Braced / Return Wall Requirement

[RFreund]

The IBC Section 2308.9 in the 2009 edition covers wall bracing. Basically a return wall that is similar to a shear wall but is not necessarily a shear wall. This wall is referred to as a braced wall as it is bracing the wall running perpendicular to it. The IBC then states that you need a braced wall ever 25' or 35' depending on seismic design category.

Question - If diaphragm strength and deflection criteria are met and shear wall strength and deflection criteria are met are braced walls still required?

EIT

http://www.HowToEngineer.com

 

[JAE]

I think section 2308 is the empirical design section for light framed construction. In that section you don't calculate lateral wind/seismic loads at all but rather just meet the requirements of the section.

 

[Cadair]

The bracing walls are to help resist uplift. They are there instead of using a hold-down. If you don't have them, how are you resisting the uplift?

 

[RFreund]

@JAE - Thanks for the reply. That is what I thought as well. I am attending an SE Review course and the presenter made it 'seem' otherwise. However I must say the the EQ presenter is doing a poor job.

@Cadair - Uplift would be resisted by holddown anchors at the ends of the shear wall.

I have never used the 'prescriptive/empirical' approach, I've always done the analysis and designed the load path accordingly.

EIT

http://www.HowToEngineer.com

 

[Cadair]

If the uplift is resisted by holddowns, then why are you using braced wall procedures? Engineered walls don't require return walls for bracing.

 

[RFreund]

Ahh, Well that was really my original question or what I was trying to get at.

I didn't think that they were required if you did a full analysis/design but the presenter (who is not doing a very good job IMHO) made it 'seem' otherwise.

EIT

http://www.HowToEngineer.com

 

[FSS]

You have choice of doing presecriptive or engineered. The 24" return wall is prescriptive. If you don't have it, the presecriptive tells you to add holdown. If you engineer the design, then you put in shear walls where you want and the holdowns required per your analysis. You can also just engineer a single wall line that falls outside of the presecriptive, while using presecriptive for the rest of the structure. At least I know that is the case for IRC.