Shear Wall Holddown loads

[highwindguy]

As of late I have been increasing my floor diaphragm sheathing thickness with my exterior shear wall sheathing thickness and finally my panel nailing pattern... all of these items will create a stronger home to reduce the high load I am getting for Holddowns... my question is this... what else can I beef up on within the structure to reduce the holddown loads?

 

[DaveAtkins]

I don't believe the items you mention will reduce the uplift at holddowns. Can you add more shear walls?

DaveAtkins

 

[highwindguy]

I agree, we use other items for uplift... the overturning and shear I am trying to transfer to other locations.

Also, as any structure is sometimes we have interior walls and other times we don't.

I have in the past placed a holddown in a corner of a home and then another 16" inward "with a reduction of course" to get the high loads that the shearwall panel needed.

But the problem is the load I need is very high and even doing that the entire length of the shearwall by the time I get to center of wall my holddown isn’t doing anything.

 

[UcfSE]

Increasing the sheathing or nailing pattern will not reduce hold-down loads.

Have you tried perforated shear wall designs? How high of a magnitude are you talking about?

 

[highwindguy]

If you increase the floor diaphragm strength, you can create longer interior shear walls thus reducing the lateral loads for the outside of a home.

But the house I have has many open areas with not much wall, and I was wondering of other idea's that some have had that are working?

Corner holddown = 14 kips, and into a "superior wall", which I will not even get into that one!

 

[csd72]

I have designed a few coastal buildings as a tube, with the entire windward wall restisting the uplift. The sheathing distrubutes the load across.

it only really works if the height is greater than or equal to the width.

csd

 

[highwindguy]

thank you very much for your help!

 

[msquared48]

In a residence, I usually do not use interior shear walls in the upper story as they must be extended thru the roof truss system to the roof diaphragm.

Adding more shearwalls, or using transfer beams to increase the leverage will decrease the uplift, along with trying to use bearing walls as shear walls to take advantage of the dead load to lower the overturning.

Mike McCann
McCann Engineering

 

[JJMT]

I have a similar problem in regard to seismic loads. Obviously the best choice is to try to keep a lot of dead load on your wood shear walls (floor joists, trusses, cast the walls full of concrete etc.). (When desperate I’ve been known to sharpen the pencil and track very closely the vertical distribution of the lateral forces, most times this helps, other times it creates more overturning.) Other than switching to another lateral system I think you are stuck with the larger holdowns loads and ridiculously large holdowns. Remember that some holdowns can be installed on both sides of your cord. In some situations I’ll have a steel gravity framing and use the steel columns in for holdowns (just be sure to design for the shear transfer).

 

[csd72]

as an addendum to the last point. The windward wall (i.e. all the walls) would have tie downs at 3 or 4' o.c. and you could use all of these to resist the uplift.

 

[Grizzman]

can you increase your roof and/or floor spans by removing interior load bearing walls? this would increase the dead load on the exterior sheathed walls to help reduce the uplift loads.
Of course your house may get a foot or so higher.