This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Participants may download the presentation here: http://www.awc.org/education/resources
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.
W o o d D i a p h r a g m D e s i g n4
This webinar is intended to provide general information only and does not constitute professional or engineering advice. No participant or user should act on the basis of any material contained in the webinar without obtaining proper professional advice specific to their situation. Further, the views expressed by speakers or other third parties are those of the speaker or third-party and not, necessarily, of AWC.
With regard to any information presented by a speaker or third-party, AWC does not make any warranty, express or implied, including the warranty of fitness for a particular purpose, and AWC specifically disclaims any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, product, service or process presented. Furthermore, the presentation of any material or information does not constitute or imply AWC’s endorsement of such.
Please note that this webinar is being recorded and by remaining a participant you automatically consent to such recordings. If you do not consent to being recorded, please disconnect from the session.
COURSE DESCRIPTIONThe 2018 International Building Code (IBC) specifies that structures using wood-framed shear walls and diaphragms to resist wind, seismic and other lateral loads shall be designed and constructed in accordance with AWC’s 2015 Special Design Provisions for Wind and Seismic (SDPWS). Calculation of wood-frame diaphragm deflection should account for bending and shear deflections, fastener deformation, chord splice slip, and other contributing sources of deflections. The 2015 SDPWS incorporates both a 3-term and 4-term deflection equation that accounts for these variables. This course will provide an overview and comparison of the 3-term and 4-term deflection equations. Additionally, an example showing calculation of mid-span deflection of a blocked wood structural panel diaphragm will be presented.
W o o d D i a p h r a g m D e s i g n6
LEARNING OBJECTIVES
Calculate wood-frame diaphragm deflection using the 2015 SDPWS
Wood-Frame Diaphragm Deflection
Compare the difference between the 3-term and 4-term deflection equation in the 2015 SDPWS
3-Term & 4-Term Deflections
Analyze individual components of the deflection equations to determine their magnitude of impact on total deflection.
Components of Deflection Equation
Utilize the example deflection calculation in future design work as a model for their own calculations.
Deflection Examples
Upon completion, participants will be better able to:
Diaphragms supporting Masonry or Concrete Structural Walls -Seismic Design Category C, D, E, & FDiaphragms shall be provided with continuous ties or struts between diaphragm chords to distribute these anchorage forces into the diaphragms (ASCE 7 - 16 sec. 12.11.2.2.1)
COMPARISON: 3-TERM VS. 4-TERMEXAMPLE C4.2.2-1 Derive Ga in SDPWS Table 4.2ADerive Ga in SDPWS Table 4.2A for a blocked wood structural panel diaphragm constructed as follows:
Sheathing grade = Structural I (OSB)Sheathing layup = Case 1Nail size = 6d common
(0.113″ diameter, 2″ length)Minimum nominal panel thickness = 5/16 in.Boundary and panel edge nail spacing = 6 in.Minimum width of nailed face = 2x nominalNominal unit shear
capacity for seismic, s = 370 plf SDPWS Table 4.2AAllowable unit shear capacity for seismic: s(ASD) = 370 plf/2 = 185 plf
W o o d D i a p h r a g m D e s i g n2 8
COMPARISON: 3-TERM VS. 4-TERMEXAMPLE C4.2.2-1 Derive Ga in SDPWS Table 4.2A (cont.)
Panel shear stiffness:Gv tv = 77,500 lb/in. of panel depth Table C4.2.2A
Nail load/slip at 1.4 vs(ASD):Vn = fastener load (lb/nail)
EXAMPLE C4.2.2-3 Calculate Mid-Span Diaphragm Deflection
L=48’16’ 16’
Diaphragm chord joint
W=
24’
Case 1 blocked diaphragm, 7/16” OSB sheathing, 8d common nails at 6”o.c. at all panel edges
A B
Allowable stress design load, =255 plf
W o o d D i a p h r a g m D e s i g n3 8
WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS CommentaryCalculate mid-span deflection for the blocked wood structural panel diaphragm shown in Figure C4.2.2-2. The diaphragm chord splice is sized using allowable stress design loads from seismic while deflection due to seismic is based on strength design loads in accordance with ASCE 7.
4. Which of the following contributed the most to the deflection of the diaphragm?a) Bending and chord deformationb) Shear, panel shear and nail slipc) Chord splice slipd) All of the above
W o o d D i a p h r a g m D e s i g n5 8
OUTLINE
• Basic Lateral Load Overview and Code acceptance of 2015 SDPWS
Q: Is diaphragm deflection cumulative with shear wall deflection?
A: Yes. Shear walls supporting a horizontal diaphragm would also be evaluated for deflection. Cumulative deflection would then be calculated to determine the maximum anticipated movement to compare with allowables.
W o o d D i a p h r a g m D e s i g n7 0
FREQUENTLY ASKED QUESTIONS
Q: Are there provisions to calculate the deflection for a diaphragm that is only partially blocked (i.e. at ends only) or is it proper to base the deflection on the entire diaphragm being unblocked?
A: There are no provisions for a partially blocked diaphragm. Suggest calculating for both a blocked and unblocked diaphragm to determine magnitude of difference and use engineering judgment.
Q: When the nailing pattern in a horizontal diaphragm varies instead of being uniform, how is deflection calculated?A: One approach is to modify the nail-slip constant in the 4-term equation in proportion to the average load on each nail with non-uniform nailing compared to the average load with uniform nailing. APA’s Diaphragm and Shear Wall Design and Construction Guide (L350) provides an example: www.apawood.org.
W o o d D i a p h r a g m D e s i g n7 2
FREQUENTLY ASKED QUESTIONS
Q: Is there any benefit if wood structural panels are glued to the assembly?
A: We are not aware of any added benefit with respect to diaphragm deflection.
Q: Is there a multiplier to use for a long-term consideration due to possible enlargement of nail holes or is that all included in the nail slip deflection calculations?
A: Testing done to verify diaphragm deflection calculations is based on full reverse cyclic loads, so the effects of nail hole enlargement has been addressed.
W o o d D i a p h r a g m D e s i g n7 4
FREQUENTLY ASKED QUESTIONS
Q: For large diaphragm, what adjustments to deflection equations need to be made to obtain inelastic diaphragm deflection?
A: ASCE 7 Minimum Design Loads for Buildings and Other Structures, Section 12.8.6 includes an amplification factor Cd which is used for story drift and seismic gaps.
T h i s p r e s e n t a t i o n i s p r o t e c t e d b y U S a n d I n t e r n a t i o n a l C o p y r i g h t l a w s . R e p r o d u c t i o n , d i s t r i b u t i o n , d i s p l a y a n d u s e o f t h e p r e s e n t a t i o n w i t h o u t w r i t t e n p e r m i s s i o n o f A m e r i c a n W o o d C o u n c i l ( A W C ) i s