(928) 775-9119 120 Union, San Diego, CA Togawa Smith Martin Carbon 12, Portland, OR PATH Architecture By: R. Terry Malone, PE, SE Scott Breneman, PhD, PE, SE Senior Technical Directors Project Resources and Solutions Division www.woodworks.org E-mail: [email protected]Cantilever Wood Diaphragm Webinar Series Part 2-Shear Wall Design in Cantilever Diaphragm Structures A Design Example of a Wood Cantilever Diaphragm
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Cantilever Wood Diaphragm Webinar Series...Education Systems (AIA/CES), Provider #G516. Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates
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Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
Course Description
Part 2 of this series will introduce an open front diaphragm design example that will be worked through in the remaining webinars. Topics addressed will include seismic force calculation and distribution, and preliminary shear wall design taking into account nominal shear wall stiffness. The impact of factors such as horizontal and torsional irregularities on force distribution to shear walls will be examined, and design of elements contributing to shear wall rotation and overturning will be discussed. The effect of gravity loads on shear walls will also be reviewed.
1. Discuss evolutions in mid-rise building typology that have led to the need for open-front diaphragm analysis.
2. Review diaphragm flexibility provisions in ASCE 7 and the 2015 Special Design Provisions for Wind & Seismic (SDPWS).
3. Explore one option for open-front diaphragm analysis under seismic and wind loading in a wood-frame structure.
4. Highlight how to calculate story drift, diaphragm deflection and torsional irregularities, and discover their effects on load distribution through a cantilever diaphragm structure.
Learning Objectives
Fasten Your Seatbelts
5 out of 5 Calculators
Example and Method of Analysis:
• The solutions paper and this webinar were developed independently
from the AWC task group for open-front diaphragms. The method of
analysis used in this example is based on our engineering judgement,
experience, and interpretation of codes and standards as to how they
might relate to open-front structures.
• The analysis techniques provided in this presentation are intended to
demonstrate one method of analysis, but not the only means of analysis.
The techniques and examples shown here are provided as guidance and
information for designers and engineers.
Cantilever Wood Diaphragm Webinar Series-Content
Webinar Part 1- Code Requirements and Relative Stiffness issues:
• Introduction
• Questions needing resolution
• Horizontal distribution of shear and stiffness issues
• 2015 SDPWS open-front requirements
• Review preliminary design assumptions
Webinar Part 2- Shear Wall Design in Cantilever Diaphragm Structures:
• Introduction to open-front example
• Calculation of seismic forces and distribution
• Preliminary shear wall design
• Nominal shear wall stiffness
• Verification of shear wall design
Webinar Part 3- Cantilever Diaphragm Design, Flexibility and Drift Checks :
• Diaphragm design
• Maximum diaphragm chord force
• Diaphragm flexibility
• Story drift
Webinar Part 4-Torsional Irregularity, Other Design Checks, and Final Comments :
• Amplification of accidental torsion
• Redundancy
• Transverse direction design
• Multi-story shear wall effects
Content and Learning Objectives
Shear Wall Design:
• Introduction to open-front design exampleThe design example plan layout and goal of the example will be explained.
• Calculation of seismic forces and distribution
The basic seismic forces and distribution to the shear walls will be covered.
• Preliminary shear wall design
The basic shear wall construction will be chosen. Suggestions for improving the
preliminary wall design to limit drift and reduce torsion will be discussed.
• Nominal shear wall stiffness
A new approach for determining a single shear wall stiffness will be presented.
• Verification of shear wall design
Verification of the wall capacity will be examined after the redistribution of forces
are calculated using the nominal shear wall stiffness.
Webinar Series Part 2 of 4 parts
Design Example- Longitudinal Direction
SW
Op
en
Fro
nt
Sym.
C.L.
Sym.
C.L.
Op
en
Fro
nt
SW
SW
Bearing wall
non-shear wall
Bearing wall
non-shear wall
Unit 1
Unit 4Unit 3
Unit 2
SW
SW
SW
W1 plfW2 plf
SWSW
SWSW
Disclaimer:
The following information is an open-front diaphragm example which is subject to further revisions and
validation. The information provided is project specific, and is for informational purposes only. It is not
intended to serve as recommendations or as the only method of analysis available.
Lo
ng
itu
din
al
Transverse
No
rth
Example plan selected to provide maximum information on design issues
Page 4
12’ 8’ 15’
L’=35’
SW
SW
Op
en
Fro
nt
40’
Vsw
Vsw
34
A
B
10’
10’
SW
W’
Chord continuous
at corridor walls
Walls receive shear
forces from rigid
body rotation
(torsion).Sym.
C.L.
L=76’
Sym.
C.L.
6’
Op
en
Fro
nt
12
SW
SW
SW
SW
.
