6/9/2015
Credit: APA
Seismic Design of Large Wood Panelized Roof Diaphragms
In Heavy‐Wall Buildings
Copyright Materials
This presentation has been produced by John Lawson for the exclusive use of the
American Wood Council, yet ownership remains with John Lawson. Some photos and
diagrams credited to others have different ownerships and may have copyrights in
place and have been provided here for educational purposes only. All presentation
material produced and owned by John Lawson is protected by US and International
Copyright laws. Reproduction, distribution, display and use of the presentation
without written permission of John Lawson is prohibited.
© John Lawson 2015
1
6/9/2015
•
The American Wood Council is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #50111237.
•
Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non‐AIA members are available upon request.
•
•
This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of
handling, using, distributing, or dealing in any material or product.
Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
Course Description
This presentation will focus on the engineered design of large wood panelized roof diaphragms in tilt‐up concrete and masonry wall buildings, with focus on design requirements for strength, stiffness, and proper development and resistance of wall anchorage forces. A historical perspective of how past seismic experience with this building type has influenced today's building code provides a good perspective for the participant to apply the current provisions of ASCE 7‐10, 2012 NDS and 2008 SDPWS. Various design illustrations and examples of high load wood structural panel diaphragms, wall anchorage, subdiaphragms, continuity cross ties, chords and collectors will be shown.
4
2
6/9/2015
Objectives
Upon completion, participants will be better able to:
1. Identify the characteristics of a panelized wood roof diaphragm. 2. Apply requirements for wall anchorage forces including proper detailing for distribution of these forces into the diaphragm.
3. Utilize subdiaphragms as a tool to create an efficient load path for wall anchorage forces.
4. Design wood diaphragms and their chords and collectors for seismic forces.
5
Polling Question
1. What is your profession?
a) Architect
b) Engineer
c) Code Official
d) Building Designer
e) Other
6
3
6/9/2015
Large Wood Roof Diaphragms
Subjects Covered:
•
•
•
•
Panelized Roof Structure
Wall Anchorage System
Main Diaphragm Design
Diaphragm Deformation
Photo Source: ???????????
7
Source: APA – The Engineered Wood Association
Panelized Roof Structure
8
4
6/9/2015
A Panelized Roof Structure
Subpurlin
Purlin
Girder
9
Panelized Roof Structure
Wood structural panel oriented with strength axis parallel to supports; allows all edges to be fully blocked for maximum diaphragm shears, and without added blocking pieces.
15/32” thick Structural I panels are typical for basic roof loads (no snow).
Plywood/OSB
35psf Live, 45psf Total
allowable load capacity
per IBC T. 2304.7(5)
Hanger
Subpurlin
Bracing straps
Column Cap
Hanger
Hinge
All Wood System
10
Source: Simpson Strong-Tie
5
6/9/2015
Panelized Roof Structure
11
Source: Simpson Strong-Tie
Hangers already attached to ends
12
6
6/9/2015
Panelized Roof Structure
13
©2006 APA – The Engineered Wood Association
Panelized Roof Structure
14
©2006 APA – The Engineered Wood Association
7
6/9/2015
Panelized Wood Truss System
15
Source: APA – The Engineered Wood Association
Panelized Wood Truss System
16
Source: APA – The Engineered Wood Association
8
6/9/2015
Panelized Wood I-Joist System
17
Source: APA – The Engineered Wood Association
Panelized Hybrid Roof System
18
Source: APA – The Engineered Wood Association
9
6/9/2015
Panelized Hybrid Roof System
Wood Nailers on Steel Joist and Joist Girders
Hybrid System
Source: Simpson Strong-Tie
19
Panelized Roof System
• Shop
o Hangers on sub-purlins
o Joist nailers (if hybrid)
• Field-Ground
o Full length purlins, subpurlins, and sheathing
assembled on the ground
• Erection
o Purlin and sub-purlins lifted
to roof as a “panel”
Photo courtesy of Wood‐Lam Structures, Inc.
20
10
6/9/2015
Panelized Hybrid Roof System
Photo courtesy of Panelized Structures, Inc.
