sheathing braced design of wall studs july 2010 update for aisi committee on framing standards...
TRANSCRIPT
Sheathing Braced Design of Wall Studs
July 2010 Update
for
AISI Committee on Framing StandardsDesign Methods Subcommittee
Toronto, ON
CivilEngineeringat JOHNS HOPKINS UNIVERSITY
www.ce.jhu.edu/bschafer/sheathedwalls
Overview
• Performance of sheathed walls
• Development of design method
• Current work
• Work plan and summary
www.ce.jhu.edu/bschafer/sheathedwalls
a) Bare wall with bridging b) Sheathed wall, no bridging
track
stud
bridging
board
Wall Bracing
Compression testing (full-scale walls)
Observed failure modes
Bare-Bare: FT OSB-Bare: FTOSB-Gyp: L + DGyp removed in picture
OSB-Gyp: L OSB-OSB: L
0 0.2 0.4 0.6 0.8 1 1.20
20
40
60
80
100
120
position (in)
load
(ki
p)
Comparison betw een different boards combination
2-BARE-BARE.txt
1-OSB-BARE.txt
11-GYP-GYP.txt
3-OSB-GYP.txt
9-OSB-OSB.txt
Full-scale wall tests (P-D)
Overview
• Performance of sheathed walls
• Development of design method
• Current work
• Work plan and summary
www.ce.jhu.edu/bschafer/sheathedwalls
a) Bare wall with bridging
b) Sheathed wall, no bridging
c) Single column
€
k
d) Spring-column model
track
studbridging
board
€
k
€
k
€
k
€
k
€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
e) Springs on the cross-section
Sheathed Wall - Idealization
Comparison to design methods
AISI-S100-07
AISI-S100-01
AISI-S210-07
Proposed
Proposed 1-sided
board€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
Sheathing Restraint - Bracing
xminor-axis bending
global torsion
ymajor-axis bending
flocal torsion
(distortional buckling)
board€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
Sheathing Restraint - Source
xfastener tilting/bearing
in series with
sheathing diaphragmstiffness
yfastener tilting/bearing
in series with
sheathing bendingstiffness
ffastener pull-out
in series with
sheathing bendingstiffness
board€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
Sheathing Restraint - Determination
xfastener-board test
in addition to
sheathing diaphragmequation and “APA” values
yfastener tilting/bearing
in series with
sheathing bendingstiffness via “APA” values
fFastener-board test (completed)
in series with
sheathing bendingstiffness equation and
“APA” values
and
Flexural- torsional buckling
Weak axis global
buckling
Local bucklingDistortional
buckling
Sheathing Restraint - ImpactOne-side sheathing only
Sheathing Restraint - ImpactOne-side sheathing only
Sheathing Restraint - PredictionOne-side sheathing only
€
Py 0 0
0 Px 0
0 0 Io /A( )Pφ
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥− P
1 0 yo0 1 −xoyo −xo Io /A( )
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
A1
A2
A3
⎧
⎨ ⎪
⎩ ⎪
⎫
⎬ ⎪
⎭ ⎪= 0€
u = A1 sinπz
L
⎛
⎝ ⎜
⎞
⎠ ⎟
€
v = A2 sinπz
L
⎛
⎝ ⎜
⎞
⎠ ⎟
€
φ=A3 sinπz
L
⎛
⎝ ⎜
⎞
⎠ ⎟
Or you can go back to the classical methods to find the global buckling load
€
Py =π 2EIy
2
L2
€
Px =π 2EIx
2
L2
€
Pφ =A
IoGJ +
π 2
L2ECw
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
€
Io = Ix + Iy + A xo2 + yo
2( )
Sheathing Restraint - PredictionOne-side sheathing only
€
u = A1 sinπz
L
⎛
⎝ ⎜
⎞
⎠ ⎟
€
v = A2 sinπz
L
⎛
⎝ ⎜
⎞
⎠ ⎟
€
φ=A3 sinπz
L
⎛
⎝ ⎜
⎞
⎠ ⎟
Or you can go back to the classical methods to find the global buckling load
€
Py =π 2EIy
2
L2
€
Px =π 2EIx
2
L2
€
Pφ =A
IoGJ +
π 2
L2ECw
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
€
Io = Ix + Iy + A xo2 + yo
2( )
€
Py + kxL2
π 20 kx
L2
π 2yo − hy( )
0 Px + kyL2
π 2−ky
L2
π 2xo − hx( )
kxL2
π 2yo − hy( ) −ky
L2
π 2xo − hx( )
IoAPφ + kx
L2
π 2yo − hy( )
2+ ky
L2
π 2xo − hx( )2 + kφ
L2
π 2
⎡
⎣
⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥
