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Weak Deck

redeyedfly said:
oh my, so upset over here sipping my latte.

If you were part of the development you should be able to answer this very simple question. How does wind load a deck post? That is as basic as it gets.
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OK. To me, your message seemed upset. Sorry if I misread that.

I didn't claim to be part of the development for that change (it happened a few decades ago). Well before I starting sitting on their governance board.
 
redeyedfly said:
My post was 100% about how decks don't typically fail because of posts buckling. I'm still confused as to what you're objecting.
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I'm not objecting, just adding another dynamic to what you did. Not everything here is confrontational or combative. We are simply adding to the conversation, so I'm not sure where the defensiveness is coming from. I thought I made my point clear about two of my posts ago, but you can't seem to process that information for some reason.
 
jar546 said:
I'm not objecting, just adding another dynamic to what you did. Not everything here is confrontational or combative. We are simply adding to the conversation, so I'm not sure where the defensiveness is coming from. I thought I made my point clear about two of my posts ago, but you can't seem to process that information for some reason.
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Not defensive, I actually have no idea what point you're trying to make. I said decks fail at connections and you said, no, they fail at connections... I don't understand.
 
wwhitney said:
The deck needs to resist the lateral load, so it has some sort of connection to resist moment at the top of the post. Eg knee braces.

Cheers, Wayne
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So Canada has prescriptive knee braces for deck posts that are adding bending moments enough to fail 4x4 posts and they changed the code??

I've never seen prescriptive knee braces in a code (<-- not a logical fallacy)
 
redeyedfly said:
So Canada has prescriptive knee braces for deck posts that are adding bending moments enough to fail 4x4 posts and they changed the code??
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No, the Canadian code does not require knee bracing prescriptively, but does require sufficient anchorage to the foundation to prevent lateral movement and uplift.
 
redeyedfly said:
I've never seen prescriptive knee braces in a code (<-- not a logical fallacy)
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Not sure where this thread began or will end but I just want to add that at one time, not sure if they still have them, the NC residential code had them as prescriptive option. As did the DCA 6 document. But, IIRC both prohibited them on a center post. I asked the NC state engineers office why. This was a very long time ago, so my memory may be faulty but I recall they said that it was possible that adding a knee brace to a center post could pose issues with axial loading causing bending/buckling and stress on the connections. I questioned this as a knee brace would typically not be added to just one side of a center post but I am not an engineer and I have no idea how or why they came to their conclusions. I simply have to rely on the fact that they likely didn't make it up out of thin air. I have no issue with them if they are installed on both sides of the column, and I have never had to tell someone to do that.
 
I am remembering a little more....they said the center post was typically loaded with more tributary weight (true) and that because of this they didn't want the column to have any additional lateral force from the knee brace on it AND that by using the knee braces from both sides you increase the tributary load because the center point of the beams is moved further away from the center columns to some degree, and that the prescriptive tables don't account for this.
 
redeyedfly said:
How are the posts loaded with wind? I've also never seen a moment connection on a deck post.
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If I could fire an attachment, I would. We had a post-tropical storm trundle through here a couple of years ago. That storm

a) Ripped a porch off its foundation
b) Took a carport that had been constructed to code, and lifted it up into the heavens. The owner reconstructed, with hurricane ties.
c) Ripped a deck off a house
 
Sifu said:
Not sure where this thread began or will end but I just want to add that at one time, not sure if they still have them, the NC residential code had them as prescriptive option. As did the DCA 6 document. But, IIRC both prohibited them on a center post. I asked the NC state engineers office why. This was a very long time ago, so my memory may be faulty but I recall they said that it was possible that adding a knee brace to a center post could pose issues with axial loading causing bending/buckling and stress on the connections. I questioned this as a knee brace would typically not be added to just one side of a center post but I am not an engineer and I have no idea how or why they came to their conclusions. I simply have to rely on the fact that they likely didn't make it up out of thin air. I have no issue with them if they are installed on both sides of the column, and I have never had to tell someone to do that.
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Interesting. Like I wrote, I've never seen that!

DCA 6 doesn't provide any rationale for the braces other than requiring them for posts over 2'. I don't follow the reasoning for that trigger. The braces only hurt the gravity capacity of the post. The induced bending moment from the lateral loading of the deck is essentially pre-buckling the post resulting in reduced capacity. Hence the restriction on the center posts since they are double loaded.
 
Inspector Gadget said:
If I could fire an attachment, I would. We had a post-tropical storm trundle through here a couple of years ago. That storm

a) Ripped a porch off its foundation
b) Took a carport that had been constructed to code, and lifted it up into the heavens. The owner reconstructed, with hurricane ties.
c) Ripped a deck off a house
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My comment was in reference to loading of the member itself. All of those very likely failed at the connections. I can't imagine a deck post member failing in tension from even hurricane force uplift. The connection is going to fail first.
 
redeyedfly said:
My comment was in reference to loading of the member itself. All of those very likely failed at the connections. I can't imagine a deck post member failing in tension from even hurricane force uplift. The connection is going to fail first.
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They did. However, I'd argue that the more meat in the post, the more capacity for appropriate connections.
 
redeyedfly said:
OK, that's not lateral from wind, it's from incidental contact, like someone leans against it.
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You are right. From my limited understanding of the issue, upgrading the columns to a 6x6 solved the wind load issue and the lateral loads and uplift were solved by adding prescriptive requirements at the connection points.
 
redeyedfly said:
Interesting. Like I wrote, I've never seen that!

DCA 6 doesn't provide any rationale for the braces other than requiring them for posts over 2'. I don't follow the reasoning for that trigger. The braces only hurt the gravity capacity of the post. The induced bending moment from the lateral loading of the deck is essentially pre-buckling the post resulting in reduced capacity. Hence the restriction on the center posts since they are double loaded.
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Which is part of why that didn't make it into the IRC...
 
Having limited experience with failed decks, from what I've seen, the failure was caused by rot. What might have been a fine deck with strong connections at the posts and ledger just got old. Decay set in where it wasn't visible. Then all of the fat side of the family brought it down.
 
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