21
Panelized Hybrid Roof System
Wood panelized assembly
Photo courtesy of Panelized Structures, Inc.
22
11
6/9/2015
Panelized Hybrid Roof System
23
Panelized Hybrid Roof System
Photo courtesy of Panelized Structures, Inc.
24
12
6/9/2015
Panelized Hybrid Roof System
Photo courtesy of Wood‐Lam Structures, Inc.
25
Panelized Hybrid Roof System
Wood Structural Panel
With 2x and 3x wood subpurlins
Photo courtesy of Panelized Structures, Inc.
26
13
6/9/2015
Panelized Roof Framing System
27
Photo courtesy of Panelized Structures, Inc.
Up to 40,000 square feet installed daily
28
Photo courtesy of Panelized Structures, Inc.
14
6/9/2015
Development of
Wall-to-Roof Anchorage
Design Provisions
29
Wall Anchorage Design
•
•
•
•
•
•
Cross‐grain Bending Issues
Wall Anchorage Design Force
Eccentricity Issues
Pilaster Issues
Continuity Ties
Subdiaphragms
30
15
6/9/2015
Cross-grain Bending
Issues
31
Wall Anchorage Design
• Background
– 1971 San Fernando Earthquake
– 1992 Landers / Big Bear Earthquakes
– 1994 Northridge Earthquake
• Cross-grain bending of wood ledgers in
pre-1973 UBC buildings.
32
16
6/9/2015
Wall Anchorage Design
•
1971 San Fernando Earthquake
33
Photo Credit: Los Angeles City Dept of Building & Safety
Wall Anchorage Design
•
1971 San Fernando Earthquake
34
Photo Source: Earthquake Engineering Research Lab, Cal Tech
17
6/9/2015
Wall Anchorage Design
•
1992 Landers Earthquake
Wall Anchorage
Improper
35
Photo Source: California Seismic Safety Commission
Wall Anchorage Design
•
1992 Landers Earthquake

Wall Anchorage
Failure
Steel deck diaphragms:
Steel decking
Masonry Block
36
Photo Source: California Seismic Safety Commission
18
6/9/2015
Wall Anchorage Design
•
1994 Northridge Earthquake
37
Photo Source: Doc Nghiem
Wall Anchorage Design
•
1994 Northridge Earthquake
– Inadequate wall anchorage
38
Photo Source: Doc Nghiem
19
6/9/2015
Wall Anchorage Design
•
1994 Northridge Earthquake
39
Photo Source: Doc Nghiem
Wall Anchorage Design
•
1994 Northridge Earthquake
40
Photo Source: Doc Nghiem
20
6/9/2015
Wall Anchorage Design
•
1994 Northridge Earthquake
41
Photo Source: EQE
Past Performance
•
2001 Nisqually Earthquake
42
Photo Credit: Cascade Crest Consulting Engineers
21
6/9/2015
Wall Anchorage Design
•
1994 Northridge Earthquake
43
Photo Credit: Cascade Crest Consulting Engineers
Wall Anchorage Design
•
1994 Northridge Earthquake
44
Photo Source: EERI
22
6/9/2015
Wall Anchorage Design
•
1994 Northridge Earthquake
Ledgers fail in cross‐grain bending
Nails pulled through plywood edge
45
Photo Source: Doc Nghiem
Wall Anchorage Design
Pre‐1973 UBC
46
23
6/9/2015
Wall Anchorage Design
• Since the 1970s
–
–
–
–
No wood cross-grain bending or tension allowed
Direct connection required
No use of toenails or nails in withdrawal
No use of wood diaphragm sheathing as the tension tie
- ASCE 7-10: SDC C-F
47
Wall Anchorage 1980s
Wall Anchorage (Wood Roof)
See manufacturer’s
recommendations for
embedment depth
Member width
per manufacturer’s
recommendations
48
Source: Simpson Strong-Tie
24
6/9/2015
Wall Anchorage Design
Wall Anchorage (Wood Ledger)
49
Source: SEAOC Structural / Seismic Design Manual
Wall Anchorage Design
Wall Anchorage (Wood nailer on steel ledger)
50
Source: Simpson Strong-Tie
25
6/9/2015
Wall Anchorage Design
