Bracing example...

[jimtheengineer10]

I have been reading/researching about wall bracing as I have not dealt with it much. I think I am starting to understand the concept and solutions when it comes to a garage wall but how would you brace the upper portion of the attached image? The whole wall is basically windows and I don't think there is enough space to install shear panels. What would some other options be? This is not an actual project just something I saw and was wondering how it would be done. Thanks.

 

[BAretired]

Try to find enough shear resistance elsewhere. The wall shown cannot be considered a shearwall.

BA

 

[JAE]

If this is a house I would suggest it falls under a residential code such as the IRC.
Under the IRC, there is a concept of "braced wall lines" that are required. You should review the applicable code and educate yourself on the requirements there.

Typically many of the perimeter walls and the interior walls can all be utilized as braced wall lines to achieve the empirical lateral stiffness that you need.

This is also found in section 2308 of the IBC.

 

[jimtheengineer10]

What is an option of getting the shear resistance from somewhere else

 

[BAretired]

Interior walls.

BA

 

[jimtheengineer10]

See the attached image for reference. The left side of the Typical Braced Wall Plan image is pretty much the same as the situation I am talking about. TABLE R602.10.1.3 BRACED WALL LINE SPACING says that the maximum spacing is 60' for wind bracing and 25' for seismic bracing. So if the width of the upper portion I am talking about is less than 25' then no bracing needs to be provided because the two exterior walls at each end of the wall are perpendicular and provide the bracing? Am I interpreting this correct? Thank you.

 

[SteelPE]

House bracing still confuses me to some degree. There are many ways to achieve the same result. I so some work with a company that specializes in wood framed construction. We help each other out from time to time. Every time I don't think something can be done they take out some APA document or Simpson document that proves their reasoning. from what I understand, the options you are looking at are just one of many that can be used when designing a house.

One thing you might want to look into is an APA document on portal frames or you might want to take a look at some of the Simpson options shear walls, strong walls etc... I believe they even make a pre-manufactured steel moment frame. I don't know if any of these will work in your instance.... but they are worth the look.

 

[nac521]

This braced wall line would not meet the IRC prescriptive requirements for wall bracing and therefore would need to have an engineered design. If this was an actual project, I would try to convince the architect to increase full height wall segmented (eliminate some windows) to meet the prescriptive requirements OR tell them what is involved in an engineered design (interior shear walls, Simpson strong walls, hold down. collectors, etc.)

Although the prescriptive bracing requirements have been in the code for over a decade, just now am I starting to see the majority of code officials question the bracing amounts.

 

[jimtheengineer10]

So is my interpretation of the 25 foot spacing in my post above wrong

 

[focuseng]

You will never have "NO BRACING" just because you have less than 25', you just have "Less" required. I think 4' gets you to zero. So Your interpretation does seem wrong but is not necessarily wrong but rather incomplete and overly simplified in a rather complicated arrangement (a plan of the example building rather than an elevation would be more instructive). The # of braced wall lines is only one part. Spacing is another. You also do need to consider the location of the walls within the building footprint (exterior walls and offsets matter) and the amount of possible bracing within each wall based on the wall spacing (wind) and length (seismic). The required length is then based on a number of factors. You have to balance all of these together. The wall bracing provisions make more sense if you have first attempted lateral engineered designs. Straight out -If you have never engineered MWFS or a wood perforated-shear-wall or a wood diaphragm with respect to the MWFS then this is all hocus-pocus to you. If you have, then the wall bracing provisions make sense but be prepared to dance a lot. Your best bet right now is to provide an actual plan of the example house not just the elevation. I possibly could make the elevation work if the plan was arranged just so but I can't say right now.

While we are on topic (allow me to hijack!).
One thing I don't understand and have a problem with all the time: # of braced wall lines adjustment factor in the wind tables (Table R602.10.1.2(1)

http://publicecodes.cyberregs.com/i...tm?bu=IC-P-2009-000002&bu2=IC-P-2009-000019).

If anyone can give a rational explanation of this one I would love to hear it (it has been in each of the 2006-2012 codes and I don't have a commentary to reference). I play the devils advocate with myself in this game all the time just to see how bad it can get sometimes. I have found that if I put in more walls (up to 5) then I actually have more bracing in each wall then if I took out all of them and only used 2 making it possible to have 2-3x as much bracing required just because I added more wall lines as each wall adds up. I understand that stiffness attracts a load and sometimes a flexible diaphragm is not always a true conclusion in wood structures but the 1.6 multiplier is a stiff penalty to pay. What gives!

______________
MAP

 

[jimtheengineer10]

it the upstairs was all open (no interior walls) then would you have to install a steel frame around the whole opening basically or what would an option be? Thanks

 

[jimtheengineer10]

Here is the first floor plan that goes with it

 

[jimtheengineer10]

Here is the 2nd floor plan

 

[focuseng]

All values are using some assumptions and this is only for prescriptive wall bracing. Also only looked at the wind tables and not the seismic tables so do your own homework and a lot of other things need to be considered. This is a cursory look at the situation.

In the plan you provided, there is 11'9" between the north wall and the interior wall - you need 2.2625' (interpolated) wall bracing in the the North wall. (assuming no modification factors and a 90 mph wind speed). There are three wall however and you need to multiply by 1.30 for a total of 2.94' bracing (see my previous post rant). To achieve this I would propose 6:1 portal frame at the two outside windows. You need 1'-6" for each these so the windows need to be modified. Alternate is to use a stacked shear brace like i-level or strong tie where you can get a 12" wide manufactured panel and can count for up to 4' for each unit. both scenarios require modifying the window arrangement. The manufactured panels will cost real $$ which has not been figured by anyone into the budget.

If you choose to ignore the interior wall then the wall spacing is 24'-11 and the wall bracing amount goes up to 7.75' for each of the north and south wall. Thus you must use the manufactured panel or eliminate windows or some sort of other device.

Alternately you can use an engineered diaphragm and shear wall system to try to ignore the North wall altogether. You may be able to find some lateral stability in the lower roof as well.


______________
MAP

 

[dhoward26]

I agree with focuseng.

If there wasn't 11'-8" to the interior wall...say 6'-0" or less, you could easily cantilever the diaphragm and transfer the load to the interior wall.

Without removing windows, or reducing window sizes, in this situation, without using full height timbers or steel. One could justify a full height 6x or glulam that is braced at the first story diaphragm. You would then need to design the 6x or glulam as a cantilever braced at the first story. You would have to transfer that force through the plates at that point. The other option is steel frames, and people in residential don't like that unless you are talking very expensive homes.