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Old 10-22-2013, 10:56 PM   #16
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6x6 post notch


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Originally Posted by dabeast View Post
Yea don't pergolas over a new deck notch the post for the decking? With the post going from ground to the top.
Sorry. I'm not following you. Sure, posts can serve double duty, but I'd never notch them near their base to make that happen. Beams can be fastened to a post with hangers meant for that purpose. That's how I would design what you just described.

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Old 10-23-2013, 11:43 AM   #17
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6x6 post notch


I think what cortell is trying to say is that by notching the 6x6 you create a stress concentration in that notch. Now with the notch being so far away from the line of action (railing) you are creating a much larger moment force (torque = force x moment arm) and that moment created might cause the remaining 3" of 6x6 to develop a crack.

Now I have a tendency to think that if you glue the 2x10's in place and use a nice large washer ( to increase the bearing area ) on both sides of your lag bolt I think you would increase the strength of that joint and wouldn't see any ill effects.
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Old 10-23-2013, 12:18 PM   #18
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6x6 post notch


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Originally Posted by brockmiera View Post
I think what cortell is trying to say is that by notching the 6x6 you create a stress concentration in that notch. Now with the notch being so far away from the line of action (railing) you are creating a much larger moment force (torque = force x moment arm) and that moment created might cause the remaining 3" of 6x6 to develop a crack.

Now I have a tendency to think that if you glue the 2x10's in place and use a nice large washer ( to increase the bearing area ) on both sides of your lag bolt I think you would increase the strength of that joint and wouldn't see any ill effects.
I was planning on using 2 lag bolts on each corner post to attach the beam. Wonder if I could get a steel strap to put on the front and back also kinda like the ones you see on open frame log home trusses.

Something like this http://www.strongtie.com/products/co...urce=strapscat only straight?

Last edited by dabeast; 10-23-2013 at 12:22 PM.
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Old 10-23-2013, 12:39 PM   #19
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6x6 post notch


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Originally Posted by brockmiera View Post
I think what cortell is trying to say is that by notching the 6x6 you create a stress concentration in that notch. Now with the notch being so far away from the line of action (railing) you are creating a much larger moment force (torque = force x moment arm) and that moment created might cause the remaining 3" of 6x6 to develop a crack.

Now I have a tendency to think that if you glue the 2x10's in place and use a nice large washer ( to increase the bearing area ) on both sides of your lag bolt I think you would increase the strength of that joint and wouldn't see any ill effects.
Sort of. Notching the lumber can lead to a crack (maybe a month later, maybe a year later, but there's a decent chance it will happen). The crack will likely be caused by moisture cycles, not by lateral loads (someone pushing on the post). If the crack develops, that railing post will become a hazard.

But that's not my biggest concern. As I mentioned, even if you assume no cracking, any outward or inward forces on that post will act to rotate, and possibly displace, the deck's beam. That is a far greater hazard.

Neither of these concerns are addressed by improving the fastener. In fact, the latter concern is made worse by a stronger connection. Best case failure scenario, only the railing post fails (the fasteners fail). Worse case, the railing and deck's structure simultaneously fail when the beam is displaced from its post.
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Old 10-23-2013, 01:22 PM   #20
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6x6 post notch


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Originally Posted by cortell View Post
Sort of. Notching the lumber can lead to a crack (maybe a month later, maybe a year later, but there's a decent chance it will happen). The crack will likely be caused by moisture cycles, not by lateral loads (someone pushing on the post). If the crack develops, that railing post will become a hazard.

But that's not my biggest concern. As I mentioned, even if you assume no cracking, any outward or inward forces on that post will act to rotate, and possibly displace, the deck's beam. That is a far greater hazard.

Neither of these concerns are addressed by improving the fastener. In fact, the latter concern is made worse by a stronger connection. Best case failure scenario, only the railing post fails (the fasteners fail). Worse case, the railing and deck's structure simultaneously fail when the beam is displaced from its post.
Can you draw a scenario like the one you are describing? It might be my engineer brain but I can't understand which direction your forces are acting that would cause it to rotate. And rotate around which axis? Vertical?
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Old 10-23-2013, 01:34 PM   #21
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Can you draw a scenario like the one you are describing? It might be my engineer brain but I can't understand which direction your forces are acting that would cause it to rotate. And rotate around which axis? Vertical?
Imagine a football player on the deck, applying 500 lbs of force on the post in the direction away from the deck (towards, say, the the backyard's rear fence).

Looks at the OP's drawing and assume the post does not come apart at the notch (assume no cracks have developed). I think you'll see the rotational forces on the beam I'm referring to (clockwise, relative to OP drawing) . The commonly used Simpson post base connector is not designed to resist that type of load (i.e, you could not use them to install a fence post, e.g.,). The end result may be that the beam is displaced. For this reason, I recommend not tying a railing post to the deck beam. I also recommend not notching the post. Two reasons to avoid the design in question.

If you think a 500lb lateral load is unreasonable, read the jlc article.

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Old 10-23-2013, 01:52 PM   #22
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6x6 post notch


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Imagine a football player on the deck, applying 500 lbs of force on the post in the direction away from the deck (towards, say, the the backyard's rear fence).

Looks at the OP's drawing and assume the post does not come apart at the notch (assume no cracks have developed). I think you'll see the rotational forces on the beam I'm referring to (clockwise, relative to OP drawing) . The commonly used Simpson post base connector is not designed to resist that type of load (i.e, you could not use them to install a fence post, e.g.,). The end result may be that the beam is displaced. For this reason, I recommend not tying a railing post to the deck beam. I also recommend not notching the post. Two reasons to avoid the design in question.

If you think a 500lb lateral load is unreasonable, read the jlc article.
True, I guess I was also assuming the post wouldn't be cantilevered meaning it would also be connected in at least two direction horizontally with a rail connecting to another post. If it is a free standing post I agree with you.
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Old 10-23-2013, 02:21 PM   #23
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6x6 post notch


It would be connected to other railing posts both front to back and side to side.


Also that article only tested 4x4s would it make a difference since i'm using 6x6's?
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Old 10-23-2013, 02:48 PM   #24
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6x6 post notch


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It would be connected to other railing posts both front to back and side to side.


Also that article only tested 4x4s would it make a difference since i'm using 6x6's?
Predicting post performance becomes significantly more difficult when you start throwing in its interaction with the rest of the system (will the rest of the railing system save the day?). The last thing this discussion needs are more "what ifs"

On the other point...IMO, 6x6 over 4x4 slightly mitigates the notch/cracking concern. I say slightly because we're talking about a difference of 1/2" between your situation and the notched scenario one in the article. You're notching a 6x6 for two 2x. The authors of the article notched a 4x4 for a single 2x. For the column support displacement concern, the 6x6 is actually worse than a 4x4. I'd rather the post fail than the beam be displaced.

And that's all I've got for this topic. Best of luck to you.
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Old 10-23-2013, 02:52 PM   #25
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6x6 post notch


Maybe a sketch of the overall design would help the situation. I personally think 3" of wood left in the 6x6 would be enough but I agree with Cortell saying we need more information.
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Old 10-23-2013, 04:04 PM   #26
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6x6 post notch


I am probably just going to remove the railing all together as it is a low deck, it will save time and money.

I just wanted to know why/how it was a bad idea for my own knowledge.

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