Wall Anchorage (Steel ledger)
Proprietary Pneumatically Driven Pins
51
Source: Simpson Strong-Tie
Wall Anchorage Design
Wall Anchorage (Purlin to wood ledger)
Pre-engineered wall tie hardware
52
Source: Simpson Strong-Tie
26
6/9/2015
Wall Anchorage Design
Wall Anchorage (Steel joist to embed plate)
53
Source: SEAOC Structural / Seismic Design Manual
Polling Question
2. Which of the following can be used to provide wall anchorage to a wood diaphragm:
a) Wood members in cross‐grain bending
b) Wood members in cross‐grain tension
c) Toenails
d) Subpurlins
e) Nails loaded in withdrawal
54
27
6/9/2015
Wall Anchorage
Design Force
55
Wall Anchorage Design
• ASCE 7-10 force levels
Fp  0.4 S DS k a I eW p
Not less than…
Sec. 12.11.2.1
Similar force levels since 1997 UBC for SDC D+. New for SDC B and C in ASCE 7‐10.
Fp  0.2k a I eW p
where…
k a  1.0 
Lf
100
ka need not be greater than 2.0
– In response to past performance problems, these forces have been
factored up to maximum expected force levels
• 3 to 4 times the ground accelerations
56
28
6/9/2015
Wall Anchorage Design
120’
Ka = 2.2, Use 2.0
Fp = 0.8SDSIeWp
40’
Ka = 1.4
Fp = 0.56SDSIeWp
Lines of shear resistance
57
Wall Anchorage Design
Lines of shear resistance
Ka = 1.8
80’
Fp = 0.72SDSIeWp
58
29
6/9/2015
Wall Anchorage Design
Example Wall Force Calculation
Fp = 0.8SDSIeWp
59
Source of Illustration: WoodWorks
Wall Anchorage Design
• Wall anchorage force Example:
Fp
33’
30’
8” thick
concrete
Fp  0.8S DS I eW p
Given: SDC = D
SDS = 1.0g
Ie = 1.0
8’‐0” anchor spacing
 332 
8"
  14,520 lbs
W p  150 pcf  8' 
12
 230  
Fp  0.81.0 g 1.0 14,520lbs   11,616 lbs
60
30
6/9/2015
Eccentricity Issues
61
Wall Anchorage Design
Wall Anchorage (Purlin to wood ledger)
Pre-engineered wall tie hardware
(both sides?)
62
Source: Simpson Strong-Tie
31
6/9/2015
Wall Anchorage Design
- ASCE 7-10: SDC C-F
Ledger
Purlin or Subpurlin
Plan
View
e
63
Wall Anchorage Design
- ASCE 7-10: SDC C-F
Moment = Tie Force x eccentricity
M
Plan
View
T
Purlin or Subpurlin
e
Combined Axial Tension and Bending Moment
64
32
6/9/2015
Wall Anchorage Design
- ASCE 7-10: SDC C-F
Concentric Loading Desired
Source: Simpson Strong-Tie
65
Pilaster
Issues
66
33
6/9/2015
Anchorage to Pilasters
•
1994 Northridge Earthquake
67
67
Photo Source: Doc Nghiem
Anchorage to Pilasters
•
1994 Northridge Earthquake
Load focused at pilasters
68
Photo Source: Doc Nghiem
34
6/9/2015
Anchorage to Pilasters
•
1994 Northridge Earthquake
69
Photo Courtesy of EERI
Anchorage to Pilasters
• 2014 Napa Earthquake
– Inadequate pilaster anchorage
70
Photos Courtesy of Maryann Phipps
35
6/9/2015
Anchorage to Pilasters
• 2014 Napa EQ
– Pilaster anchorage
71
Photo Courtesy of Maryann Phipps
Anchorage to Pilasters
• 2014 Napa Earthquake
Masonry Building Pilaster
Pilaster support failure
72
Photo Source: Abe Lynn, Degenkolb
36
6/9/2015
Anchorage to Pilasters
• 2014 Napa Earthquake
Masonry Building Pilaster
73
Photo Source: Josh Marrow
Anchorage to Pilasters
• 2014 Napa Earthquake
74
Masonry Building Pilaster
74
Photos Source: Abe Lynn, Degenkolb
37
6/9/2015
Anchorage to Pilasters
• ASCE 7-10
- Wall Anchorage at Pilasters
- ASCE 7-10: SDC C-F
75
Anchorage to Pilasters
• Pilaster’s tributary area for anchorage load
Repetitive Roof Anchorage
Parapet
Roof
Reaction?
