1. CEE 626 MASONRY DESIGN Lateral Loads Flexible and Rigid Diaphragms Slide Set 8 Spring 2015

2. Look first at Out of Plane Loads Need to account for openings
The wall spans vertically placing a load on the floor or roof diaphragm
Diaphragm reaction
The wind load
transfers a reaction
To the top and bottom
Wind load generally uniform except
at corners for low rise buildings
How is load at diaphragm transferred to resisting elements (shear walls)?
Depends on whether diaphragm flexible or Rigid V V
Shear walls
Shear walls
Wind load generally uniform except
at corners for low rise buildings at
diaphragm level

3. Shear Walls and Diaphragms
Whether a Diaphragm is “Rigid” or “Flexible” depends on the relative stiffness of the diaphragm and the shear walls.
ASCE7 Says Diaphragm Deflection <2 x Shear wall deflection – You can consider diaphragm rigid

4. Shear Walls and Diaphragms
Generally concrete slabs are rigid and steel and wood systems are flexible diaphragms. However, some low aspect ratio wood and steel diaphragms are semi-rigid. This is beyond the scope of this course but most designers would look at these as a flexible and then as Rigid then design for the worst case – see ncma.org – TECK14-12-B– bia.org –Tech note 24c

5. Shear Walls and Diaphragms
Plan view at diaphragm level

6. Shear Walls and Diaphragms
Plan view at diaphragm level
d=L1/2
Note this is approximate and does not account for
Shear deformations of metal and wood panel slip

7. Shear Walls and Diaphragms

8. Shear Walls and Diaphragms
For instance a 8” CMU wall for a 12.7’ height (h/t = 20) can allow a deflection of x7.625 = .041” (for Ft +fa = 20 psi)

9. Shear Walls and Diaphragms

10. Shear Walls and Diaphragms
However most walls not fully grouted and have flashing at base – It is best to assume Pin-Pin supports for walls out of plane

11. Shear Walls and Diaphragms

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13. Shear Walls and Diaphragms

14. Shear Walls and Diaphragms
Once you distribute the Loads to a shear wall line in a flexible diaphgram system you must then distribute the shear to each shear wall element in the line.
Code say this is done w.r.t. relative rigidities
Perforated Shear walls
Load on a shear wall line V
distributed to Shear wall elements Vi
V = S Vi and Dis tribute w.r.t to relative rigidities of elements Vi V V Vi
Shear walls
Shear walls

15. Shear Walls and Diaphragms
Must look first at deformation of shear wall elements (Slides from Dan Abrams Class Notes)

16. Shear Walls and Diaphragms
Fixed - Fixed

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22. Shear Walls and Diaphragms
There are a number of methods to address load distribution for shear walls with various sized openings (see Schnieder and Dickey, The MDG 4 etc). These help address the issue where you may have a condition that suggests a section with openings will be stiffer than a section without.
If it gets complicated – Usually use Finite Element analysis.

23. Shear Walls and Diaphragms

24. Shear Walls and Diaphragms
Assume all are fixed-fixed
Code beff = 6t Compression and 1/2h tension

25. Multi-story shear walls in a line also have
effects of overturning adding axial load
on top of shear wall segments
Do Solid 2 story wall on Board

26. Shear Walls and Diaphragms
Multi-story shear walls in a line also have effects of
overturning adding axial load on top of shear wall segments

27. Shear Walls and Diaphragms
Multi-story shear walls in a line also have effects of
overturning adding axial load on top of shear wall segments

28. Shear Walls and Diaphragms
Additional axial load on shear wall segments small and neglected on low rise single story buildings .
Only an issue where shear walls are broken up with openings along a given line –”Perforated Shear Walls” – “to account for moments from above”.
Normally ignore in one story walls.

29. Shear Walls and Diaphragms

30. Shear Walls and Diaphragms

31. Shear Walls and Diaphragms
(PCL)

32. Shear Walls and Diaphragms
Look at lowest level

33. Shear Walls and Diaphragms
Look at lowest level

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38. Shear Walls and Diaphragms
Note the negative signs are reversed

39. Perforated Shear Walls
You would then design the segments for the appropriate load combinations for either ASD or SD as before.
Note there is a discrepancy in the pier c analysis - K , V and M is based on full height and P is base at opening height it is conservative to assume Peq is applied at the top of this pier, even though it is calculated at the opening height.

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42. Shear Walls and Diaphragms
Now on to Rigid Diaphragms Diaphragms
diaphragm flexible or Rigid V V
Shear walls

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48. Shear Walls and Diaphragms
Additional Flexible and Rigid Diaphragm designs with segmented and perforated shear walls will follow.