Diagphragms, Shearwalls and Drag Struts
Diagphragms, Shearwalls and Drag Struts
(OP)
There is a debate in my office regarding the use of drag struts when the length of shearwalls are less than the width of the diaphragm
We have a typical apartment style building with a center longitudinal corridor with units on either side. In most cases, the demising walls between the units are the shearwalls and they extend from the exterior wall to the corridor walls. In some cases the shearwalls do not line up across the corridor. The questions/debate is as follows so i am curious what others are doing.
1.When looking at the diaphragm, some have suggested using 2 diaphragms (a leeward and windward). By doing this, the diaphragm chords are the exterior wall and corridor walls. By doing this, the shearwall extends the length of the diaphragm and no drag struts are needed.
2. Look at the building diaphragm as one full-with diaphragm and provide drag struts at each shearwall that is not the full width of the diaphragm. (i.e. at every shearwall since the corridor breaks them up.
3. Look at the building diaphragm as one full-with diaphragm, and check the diaphragm capacity based only on the length of the shearwall. If the capacity is greater, than no dragstrut is required. I.e. provide a dragstrut only when a width of diaphragm greater than the shearwall length is required.
Just out of curiosity, what are most of you doing/seeing? I have been reviewing many example sets of plans from engineers across the country, and it appears that either method #1 or #3 above is being utilized. There are even some cases where the shearwall do not extend to the corridor and no drag strut is called out, leaving me to believe that Option #3 is used.
Thoughts?
We have a typical apartment style building with a center longitudinal corridor with units on either side. In most cases, the demising walls between the units are the shearwalls and they extend from the exterior wall to the corridor walls. In some cases the shearwalls do not line up across the corridor. The questions/debate is as follows so i am curious what others are doing.
1.When looking at the diaphragm, some have suggested using 2 diaphragms (a leeward and windward). By doing this, the diaphragm chords are the exterior wall and corridor walls. By doing this, the shearwall extends the length of the diaphragm and no drag struts are needed.
2. Look at the building diaphragm as one full-with diaphragm and provide drag struts at each shearwall that is not the full width of the diaphragm. (i.e. at every shearwall since the corridor breaks them up.
3. Look at the building diaphragm as one full-with diaphragm, and check the diaphragm capacity based only on the length of the shearwall. If the capacity is greater, than no dragstrut is required. I.e. provide a dragstrut only when a width of diaphragm greater than the shearwall length is required.
Just out of curiosity, what are most of you doing/seeing? I have been reviewing many example sets of plans from engineers across the country, and it appears that either method #1 or #3 above is being utilized. There are even some cases where the shearwall do not extend to the corridor and no drag strut is called out, leaving me to believe that Option #3 is used.
Thoughts?






RE: Diagphragms, Shearwalls and Drag Struts
But to answer your question, which is also applicable to floor diaphragms, I typically use method 1, since if you have a lot of shear walls, you don't need a large, deep diaphragm.
DaveAtkins
RE: Diagphragms, Shearwalls and Drag Struts
RE: Diagphragms, Shearwalls and Drag Struts
When they're not quite aligned across a corridor, I've also done a little subdiaphragm similar to what Terry Malone does with disrupted chords in the book referenced above. There's also a shorter paper that is freely available from Terry Malone that covers this, though briefer: Link. Instead of moving a chord force over in plan, you're moving a drag strut force over in plan and then from an analysis standpoint your two walls across the corridor are locked together and thus behave as if they're in the same line. That way you don't have to extend drag strut across the whole building but still maintain a continuous load path.