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05/12/2014
1
Overview of Changes to CSA O86-2014 &
Structural Design Provisions for Mid-Rise in OBC
Wood Solutions Fair, 2014, Toronto
Jasmine Wang, Ph.D., P.Eng.
Canadian Wood Council
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Outline
Mid-rise Related Changes in Building Codes
Overview of Changes to CSA O86-2014
Technical Resources for Engineering Design for Mid-Rise
Photo credit: Steven Street, WoodWORKS!ON
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Mid-rise Related Changes in Building Codes
National (proposed) and Provincial building codes allow wood construction of up to 6 storeys
Firstly adopted in amendment to 2006 BCBC in 2009
Proposed for 2015 NBCC
Different fire provisions
Essentially the same structural/seismic provisions but with broader scope
Recently adopted by OBC
Different fire requirements
The same structural/seismic provisions as NBCC 2015
Mid-rise Related Changes in NBCC 2015 & OBC - Structural/Seismic Design Aspects
Restrictions on irregularities (Sentence 4.1.8.10.(4))
For medium and high seismic zones (IEFaSa(0.2)>=0.35), Type 4 or 5 Irregularities are not allowed in 5 or 6 storeys of continuous wood construction
(a) offset: Shear wall location moves (b) lateral stiffness: Shear wall has more openings in a storey below
(a) (b)
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Increased static design force level (Sentence 4.1.8.11.(11))
Only for seismic design;
If the empirical code period is used, no need to increase the base shear
When the fundamental period is determined using established methods of mechanics other than the empirical code period, the static base shear shall be increased by 20%, but need not exceed the maximum.
Increased dynamic design force level (Sentence 4.1.8.12.(12))
Only for seismic design;
Having a fundamental period as determined using established methods of mechanics other than the empirical code period, the base shear shall be the larger of dynamic design force and 100% of static design force.
Mid-rise Related Changes in NBCC 2015 & OBC
- Structural/Seismic Design Aspects
Outline
Mid-rise Related Changes in Building Codes
Overview of Changes to CSA O86-2014
Technical Resources for Engineering Design for Mid-Rise
05/12/2014
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Overview of CSA O86-2014 Changes
Published in July 2014 (PDF format)
Mid-rise related changes
Shear resistance of shearwalls and diaphragms
Shear and bending moment resistance of glulam
Withdrawal resistance of lag screws
Other changes
Mid-Rise Related Changes in CSA O86-2014
Requirements for Anticipated Building Movements due to Moisture
Content Change
Requirements for Calculation of Deflection for Multi-Storey Shearwalls
Requirements for Shearwalls Using Gypsum Wallboard
Shear Resistance of High Capacity Shearwalls and Diaphragms
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Requirements for Anticipated Building Movements due to
Moisture Content Change
O86-2014 Clause 5.4.6 Building movements due to moisture content change
O86-2014 Clause A.5.4.6 Shrinkage and swelling of wood members
Information on the effect of shrinkage on differential movements and overall lateral drift calculations &
how to mitigate shrinkage
Information on areas that should be paid attention to:
Information on how to estimate shrinkage
Requirements for Anticipated Building Movements due to MC Change
Estimate of shrinkage
In multi-storey wood frame buildings
Shrinkage occurs mainly in horizontal members
Cumulative shrinkage in studs (parallel to grain) may be considerable in 5 & 6-storey buildings
Table 1: Estimated vertical movement in a 4-storey building (mm)
Table 2: Estimated vertical movement in a 5-storey building (mm) Examples:
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Shrinkage in multi-storey wood buildings
Shrinkage can contribute to overall lateral drift
Interstorey drift ratio may become the governing
factor
2.5% for earthquake design (normal occupancy)
0.2% for wind design
Can be mitigated by
Using shrinkage compensators, and
Using material subjected to less dimensional
change
Shrinkage Take-Up Devices
(Source: Simpson Strong-Tie)
TUD
CTUD
Requirements for Calculation of Deflection for Multi-
Storey Shearwalls
Current equation in CSA O86-09 applies to single-storey shearwall segments
Clause 11.7.1 (CSA O86-2014) Deflections of shearwalls
In the calculation of deflection for multi-storey shearwalls, multi-storey effects shall be considered
Note: See Clause A.11.7.1 for additional information on multi-storey effects
Clause A.11.7.1 Deflection of shearwalls in multi-storey buildings
A purely mechanics-based approach;
Appropriate for a typical shearwall cantilevered from its base and stacked for the full height;
Comprised of interstorey drift due to bending, panel shear, nail slip and vertical elongation of the wall anchorage system;
Takes into account the cumulative rotational effects from the storeys below;
The methodology is the same as the one given in APEGBC Bulletin.
