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