Transcript SEISMIC BEHAVIOR, EVALUATION, AND RETROFIT OF EXISTING REINFORCED CONCRETE STRUCTURAL WALLS A Ph.D.

SEISMIC BEHAVIOR, EVALUATION, AND
RETROFIT OF EXISTING REINFORCED
CONCRETE STRUCTURAL WALLS
A Ph.D. Research Proposal
by
Hua Jiang
Advisor: Dr. Kurama
Department of Civil Engineering and Geological Sciences
University of Notre Dame
Notre Dame, Indiana
August 22, 2003
Seismic Performance of Older RC Buildings
Significant Risk to Public Safety and Economy
Research Objectives
• To analytically evaluate the seismic behavior of
older RC walls
• To investigate the need, feasibility, limitations,
and effects of available retrofit measures
• To develop design recommendations and
guidelines for seismic retrofit applications
Outline of Presentation
• Design and behavior of RC structural walls
• Prototype structures
• Analytical modeling of RC walls
• Preliminary analysis and retrofit of prototype walls
• Preliminary conclusions and remaining tasks
Seismic Provisions for RC Walls in ACI 318
Edition
Significant changes
1963
No seismic provisions for RC walls
1971
Seismic provisions for wall detailing
1977
Seismic provisions for detailing of wall
reinforcement
1983
Seismic provisions for shear design of RC walls
1989
Improved seismic provisions for detailing of wall
reinforcement
1999
More detailed seismic provisions on wall detailing
and detailing of wall reinforcement
Wall Critical Details
one curtain of light distributed
reinforcement
no boundary element
Wall Classification
Lw
Paulay and Priestley (1992):
•Slender walls: aspect ratio > 4.0
Hw
•Intermediate walls:
2.0 <= aspect ratio <= 4.0
•Squat walls: aspect ratio <2.0
Walls Behavior:
• Slender walls: flexure-dominated
Aspect ratio
= Hw/Lw
• Intermediate walls: difficult to identify
• Squat walls: shear-dominated
Failure Modes of RC Walls
• Flexure-dominated failure:
Axial-flexural concrete crushing
Longitudinal steel bar fracture
Steel bar buckling
Steel bar pull-out
• Shear-dominated failure:
Web concrete crushing
Diagonal tension failure
Sliding shear
Experimental Evaluation of RC Walls
Oesterle et al.
(1976, 1979)
[
Portland
Cement
Association
Wall aspect
ratio = 2.4
]
Flexure-Dominated Failure
Axial-flexural
concrete crushing
Oesterle et al.
(1979)
Flexure-Dominated Failure
Steel bar buckling
Oesterle et al. (1976)
Shear-Dominated Failure
Web concrete crushing
Oesterle et al. (1979)
Outline of Presentation
• Design and behavior of RC structural walls
• Prototype structures
• Analytical modeling of RC walls
• Preliminary analysis and retrofit of prototype walls
• Preliminary conclusions and remaining tasks
Prototype Structures
RC bearing wall hotel building
Elevation
12ft X 10 = 120ft
column
slab
foundation
25ft X 8 = 200ft
Longitudinal direction
Elevation
slab
12ft X 10 = 120ft
column
wall
25ft X 2 +8 ft = 58ft
Transverse direction
Major Design References
• Building Code Requirements for RC, ACI 318-63
• Recommended Lateral Force Requirements by
SEAOC (1959)
• Design of Multistory Reinforced Concrete Buildings
for Earthquake Motions by Blume et al. (1961)
• Suggestions from two senior practicing engineers:
James O. Malley and Loring A. Wyllie (Degenkolb
Engineers)
Design Variables for Prototype Walls
• Amount of flexural reinforcement in the
column regions
• Amount of confining reinforcement in the
column regions
• Shape of wall cross-section:
Barbell-shape, rectangular-shape
Six prototype walls:
BCDF, BCRF, BUDF, BURF, RUDF, RURF.
