multi-story shear wall design - seaon

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SEAONNovember 18th, 2010Design of Multi-Story Light-Frame Shear Walls

Shane Vilasineekul, P.E.

Design Wood or CFS Shear Walls?

CODE

ASCE 7-05§ 1609 Wind§ 1613 Seismic

AISI S213-07§ 2210.6 CFS Lateral Design

AF&PA SDPWS-08§ 2305.1 Wood Lateral-Force-Resisting Systems

Wood Shear Walls

Free download at: www.awc.org

http://www.awc.org

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Shear Wall Types:, ,

Shear Wall Types:–



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Shear Wall Types:, , Shear Wall Mechanics

Racking Sliding

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Overturning Overturning Resistance

AF&PA SDPWS-08 Table 4.3.4• Typically 2:1• 3½:1 for some applications

• Blocked WSP for wind• Blocked WSP for seismic

with reductions

AISI S213-07 Tables C2.1-1, C2.1-2, C2.1-3• Typically 2:1• 4:1 for some applications

• 7/16 OSB with reductions• 27 mil steel sheet

Maximum Aspect Ratio: h/b Overturning Restraint

AF&PA SDPWS-08: § 4.3.6.4.2• Anchoring device required when DL

stabilizing moment is not sufficientAISI S213-07: § B2• Shear resistance based on principals of

mechanics• Hold-down anchors required “even

though calculations may demonstrate that hold-down anchors are not necessary” <S213 -07 commentary>

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Overturning Mechanics

bVv /=

hvbhVT ⋅=⋅= /

xbbhVT D

−⋅−⋅

= 22ω

xbhVT

−⋅

=

1

2 2++

−⋅−⋅

= iD

i Txb

bhVTω

2bhvT D ⋅−⋅= ω

Given:Width, b = 4’Height, h = 10’Force, P = V = 1,000 lbs

Solution:Tension, T = C =V x h / b =1,000 lbs x 10’ / 4’= 2,500 lbs

1,000

TC

Multi-Story Shear Walls

Given:Width, b = 4’Height, h = 10’Force, P1 = V1 = 1,000 lbs

P2 = 500 lbs, V2 = 1,500 lbsSolution:Tension, T2 = C2 =V2 x h / b + T1 =1,500 lbs x 10’ / 4’ + 2,500= 6,250 lbs

1,000

T1 C1500

T2 C2


Given:Width, b = 4’Height, h = 10’Force, P1 = V1 = 1,000 lbs

P2 = 500 lbs, V2 = 1,500 lbsP3 = 500 lbs, V3 = 2,000 lbs

Solution:Tension, T3 = C3 =V3 x h / b + T2 =2,000 lbs x 10’ / 4’ + 6,250= 11,250 lbs

1,000

T1 C1500

T2 C2


500

T3 C3

= 13,585 lbs when using Center-of-T to Center-of-C

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Shrinkage

§ 2304.3.3 Shrinkage.Wood walls and bearing partitions shall not support more than two floors and a roof unless an analysis satisfactory to the building official shows that shrinkage of the wood framing will not have adverse effects on the structure…

Shrinkage Amount DOC PS 20-05

§ 6.2.3.10.25% Shrinkage for each 1% change in moisture content of dry lumber

(11.25”)*(0.0025)*(19%-9%) = 0.28”

Shrinkage

1st

Story

2nd

Story

3rd

Story

4th

Story

Tie-Off at Every Floor

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Seismic Requirements

ASCE 7-05• Table 12.2-1: R=6.5 for light-framed bearing wall systems

sheathed with WSP or steel sheets• § 12.10.2.1: collectors, splices, and connections in structures

braced only with light-frame shear walls exempt from overstrength design

AISI S213-07• § C1.1: R≤3.0, no special requirements (SDC A-C only)• § C5 Special Seismic Requirements for R>3.0

– Connections - Available Strength shall exceed lower of:a) Amplified Seismic Load (Ω0 load) or, b) Nominal Tensile Strength of the member

– Vertical Boundary Members and Uplift Anchorage - Nominal Strength to resist lower of:

a) Amplified Seismic Load (Ω0 load) or, b) Loads the system can deliver

Shear Wall Deflection

Bending Shear

Nail Slip

Wall Anchor

Slip

Shear Wall Deflection

• IBC-09 Eqn. 23-2

• AF&PA SDPWS-08 Eqn. 4.3-1

• AISI S213-07 Eqn. C2.1-1

vsheathingcs b

hvGt

vhbAE

vhδ

βωωωω

ρωωδ +

++=

2

43245

121

38

bhdhe

Gtvh

EAbvh

an +++=∆ 75.08 3

bh

Gvh

EAbvh a

aSW

∆++=

10008 3

δ

Shear Distribution

Rigid Diaphragm• ΔD ≤ 2ΔS• Distributes forces based

on relative stiffness of shear walls below

• Can distribute torsional moment

Flexible Diaphragm• ΔD > 2ΔS• Distributes forces based

on tributary area of shear walls below

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• ASCE 7-05: Idealized as Flexible– § 12.3.1.1 WSP & untopped steel deck diaphragms in

one- and two-family buildings– § 12.14.5 WSP & untopped steel deck diaphragms

when using the simplified seismic design procedure• IBC-09: Idealized as Flexible

– § 1613.6 WSP & untopped steel deck diaphragms meeting the following:

1. Limited toppings2. Story drift limits3. WSP or steel sheet shear walls4. Cantilevered diaphragm design

Alternative to Shear Wall & Diaphragm Deflection Calcs.

NEESWood Capstone Test:World’s Largest Earthquake Test

NEESWood• Network for Earthquake

Engineering Simulation Wood

• 2005 NSF Funded Project

• 4-Year, 5-University Program

• Goal: Develop Performance-Based Seismic Design (PBSD) Philosophy for Mid-Rise Wood-Frame Construction

• Culminated in 2009 Capstone Test


Capstone Test Objectives1. Confirm NEESWood-developed PBSD philosophy

satisfies objectives2. Provide data set for verification/calibration of

nonlinear dynamic models3. Confirm PBSD philosophy for steel/wood-frame


Capstone Building• 4-months to construct• 6-stories of wood framing on 1-story steel frame• 14,000 ft2 wood building• 628-kip wood building (with steel plates added)• Largest building ever tested on a shake table• Worlds Largest Shake Table: Miki City, Japan

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Capstone Test3 Tests using the Canoga Park Record of Northridge Earthquake (6.7 magnitude)• Test 1: 53% of record, 0.22g, 72-yr return period• Test 2: 120% of record, 0.50g, 475-yr return period• Test 3: 180% of record, 0.76g, 2500-yr return period

-0.7-0.6-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

0 5 10 15 20 25 30

Time (sec)

Acc

eler

atio

n (g

's)

-0.7-0.6-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

0 5 10 15 20 25 30

Time (sec)

Acc

eler

atio

n (g

's)


Capstone Test Results• Excellent performance

• Maximum average drift at roof ~ 8-inches

• Average story drift ~ 2%

• Confirmed NEESWood PBSD philosophy

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multi-story shear wall design - seaon

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