
the wall. We are fixing the bearing problem but that is where my question 
comes in.  How do you determine how much bearing length you need for the beam 
on concrete based on the edge distance?<<