How much load travels to pilaster?
Floor
Pilaster
76
38
6/9/2015
Anchorage to Pilasters
• Yield Line Theory
(Borrowed from Two‐way Slabs)
77
Anchorage to Pilasters
• Pilaster’s tributary area for anchorage load
Repetitive Roof Anchorage
Equal
Parapet
Roof
Equal
Equal
Equal
Equal
Floor
Pilaster
78
39
6/9/2015
Anchorage to Pilasters
• Pilaster’s tributary area for anchorage load
Repetitive Roof Anchorage
Equal
Parapet
Roof
Equal
Equal
Equal
Equal
Floor
Pilaster
79
Anchorage to Pilasters
• Wall anchorage force focused on Pilaster
Parapet
Roof
Fp
Fp  0.4k a S DS I eW p
Pilaster
Floor
80
40
6/9/2015
Polling Question
3. Wall anchorage at pilasters…
a) results from a uniform wall load
b) attracts more load from the wall
c) causes eccentric loading
d) Is not allowed per code
e) has no effect
81
Continuity Ties
82
41
6/9/2015
Continuity Ties
83
Photo Credit: Doc Nghiem
- ASCE 7-10: SDC C-F
Continuity Ties
• 1994 Northridge Earthquake
– Inadequate wall anchorage
The diaphragm sheathing in tension is not an effective continuity tie.
Cross‐grain tension
84
Photo Source: Doc Nghiem
42
6/9/2015
Continuity Ties
•
1994 Northridge Earthquake
85
Photo Source: Doc Nghiem
Steel Element
Issues
86
43
6/9/2015
Wall Anchorage Steel Elements
•
1994 Northridge Earthquake
Net section rupture. Limited ability to yield Photo Source: Doc Nghiem
87
Wall Anchorage Steel Elements
• Since the 1997 UBC
– Ductility cannot be counted on
– Steel elements are vulnerable
- ASCE 7-10: SDC C-F
88
44
6/9/2015
Wall Anchorage Steel Elements
• Capacity of Wall Anchorage System
– The design forces 0.4SDSkaIeWp have been
carefully coordinated with the expected material
overstrengths of the anchorage materials.
• Steel Elements
– Steel elements need an additional 1.4 load factor
(Sec. 12.11.2.2.2)
• Wood Elements
– No additional load
factors needed for wood
elements, including
bolts, screws and nails.
89
Continuity Ties
Typical Tie Connection
Typical Continuity Tie
90
45
6/9/2015
Continuity Ties
91
Source: Simpson Strong-Tie
Continuity Ties
92
Source: SEAOC Structural / Seismic Design Manual
46
6/9/2015
Continuity Ties
93
Panelized Wood Truss System
94
Source: APA – The Engineered Wood Association
47
6/9/2015
Continuity Ties
95
Photo Credit: John Lawson SE
Continuity Ties
96
Photo Credit: John Lawson SE
48
6/9/2015
Continuity Ties
Source of Illustration: WoodWorks
97
Continuity Ties
• Force same as wall anchorage
Fp  0.4 S DS k a I eW p
• 1.4 steel element load factor on steel
straps and steel joists
• Extend tie from chord to chord
98
49
6/9/2015
Continuity Ties
99
Continuity Ties
purlin 100
Source: SEAOC Structural / Seismic Design Manual
50
6/9/2015
Continuity Ties
101
Source: SEAOC Structural / Seismic Design Manual
Subdiaphragm Design
102
51
6/9/2015
Subdiaphragm Design
Subdiaphragm is a portion of a larger wood diaphragm designed to anchor and transfer local [wall] forces to primary diaphragm struts and the main diaphragm
Their use is permitted under ASCE 7‐10 Sec. 12.11.2.2.1
(SDC C‐F)
103
Subdiaphragm Design
104
52
6/9/2015
Subdiaphragm Design
Subdiaphragm Typ.
