Gable End and Interior Shearwalls 4

[medeek]

I've been mucking around with the Woodworks software and reading through some of its documentation. I noticed that the uplift forces being calculated for the holdowns was different than I was calculating manually for gable end shearwalls. Looking through the help files I noticed that the height being used to calculate the holdown force was not the wall height but actually the average height to the roof diaphragm for that segment (see diagram below):

When a roof like the one shown above is composed of closely spaced trusses (max. 24" o/c) my thinking was they would act like mini shearwalls of their own and bring the diaphragm load down to the ceiling level where it would be transferred to the walls. I suppose the same argument can be made for interior shearwalls as shown above as well. However, I am now having to rethink this assumption.

The exterior shearwalls parallel to the ridge obviously are same height as the wall height but how is everyone else handling the gable end and interior shearwall heights?

A confused student is a good student.

 

[medeek]

Based on all of the comments thus far I'm heavily leaning towards Detail 3 for interior shearwalls parallel to trusses. Details 2,5 and 6 all seem problematic to me and given the amount of deflection in a typical 40' truss I wouldn't be surprised if something popped somewhere in the life of the structure. I think we need to take the gravity loads out of the equation by providing a direct load path to the ground, then we can properly deal with the lateral loads.

Hence, in all cases simply call out a drag truss that is inline with the shearwall. If this requires an additional truss I don't think the expense will be too great and it is the safe bet.

I'm liking the blocking at the ceiling level more and more. If the drag truss is load in compression it will tend to buckle at the bottom chord, gypsum will provide some bracing but is it enough? I agree with Jayrod12 that for a lightly loaded shearwall Detail 1 is probably adequate however the safe bet once again is Detail 3.

I think Malone's solution to the configuration in Detail 5 and 6 is good in theory but the lack of a really solid connection there just doesn't sit well with me. I don't think the plywood or OSB would snap provided the wall was centered between the trusses however if there was significant deflection, let's say an 1.0-1.5 inches, then the fasteners connecting the plywood to the truss would be pried loose both laterally and in withdrawal. Over the life of the structure they could potentially we worked loose enough that there capacity to resist the lateral loads could then become questionable.

A confused student is a good student.

 

[slickdeals]

@medeek,
What's the Malone book you are referring to? Is it the one on irregular buildings? Is it a good reference, have been considering purchasing it. Would appreciate some feedback.

Also you may want to consider changing (Mechanical) in your handle.

 

[medeek]

Listing on Amazon

Yes, The Analysis of Irregular Shaped Structures by Terry Malone and Robert Rice. It is quite technical though and not as well written and as easy to follow as Breyer's book. However, it does fill in some gaps that are otherwise missed in more basic texts. I've had a bit of a hard time justifying the price tag, but so far it has helped me with interior shearwalls and portal frames.

I wish there were more texts like this that really delve into the nitty gritty of "real" wood design. Most residential designs are not your run of the mill rectangular floor plan anymore.

How do I change the (Mechanical) in my handle?

A confused student is a good student.

 

[RFreund]

Someone tell Simpson to develop an adjustable connector that fits between trusses, allows for vertical deflection and transfers shear. Actually tell Simpson that i have a patent on this connector and that they should buy it from me.

I would second the Malone book and yeah it is a bit pricey. Also the title should be Wood diaphragms and shear walls... It is good but almost too good where you are left wondering, does anyone actually do this? and How are they getting paid enough to have the time to do so? But at least it sheds light on some gray areas.



EIT

http://www.HowToEngineer.com

 

[medeek]

Is this what you have in mind?

A confused student is a good student.

 

[KootK]

Love it!!

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Brad805]

That is a good idea.

 

[KootK]

Throw some bushings in there to make it convincing. And screws into the shear wall.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[RFreund]

I see what ya did there

EIT

http://www.HowToEngineer.com

 

[medeek]

I don't think the bolts would work as I've shown, the moment on them would tend to bend them over and bend the 12 - 7 GA metal they are attached to. I still think Detail 3 is the way to go even if I had something like these brackets at my disposal.

A confused student is a good student.

 

[jayrod12]

I think that bracket would work wonderfully provided it was manufactured correctly. With the right gauge of sheet metal and the correct ribbing it would end up being stronger than you imagine.

Call up the simpson guys and tell them you'll sell them the concept for a nominal fee.

 

[woodman88]

I think the standard wood framing details that exist, works on 99% of the wood frame construction. IMHO. For the issues of drywall ceiling cracking adding beams to support the wood trusses is a better choice in my opinion.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[KootK]

Can you elaborate on the beam arrangement that you mentioned woodman? I'm not sure that I understand how it works.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Archie264]

Wow, Medeek, you sure can draw!

 

[Brad805]

I think that bracket of MeDeek has great promise. I wouldn't use screws to achieve the vertical movement. I suggest slotted nail holes. This will allow the bracket to be much shorter and the framers would not need any other tools in their belt. Plus Simpson already has connections that use slotted holes, so they have a basis to start from. The next step is to make the bracket in two pieces to deal with unique truss spacing. That would be easy for Simpson.

I searched around as I was certain I have seen something along these lines, but I did not find anything. I too think you should float the idea to Simpson.

 

[medeek]

I think the key with this bracket is how to deal with the slotted holes for the vertical movement once that is figured out the rest is probably simple. I think it would be better to make specific sizes (ie. 12", 16", 19.2" and 24" rather than a two piece system. Two pieces would be inherently weaker and more expensive but I could be wrong.

A confused student is a good student.

 

[woodman88]

Where the span of a wood truss (from exterior wall to exterior wall) has a large deflection. For a "straight" non-cracking ceiling the best choices is to make all the interior walls non-bearing or make most of them bearing with beams between to keep all the truss spans similar in length.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[medeek]

This thread is a bit dated but to bring it back on topic and close it out properly I've spent some time tonight putting together a very simple spreadsheet for a sloped shearwall based on the paper presented by Thor Matteson:

http://design.medeek.com/resources/shearwall/SLOPED_SHEARWALL.xls

http://design.medeek.com/resources/shearwall/SLOPED_SHEARWALL.pdf

I just recently ran into another shearwall on a balloon framed gable end, as they say necessity is the mother of invention.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com