Barbell-Shaped Prototype Wall BCDF
14”X14”
16”X16”
Aspect
ratio ~
= 4.5
Wall
thickness
= 6”
7”
10X144”
= 1440”
9#14S, 1#4
18”X18”
#4@8”
10”
20”
CL
20”X20”
9”
#4@8”
CL
8”
10”
300”
Elevation
140”
Section at base
20”
Variation of Wall Flexural Reinforcement
20”
9#14S, 1#4
20”
9#7
20”
#4@8”
20”
#4@8”
140”
#4@8”
140”
#4@8”
CL
CL
CL
CL
10”
10”
Wall BCDF
Wall BCRF
Variation of Wall Confining Reinforcement
20”
9#14S, 1#4
20”
9#7
20”
#4@8”
20”
#4@8”
140”
#4@8”
140”
#4@8”
CL
CL
CL
CL
10”
10”
Wall BUDF
Wall BURF
Variation of Wall Cross-Section
8#5
4#14S, 4#11
160”
#4@8”
#4@8”
160”
#4@8”
#4@8”
CL
CL
10”
Wall RUDF
CL
CL
10”
Wall RURF
Outline of Presentation
• Design and behavior of RC structural walls
• Prototype structures
• Analytical modeling of RC walls
• Preliminary analysis and retrofit of prototype walls
• Preliminary conclusions and remaining tasks
Analytical Models for RC Walls
• Fiber element wall models (DRAIN-2DX)
• Finite element wall models (FINITE)
Fiber Beam-Column Element in DRAIN-2DX
node
fiber
element
segment division point
y
x
concrete Barbell shape
crushing
Rectangular shape
length,
Lcr
1st story 2nd
story
3rd story 4th story
Fiber Element Wall Models
base
Wall Cross-Section Discretization
Fiber Stress-Strain Relationships
stress-strain
relationship
for for
C-type
concrete
fiber
stress-strain
relationship
S-type
steel fiber
Model Verification
PCA wall specimen B4 [Oesterle et al. (1976, 1979)]
Measured behavior
Predicted behavior
Model Verification
PCA wall specimen B3 [Oesterle et al. (1976, 1979)]
Measured behavior
Predicted behavior
Proposed Model Modifications
• Modeling of bar buckling
• Modeling of bar fracture
• Modeling of nonlinear shear behavior
Proposed Steel Fiber
Modeling of Nonlinear Shear Behavior
shear stress, τ
τfail
shear force
distribution
of axial-flexural stresses
τy
Ginel=αGel
Gde
fiber
τde
distribution
of shear stresses
Gel
γ
γ GelA
γ
y
shear force
fail
de
shear strain, γ
shear stress, τ
shear deformation
slice
shear
sheardeformation
strain, γ
Finite Element Wall Models (FINITE)
P P
P P
Displacement control
at corner node
Steel elements
Nodes
Concrete element
Sittipunt and
Wood
(1993, 1995)
Characteristics of FINITE Models
• Nonlinear material model for concrete
– Normal stress function (eight parameters)
• Crack closing and crack reopening
• Compression softening
• Degradation of concrete properties under cyclic loading
– Shear stress function (nine parameters)
• Aggregate interlock
• Dowel action
• Strength reduction under cyclic loads
• Nonlinear material model for steel
– Strain hardening
– Baushinger effects
Measured Behavior versus FINITE Model
PCA wall specimen B1 [Oesterle et al. (1976, 1979)]
Bar buckling
Measured behavior
Calculated behavior
Comparison of Failure Modes
Wall
Observed behavior
Calculated behavior (FINITE)
R1
Bar buckling in 2nd cycle to +3 in.;
bars fracture in 2nd cycle to 4 in.
Bar buckling in 2nd cycle to +3 in.;
four additional bars buckled later
R4
Concrete in boundary element
crushing during cycles to +3 in.
Concrete in boundary element
crushing during cycles to ±4 in.
B4
Bar fracture at displacement of 8.5 Bar fracture at displacement of 7.8
in.
in.
B5
Web crushing during cycle to +3
in.
Web crushing during cycle to ±3
in.