Continuity Ties
Source of Illustration: WoodWorks
105
Subdiaphragm Design
• A part of the Wall Anchorage System
– Thus same force:
Fp  0.4 S DS k a I eW p
• Aspect Ratio Limits:
– L/W = 2.5 maximum
106
53
6/9/2015
Subdiaphragm Design
 The maximum length-to-width ratio of the
structural subdiaphragm shall be 2½ to 1.
(ASCE 7-10 §12.11.2.2.1)
Fp
2½
1
Subdiaphragm chords
Continuity Tie
107
Source of Illustration: WoodWorks
Continuity Tie Connections
Continuity Tie
Connections
108
Source of Illustration: WoodWorks
54
6/9/2015
Continuity Tie Connections
• Continuity Ties are a part of the Wall
Anchorage System
– Thus same force:
Fp  0.4 S DS k a I eW p
• Check minimum interconnection force:
Fp (min)  0.133S DSW
109
Continuity Tie Connections
F p (min)  0.133 S DSW
Continuity Tie
Connections
110
Source of Illustration: WoodWorks
55
6/9/2015
111
Hinge Connector
Note bolt locations in vertical slots
Seismic Continuity Tie
Hinge Connector with tie capacity
112
Source: Simpson Strong-Tie
56
6/9/2015
Continuity Tie Connections
113
Source: SEAOC Structural / Seismic Design Manual
Evolution of Wall Anchorage Design
San Fernando Loma Prieta Landers Northridge
1.1
Seismic Coefficient (Strength)
1
0.9
Wall ties &
cross ties req’d.
No wood crossgrain
bending
0.8
0.7
Subdiaphragms
Concentrically loaded & Special pilasters rules
Steel elements
Wood, Conc., Masonry
0.6
0.5
0.4
0.3
0.2
0.1
0
Zone 4
SDS=1.0
SD1=0.6
114
UBC/IBC Edition
Wall Anchorage Forces (Strength‐Level)
© John Lawson SE
57
6/9/2015
Polling Question
4. Which one of the following is not a special consideration for wall anchorage?
a) 1.4x more design force at wood elements
b) Moments at eccentric connections
c) Ties continuous across building
d) Higher loads at pilasters
e) Subdiaphragms permitted
115
Questions?
116
58
6/9/2015
Main Diaphragm Design
117
Main Diaphragm Design
North
North/South Seismic Loading
East/West Seismic Loading
Wood Structural Panel Diaphragm
200‐ft
9¼” Tilt‐up Concrete Walls
33’ top of wall
30’ top of roof
400‐ft
25’
TYP.
118
59
6/9/2015
Main Diaphragm Design
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
56’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
56’‐0”
2x4 DF #2 subpurlins
at 24” o.c.
119
15/32” Structural I OSB
with staggered layout
9 ¼” Concrete Wall Panels, typ.
Purlins at 8‐ft o.c.
Main Diaphragm Design
•
•
•
•
•
•
Shear Nailing
Chords and Collectors
Irregularity Considerations
Diaphragm Deflections
Deformation Compatibility
Questions
120
60
6/9/2015
Shear Nailing
121
Main Diaphragm Design
Diaphragm Forces per ASCE 7‐10 Section 12.10
n
F px 
F
ix
n
w
ix
North/South Seismic Loading
i
w px
i
FROOF
Fpx
Fp max  0.4S DS I e w px
Fp min  0.2S DS I e w px
200‐ft
33’ top of wall
30’ top of roof
400‐ft
25’
9¼” Tilt‐up Concrete Walls
TYP.
