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8/11/2019 Retrofit Sub
http://slidepdf.com/reader/full/retrofit-sub 1/57
Retrofit Measures
or
Derrell Manceaux, P.E.
8/11/2019 Retrofit Sub
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Pur ose
To describe typical retrofit measures for:
Piers and columns Cap beams
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Retrofit Methods
Column replacement
Su lemental columns Shear & flexure strengthening
mprovemen o uc y Steel jacketing
Active confinement w/ prestressing wire
Com osite fiber/e ox acket
Reinforced concrete jacket
8/11/2019 Retrofit Sub
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Column re lacement
Replace when: Damaged column
Flexure is greatly insufficient
Space limits other measures
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Column re lacement
Column anchorage-(headed bars)
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Column re lacement Supplemental column
loads.
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Flexural stren thenin
Not desirable in many cases
Shear capacity increases which attracts force to
the pier cap and foundation
Desirable case
new location
Concrete overlay (additional reinforcement) Adding reinforcement with steel shell
8/11/2019 Retrofit Sub
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Flexural stren thenin
Concrete overlay
Concrete alone adds strength due to moment arm
Long steel adds additional strength Must provide shear transfer with dowels
Must rovide confinement- hoo s
ties
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Column stren thenin Adding reinforcement with steel shell
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Column stren thenin Adding reinforcement with steel shell
us ensure s ear rans er
Provide development length into footing/cap
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Column stren thenin Adding reinforcement with steel shell
eve opmen o s ee s e o ensure p as c s ra n
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Ductilit and shear im rovement
Low ductility occurs from using starter bars at
base of column Concrete splits due to radial stresses from
Proper confinement may stop splice failure
Extend confinement to 75% of maximum
moment or column diameter
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Ductilit and shear im rovement
Failure path of an unconfined column
Spalling begins at strain =0.005 Ties began carrying more stress at this point and
fail
Confinement is lost and concrete core crushes
Conc core fractures and loses axial, flexural and
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Ductilit and shear im rovement
Steel acketin
Use 2 half shells and weld
Confinement is provided AFTER expansion of
Place 1-2” gap at end of jacket and supporting
R factors=4-6 may be used t ness ncreases - - na yze w t new
stiffness
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Ductilit and shear im rovement
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Ductilit and shear im rovement
Shell for rectangular columns
Rectangular shells do not have membrane action
like circular shells-They act like bending members
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Steel Shell Retrofit Exam le
(for splice) Provide data
Perform sim lified d namic anal sis Conduct shell design
er orm es gn c ec Deflection capacity
Shear capacity
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Structural confi uration
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Re uired data additional Superstructure weight W 1000 ki
Ground acceleration FvS1 .6 g
Concrete strength
4
f' 5 ksi ksi
Effective inertia e.
Nominal shear capacity V N 110.6k
(corresponding shear)
Concrete cover cover 2 in
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Sim lified d namic anal sis
3 E I eff k ruc ura s ness c
L3
c .ft
Mass m g m 31.056 k sft
Structural periodT 2
m
k c
T 1.737
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Sim lified d namic anal sis
(cont’d) Spec acc a
T S a 0.345 g
EQ shear V EQ S a W V EQ 345.454 ki
EQ moment M EQ V EQ M EQ 10363.61 k f
EQ deflection EQ
V EQ
k c
EQ 0.85 ft
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Shell desi n
FBD
fl .3 ksi
Confinement stress
s
fs=stress induced in jacket=29 ksi at strain =0.001
fl=confinement stress=300 psi
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Shell desi n
e c ness
Use 10mm=3/8 in fort f l
2 f t 0.25 i in
Ductility factor R eff M EQ
M n R eff 3.12Rdemand
Rdemand
<
Plastic hinge zone p . p .
