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Design Considerations of Ultra Durable High Performance Concrete (UDHPC) for Underwater Structures
presented by Structural Research Team
Dr. Soerya Widjaja (Research Fellow)
Jimmy Chandra (PhD candidate)
Niki Ng Jun Kai (PhD candidate)
Vu Duc Hieu (Project Officer)
Rhahmadatul Hidayat (Project Officer)
and
Assoc Prof. Susanto Teng
School of Civil and Environmental Engineering
NTU-JTC Workshop -8 Feb 2012
Underwater Structures Scheme:
RC Slabs, Beams and Walls
• Cylindrical Structure dia = 20 to 30m
• Height = 20 to 30m
• Large Beam-Slab and Flat Plate systems = up to
2m thick
• Wall = up to 500mm thick
• Ultra Durable High Performance Concrete
(UDHPC) = up to 200MPa
RC Beams & Slabs
RC Walls
RC SLABS
FACTORS INFLUENCING RC SLABS DESIGN
• Concrete compressive strength
• Reinforcement ratio (As/bd)
• Size effect (the thicker the slab, the weaker it is)
• Shear enhancement by shear reinforcement
Effect of concrete compressive strength
Comparison of code expression with test results reported by Ghannoum (1998) and
McHarg et al. (2000).
ACI and EC2 underestimate Shear Stress at Failure more at higher concrete strength
(cylindrical concrete strength limits: BS=40MPa, EC2=50MPa, ACI=68.9MPa)
Limited Data for High Strength Concrete
Effect of reinforcement ratio
Stevano Guandalini, et.al, 2009, “Punching Test of Slabs with Low Reinforcement Ratio”, ACI Structural
Journal 106-S10
No consensus for effect of
flexural reinforcement ratio
among codes
Effect of Size Effect
BS 8110 (7) and EC2 (8) size effect factors
underestimate the stress reduction in HSC slabs.
Tested by Susanto Teng and Lee Sai Cheng (2004) in NTU
PROPOSED EQUATION FOR PUNCHING SHEAR
STRENGTH (Teng, et.al, 2004) – (1)
where :
vc= punching shear strength of slab-column
connections;
= flexural reinforcement ratio
fc’=concrete cylinder strength (MPa)
*Susanto Teng, et.al., 2004, “Punching Shear Strength of Slabs with Openings and Supported on Rectangular
Columns”, ACI Strucutural Journal No.101-S67, Sep.-Oct., pp.678 -687.
MPa)( '6.0 31
31
cc fv
Punching shear failure of edge
connection tested in NTU
The proposed equation is simple but can it be
used for high strength concrete?
Even though flexural strength is not an issue but
the predictions of punching shear strength still
vary from code to codes
PROPOSED EQUATION FOR
PUNCHING SHEAR STRENGTH
(Teng, et.al, 2004) – (2)
*Susanto Teng, et.al., 2004, “Punching Shear Strength of Slabs
with Openings and Supported on Rectangular Columns”, ACI
Structural Journal No.101-S67, Sep.-Oct., pp.678 -687.
Tested by Susanto Teng and Lee Sai Cheng (2004) in NTU
EXPERIMENTAL PROGRAM
Phase 1: testing of 12 RC slabs
• 120 MPa
• Varying reinforcement ratios
• Column rectangularity
Phase 2: testing of 12 RC slabs
• Size effect (varying depth)
• To propose practical design equations incorporating
reinforcement ratio, concrete strength and size effect
• To explain the behavior and design of high strength concrete
slabs
The current code equations are still safe, even though they are too
safe, so that next experiment will investigate concrete strength of
120 MPa and above.
PURPOSES OF EXPERIMENTAL PROGRAM
RC BEAMS
STRUCTURAL CONSIDERATIONS
Flexural Design:
• Ductile failure mode
• Well predicted by flexural theory
Shear Design:
• Sudden, Brittle failure
• No simple, analytically derived,
formula to predict the shear
strength of RC beams
Shear failure in 1m beam: U.S. Air Force
Warehouse (1955)
PARAMETERS INFLUENCING SHEAR CAPACITY
• Size effect (effective depth d)
• Concrete compressive strength (fc)
• Longitudinal reinforcement ratio ()
• Shear span/depth ratio (a/d)
• Aggregate size
• Amount of shear reinforcement ratio (v)
When the beam depth increase → shear stress decrease accordingly
Series of test done by Toronto University and Japanese researchers
Size Effect (effective depth, d)
Increase in strength of the concrete → increase in its brittleness
and smoother shear failure surface.
Crack in high strength concrete through
aggregates
→ shear carried by aggregate
interlock decreases as
concrete strength increases
→ a shear strength deficiency
may be produced which is not
accounted for by present
design equations
Concrete compressive strength due to UDHPC
• Adding minimum shear reinforcement → increasing shear strength
and more ductile failure
• Is the minimum stirrup suggested by the current codes sufficient for
high strength concrete large beam?
Higher tensile strength of HSC higher cracking shear is expected
require a larger amount of minimum shear reinforcement!
• Can stirrups suppress size effect on shear strength of RC concrete?