122
61
6/9/2015
Diaphragm Shear Nailing
A
400’
200
’
1
wEW = 0.25wp
J
wNS = 0.25wp
5
R  4,
S DS  1.0
123
Diaphragm Shear Nailing
(Unfactored)
124
124
62
6/9/2015
Diaphragm Shear Nailing
• Diaphragm Construction (Panelized)
– 15/32” Structural I
– Fully Blocked
– Case 2 & 4 layouts
125
Diaphragm Shear Nailing
ASD values are “Nominal” divided by 2
15/32” Struct I w/ 10d nails (0.148” dia)
126
Source: SDPWS courtesy of AWC
6”/6” o.c.
320plf
4”/6” o.c.
425plf
(ASD)
(ASD)
2
1
2x framing 2x framing
2½”/4” o.c.
640plf (ASD)
3
2x framing
2”/3” o.c.
820plf
(ASD)
4
3x framing
63
6/9/2015
Diaphragm Shear Nailing
ASD values are “Nominal” divided by 2
15/32” Struct I w/ 10d nails (0.148”) with 4x framing
2 lines of 2½”/4” o.c.
1005plf (ASD)
2 lines of 2½”/3” o.c.
1290plf (ASD)
5
4x framing
6
4x framing
127
Source: SDPWS courtesy of AWC
Diaphragm Shear Nailing
1
6
5
1157 PLF ASD
2
4
972
3
417
4
3
602
787
5
2
278
417
278
602
972
ASD
1157 PLF
1
6
128
787
(Unfactored)
64
6/9/2015
Diaphragm Shear Nailing
129
North/South Loads
1
10d at 6,6,12
4
10d at 2,3,12 w/ 3x framing
2
10d at 4,6,12
5
2 lines of 10d at 2½,4,12 w/ 4x framing
3
10d at 2½,4,12
6
2 lines of 10d at 2½,3,12 w/ 4x framing
Diaphragm Shear Nailing
East/West Loads Added
A
J
32’
32’
32’
32’
24’
96’
1
24’
32’
32’
32’
32’
2
3
4
5
6
20’
6
5
4
3
2
1
160’
20’
5
130
1
10d at 6,6,12
4
10d at 2,3,12 w/ 3x framing
2
10d at 4,6,12
5
2 lines of 10d at 2½,4,12 w/ 4x framing
3
10d at 2½,4,12
6
2 lines of 10d at 2½,3,12 w/ 4x framing
65
6/9/2015
Chord Design
131
Diaphragm Shear Nailing
w
L
CHORD COMPRESSION
B
CHORD TENSION
w = distributed diaphragm load
L = diaphragm span length
B = diaphragm breadth (width)
8
132
66
6/9/2015
Collector Design
133
Collector Design
48’‐0”
56’‐0”
134
67
6/9/2015
North/South Loads
Collector Design
Line of lateral resistance
Diaphragm’s unit shear diagram (plf)
Collector
Line of lateral resistance
Line of lateral resistance
v2
v1
135
North/South Loads
Collector Design
v1
v2
Collector
L
FCollector= (v1+v2)L
v2
136
68
6/9/2015
Collector Design
East/West Loads
Line of lateral resistance
Line of lateral resistance
Collector
v2
v1
Diaphragm’s unit shear diagram (plf)
137
Line of lateral resistance
Collector Design
East/West Loads
Collector
v1
v2
L
v2
FCollector= (v1+v2)L
138
69
6/9/2015
Irregularity Considerations
139
56’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
56’‐0”
48’‐0”
56’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
Reentrant Corner Irregularity
2x4 DF #2 subpurlins
at 24” o.c.
140
15/32” Structural I OSB
with staggered layout
9 ¼” Concrete Wall Panels, typ.
Purlins at 8‐ft o.c.