Chord fixity at
corridor walls
Lds
Chord
Bearing wall
non-shear wall
Diaphragm
Case 1
e
Lo
ng
itu
din
al
Transverse
Bearing wall
non-shear wall
Co
lle
cto
r
Shear panels or blocking
over entire wall lines if
framing is in this direction
20’
20’
Unit 1
Unit 4
Unit 3
Unit 2
10’
5’
5’
SW
SW
SW
Additional
units as occurs
Walls at grid lines 1
& 4 have no
stiffness
accidental
torsion
Case 3
No
rth
A.R.=1.25:1A.R.=1.25:1
A.R.=1.25:1A.R.=1.25:1
A.R
.=1:1
Example PlanPage 5
GL BM Chord GL BM Chord
GL BM Chord GL BM Chord
GL BM Chord GL BM Chord
Roof sht’g.
Blk’g.
Alt.-Top Chord Bearing Truss
Roof
sht’g.
WSP sht’g.
Blocking
Joist
hanger
Bracing Bracing
Roof
joist
Hangered Roof Joist
10”-0”
to F.F.
Ledgered Roof Joist
Ledger
Joist
hanger
Blocking
10”-0”
to F.F.
Clip
Top chord
bearing truss
(Platform framing not shown)
Typical Exterior Wall Sections
Diaph. chord
Diaph. chord
Diaph. chord
Opening
Floor or roof
sheathing
Blocking or
continuous
rim joist
Continuous rim joist, beam, special truss or
double top plate can be used as strut / collector
or chord.
Opening
Header
SW SWOpening
Column
Semi-balloon framing Platform framing
Splice at all joints
in boundary element
Header
Bm./Strut
Typical Exterior Wall Elevations at Grid Lines A and B
Trusses, top chord
bearing with blocking
between (shown)
Bm./Strut
SW
SW
Strut/collector
Typical shear
panel
Header
collector
Header
collector
Roof
sht’g..Blocking
Corridor
roof
joistsRoof
truss
Corridor
roof
joists
Shear
panelRoof
truss
Platform Framing at Corridor
Semi-balloon Framing at Corridor
Optional top
flange hanger
Section at Corridor
Section at Corridor(Similar to example)
Typical Wall Sections at Corridor Walls
Alt.-extend
WSP full hgt.
eliminate
Shear panels
Blocking
between
trusses
Optional struts
between SW’s
Diaphragm
Design
Calculate lateral
(seismic) force
Shear wall
design
Story Drift
Verify Rho
ρ
Verify accidental
ecc. ampl., Ax
SW stiff.
based on
wall length
Max. diaphragm
chord forces
ρ=1.0,
Ax=1.25
ρ=1.3, Ax=1.25
Analysis Flow- Not in paper
ρ=1.0
Ax=1.0
Table 12.3-1
ρ=1.0
ρ=1.3
Ax=1.25
Increase
Diaph./ SW
Stiffness?
Assuming
rigid
diaphragm
Fpx, o r
Chord splice
loc’s./slip
Diaphragm construction
based on max. demand
(Sht’g. / nailing)
Lateral load
distribution
Diaphragm
Flexibility
SW construction
Max. demand
Ax=1.25
Ax=1.0
ρ=1.0
Determine flexibility, Drift
SW & Diaph. Design
Determine Tors. Irreg., ρ, Ax
Engineering judgement required
Legend
based on
experience
ρ and Ax
not relevant
Longitudinal DesignStep 1
Page 6
Step 2
Page 7Step 3
Page 12
Step 4
Page 28
Step 5
Page 39, 41
Step 6
Page 44
Step 7
Page 51
Step 8
Page 54
Step 9
Page 54
Step 10
Page 58
Step 11
Page 60
Step 12-Page 61
ρ=1.0
Ax=1.0
ρ=1.0 Ax=1.0
ρ=1.3
Lo
ng
itu
din
al
Transverse
(i.e. Diaph. or MSFRS Forces) Establish nominal
SW stiffness (D+E)
ρ=1.3
Ax=1.25
Verify Final
Diaph. Design
Diaph. Inertial
Design Force
Fpx or MSFRS
Transverse Design
Verify Drift and
Torsional Irreg.
Verify Rho
ρ
ρ=1.0 Ax=1.0 ρ=1.0 Ax=1.0
Example Plan
Use for remaining checks
Re-distribution
Lateral loadsVerify Torsional
Irregularity
Ax=1.25
ρ=1.0
Verify Strength
ρ=1.3 Ax=1.25
ρ=1.3 Ax=1.0
ASD Design STR Design
Ax=1.25 ρ=1.3
Flexible assumed
Flow Chart based on
assumptions made.
ρ and Ax as noted
Page 16
Page 14
Page 36
Page 33
Page 26
Page 25
Page 37
SDC D, Type 1a torsional irreg. assumed
Typical SpreadsheetRequires Input
Longitudinal LoadingGrid Line kx Ky dx dy kd Fv FT Fv+FT Rho= 1