Shearwall location
Shearwall location
(OP)
Hi - I'm doing a lateral wind/seismic analysis for a garage. The plans call for the garage doors to be positioned close to the west wall (please see attached .jpg file). I'm planning on using the wall segment east of the doors for the shearwall on this front wall. This wall is approximately 25% of the length of the front wall.
Typically I like to have the shearwall(s) more evenly distributed along the wall, but in this case this is the only wall segment I have to work with. I can show this wall good for the critical load. Are there any issues that I also need to consider since the wall is not symmetrically located along the wall?
Thanks for your input!
Typically I like to have the shearwall(s) more evenly distributed along the wall, but in this case this is the only wall segment I have to work with. I can show this wall good for the critical load. Are there any issues that I also need to consider since the wall is not symmetrically located along the wall?
Thanks for your input!






RE: Shearwall location
RE: Shearwall location
RE: Shearwall location
ash060 - agree - there needs to be a collector along the full width to drag the roof diaphragm into the shearwall at the end.
RE: Shearwall location
Regarding the diaphragm - ASCE 12.3.1.1 says the following: "Diaphragms of wood structural panels or untopped steel decks in one- and two-family residential buildings of light-frame construction shall also be permitted to be idealized as flexible." So I think I can consider it to be flexible, unless I'm misinterpreting this.
For the collector force, its maximum value would be the diaphragm unit shear times the length of the wall opening (= total length of the wall less the length of the shearwall), correct?
RE: Shearwall location
However, we usually assume wood diaphragms to be flexible...just not sure what that section is really aiming at without reading through the code logic.
Well - sort of. For wind the answer is yes. For seismic, it gets a bit more complicated as the connections between diaphragm and collector, the collector itself, and the collector-to-shearwall connections may have to be amplified by the overstrength factor.
RE: Shearwall location
I looked up the overstrength factor in ASCE 7 - it looks like there is an exception to the requirement for the application of the overstrength factor (section 12.10.2.1) - if the structure is braced entirely by light frame shearwalls the collectors only have to be designed for the diaphragm forces.
Thanks again, I really appreciate your input!
RE: Shearwall location
Keep in mind that you don't just check wind vs. seismic using the overall lateral forces from each, pick the higher one, and then discard the other.
Each element must be checked for both throughout the whole building. In some cases the seismic overstrength factor, seismic detailing requirements, etc. might control in a single element over the wind force for that element.
RE: Shearwall location
RE: Shearwall location
Since you said "wind controlled" I assumed you were calculating wind pressures. I'm referring to section 2308 in the IBC.
However, in ASCE 7, it doesn't appear that the term "light-framed" means the same thing as in IBC section 2308.
Thus, your reference to section 12.10.2.1 in ASCE 7 does appear to simply use the term as a descriptor of sheathed wood shearwalls and so the overstrength factor wouldn't apply as you suggest.
RE: Shearwall location
IBC 2006, section 202, Light-frame construction: A type of construction whose vertical and horizontal structural elements are primarily formed by a system of repetitive wood or light gage steel framing members.
ASCE 7-05 Chapter 11, page 111, Light-frame construction: A method of construction where the structural assemblies (e.g. walls, floors, ceilings, and roofs) are primarily formed by a system of repetitive wood or cold-formed steel framing members or subassemblies of these members (e.g. trusses).
IBC 2308 is for Conventional Light-Frame Construction... which as I understand it is prescriptive and does not require design by an engineer. Light-framed construction that does not meet the limitations of this section must be engineered.
RE: Shearwall location
RE: Shearwall location
RE: Shearwall location
My question is would it be better to incorporate the narrow walls between the doors in my design (i.e. a portal frame like the attached .jpg file)?
RE: Shearwall location
So you might end up going to a lot of trouble to hold down tall narrow shearwalls for very little gain. If you main, 8 ft. segment can take the load OK I'd stick with that.
RE: Shearwall location
RE: Shearwall location
RE: Shearwall location
RE: Shearwall location
So my question is - if I specify a glulam beam than runs the entire length of the front garage wall, can I eliminate the double top plate on this side and just make sure that the ends of the header are sufficiently strapped to the top plates coming in at the corners?
I didn't really see anything in the IBC that addressed this...
RE: Shearwall location
RE: Shearwall location