70
6/9/2015
56’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
56’‐0”
48’‐0”
56’‐0”
48’‐0”
50’‐0”
50’‐0”
50’‐0”
Reentrant Corner Irregularity
50’‐0”
50’‐0”
Seismic Design Categories D, E, F
141
50’‐0”
50’‐0”
Reentrant Corner Irregularity
50’ >0.15L
56’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
L=296’ > 0.15L
L=400’
50’‐0”
50’‐0”
50’‐0”
L=250’
‫ ؞‬Plan Irregularity Exists
142
71
6/9/2015
Reentrant Corner Irregularity
143
Reentrant Corner Irregularity
56’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
56’‐0”
56’‐0”
48’‐0” Collector
50’‐0”
50’‐0”
50’‐0”
Collector
50’‐0”
50’‐0”
48’‐0”
North/South Loading
and
East/West Loading
144
72
6/9/2015
Reentrant Corner Irregularity
Diaphragm nailing not
subject to 25% increase
Anchor Bolting of ledger:
Design for 25% more shear
145
Reentrant Corner Irregularity
Diaphragm nailing not
subject to 25% increase
Collector
146
73
6/9/2015
Reentrant Corner Irregularity
Diaphragm nailing not
subject to 25% increase
Bolting of nailer:
Design for 25% more shear
Collector
147
Reentrant Corner Irregularity
Emh = ΩoQE
Collector forces likely comply with exception per ASCE Sec. 12.10.2.1
148
74
6/9/2015
Diaphragm Deflection
149
Diaphragm Deflection
• Calculation Methods
– 2008 SDPWS
• Deflection limits
150
75
6/9/2015
Diaphragm Deflection

Bending
5vL3
0.25vL  X C


8 EAb 1000Ga
2b
Shear/Nail Slip
L = Length (ft)
b = Width (ft)
A = Area of Chord (in2)
v = Max Shear (lbs/ft)
(unfactored E or W)
(2008 SDPWS Eq. 4.2-1)
Chord Slip
E = Elastic Modulus (psi)
Ga = Apparent Shear Stiffness (k/in)
c = Chord Slip (in)
X = Distance to Nearest Support (ft)
151
Diaphragm Deflection
5wL4

384 EI
Beam Analogy:
Bending:
L
v
v
b
W(unfactored)
We want accurate estimate of 
so we use Eaverage and unfactored W
152
76
6/9/2015
Diaphragm Deflection
Derivation:
Δ
bending
Uniformly loaded beam
5wL
5( w / 12)( L  12) 4 45wL4



384 EI
384 EI
2 EI
4
Reaction 
wL
 vb
2
w
Convert:
L in feet
w in lbs/ft
v
2vb
L
is the maximum unit
diaphragm shear in lbs/ft
and b is the diaphragm
width in feet.
Now substituting:
 bending
45  2vb  L3 45vbL3


2 EI
EI
153
Diaphragm Deflection
L
v
45vbL3
EI
Replace I in terms of A & b:
 bending 
v
b
Achord
I   I x   Ad 2 where d = “b/2”, and Ix is negligible
2
b

I   Ad  2 A  12   72 Ab 2
2

2
 bending
45vbL3
5vL3 Matches code equations


E  72 Ab 2 8 EAb
154
77
6/9/2015
Diaphragm Deflection

Bending
5vL3
0.25vL  X C


8 EAb 1000Ga
2b
Shear/Nail Slip
L = Length (ft)
b = Width (ft)
A = Area of Chord (in2)
v = Max Shear (lbs/ft)
(unfactored E or W)
Chord Slip
E = Elastic Modulus (psi)
Ga = Apparent Shear Stiffness (k/in)
c = Chord Slip (in)
X = Distance to Nearest Support (ft)
155
Diaphragm Deflection
Shear/Nail Slip:
Deformed shape consists
of parallelograms
w
156
78
6/9/2015
Diaphragm Deflection
Shear/Nail Slip: 0.25vL
1000Ga
•Ga = Apparent shear stiffness (kips/inch)
•Combines: *Shear deformation of sheathing and
*Deformation from nail slip
•Ga from SDPWS Tables 4.2A, 4.2B, 4.2C
•Ga empirically derived from tests.
