bearing capacity of thru-bolts on brick

[abusementpark]

Ok, here is the scenario: I need to put a channel to span across two existing brick walls and need to thru-bolt into the brick walls to support the channel.

Firstly, what would you consider a good bearing stress on the brick to use as an upper limit? Also, how would you distribute the reaction to the thru-bolts? For instance if I have 4 thru-bolts at each support side spaced at 6" o.c, the first one will clearly take the most load, but how much can I count on the other ones to take? I know this isn't an exact science, but I would like to hear what you guys think.

 

[Lion06]

I, apparently, am not picturing the connection correctly.

Abusementpark-
Can you post a sketch?

 

[dougantholz]

Okay, here is a rational method for determining the capacity of thru bolts in a wall:
1. The thickness of the wall is immaterial - the bolt is generally stiffer than the crushing capacity of the masonry. Therefore the failure you are looking for is crushing of the outer wythe of brick.
2. ACI 530-05 Eq's 2-5 & 2-6 give us the capcity of bolts bearing on brick:
2-5: Bv = 350 (f'm x Ab ) ^(1/4)
2-6: Bv = 0.12 Ab x fy
we can probably say by inspection 2-6 won't control. In order to solve 2-5 we need to make an approximation of f'm.
3. In order to determine f'm for existing clay masonry, I usually turn to FEMA 273 (or its more modern sister documents) on the seismic evaluation of existing masonry. For clay masonry I believe it gives three expected lower bound values for f'm depending on your visual observations of the base:
f'm = 900 psi - masonry is in excellent condition
f'm = 600 psi - masonry is in good condition
f'm = 300 psi - masonry is in poor condition.

Now its left up to judgement. I only use 900 psi for masonry that is interior and has never been exposed to weather (rain that is). If I can scratch the mortar easily with a pocket knife or screw driver it is 300 psi masonry. Everything else gets treated as 600 psi.
So there you go.

 

[abusementpark]

Sorry for the delay guys. I have had a busy day and haven't had time to read the latest responses. I did put together a cross-section of the connection to clear up any confusion.

 

[youngstructural]

Okay, so I stand by my recommendation of Hilti product, and I would offer you three more words of advice: Far Side Plate.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[youngstructural]

A couple of possible ideas... I usually find that it is the moment which kills; And you certainly cannot neglect moment and treat a connection like a pin (a la Steel, and sometimes concrete) when working in Masonry and Timber!!!

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[dougantholz]

Please don't forget to check the existing wall to make sure the tension created is negligible.