− P
1 0 yo0 1 −xoyo −xo Io /A( )
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
A1
A2
A3
⎧
⎨ ⎪
⎩ ⎪
⎫
⎬ ⎪
⎭ ⎪= 0
€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
Sheathing Restraint - ImpactOne-side sheathing only
pinfix
pin
fixpinfix
K=0.5K=1
a) Contact stud and track
End conditions(comparison to unsheathed specimens)
Sheathing Restraint - ImpactOne-side sheathing only
pinfix
pin
fixpinfix
€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
ky lowerboundAdd bending stiffnessof sheathing, but non-compositeky upperboundFully composite bending stiffness+ “Ad2” stiffness
Fixed end conditions kx, kf, and ky (lowerbound) found to be consistent with tests
Now, considering again all cases…
AISI-S100-07
AISI-S100-01
AISI-S210-07
Proposed
Proposed 1-sided
Design Method Outline• Determine sheathing restraint
– x, fastener-stiffness test + equations and “APA” for sheathing
– y, equations and “APA” for sheathing or composite test?– f, rotation test or COFS table, + eqn’s and APA for
sheathing• Determine Member Strength
– Global, add kx, ky, kf springs to classical equations or FSM, to findFe (main Spec.) Pcre (DSM)then launder through the column curve to getFn (main Spec.) Pne (DSM)
– Local, ignore spring restraints, determine local-global capacityAeFn (main Spec.) Pnl (DSM)
– Distortional, use kf classical, or kx and kf rational/FSM, to findFd (main Spec. C4.2) Pcrd (DSM)then launder through the distortional strength curve to getPn (main Spec. C4.2) Pnd (DSM)
• Check Fastener Demands
Overview
• Performance of sheathed walls
• Development of design method
• Current Work
• Work plan and summary
www.ce.jhu.edu/bschafer/sheathedwalls
Modeling (for fastener demands)
€
kx
€
kφ€
ky
€
kx
€
kφ
€
ky
imperfections…
Example fastener forces
0.5%Pn
further analysis and comparison with analytical predictions underway
y
f
Overview
• Performance of sheathed walls
• Development of design method
• Current Work
• Work plan and summary
www.ce.jhu.edu/bschafer/sheathedwalls
Basic summary of work plan• Literature summary
– existing methods– existing predictive capabilities
• Computational modeling– to support testing– to support design method creation
• Phase 1 testing– 8’ wall, single stud type, different sheathing configurations, axial only– Fastener translational stiffness/strength tests– Single column with sheathing tests
• Phase 2 testing– Axial + bending tests, 8’ wall, final details TBD– Axial + bending single member tests, w/ sheathing
• Development of new design methods– identify limit states, potential design methodologies, calcs, examples
red = added to initial work plan
Basic summary of work products• Literature summary
– existing methods (summary report, corrections to Simaan and Peköz)– existing predictive capabilities (Mathcad form)
• Computational modeling– to support testing (CUFSM and ABAQUS)– to support design method creation (reliability study on 2a, fastener spacing
studies, fastener demands in bending due to torsion begun)
• Phase 1 testing– 8’ wall, single stud type, different sheathing, axial only (report and
paper posted)– Fastener translational stiffness/strength tests (report and paper posted)– Single column with sheathing tests (report and paper posted )
• Phase 2 testing– Axial + bending tests, 8’ wall, final details TBD (materials ordered)– Axial + bending single member tests, w/ sheathing (materials ordered)
• Development of new design methods– identify limit states, potential design methodologies, calcs, examples
red = added to initial work plan blue = comment on work product
www.ce.jhu.edu/bschafer/sheathedwalls