Design of anchor bolts embedded in concrete masonry per ACI-530 / TMS 402

[hetgen]

Hi,


Is it okay to use the infill concrete strength instead of f'_m ( specified compressive strength of masonry, psi (MPa))in Eqn. 7 when checking the shear capacity of an anchor embedded in concrete masonry as shown in the first picture below?

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Thanks.

 

[EZBuilding]

I am assuming you are asking about using the grout strength in liue of the f'm. I don't think this is acceptable and would use f'm instead.

If you are in a bind and need help in justifying - I would recommend you review how you are achieving f'm. The unit strength method has increased the f'm based on the same net area compressive strength of the masonry block across the last several years.

 

[hetgen]

Yes, that is what I'm asking, using the grout concrete strength in lieu of the f'_m, but only for Eqn 7 (allowable shear load as governed by crushing of the masonry).

why do you think it is not acceptable?

 

[strucbells]

Wouldn't the weaker face shell just beyond the grout crush if you designed to the grout strength? Hence why f'm is used, it covers the strength of the assembly as a whole.

 

[KootK]

I think that you might design to the grout if, and only if, your edge distances did not include any masonry and no masonry was relied upon to support the bolts in bearing.

 

[southard2]

Well it is true f'm is the assembly strength of the block and mortar. It doesn't really include the grout strength at all because most of the time wall design result in the compression bock being totally in the faceshell. But remember masonry uses grout NOT concrete. Grout is different because it purposefully has more water in the mixure since the masonry will absorb significat amounts of water out of the mix. But I think the main thing is that material variability is a lot higher with masonry and hence the higher factor of safety. I wouldn't use the ACI code at all even if you did discount the faceshells.

If you have trouble getting tension to work on bolts at the top of the wall i will usually solve the problem one of two ways.

1) Pour a concrete tie beam at the top of the wall and use headed anchord studs and ACI for my calculations or

2) weld D2L deforemed concrete bar anchors to my embeds. These can be 24 to 36 inches long and since they are both weldable and are deformed can be lapped with the vertical rebar in the wall to create a tension tie. I also terminate the vertical wall reinforce with a hook at the top just to make sure everything stays together. But in this instance you are transfering the tension directly into the walls tensile steel via a splice lap.

Usually I just pour a concrete tie beam as its a lot less likely to be constructed wrong.

John Southard, M.S., P.E.

https://www.pdhlibrary.com/