Masonry wall top plate design 2

[WARose]

I have been inspecting a existing building made sometime in the 50's/60's. It's basically a barn. It has a lot of (unreinforced) masonry shear/bearing walls. The roof rafters are at about 18" o.c. (sitting on the walls). The rafters are toe nailed down to a wood top plate that runs on top of the wall. The top plate is held down to a wall with a bolt (apparently grouted into one of the cells) @ about 6 feet o.c..

By my numbers, that top plate can't handle the uplift (in bending) between the bolts (at that spacing).

Is there possibly something I am missing? (Aside from the fact they didn't consider enough uplift, which isn't that unusual for the era.)

One thing that I've wondered about is that toe nail. The head on that beast suggests it is quite long (certainly longer that the thickness of the parts it is connecting). But how could they have pounded it into a cell with hardened grout? Can't picture that.

Anyway, if you are familiar with structures of that era....any ideas welcome.

 

[phamENG]

Sounds like just another building that has been fortunate enough to not see current code design loading. As for the toenail vs grout...it's possible that the bolt is actually set in a mortar joint? I have a detached garage/barn with a single course of CMU above the slab - the sole plate is bolted down with anchor bolts set in the head joints. If we get hit by a very big storm, I'll get a new garage...

Short of attempting to grade the plate in place, you're probably right. I'm assuming you used the flat use factor?

 

[WARose]

I'm assuming you used the flat use factor?

Of course. It won't begin to address the issue.

 

[phamENG]

Worth a shot. 10% is better than a stick in the eye, after all.

 

[XR250]

Well, it has survived this long. It probably ain't going anywhere.
Have you considered catenary action once it deflects far enough?
Also, roof rafters is redundant! (My pet peeve)

 

[WARose]

Well, it has survived this long. It probably ain't going anywhere.

I'm pretty sure they haven't seen a design wind event. But in any case, I have to note it for the record.

 

[dik]

Is there only grout at the bolt locations? Can you use tapcons or something in between? What is the detail at the truss heal and top plate? Can you add a 2x4 or 2x6 vert to improve the moment resistance of the plate? Do the bolts address the uplift?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WARose]

Is there only grout at the bolt locations? Can you use tapcons or something in between? What is the detail at the truss heal and top plate? Can you add a 2x4 or 2x6 vert to improve the moment resistance of the plate?

All that isn't what I am asking. I know how to fix it. I was just hoping someone who has been around a while might have an idea as to what they were thinking. (If anything at all.)

 

[XR250]

I believe standard practice back then was 6 foot on center – so that is what they were thinking

 

[dhengr]

They were doing what had worked for years and years, on the job, having much experience at their trade. They didn’t carry around truck loads of books and codes which supposedly gave them a formula and a solution for every detail and problem in the universe, nor did they have little black boxes which spit out answers and solutions which they couldn’t comprehend. They were thinkers and learners, they learned by real experience from tradesmen who knew what they were actually doing. They didn’t have someplace they could go to where all the answers just flowed to them, out of the ether, either. They didn’t spend years pondering the probabilistic possibility of some possible occurrence which might happen once in several lifetimes. And, they built practical, fairly clean and simple structures which worked, with minimal choices of materials, fasteners and hardware which would allow them to do all kinds of crazy things, but took them days of pondering to select, from way too many choices, in a big pretty catalog of expensive parts. And, finally, they lost surprisingly few buildings, except those caused by an act of God or poor maintenance. Hell, one farmer once saw a tornado pick up his horse and toss it 10-15’ in the air. The horse got up, shook its head and went back to grazing in a few minutes. And, the farmer didn’t pull out a bunch of probabilistic crap and Greek letters to determine that he should or shouldn’t nail the horse to the ground, so that didn’t happen again. Intuitively, he knew that that wasn’t what shoe nails were for, and that he couldn’t plow tomorrow if his horse couldn’t move, because some code said so.

 

[XR250]

But how could they have pounded it into a cell with hardened grout?

Cut nails can hammered into concrete so that does not seem like a stretch. It probably was not too hard at the time - maybe only days old.

 

[KootK]

I was just hoping someone who has been around a while might have an idea as to what they were thinking. (If anything at all.)

If they were thinking of anything deeper than just following a typical detail, my money is on consideration of how the roof framing restrains the top of the walls against out of plane wind loads. This detail still might not work for that purpose but, at the least, the load path is more sensible.

 

[WARose]

If they were thinking of anything deeper than just following a typical detail, my money is on consideration of how the roof framing restrains the top of the walls against out of plane wind loads. This detail still might not work for that purpose but, at the least, the load path is more sensible.

It's got a diaphragm.....but it really doesn't change anything. (Just provides [not enough] dead load.)

 

[KootK]

It's got a diaphragm.....but it really doesn't change anything. (Just provides [not enough] dead load.)

No dead load is required for the effect that I spoke of. That, in part, is why I feel it a likely candidate for the "what were they thinking of" question.

 

[WARose]

No dead load is required for the effect that I spoke of. That, in part, is why I feel it a likely candidate for the "what were they thinking of" question.

Are you talking about the diaphragm/framing making some redistribution possible to where [a lot of] the top plate going into uplift will not be necessary? (If not, please be explicit. Thanks.)

 

[KootK]

Nope, I am saying that:

1) I doubt that they explicitly considered uplift and;

2) I speculate that they may have considered the shear connection that resists out of plane wind at the top of the wall.

 

[WARose]

Ah. Thanks Kootk.