Evaluation of FINITE Wall Models
• A large number of material parameters need to
be adjusted for each group of test
• Nonlinear dynamic analyses have not been
conducted
Outline of Presentation
• Design and behavior of RC structural walls
• Prototype structures
• Analytical modeling of RC walls
• Preliminary analysis and retrofit of prototype walls
• Preliminary conclusions and remaining tasks
Preliminary Analysis Results
800
Base shear (kips)
Base shear (kips)
800
400
Wall BCDF
0
400
Wall BUDF
0
0
0.06
0.03
0
Roof drift
800
Base shear (kips)
Base shear (kips)
0.01
Roof drift
800
Wall BCRF
+
400
0
0.005
0
0.03
Roof drift
0.06
Wall BURF
400
0
0
0.005
Roof drift
0.01
Preliminary Analysis Results
800
Wall RUDF
Base shear (kips)
Base shear (kips)
800
400
0
0
0.005
Roof drift
+
0.01
Wall RURF
400
0
0
0.005
Roof drift
Base shear—roof drift curve from DRAIN2DX
Cross section cracking at base
First flexural bar in boundary column yielding in tension
Last flexural bar in boundary column yielding in tension
First flexural bar in wall web yielding in tension
Last flexural bar in wall web yielding in tension
First flexural bar in boundary column fracturing
Wall web concrete crushing at base
Wall web concrete crushing at midheight of first story
Boundary column crushing at base
0.01
Target Building Performance Levels
Increasing Performance
Retrofit Objectives [FEMA-356 (ASCE 2000)]
Basic Safety
Objective
Collapse
Prevention
Life Safety
Basic Safety
Objective
Immediate
Occupancy
Operational
50% in 50 years 20% in 50 years 10% in 50 years 2% in 50 years
Earthquake Hazard Level
Increasing Hazard
Retrofit Methods for Existing RC Walls
• Addition of Wall Boundary Elements
• Addition of Confinement Jackets at Wall Boundaries
• Reduction of Flexural Strength
• Increasing Shear Strength
• Coupling of Walls as a Retrofit Method
Preliminary Analysis Results
800
Wall BUDF
Wall BCDF
Base shear (kips)
Wall RUDF
Wall BURF
Wall BCRF
400
Wall RURF
0
0
0.03
Roof drift
0.06
Retrofit Measures of Prototype Walls
• Walls BCDF and BCRF:
No need for retrofit to achieve Basic Safety Objective
• Walls BUDF and RUDF:
Addition of confinement jackets needed for increasing
lateral deformation capacity to achieve Basic Safety
Objective
• Walls BURF and RURF
Addition of confinement jackets needed to achieve
Limited Objectives; further retrofit for Basic Safety
Objective
Outline of Presentation
• Design and behavior of RC structural walls
• Prototype structures
• Analytical modeling of RC walls
• Preliminary analyses and retrofit of prototype walls
• Preliminary conclusions and remaining tasks
Summary and Preliminary Conclusions
• A literature review on the seismic behavior, design,
evaluation, and retrofit of existing RC walls
• Prototype structures for the research project
• Effectiveness and limitations of current analytical
models
• Proposed modifications on the current wall models
• Potential seismic retrofit measures for the prototype
walls
Remaining Tasks
• Improve the current analytical wall models
• Complete the design of the prototype walls
• Conduct nonlinear static and nonlinear dynamic
analyses
• Evaluate the need, effectiveness, and limitations
of different retrofit measures
• Develop performance-based design
recommendations and guidelines for seismic
retrofit application
Schedule for Remaining Tasks
Task
Improve analytical models
Complete design of
prototype walls
Conduct nonlinear analyses
Evaluate retrofit measures
Develop retrofit guidelines
Month
2
4
6
X
X
X
X
8
10
12
X
X
X
X
14
16
X
X
X
X
X
Acknowledgement
• Research Advisor:
Dr. Yahya C. Kurama
• Examination Board:
Dr. Tracy Correa
Dr. Lynn Salvati
Dr. David J. Kirkner
• Practicing Engineers:
James O. Malley
Loring A. Wyllie
Thank you.
Questions?