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Old 12-09-2011, 07:14 PM   #16
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Long deck poles


OK, seriously, can we talk about my question?

In hopes of moving on: I drew up the plans myself. I specified 6x6 posts, but they are not available in 23 foot lengths. I may end up just stacking them up to make the span, but I want to explore other options.

Yes, I have a permit, and my plans have been approved, and I have had preliminary inspections.

I know that some will now be tempted to chastise me for doing things on my own and not hiring professionals to do the design, construction, and interior decorating. But this is a Do-it-yourself forum, not a Hire-someone-else-to-do-it-for-you forum. So if there are any comments about using cedar trunks.....

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Old 12-09-2011, 07:16 PM   #17
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Originally Posted by tcleve4911 View Post
You could also do a "Box Beam"
2 -4x4x12' (24') in the middle wrapped with 2x6 and 2x8
Scarf / 1/2 lap the joints of the two 4x4s
Belated thanks for this suggestion. I've been sketching a bunch of potential cross sections.
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Old 12-10-2011, 07:22 AM   #18
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Long deck poles


The design of a long column such as you describe is generally driven by buckling considerations, not by axial (vertical) compression issues. The allowable buckling load is computed by analyzing the total vertical load on the post, any eccentricity of the load (i.e. the load is not centered on the post), and bending moment at the ends of the post, and the method of attachment of the the post at the top and the bottom.

The critical dimension is the effective unbraced length of the post. If the post is braced at the midpoint, which is common, then the effective unbraced length is typically taken as the distance from the bracing point to either the top or bottom of post, whichever is larger.

Once you know the dimensions and the connection geometry, you select a post size (4x4, 6x6) and test it mathematically against buckling, applying the code mandated safety factor. Of course you also check for bending stress and direct compression, but they almost never control.

In standard residential construction, the length of posts (studs) is almost never over 10 feet (unless you are doing balloon construction), so buckling is almost never a problem, and is generally not calculated. Buckling is rare in residential construction because long, slender poles subjected to large compression loads are rarely used. Your project seems to be a bit different, you have an unusually long post, and it may be subject to substantial load. In any case, that is where you start, compute the vertical load on your post, analyze the geometry, adjust for mandatory safety factor, then you can size the minimum post size. This is usually done by an engineer, but of course this is DIY, so you may want to take a crack at the analysis yourself. The equation used is called the Euler buckling theorem, so you know where to start.
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Old 12-10-2011, 08:28 AM   #19
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Long deck poles


Quote:
Originally Posted by Okie0030 View Post
And I would not likely be getting an inspection unless I had a permit.
Quote:
Originally Posted by Joe Carola View Post
How come you're not getting a permit?

Quote:
Originally Posted by Okie0030 View Post
Yes, I have a permit, and my plans have been approved, and I have had preliminary inspections.

Now, all of a sudden you have a permit.




Quote:
I know that some will now be tempted to chastise me for doing things on my own and not hiring professionals to do the design, construction, and interior decorating.But this is a Do-it-yourself forum, not a Hire-someone-else-to-do-it-for-you forum. So if there are any comments about using cedar trunks.....
This is where you fly-by-night Diy'ers are WRONG!! You people can do SOME work yourselves...no problem...problem with the way you people think is that you can do EVERYTHING yourselves and come here and ask and expect to get all the answers. The SIMPLE answer is that a DIY'er and a DIY'er forum is not the place to size a 23' post for your project. There are certain things that a DIY'er cannot do....this is one of them.

What makes you people think that you can become an architect or engineer overnight? I'd love to hear your thinking. No one is telling DIY'ers to call in a professional for everything. We are just telling you that there is no way that a DIY'er can do everything...there are certain things that HAVE to be done by an architect or engineer....a 23' post is one of them....it's just common sense!!!

Your mentality is like coming to a Diy'er forum and asking how to build a plane and expecting to get the answers just because this is a Diy'er forum and you want to do it yourself.......again...there are many things that can't be done yourself.....it's so simple!!!
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Old 12-10-2011, 07:33 PM   #20
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And by that I mean the post on the forum.

I just wanted to know if there was some sort of post material I had not considered.

Nevertheless, thank you, Daniel, for the very detailed comments. I don't think I made it clear that I was talking about balloon construction. The post will go up 2 feet to the first deck, then about 9 feet to the next deck, then 11 feet to the peak of the roof. So the post will have bracing around the halfway point to mitigate buckling. Hence, I don't see the need for any serious engineering. Nothing all that out of the ordinary. I was thinking about balloon construction for aesthetic purposes.

I do appreciate the encouragement and guidance with regard to to calculating loads.
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Old 12-10-2011, 07:43 PM   #21
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Hey Joe. I'm not a fly-by-nighter. I've read and studied countless hours for this project. The purpose of this inquiry was not to have someone engineer a post for me. I just wanted to know about what materials were out there. I am doing this project right. I've hired engineers for the things I'm not sure of. I've had a permit from the beginning (inspections are mentioned in the first post). Sorry to have riled you up, but just about every member of my family has built a house going back 200 plus years and none were professional carpenters, engineers, architects or any of that. So I KNOW it can be done.
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Old 12-11-2011, 12:37 AM   #22
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Long deck poles


5" diameter pipes, wrap them as fat as you want.
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Old 12-11-2011, 06:44 AM   #23
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Long deck poles


So now that we have established that buckling is not an issue. Steel pipe is available in essentially any length that can be trucked over the road. Size the pipe as per my post. Glulam beams are available in essentially any size that can be trucked over the road. Size the beam as per my post. Want to make your own beams? This can be done using scarf joints, exterior class glue, and some careful fabrication of the joints. You can make any length you want if you have the skills and the time, and you can make the post using any commercially available wood that glues up well. Size the beam as per my post.

Want to get more exotic? You can get an entire tree milled to whatever spec you desire, just find a sawmill willing to make the cuts. Only problem is the post is likely to twist as it dries, introducing eccentricity, but as you noted the post is braced at intermediate points, so perhaps you can live with a twisted post.

Aluminum poles, hollow and solid, are available in any length that can be trucked over the road. You could also use reinforced concrete, although the size might be a little large (rebar cover requirements), and the detailing on the intermediate connections would be tricky.

There you have it, many ways to deal with your issues. Just make sure your intermediate braces are solid, and perform the job reducing the effective length of the pole.

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