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v = maximum shear force per unit length due to specified lateral loads Hs = shearwall segment height A = cross-sectional area of chord members E = modulus of elasticity of chords Ls = length of shearwall segment
v = maximum shear force per unit length due to specified lateral loads Hs = shearwall segment height
Bv = shear-through-thickness rigidity (Tables 7.3 A~C of CSA O86)
en = nail deformation for a particular load per nail (Table 8.2 of WDM) Hs = shearwall segment height
Hs = shearwall segment height Ls = length of shearwall segment
da = total vertical elongation of the wall anchorage system
Deflection of single-storey shearwalls
Deflection of shearwalls in multi-storey buildings
Bending Anchorage system elongation
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Deflection of shearwalls in multi-storey buildings
Fastener slip, en, for shearwall and diagram deflection calculation (Clause A.11.7 O86-2014)
en table was replaced with one equation
1. For nails used in wood-based
sheathing with dry lumber:
2. Multiply by 2 for green
lumber
3. en may be taken as 0.76
mm for GWB with dry lumber
Requirements for Shearwalls Using Gypsum Wallboard
O86-2014 Clause 11.8.8 Seismic design requirements for shearwalls using
gypsum wallboard
Gypsum wallboard shall not be considered to provide lateral resistance when the
interstorey drift ratio exceeds 1%.
For buildings higher than 4 storeys the contribution of the gypsum wallboard shall not
be accounted for in seismic resistance.
Different from APEGBC Bulletin
O86-2014 Clause 11.8.9 Load bearing walls constructed with gypsum
wallboard only
When interstorey drift exceeds 1% the design should be based on the assumption that
GWB provides no lateral support to studs.
Alternatively a secondary blocking system shall be used
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Shear Resistance of Shear Resistance of High Capacity
Shearwalls and Diaphragms
Clause 11.5.1, 11.5.2 & 11.5.3.4 of CSA O86-2014:
A mechanics-based approach was adopted to calculate the shear
resistance of shearwalls and diaphragms
Makes it possible for designers to design for high capacity shearwalls
& diaphragms
Mid-panel shearwalls
Diaphragms with multiple rows of fasteners
Overview of CSA O86-2014 Changes
Published in July 2014 (PDF format)
Mid-rise related changes
Shear resistance of shearwalls and diaphragms
Shear and bending moment resistance of glulam
Withdrawal resistance of lag screws
Other changes
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Shear resistance of shearwalls and diaphragms
Tabulated values in CSA O86-09
Based on test data
Limited to assemblies constructed with dimension lumber, common nail and sheathing of discrete thicknesses
A mechanics based approach was adopted in CSA O86-2014
Shear resistance of shearwall/diaphragm sheathed with wood-based structural panels governed by the smaller of:
Sheathing-to-framing connection
For seismic design nail shall be designed to fail in the modes where plastic hinge(s) form to ensure sufficient ductility
Sheathing panel buckling
Advantages
More engineering sense
More flexibility in terms of the assemblies
High capacity shearwalls and diaphragms: mid-panel shearwalls and diaphragms with multiple rows of fasteners
Shear resistance of shearwalls and diaphragms
Sheathing-to-framing connection
Sheathing panel buckling
Selection tables will be provided in
WDM 2015
Seismic
design
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High capacity shearwalls and diaphragms
Mid-panel shearwalls – double shear
Diaphragms with multiple rows of fasteners
Nail in single shear
Nail in double shear
Sheathing Stud or
Plate
Grain direction
89 mm
Stud or Plate
38 mm 38 mm
ns = 2
Overview of CSA O86-2014 Changes
Published in July 2014 (PDF format)
Mid-rise related changes
Shear resistance of shearwalls and diaphragms
Shear and bending moment resistance of glulam
Withdrawal resistance of lag screws
Other changes
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Bending Moment Resistance of Glulam
Design provisions in CSA O86-09
Design provisions in CSA O86-2014
Shear resistance of glulam with tension side notch at supports
Design provisions in CSA O86-09 (Clause 6.5.7.2.1)
Design provisions in CSA O86-2014 (Clause 7.5.7.4)
Longitudinal shear resistance of residual member above notch
Tension side notch not exceeding 0.25d
Within a distance “d” from the inner edge of the closest support to the furthest edge of the notch
Fracture shear resistance at notch
No reduction in shear resistance calculated using gross cross sectional area
05/12/2014
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Overview of CSA O86-2014 Changes
Published in July 2014 (PDF format)
Mid-rise related changes
Shear resistance of shearwalls and diaphragms
Shear and bending moment resistance of glulam
Withdrawal resistance of lag screws
Other changes
Withdrawal resistance of lag screws
Design provisions in O86-09 (Clause 10.6.5)
Design provisions in O86-14 (Clause 12.6.5)
• Based on the density of various wood products
• Apply not only to lag screws but also self-drilling
fasteners compliant to appropriate product
standards or product evaluation reports
05/12/2014
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Overview of CSA O86-2014 Changes
Published in July 2014 (PDF format)
Mid-rise related changes
Shear resistance of shearwalls and diaphragms
Shear and bending moment resistance of glulam
Withdrawal resistance of lag screws
Other changes
Other changes
Reduction in the concentrated loaded area on roof deck
Commentary information on plank decking and structural sheathing
Requirements for lateral brace forces for metal-plate-connected wood
truss compression webs (Clause 5.5)
1.25% of the axial compressive force in the member