Amount of shear reinforcement
VALIDITY OF THE CURRENT DESIGN EQUATIONS
Most of building codes equation are empirical and based on limited data
range (conventional concrete, small beam depth and large ratio of
longitudinal reinforcement)
Actuators
800
Concrete support
Strong Floor
200 L/2 200L/2
21 6 7 4 3
LVDTs5
Bearing plates Swivel heads
135
Specimen
Roller Support
EXPERIMENTAL PROGRAM (Teng and Lihua, NTU)
200 A-A
A
185
250 2T13
3T25 A
700 500 700 200
B-3.5-200
V-3.5-200
VV-3.5-200
200
B-3.5-400
V-3.5-400
VV-3.5-400
B-3.5-700
V-3.5-700
VV-3.5-700
A-A
475
185
2T13
6T25
A
A
A-A
1400 1000 1400 200
T6
T10
400
A
185
825
2T16
9T25+2T22 A 2450 1750 2450 400
T10
lifting hook
reinforcement cage
• a/d = 2; 3.5
• d = 200, 400, 700 mm
• web reinforcement percentage
• fc = 100 MPa
Beams with web reinforcement
with a/d of 3.5
Beams without web reinforcement
with a/d of 3.5
Code Comparisons (Teng and Lihua, NTU) – (1)
ACI 318-11:
6
'
c
c w
fV b d
EC 2:
1 30 18100
2001 2
/.( )
, 0.02
c w
c
V k b d
kd
Code Comparisons (Teng and Lihua, NTU) – (2)
52 Normal to High Strength Shallow Beams without Shear Reinforcement
Canada Code CSA 2004:
• Longitudinal strain at mid-depth
• Effective crack spacing:
Code Comparisons (Teng and Lihua, NTU) – (3)
52 Normal to High Strength Shallow Beams without Shear Reinforcement
Code Comparisons (Teng and Lihua, NTU) – (4)
97 High Strength Concrete Shallow Beams
For Design of HSC large beam:
• For 800 mm HSC beams of deeper and made of concrete of Grade
higher than 100 MPa, Eurocode 2 and ACI Code may over
estimate the shear strength by more than 20%.
• We are currently investigating UDHPC concrete beams with Grade
120 and above.
DESIGN SUGGESTION (1)
• HSC beams should be provided with at least minimum shear
reinforcement for all beams with high importance for the integrity of the
structure.
Minimum shear reinforcement recommended by EC2:
Spacing of shear reinforcement also should be limited (EC2)
• Maximum longitudinal spacing between shear links:
sl,max = 0.75d for vertical stirrups
• Maximum transverse spacing between legs in a series of shear links:
sb,max = 0.75d ≤ 600 mm
,min
0.08 cksww w
w yk
fA
sb f
DESIGN SUGGESTIONS (2)
Experimental Study
• Testing of several ultra HSC beams (fc = 120 MPa) to study the
influence of effective depth, concrete strength and shear
reinforcement ratio on the shear capacity of ultra HSC beams
Theoretical Study
• To propose and verify a minimum amount of web reinforcement
for HSC beams.
• To develop a rational model to predict the shear strength of
reinforced concrete beams with shear reinforcement.
FUTURE WORK
EXPERIMENTAL PROGRAM
• Testing of 11 UHPC beams (f’c = 120 MPa) under symmetrically
concentrated load.
• Two main variables:
– Beam depth (d): 450, 900, 1350, 1800 (mm)
– Amount of shear reinforcement (v)
RC WALLS
Sustaining Lateral loadings:
Earthquake, tsunami, wave loads, impact loads from ship, etc.
Sustaining Gravity loadings:
Self weight of structures, gravity loads from upper structures, etc.
STRUCTURAL CONSIDERATIONS
FACTORS AFFECTING STRUCTURAL WALLS
STRENGTH
• Shear span ratio ( H / L )
• Axial load ratio ( P / [fc x Ag] )
• Reinforcement ratio ( ρl, ρt )
• Concrete strength ( fc )
• Reinforcement strength ( fy )
• Walls shape and size
PREVIOUS STUDY ON STRUCTURAL WALLS
(CHANDRA, LIU, AND TENG, 2011) – (1)
Data collected from literatures:
• Normal strength walls (fc < 60 MPa):
– Flexural behavior: 50 specimens
– Shear behavior: 60 specimens
• High strength walls (fc > 60 MPa):
– Flexural behavior: 33 specimens
– Shear behavior: 33 specimens
Objectives of the study:
• To evaluate strength of structural walls based on
several building codes (ACI, AIJ, and Eurocode).
• To compare actual strength of walls with those
obtained from building code formulas.
PREVIOUS STUDY ON STRUCTURAL WALLS
(CHANDRA, LIU, AND TENG, 2011) – (2)
• Flexural strength:
– Flexural strength of walls can be predicted quite
well using flexural theory.
• Shear strength:
– Most of building code formulas underestimate the
shear strength of walls.
• Neglected contribution of longitudinal
reinforcement.
• Limitation of maximum wall shear stress.
PREVIOUS STUDY ON STRUCTURAL WALLS
(CHANDRA, LIU, AND TENG, 2011) – (3)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Ve
xp / V
ca
l
Shear Span Ratio ( H / L )
ACI
AIJ
EC
ACI
AIJ
EC
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
0 20 40 60 80 100 120 140
Ve
xp / (
Ac√f'
c)
f'c (MPa)
Limit of maximum
shear stress by
ACI code
CONCLUSION OF STUDY
There is no comparison of HSC walls with codes, so we
cannot conclude anything about codes performances.
ACI and EC2 validity for Concrete Grade 100 MPA and
above requires further study
NEW EXPERIMENTAL STUDY
• Testing of seven UDHPC walls (fc = 120 MPa) under axial
loading and cyclic lateral loading with varying:
– Shear span ratio
– Longitudinal and transverse reinforcement ratio
– Specimen shape and size
OBJECTIVES OF NEW EXPERIMENTAL STUDY
• To investigate shear behaviour of UDHPC walls and
factors affecting it.
• To develop a general expression for predicting the
shear strength of walls based on certain analytical
models such as truss model, strut and tie model, etc.
THANK YOU