157
Diaphragm Deflection
5vL3
0.25vL  X C



8 EAb 1000Ga
2b
Bending
Shear/Nail Slip
L = Length (ft)
b = Width (ft)
A = Area of Chord (in2)
v = Max Shear (lbs/ft)
(unfactored E or W)
Chord Slip
E = Elastic Modulus (psi)
Ga = Apparent Shear Stiffness (k/in)
c = Chord Slip (in)
X = Distance to Nearest Support (ft)
158
79
6/9/2015
Diaphragm Deflection
Chord Slip:
 X
C
2b
C
Sum all tension and compression
chord slips together
Sometimes. Connections only slip in tension…
159
Diaphragm Deflection
Chord Slip:
 X
C
2b
Each chord connection
slips by C
w
160
80
6/9/2015
Diaphragm Deflection
For seismic only, the actual deflection is inelastic.
δe = ∆, and needs to be increased.
δe
elastic
δM = (Cd δe)/Ie
ASCE 7-10 Sec. 12.12.3
Maximum inelastic
seismic response
161
Diaphragm Deflection
• Purpose of Limits
– Avoid Impact with Adjacent Structures
– Setback from Property Lines
– Maintain Structural Integrity
“Permissible deflection shall be that deflection that will
permit the diaphragm and any attached elements to
maintain their structural integrity and continue to
support their prescribed loads as determined by the
applicable building code or standard.”
2008 SDPWS Sec. 4.2.1
162
81
6/9/2015
Deformation Compatibility
An Example: Reentrant Corners
163
Deformation Compatibility
48’‐0”
48’‐0”
48’‐0”
48’‐0”
56’‐0”
48’‐0”
Without a collector, roof structure will tear from wall here
Collector
56’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
48’‐0”
164
Deflected shape with a collector
Deflected shape without a collector
82
6/9/2015
Deformation Compatibility
Wall Anchorage
Failure
• 1992 Landers Earthquake
Steel decking
Masonry Block
165
Photo Source: California Seismic Safety Commission
48’‐0”
48’‐0”
48’‐0”
48’‐0”
48’‐0”
56’‐0”
48’‐0”
For short reentrant corners, a strut is still needed to force the short wall to rock this distance.
Strut
56’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
50’‐0”
Deformation Compatibility
166
83
6/9/2015
Deformation Compatibility
Strut
Controlled rocking requires complete freedom of wall to rotate.
Strut should be conservatively designed for the force required to rock the wall including any additional restraint forces.
167
Deformation Compatibility
Another Example: Hinging of wall base out‐of‐plane
168
84
6/9/2015
Deformation Compatibility
• Pilaster restraint against rotation
169
Deformation is exaggerated for illustration purposes
Deformation Compatibility
• 2014 Napa Earthquake
– Pilaster restraint against rotation
170
Photo Courtesy of David McCormick
85
6/9/2015
Deformation Compatibility
• 2014 Napa Earthquake
– Pilaster restraint against rotation
171
Photo Courtesy of David McCormick
Deformation Compatibility
• ASCE 7-10
- Permissible Diaphragm Deflection
172
86
6/9/2015
Polling Question
5. Diaphragm deflection should be considered to:
a) Determine if the system will continue to support its loads
b) Avoid impact with adjacent structures
c) Maintain structural integrity
d) Avoid crossing property lines
e) All of the above
173
Closing Comments
174
87
6/9/2015
Closing Comments
• Building Code Provisions:
– A reaction to past events.
• Current Wall Anchorage Design:
– Hopefully solves code inadequacies.
– But, not tested by a design earthquake yet.
• Plenty of Old Inventory
– Failures will continue until older buildings are
retrofitted or demolished.
175
Closing Comments
• 2015 Special Design Provisions
For Wind and Seismic (SDPWS)
Available as a free download from AWC
176
88
6/9/2015
Questions?
• This concludes The American Institute of Architects Continuing Education Systems Course.
• For additional information on educational programs available from the American Wood Council.
info@awc.org
www.awc.org
177
89