Log cabin Roof Framing

[johnwow]

I've got someone who wants to knock out the fireplace in the middle of the house. It's already been removed (not a masonry FP, just stone veneered on stud), but what's left are two 8x8 solid timber posts which extend from the 2nd floor up to the ridge timber. Then there is a composite type pair of posts that most definitely supports the beam supporting the 2nd floor joists.

The rafters and ties are all fastened with large lags or wood dowels. There's a very similar type of setup in another part of the house which I've attached a picture of which has no posts supporting it. That leads me to believe these posts were not there to support the ridge, only stability for the FP.

We'll be swapping out the 2nd floor beam for steel but for these 8x8's, I'm inclined to just have them take them out. However, I wanted more data so we're going to set up a string line or laser and take out of the timbers to see how much the roof deflects, if any.

Has anyone come across a similar setup like this?

 

[Craig_H]

I see a half-lap joint in the ridge beam directly above one of the 8x8s you plan on removing. I wouldn't be taking it out.

There's a very similar type of setup in another part of the house which I've attached a picture of which has no posts supporting it. That leads me to believe these posts were not there to support the ridge, only stability for the FP.

Having designed these types of fire places, there are definitely cheaper ways to laterally brace the wood stud framing than by adding 8x8 columns. Your justification for removing the supports seems to rely on another portion of the roof with a similar visual appearance. Have you modeled the roof structure to evaluate the load paths and determined that removing these two columns is permissible?

 

[johnwow]

Good eye. Yes we were aware of that so we took out the other one. Got a call from the builder this morning and it dropped 5/16". We're either going with a steel beam or try to incorporate some low profile steel columns in place of the timber posts for support.

There's always an option to model it but that would have been a lot of time and cost given the complexity of it and may end up having to add support anyway. Made the call to provide support regardless.

 

[Craig_H]

Wow. I can't say that I've ever engaged in the engineering discipline of "remove it, observe deflection, then add a support based upon that".

There's always an option to model it but that would have been a lot of time and cost given the complexity of it

I'm genuinely curious, how do you plan to size the new support columns without knowing the magnitude of load applied to them?

 

[johnwow]

I guess that's why I'm here. I'll either calc up a FBD with a enough of a factor of safety incorporated into it or size a column that meets or exceeds the strength of an 8x8 rough sawn timber if we are replacing at the same locations.