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Desi n check
Perform moment curvature analysis to
determine rotational capacity Conduct pushover analysis to determine
Verify capacity is greater than demand
or e ect on
For shear
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Desi n check
Perform moment curvature analysis with shell
and existing reinforcing
Plastic rotation capacity p 0.0591 ra
L x (Øu – Øy)
0.03211
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Desi n check
Perform pushover analysis
Target displacement from elastic analysis
1.5 T 1.27 i ft
Plastic displacement
p T p. n .
Check rotation demand vs ca acit
pL
p 0.04 rad 0.03 rad
p 0.04 rad p 0.0591 ra<0.03 rad
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Desi n check
Retrofitted column can handle twice the
plastic rotation. Actual required thickness would be about
.
shell
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Desi n check
Shear check outside plastic hinge region
Target shear
V p 1.5 V V p 165.9 ki
ear capac y
'2 .8
1000
.
OK
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Prestress Wra in Better system for confinement (active system)
,
High losses due to friction
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Prestress Wra in
Prestress wrapping with
wedges Machine pulls strand
away from pier and
wedges are placed toestablish tension
Minimum losses
No data on rectan ularsystems
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Prestress Wra in
P t W i
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Prestress Wra in
Semi-circular reinforcing bars (same effect as
prestress)
D tilit d h i t
8/11/2019 Retrofit Sub
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Ductilit and shear im rovement
Semi-circular reinforcing bars
D tilit d h i t
8/11/2019 Retrofit Sub
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Ductilit and shear im rovement
Composite fiber jacketing High strength glass (E-glass)
Carbon Aramid fibers
Passive system is preferred method
ac ve sys ems creep an rup ure
Loses strength due to moisture absorption R=4 for most columns
I fill h ll
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Infill shear wall
I fill h ll
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Infill shear wall Increases shear capacity Prevent hin es from formin transverse
Must act composite with existing members (dowels)
V ti l it ti
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Vertical ca acit reservation Type “P” retrofit
Rubble is retained in shell to give vertical support
ery cos e ec ve
Li it ti f l f
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Limitation of column forces
Isolation bearings
Flexural stren th reduction
Limitation of column forces
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Limitation of column forces
Sierra Point Overhead
Limitation of column forces
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Limitation of column forces Isolation
Limitation of column forces
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Limitation of column forces
Not suited for isolation
Bridges on soft soil (acc increases) Long period structures (little is gained)
Period shift
Limitation of column forces
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Limitation of column forces Flexure strength reduction
e uces p as c momen an s ear eman
Must improve ductility capacity
Consider making hinge on frames
Concrete ier wall retrofit
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Concrete ier wall retrofit Stiff and strong in transverse direction
nsure oun a on can carry oa
Retrofit usually not required unless starter bars exist
Concrete ier wall retrofit
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Concrete ier wall retrofit
Bent ca confi urations
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Bent ca confi urations Pinned connections have minimum stress
forces
Bent ca confi urations
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Bent ca confi urations Outrigger piers have high torsional stresses
Pier ca / oint re lacement
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Pier ca / oint re lacement
Difficult
Expensive
Bent ca stren thenin
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Bent ca stren thenin Add bolster to side
us ac compos e o prov e exure an s ear
Dowels help ensure composite action by shear friction
Add extra reinforcing and prestress
Bent ca stren thenin
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Bent ca stren thenin Integral caps more difficult to retrofit
Add bolsters to lower side of cap for positive moment
res ress ng may e mos econom ca
Reduction in ier ca forces
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Reduction in ier ca forces Link beam retrofit
Limits shear in column to value just below link
elastic
Stren thenin of column and
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Stren thenin of column and
beam joints Integral bent cap retrofit
Stren thenin of column and
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Stren thenin of column and
beam joints Knee joint retrofit
Pier and column limit states
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Pier and column limit states
Pier and column limit states
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e a d co u t states
Summar
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To describe typical retrofit measures for:
Piers and columns Cap beams
8/11/2019 Retrofit Sub
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What questions do you have?