seismic rehabilitation using infill wall systems
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Seismic Rehabilitation using
Infill Wall Systems
Robert J. Frosch
Non-Ductile Frames
• Columns and Beams
– Inadequate capacity
• Flexure
• Shear
– Lack of confinement
– Lack of column tensile lap splices
• Beam-Column Joints
– Lack of confinement
– Inadequate joint shear capacity
– Strong beam – Weak column
Economical Rehabilitation
• Construction Cost
• Construction Time
• Maintain Building Operations
Total Rehabilitation Cost
Rehabilitation Techniques
• Increase frame ductility and strength
– Frame jacketing
• Reduce seismic stresses
– Braces
• Change lateral load system
– Infill Wall
Infill Wall
New footing
Reinforcement
Dowels
Interface Dowels
Field Experience
Objectives
• Eliminate interface dowels
• Eliminate extensive formwork
• Eliminate large volumes of concrete
– Movement
– Placement
• Increase column tensile capacity
– Without jacketing
Precast
Panels
Steel Pipe
Grout Strip
Reinforcement
Existing
Frame
Precast Infill Wall System
Existing Column
Precast Wall
Post Tensioning
Grout Strip
Post TensioningDucts
Column Tensile Capacity
Precast Infill Wall
• Ease of Construction
• Ease of Fabrication
– Avoid Protruding Bars
• Provide Force Transfer
– Shear Keys
Model Test StructureP
P/2
6 in. Wall
4 in. Wall
8’
8’
16’
Precast Panels
Panel Installation
Shear Lug
Grouting
Grouting
Completion
Before After
Rehabilitation
Frame Test
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
-0.3 -0.2 -0.1 0 0.1 0.2 0.3
Total Drift (%)
Ba
se S
hea
r (k
ips)
300
Total Drift (%)
Ba
se S
hea
r (k
ips)
Infill Wall Test 1: Flexural HingePost Tensioning = 237 kips
-300
-200
-100
0
100
200
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6
Splice Failure
2 - 1” Bars2 - 1” Bars
2 - 1 1/4” Bars2 - 1 1/4” Bars
Splice Failure
-300
-200
-100
0
100
200
300
-1000 -500 0 500 1000 1500 2000 2500
Micro-Strain (in./in.)
Ba
se S
hea
r (k
ips)
Decompression LoadColumn PT: Test 1 (PT = 237 kips)
e PT
PTe
VDC = 85 kips
Decompression
Load
Total Drift (%)
Ba
se S
hea
r (k
ips)
Infill Wall Test 2: ShearPost Tensioning = 507 kips
-500
-400
-300
-200
-100
0
100
200
300
400
500
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
2 - 1” Bars
2 - 1 1/4” Bars
2 - 1” Bars
2 - 1 1/4” Bars
Splice Failure
4 -1” Bars4 -1” Bars
Cracking Pattern
Benefits
• Provide an economical system for strengthening RC buildings
• Decrease damage costs from an earthquake
• Decrease nonstructural damage
• Increase life safety
-500
-400
-300
-200
-100
0
100
200
300
400
500
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Total Drift (%)
Ba
se S
hea
r (k
ips)
Analysis of Wall BehaviorTest 2
Decompression
Load
P.T. Model
Ig,Ag
P.T. Model
Icr,AgP.T. ModelP.T. Model
Flexural Design
• Capacity Controlled by Post-
Tensioning System
• Provide Adequate Anchorage of
Post-Tensioning System
Splice Failure
MPost Tensioning
d
T
Anchorage
( )2
n
aM T d= −
V/3
V/3
Panel Shear Panel Shear ≥≥ Pipe YieldPipe Yield
φ Vn ≥ α Vn
Panel PipeV/3 V/3
V/3
Joint Capacity Joint Capacity ≥≥ Pipe YieldPipe Yield
µ = 1.4
Vn = Avf fy µJoint
φ Vn ≥ α Vn
Joint Pipe
ACI ShearVn
Panel⇒
Wall Component Design
V
General Design Requirements
• Minimum Design Forces according to UBC or NEHRP recommendations
• Monolithic Behavior
• Shear Strength Sufficient for Flexural Hinge Formation– R consistent with codes
– R = 1 if shear control
• Assess Effects of the Change in Lateral Load System
Shear Design
Splice FailureV
Vn = Σ Vn
Pipe Vn = Pipe Yield Strength= 0.6 As Fy
dw
df
Frame SideFrame Side
Wall SideWall Side
pp
∅∅o
do
d
(Bearing Stress)(Area) ≥ Pipe Capacity
Provide Adequate EmbedmentProvide Adequate Embedment
fb ∅od d ≥ α Vn
Pipe
Pipe
8'
8'
16'
Front Elevation Side Elevation
P
P
1
2
Large-Scale Model Test Structure
Research Goals
Determine minimum design and detailing requirements for the precast wall system.
Provide a rational analysis method of precast infill-frame interaction.
Gain a better understanding of shear transfer in concrete.
Gain a better understanding of concrete - steel pipe shear transfer.
-60
-40
-20
20
40
60
80
100
-0.25 -0.2 -0.15 -0.1 -0.05 0.05 0.1 0.15 0.2 0.25
Load (
Kip
s)
Displacement (Inch)
Panel Connection TestSpecimen PC-AL-A
VVariables
Panel Connection Test Specimen
• Shear Key Configuration
• Shear Key Size• Vertical Strip Steel
• Panel Spacing• Grout Strength
-80
-60
-40
-20
0
20
40
60
80
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
Displacement (in.)
Lo
ad
(kip
s)
Panel Connection TestSpecimen PC-5 (2#3)
Loa
d (
kip
s)
0.4-80
-60
-40
-20
0
20
40
60
80
100
120
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3
Displacement (in.)
2 #3 BarsSpecimen PC-5
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
Displacement (in.)
4 #3 BarsSpecimen PC-9
Effect of Vertical Reinforcement
Panel Connection Results
• No significant effect of shear key size, configuration, and panel spacing
• Failure controlled by weaker of grout strip or precast panel
• Vertical reinforcement affects peak and residual capacity
• Residual capacity reliably estimate by shear friction
V
Frame Connection Test Specimen
• Pipe Embedment Length• Vertical Strip Steel
• Grout Strength
Variables
-80
-60
-40
-20
0
20
40
60
80
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
Displacement (In.)
Lo
ad
(kip
s)
Frame Connection TestSpecimen FC-2 (2 1/2” XS)
Frame Connection Results
• Embedment of pipe determined by concrete bearing on projected area
• Residual capacity determined by shear yielding of shear lug
Out-of-Plane Resistance
• Continuous vertical reinforcement
• Shear lugs
• Boundary element constraint
– In-plane compression
developed under bending
w
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