2006 IRC Braced Walls for Townhouses

[Berniedog]

I am reviewing braced walls for essentially three story townhomes. Bottom level is a garage and there is no basement.

With how narrow these units are and with all the windows, there is not much room for braced wall panels and the panels are not wide enough for engineered shear walls. These units will be built side by side.

How do any of you handle this? Put holdowns at the end of each unit and call it a day?

 

[MiketheEngineer]

Probably won't meet IRC 2003 or 06...

I have had to resort to steel moment frames in a few cases.

Check your wind and seismic forces. Try to use shear walls if possible - but you say not possible.

And I have seen a brand new 3-story town house that "tipped" right at the garage door openings from a less than design wind load. Very expensive to fix.

 

[Berniedog]

MiketheEngineer:

Where did this tip happen? How many stories high was your moment frames?

Did you design the townhouse to stand alone or as a row of townhouses?

 

[msquared48]

Perforated shearwall analysis will not work?

Although they are very expensive, what about prefabricated Simpson shearwall panels?

I have had to resort to steel frames before, but only on the lower story at the garage walls.

Ayt least on the bottom story, is there any chance of raising the concrete stemwall height to decrease the h/d shearwall ratio to the minimum of 3.5:1 or less?

Mike McCann
MMC Engineering

 

[lrhg]

I had exactly the same problem last year!

IBC 2006, Seismic design Cat B, all brick veneer, 90 mph wind. We had shear wall issues on the front wall as well on garage wall on 19' wide buildings. Part of the probelm is the requirement for tall floor-to-floor heights. The builder thought we had lost our minds with the holds-downs and nailing we were specing out. (he was building an "architect-designed" version a few 'burbs away - probably one that will "tip" someday!) The local code required complete structural separation of the units.

In the end, we used a concrete/steel frame at the garage for one story. (the builder said concrete was more cost-effective for him than CMU). We looked into Simpson panels and they did not have any test data or current application in the bottom level of a three story building - tested only in 2-story. We met with the local code officials and pulled a variance on the separation requirement. We used steel straps with TNEMC paint to tie two units together at the diaphragms. Working with the architects, we mananged to reduce/shift the window openings to get working shear walls for the top two stories on the front and rear elevations. Most were designed as perforated shear walls.(there were esentially no interior walls). Each unit was designed to carry 50% of the full design wind load.

I think CMU for the entire first story would have been a good alternate, as I still have a concern with the long term shortening of the wood walls next to the concrete/steel frame.