Shear Walls

1
Shear Walls

• Section 3

2
Typical Shear Wall
3
Location of Shear Walls

• Create box structure
• Equal length symmetrical

Even Distribution of Shear Walls
4
Break in Load Path
Exterior Shear Wall
Interior Partition
Interior Shear Wall
Cripple Wall
Continuous Load Path
Floor Must Support Shear Wall
5
Vertical Offset of Shear Wall
6
Shear Wall OverFloor Beam
7
Horizontal Shear Forces
8
Uplift Forces OnShear Wall
9
(No Transcript)
10
Two Functions of a Shear Wall
STIFFNESS Control Sidesway
Earthquake Force
STRENGTH
Resist Shear
Connection For Uplift Resistance
Connection For Sliding Resistance
11
What Provides Shear Wall Strength?

• Lumber
• Sheathing
• Fasteners

12
LumberStrengthFailure
13
Sheathing Strength Failure
14
FastenerStrengthFailure
15
Combining Different Material Strengths

• Different sheathing materials DO NOT combine
  strength
• Sheathing materials reach ultimate strength at
  different wall displacements

16
Sheathing Material Strengths
17
C
T
Earthquake Force
End Stud in Tension
Earthquake Force
End Stud in Compression
C
T
Resisting Force from Connection
18
Most Important Factors
Height
Weight
ARE STIFFER THAN
Tall Narrow Walls
Long Short Walls
19
Allowable Aspect Ratios
20
Northridge EarthquakeShowed Us

• Most materials did NOT do as well as predicted
• More material and wider walls needed

21
Reduced Code Values
22
Drywall Failure
23
Stucco Failure
24
NarrowPanelFailure
25
Successful Plywood Coverage
26
Wood Structural Panel Shear Walls

• Lumber type
• Lumber size
• Condition of existing wood

27
Douglas Fir-Larch
Stronger
Weaker
Hem Fir
28
Effect Of Lumber Species On Strength
Allowable Shears (lbs/ft) Based on Lumber Species
Nail Spacing at Panel Edges
Common Nail Sizes
Wood Structural Panel
Redwood Open Grain
Hem- Fir
Douglas Fir-Larch
Thickness
Panel Grade
15/32 in
Structural 1
8d
4
430
355
280
15/32 in
Structural 1
8d
3
550
450
360
Structural 1
15/32 in
10d
3
665
545
430
29
Use Proper Size Stud

• Framing members split at ultimate loads when
  sheathing nails are closely spaced
• Shear Walls 17 stronger when 3 framing used
  throughout

30
2 Adjoining Stud
31
Install Proper Size Blocking

• Fasten all edges to framing members or blocking
• Provide blocking if panel members are unsupported
  between framing members

32
Cripple Wall Blocking
33
3 Flat Blocking
34
Reinforced Window Opening in Shear Wall
35
Blocking For Opening Reinforcement
36
How is the Length ofShear Wall Measured?

• Horizontally along sheathing between wall ends
  with hold-downs
• NOT length of plywood
• IS measured by hold-down location

37
Whats Wrong?
Too close to end wall countersunk
38
Whats Wrong?
Too far from shear wall end
39
Acceptable Hold-Down Location
40
Lumber Grade
41
Effect of Lumber Grade onHold-Down Capacity
42
Penetration Through Shear Wall
43
(No Transcript)
44
(No Transcript)
45
Wood Decay
46
Termite Damage
47
Crawl Space Ventilation
48
Installing the Sheathing

• Use specified wood structural panel
• OSB
• Plywood

49
Construction of Oriented Strand Board Panel
50
Construction of Plywood
3 ply 3 layer panel
4 ply 3 layer panel
5 ply 5 layer panel
51
Minimum Recommended Thickness

• 15/32
• Both 4-ply and 5-ply
• More plies ð stronger sheathing

52
Use Correct Panel Grade
53
Sheathing Orientation
54

• Use proper size panel
• 21 aspect ratio
• 4 x 8 panel minimum
• Mark stud locations on panels
• Avoid improper fastening
• Maintain fire resistive and sound-rated
  construction
• Dont change anything!

55
Cripple Wall Ventilation
56
Shear WallFasteners
57
Use Common Nails
58
Use ProperNail LengthandHead Size
59
Performance Losses for Nail Substitutions
60
Nail Gun With Flush Attachment
61
Round-Head Nails(P-Nails)
ModifiedRound-Head Nails (P-Nails)
62
Clipped Nail Head
Smaller nail head areas è smaller shear wall
strengths
63
1994 UBC
Nail should not fracture the surface of the
sheathing
1997 UBC
The head or crown of the nail is flush with the
surface of the sheathing
Overdriven nails reduce shear wall strength
64
Overdriven Nails
Improper Edge Distance
65
Important

• Install nails flush to sheathing
• Maintain proper sheathing edge distance
• Check for splitting
• Remove improperly installed nails
• Provide proper edge nailing

66
OOPS!
67
How to Nail a Shear Wall

• Edge nail
• hold-down stud(s)
• upper top plate
• sill or sole plate
• blocking for individual panel edges
• blocking for opening reinforcement
• Field nail the studs between the panel edges