replacing a structural post and need some advice

[GN4WHLN]

I need to replace two support posts on my patio cover. They are rotting on the bottom because they sat in water for years prior to when I bought the house. They also seem small for the load they hold and a poorly designed support system for a home in an earthquake area.

If you look at the bottom, they are held in place by a bracket in the cement and the bracket was set too close to the edge and has cracked some of the edge piece away. The patio was built by the builder and is an optional room so it sits on an extension of the slab. Below it is an exposed patio I put in.

On the top, it has a 4x6 header that supports one of the open sides of the cover. Two other sides are supported by the house. The structure is 2x6 on 12" covered in sheet and mineral roll. It looks fairly heavy for a 20'X30' patio cover.

What I want to do is replace the 4x4's with 6x6's. I've thought about sistering the 4x6 header with another and shifting the 6x6's back away from the edge a little. As far as brackets to bolt it together, I will probably have to make the top ones. I am more than capable enough to design, cut, and weld them from 1/4 plate. What I am not sure about is what to do with the bottom. Can I simply bolt new mounts to the cement? Do I need to epoxy the anchors in?

One thing I thought about was casting a cement pier to support a new mount, but I have no idea if this would be structurally sound. It would seem so, but actuality is often something else.

Any help would be appreciated.

 

[Daedalus]

I'm pretty sure Simpson Strong Tie makes the upper brackets you're looking for, at least if you stick with 4x4 posts. I don't get clearly the layout here. You're saying a 20' long "free edge" consists of 20' of 4x6, supported by 2 4x4 posts? That would be too much span for the 4x6. The 4x4 is in compression...doesn't seem to be out of bed if the weight of the roof only needs a 4x6 to support it in both shear and bending.

The spalling of the rusting lower bracket likely contributed to the concrete cracking. Depending on the extent of the damage, I might be tempted to only replace the 4x4s, and try to do a better job of sealing out the moisture. Or, if you really want something beefier than 4x4, consider 4x6, as there are a lot of 4x-sized brackets available. You could use something similar to the bracket already there, but just anchored down to the concrete.

I would not sister in a 4x6 header and then only support 1 of the 2 headers. It's eccentric loading, and I'm guessing it's a no-no from a code standpoint.

 

[GN4WHLN]

I think the 4x6 may be a much simpler fix. The structure has two free edges and two that sit on the top plates of two of the house walls. I think those posts were done that way because the house was built in 1977 just before our city incorporated so the builder was under the county's building codes. They had a bit of a rep for letting builders have a free hand.

So, would you you think I can simply run anchors into the existing concrete slab? do I need to do anything about where the concrete has broken away?

I guess I was over thinking this a little.

 

[NUTTSGT]

I built these for the front overhang of my garage. They are 1/8 steel and have 2 pieces of 1/2" square tubing on each end for the 4x6 to sit on.

 

[NUTTSGT]

Somewhere I thought I had pics of when I made them.

 

[theoldwizard1]

A 4X6 is a pretty good header. What is the total span and the span between posts ?

I'm not sure if it is really required, but at the top, I would use a Simpson T or L ******** another 4x4 post, but use pressure treated wood for the post.

The bottom will be a challenge. With that header properly supported by temporary posts, break out the old post and mount. Dig down to the frost line an insert a SonoTube and mount the new post with a proper bracket.

The tube should be a couple of inches above grade. Simpson has a wide variety of brackets for this application.

 

[Highbeam]

I never undestood sonotubes. You want the concrete to fill the hole, I suppose for the part of the pour that extends above grade the tube acts as a form but if you put the sonotube below grade then you will never compact around the sides of the tubes.

Maybe it's a frost heave thing? The sides are slippery on purpose?

 

[wssix99]

These are interesting but probably overkill structurally since you'll have the post attached at the top and bottom.

http://www.deckbuilderoutlet.com/titananchors.html

 

[GN4WHLN]

A 4X6 is a pretty good header. What is the total span and the span between posts ?

I'm not sure if it is really required, but at the top, I would use a Simpson T or L ******** another 4x4 post, but use pressure treated wood for the post.

The bottom will be a challenge. With that header properly supported by temporary posts, break out the old post and mount. Dig down to the frost line an insert a SonoTube and mount the new post with a proper bracket.

The tube should be a couple of inches above grade. Simpson has a wide variety of brackets for this application.

10 feet between posts.

I am familiar with those ties. I'll use those or the type that wrap around and bolt through which I prefer. Currently, there is a ******** one side with lag bolts through it and it is toe nailed on the other. Not a great design in my mind. I think I'll use the 4X6 posts as was suggested and I am clear on how to R and R the old posts and fix it to the header. What I am not sure about is what to do at the bottom. Using the tubes would require cutting a hole in both the exposed patio and the covered one. The exposed is 3 1/2 inches, but the covered one is part of the foundation and is thick. I really don't want to cut it unless it is absolutely necessary.

This may be wishful thinking on my part, but can I anchor the bottom mount for the post to the existing slab? I've seen ones at HD that are 3/16ths. If Simpson or someone else does not make it from 3/16 or 1/4 I can make it. And, I know... if they don't make it, there may be a reason why.

I guess my concern is if I anchor it on top of the existing slab is that an acceptable construction method? Are the mounts simply too close to the edge of the slab?

One thing that occurred to me might be to form out a pier on top of the existing slabs with something anchoring it to the slabs, like rebar epoxied into the slabs to keep the pier from shifting and having the post support on the new pier. Again... it seems like a good idea.

