Problem with an existing roof 2

[mats12]

I am making a reconstruction of very old existing house. Existing roof has to remain pretty much intact.

There is a new extension of an existing building and roof above it - (ridge beam) represents additional load on existing roof beam.

Because of this additional load on existing roof system, Im having additional bending moments in existing column as shown in attached picture. The column cannot be replaced with a new/sufficient one since its a part of an existing roof system (I dont know how to call this system - 2 red timber frames - dont know whats the expression in english langugage). I was thinking about removing braces (horizontal bracing) and reinforce existing column with steel plate (both sides) and connect it with bolts and then add new timber braces. I will design bolts based on vertical shear flow between column and steel plates.

What do you guys think about this situation? better options?

EXISTING + NEW ROOF - plan view:

Additional load in the picture below is the result from a ridge beam of a new extension of a building.
existing column with braces:

 

[bhiggins]

Is it possible to divert the load entirely to a new ceiling beam properly sized to take the load?

 

[mats12]

It isnt...

 

[JedClampett]

Why can't you shore the current roof loads and replace the column? It sounds like a pretty major project already. It seems pretty scary, but I have contractors do it all the time.

 

[mats12]

I dont believe anyone would dare to do it...
Reinforcing existing column with steel plates isnt an OK/good option in your opinion?

 

[Once20036]

Honestly, I`m not entirely clear on how all your sketches fit together.

To focus on the 4th image, it appears that you have a new point load on an existing beam. That beam is supported by two foundation walls, two columns, and the braces off those columns. This new point load creates compression in one of the braces and that, in turn, creates bending in the column. Is that right?

Can you add a new brace immediately adjacent to the existing brace, down to the bottom of the column? This would create more truss like behavior and eliminate bending in the column...
This might create some weak axis bending in the "blue beams" that would need to be addressed - maybe that gets braced to the adjacent "blue" beams

 

[bhiggins]

Without knowing specifics, this appears to be a column stability issue. The plates would not help with bracing the column so they would not be effective in reinforcing the column in my opinion. If the column is failing due to additional moment I can think of several methods to alleviate this:

Add more column bracing to reduce effective length.
Remove knee braces to eliminate moment transfer to column, but may require beam reinforcing.
Replace column entirely.
Divert load to other members which can handle the new load.

 

[mats12]

for clarification - This is a roof system in 3D (without rafters):

 

[dhengr]

Mats12:
In the second beam sketch down, where you show the yellow kickers (knee braces) and the additional load arrow, consider the following. I wouldn’t like to try take the yellow kickers apart, from the column or the beams. Since they are likely mortised and tendoned into the column and beam you would have to lift the beam and/or cut the tendons. You have a lot going on right there in terms of room layout, stairs, bookcases, light brown stuff, etc. and it is tough to know exactly what’s going on in that area, or where the load comes in w.r.t. the existing column and frame. Try doing a little architectural rearrangement to make things work out.

I would leave the yellow kickers alone, and on the left side, under the new roof load, I would put another diagonal column, from the green beam (shown in elev.), down to the blue beam (shown in end view). The new diag. col. would start just left of the existing yellow kicker, from the underside of the green beam, making a 1m+ by 3m triangle, and this col. end connection would involve a horiz. bearing cut and a dap for a split ring or shear plate to the green beam, with a long structural screw or lag screw up into the beam. The bottom of this new column would have a vert. and horiz. seat cut, to fit to the existing column and the blue beam, and a couple screws into the column and/or blue beam. You should jack the roof up a bit, to start to unload the yellow kickers, and you want the knew diag. col. to fit tightly, so it starts picking up its share of the new load immediately, not overloading the yellow kicker first.

 

[Teguci]

On the new addition, just south of grid B, change that first line of rafters to a truss and detail it so the ridge can cantilever over the existing roof just a little. This should keep the tributary area on the existing roof the same so you might not have to revise the existing roof structure as much.

 

[mats12]

Teguci tnx for answer but I dont really understand what you mean by that. What would changing the rafters to a truss system accomplish when it comes to existing roof? additional load relief on existing beam? i dont see how existing roof and truss system above new extension can fit together. sorry English is not my first language.

 

[Teguci]

I'm sure you can get a ridge beam to cantilever off the truss and pick up at least 1 m of loading from the existing roof's tributary area. I'm not sure how to put the two systems together either. It could be as simple as putting a tie across the bottom of the last pair of rafters. Maybe even putting a tie on the valley rafters would do the trick.

My thinking is that we have a lot more control over new construction.

 

[mats12]

I ll think about your suggestion, but there may be a problem with a room space in case of truss system (not enough height).
Thank you very much for elaboration!