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Beam Bearing Plates

Beam Bearing Plates

(OP)
Hi All,

For reference, the application of this inquiry is for beam bearing plates on masonry.

This question references AISC 13th ED. SCM. On page 9-10 the code references J8 for bearing on concrete or masonry. When I go to section J8 the code only references bearing on concrete. Is this section meant to be concrete & masonry? If "Y", then in equation (a) is the engineer of record to sub f'm for f'c? If this is the case, and the engineer is using ASD, should the phi factor be 0.25 as described in ACI 530-05 2.2.1.9.3 or should equation (a) only be used for strength design of masonry rather than ASD? ACI 530-05 3.1.4.5 references the phi of 0.6 which coincides with J8 even though it is not specifically referenced in J8. If "N" then where does the engineer need to refer for bearing on masonry since 9-10 references J8?

AISC offers examples of bearing plate design but, they only reference bearing on concrete in their examples. I have posed the question to AISC but, have not gotten a response from them yet. If AISC wants the engineer to use judgement then why don't they state this in their code. Rather than reference it one section and then neglect to mention it again in another. If anyone has had any experiences with actually "designing" bearing plates what spec and/or process have you used. Thanks.

 

RE: Beam Bearing Plates

The AISC specification states that the provisions in J8 are to be used "in the absence of code regulations."  In this case, I would absolutely use the masonry specification, ACI 530, to check the bearing stresses.

Also remember that page 9-10 is not part of the specification.  The specification says that J8 is for bearing on concrete.  It doesn't say anything about masonry.  Perhaps page 9-10 is in error.  Either way, I wouldn't consider a concrete equation in the steel specification to be anything more than a starting point.

RE: Beam Bearing Plates

(OP)
Nutte, thanks for the response. AISC got back and their explanation is below. I have proceeded with 530 for my bearing widths. My main concern was combining ASD factors and strength factors and coming up with something that was overly conservative. I still use the manual for checking my beam end bearing constants first, then see if I need a plate for my beam (or add stiffeners) then proceed to 530 for distributing my load to the wall. Thanks again.


"Thanks for the notice. The Manual is incorrect in referencing section J8 for Masonry bearing design. Section J8 is only applicable to concrete bearing design as stated in its title. Even there preference is given to the documents that are authoritative in the design of concrete and masonry. I will copy our engineering director so that we can look at this again.

 

The appropriate reference for the bearing capacity of concrete is ACI 318. Therein there are no provisions for design based on service loads and you will have to modify your loads [from your ASD steel design] to strength level loads as per the load combinations in ASCE 7. For the case of bearing on Masonry the appropriate document to use is ACI 530. That document has provisions for service level design and the loads can be applied directly from ASD.

 

Section J8 of the AISC specification is only applicable "... in the absence of code regulations..." which is very rare since ACI is references in most project specifications and governing building codes."
 

RE: Beam Bearing Plates

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. This is a holdover from AISC, J9, 9th edition and many older codes. I wouldn't be surprised if many others also follow this practice.

I have design tables that I have used for many years and will continue to use them until I retire (which is only 1 or 2 years away.....Lord willing)!

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