 

[sberry]

Put a temp post each side the old one, knock all the loose stuff out, Form the damaged area up with sheet metal and use poor rock, pour it full like fixing a cavity. Make a bracket to connect the post too with plate to simply bolt a couple anchors to keep the post from being knocked out.

If you wanted to get really tricky build it to pout it all monolithic,, ha.

 

[wssix99]

This may be wishful thinking on my part, but can I anchor the bottom mount for the post to the existing slab?

Yes. No problem. Your only issue is cutting away the old stuff, patching the shipped concrete and finding a good area left to bolt in to.

I guess my concern is if I anchor it on top of the existing slab is that an acceptable construction method? Are the mounts simply too close to the edge of the slab?

That's the way the old ones were, so you should be fine. If the load was too heavy for the old slab, you'd see a lot of cracking, sinking, etc.

That type of connection is a "pin" joint. The brackets are not built to resist twisting around the base - the main thing they do is pin the bottom in place so it does not move laterally, which is all you need.

 

[MoonRise]

Had typed out a reply, it got 'lost' somewhere. Grrr.

round #2 ...

You're in 'earthquake' country. Check first if and what possible seismic 'criteria' must be met for your repair.

General approach of the repair (not taking into consideration any possible specific seismic criteria/Codes/requirements/etc) IMHO would be :

- put temp posts in to support roof beam (check beam for possible sag at this time, jack up and relevel if necessary;

- remove old post and also damaged concrete slab area;

- find out possible seismic code requirements and pick applicable Simpson (or equivalent) connectors for your replacement posts to the concrete and to the top beam;

- use PT lumber posts (be aware of corrosion issues with most 'new' PT lumber and use compatible brackets and fasteners);

- install.

Possible 'tricky' issues are seismic requirements and also the spacing/set-back requirements for the post-to-concrete brackets/connectors. Some wet-set brackets call out for ~3" concrete minimum on the 'side' of the bracket by the slab/pier edge.

Remember to incorporate (or just use the usual bracket built-in offset) stand-off spacing from the bottom of the post to the concrete (to avoid/minimize possible end rot like you have now).

Possible seismic requirements are what you really have to determine first. That will determine concrete requirements (just repair slab section, versus putting in a Sonotube-type pier/footing and how big a diameter and depth you will require).

Seismic requirements will determine what size and type of bracketry you will require, as to uplift, rotation, and lateral load requirements.

 

[nolimits76]

If I was going through all this trouble, I would do the sonotubes so you have a good solid pier foundation for the supports to set on and have good concrete coverage for the brackets. Plus if you raise the lips like NUTTSGT did, you have a little protection from standing water.

It's more work now, but in the long run I think the better way. Good luck w/ whatever you choose.

 

[GN4WHLN]

Yes. No problem. Your only issue is cutting away the old stuff, patching the shipped concrete and finding a good area left to bolt in to.




That's the way the old ones were, so you should be fine. If the load was too heavy for the old slab, you'd see a lot of cracking, sinking, etc.

That type of connection is a "pin" joint. The brackets are not built to resist twisting around the base - the main thing they do is pin the bottom in place so it does not move laterally, which is all you need.

OK, this helps me.

Also, I guess I need to make a trip the city engineer's office and make sure how I do it is acceptable as I would like to sell the house some day.

The water issue is solved. When I bought the house, the previous owner put some top soil in the back but didn't grade it properly. when it rained, water would pool on the patio and those posts wicked it up. My dad and I tore out everything in the back and redid the grading, landscape, water, gutters and so on. the new posts will remain dry.


Thanks for all the replies everyone. There is so much experience here there probably isn't any task that can't be figured out by this board

 

[sberry]

One thing that occurred to me might be to form out a pier on top of the existing slabs with something anchoring it to the slabs, like rebar epoxied into the slabs to keep the pier from shifting and having the post support on the new pier. Again... it seems like a good idea.

Yes, essentially this, make it neat like it belongs.

 

[GN4WHLN]

Yes, essentially this, make it neat like it belongs.

Oh yeah, I would make it neat. I saw a thing yesterday where structural columns were being made for a multi-story building. There was a rebar structure that had been set into the foundation, then a large sonotube was added and the column was poured. The thing was several feet in diameter and about twelve feet tall.

What I had thought about was 18x18 and about two feet tall using rebar and the proper post mount.

 

[wssix99]

Oh yeah, I would make it neat. I saw a thing yesterday where structural columns were being made for a multi-story building. There was a rebar structure that had been set into the foundation, then a large sonotube was added and the column was poured. The thing was several feet in diameter and about twelve feet tall.

These were structural columns with actual footers underneath. Your awning is feather light in comparison and you don't need any of this stuff. Your awning should be able to bear on that slab just like the old one did.

BTW - You may also cover the bottom of the post with foundation sealer so it won't wick up water if you ever have pooling again for some reason.

What I had thought about was 18x18 and about two feet tall using rebar and the proper post mount.

Doing this would be really complex given that you don't need it structurally. You'd need to tie the piers in to the slab somehow (or dig foundations through the slab for it) and rebar woudn't provide any benefit to you since the concrete would be all in compression and rebar is only used for crack control and tension reinforcement.

If you want to make the post look neat, you might look in to "post wraps" or "column covers." Depending on what you get, they will make the things look a lot stronger than they are or need to be.