Concentrate uplift load on masonry wall

[BurgoEng]

In short, I have a new column supporting a new roof, and the column is resting on an existing 12" fully grouted CMU wall. The estimated uplift load due to wind onto this column is 10k. Therefore, I need to anchor the baseplate of the post to the CMU wall, to resist this load.

I can't seem to find an anchor system (mechanical bolts, epoxy) with acceptable spacing and edge requirements that would allow this to work. Am I missing something?

Also, I have a similar situation with about 5k uplift into a new CMU wall, so I can use embedded anchors, but again, and not sure how to figure out size and spacing requirements.

 

[cap4000]

What I have done in the past for uplift is used 4 #8 bars with 90 degree hooks the full depth of a new foundation wall filled solid with concrete say for 10 feet horizontally and then the #8 bar is threaded on top to receive the heavy hex nuts. The analysis I used for the "spread" or effective length of the load is similar to a point load down on top of the wall set forth by ACI Code. For a 12 inch wall 4 feet is OK. This is stricly my take only. Your 10 kip load is very large for an existing CMU wall. Make sure you have enough concrete fill and cmu block dead weight to act as your hold down acting thru the dowels out of the footing. You will need to do some exploratory work to get the As-Built wall conditions. Good Luck.

 

[csd72]

How about you use a channel to spread the load between say 4 to 6 anchors along the width of the wall, this way you engage a wider length of wall as well as getting the necessary spacing to the anchors.

 

[UcfSE]

Following csd72's post, you could size the base plate to work around the anchor spacing.

 

[BurgoEng]

Ok, due to a bit of stupidity on my part, I was misinterpreting some capacity info provided in a Hilti catalog. What we have decided to go with is a 8"x24" baseplate, with epoxy grouted AB's staggered in a 4" x 8" offest pattern along the length of the plate. I really only need 3 bolts to meet capacity, but figured 4 would be a bit of insurance and then would make a symetrical plate.

 

[UcfSE]

There's nothing wrong with asking for another bolt. I would. You never know what's going to happen in the field. I'd ask for special inspection too. A symmtrical bolt arrangement is desireable as well so you don't overload one bolt and not use much of another.

 

[csd72]

Keep in mind that if you use an elongated base plate, the anchor bolts nearest the column will take more load than those further out, due to the flexibility of the plate.

Thats why I recommended an angle as a baseplate, to increase the stiffness.

Always be a little conservative on chemical anchor bolts, you never really know how well they are installed!

Regards
csd