Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Diaphragm transfer forces

mferg318

mferg318

Structural
Oct 26, 2017
16
How is everyone handling transfer forces from discontinuous shear walls above a diaphragm, similar to the situation shown below? I'm specifically looking for how to incorporate the shear wall loads into the shear diagram for the diaphragm. Are you adding them as point loads, or distributing across the width of the diaphragm? There seems to be mixed opinions in the literature.

1746201194166.png
 
Replies continue below

Recommended for you

Sort by date Sort by votes
A similar question i have had on this topic -

When you are designing your transfer diaphragm, how do you handle the overstrengthed upper level shear force, in combination with the inertial forces of the diaphgram at that level for a diaphragm check? 12.10.1.1 states to combine the overstrength transfer force with the inertial force, but if you are combining a ELF shear force from the primary lateral system with a calculated diaphragm force from equation 12.10-1 or 12.10-2, is that not double counting some of the load? This has always confused me.
 
Upvote 0 Downvote
RipPECity said:
A similar question i have had on this topic -

When you are designing your transfer diaphragm, how do you handle the overstrengthed upper level shear force, in combination with the inertial forces of the diaphgram at that level for a diaphragm check? 12.10.1.1 states to combine the overstrength transfer force with the inertial force, but if you are combining a ELF shear force from the primary lateral system with a calculated diaphragm force from equation 12.10-1 or 12.10-2, is that not double counting some of the load? This has always confused me.
Click to expand...

The Fpx is based on the inertial forces from that diaphragm level. The transfer forces don't show up in that as we calculate both Fx and Fpx by each diaphragm level and do not include any contribution for forces from above.

Basically the procedure is set up assuming that the inertial force is generated at the diaphragm level, and then flows into the MSFRS. Once the load is in the MSFRS it doesn't come back out into the diaphragm. This is why we have to specifically include the effect of transfer forces in addition to Fx or Fpx.
 
Upvote 0 Downvote
Deker said:
@RipPECity Read this thread and report back if you still have questions: https://www.eng-tips.com/threads/collector-design-force.512008/
Click to expand...
Thank you, that helps a lot. I think the part that had confused me was with a building w/ relatively equal floor tributary weights where the ELF distribution per floor decreased down the height of the building, being combined with the diaphragm design force, which would generate relatively equal diaphragm design forces per floor. In my hypothetical scenereo I have been thinking about/sketched out, checking a lowest floor diaphgram taking a transfer force from the entire building above would be higher than the total base shear of the building (combining ELF for all floors other than lowest & dia. design for lowest). What you said makes total sense though...I copied it below.

A reference stating that it's required, or a reference showing how to perform the analysis? It's true that the ELF force distribution doesn't necessarily occur at the same time as the peak diaphragm response at a given level, but there's no way to account for that in an ELF based design. When a transfer diaphragm experiences its max inertial response it also clearly experiences some level of transfer force from the VLFRS above. See the code snip below that requires the two load cases to be considered concurrently. If you felt that was too conservative, you could perform a nonlinear time history analysis (which is obviously way beyond what you would do for a standard building).
Click to expand...
 
Upvote 0 Downvote
You must log in or register to reply here.

Similar threads

Other Aaron
  • Locked
  • Question
CLT Diaphragm Moment Diagram & chord forces
Replies
0
Views
586
Other Aaron
Other Aaron
PRESIDENTJ
  • Locked
  • Question
Transfer of shear forces
Replies
0
Views
768
PRESIDENTJ
PRESIDENTJ
struct_eeyore
  • Locked
  • Question
diaphragm transfer 1
Replies
10
Views
694
DoubleStud
DoubleStud
palk7 EIT
  • Question
Diaphragm Tie Plate 1
Replies
11
Views
4K
XR250
XR250
TRAK.Structural
  • Question
Roof Diaphragm Openings
Replies
3
Views
2K
TRAK.Structural
TRAK.Structural

Part and Inventory Search

Sponsor

Back
Top Bottom