evaluation of mc90 application rules against bond test database

1/22University of StuttgartInstitute of Construction Materials (IWB)

Evaluation of MC90 application rulesagainst Bond Test Database

fib Task Group 4.5 „Bond Models“– 8th Meeting, November 4, 2005, Stuttgart, Germany –


General Critera for evaluation of test database:

▫Good bond conditions („bottom cast bars“)

▫No confinement by reinforcement (Asw=0)

▫No confinement by transverse pressure (p=0)

▫Concrete cover > cnom (cnom=cmin+tol.=15mm)

▫Concrete failure presumed

▫Minimum concrete strenght (fcm≥15 N/mm2)

▫Straight and ribbed bars in tension

▫All bars lapped (100 % Splice)

EVALUATION CRITERIA


MC90 APPLICATION RULES

Design lap length of bars in tension:

s,cal0 s 1 3 4 5 6 b 0,min

s,ef

Al l l l

A

with: s ydb

bd

d fl

4 f

bd 1 2 3 ctdf f

ctk,minctd

c

ff

and

(bond length)

(bond strength)

(concrete tensile strength)


For mean values:


yd smf ; ctk,min ctmf f ; c 1.0

and

s sms 1 3 4 5 6

1 2 3 ctm

d 1.0l

4 f

The lap lenght ls can be written to:

s,cal

s,ef

A1.0

A



ssm ctm 1 2 3

s 1 3 4 5 6

l 1 1 1 1 14 fd

1 1.0 ;

4 1.0 ;

5 1.0 ;

6 2.0;

1 2.25 ;

2 1.0

The mean steel stress in general:

and

For use with the test database the factors are:(straight bars)(no confinement by reinforcement)(no confinement by transverse pressure)(only used for MC90 / 100 % of bars lapped)

(ribbed bars)(good bond conditions)


ssm ctm 3

s 3

l 19 fd

The mean steel stress for use with the test database:


with: ls = lap lenght

ds = bar diameter

fctm = mean concrete tensile strength

3 = concrete confinement factor

3 = bar diameter factor


MC90 COEFFICIENTS

0 20 40 60 80 100 120Concrete Compressive Strength fcm [N/mm2]

Influ

ence

dis

trib

utio

n / T

ende

ncy

MC90

JC & Stuttgart

23

ckctm

ff 1.4

10

14

ckctm

ff 2.310

MC 90:

JC & Stuttgart:

Influence of concrete compressive strength


0 10 20 30 40 50 60Relative Lap Length ls/ds [-]

Influ

ence

dis

trib

utio

n / T

ende

ncy MC90

Stuttgart

MC90 COEFFICIENTS

1

s

s

ld

23

s

s

ld

MC 90:

Stuttgart:

Influence of relative lap length


0,00

0,25

0,50

0,75

1,00

1,25

1,50

1,75

2,00

2,25

2,50

0,00 0,02 0,04 0,06 0,08 0,10 0,12Type of reinforcement (virtual fR [-])

Coe

ffic

ient

1

[-]

plain

intended

ribbed

MC90 COEFFICIENT 1

MC 90: 1 = 1.0 for plain bars

1 = 1.4 for indented bars

1 = 1.0 for ribbed bars

Influence of type of reinforcement


0,00

0,25

0,50

0,75

1,00

1,25

Bond Condition

Coe

ffic

ient

2

[-]

moderate bond

good bond

worse better

MC90 COEFFICIENT 2

MC 90: 2 = 0.7 for moderate bond

2 = 1.0 for good bond

Influence of bond conditions


MC90 COEFFICIENT 3

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0 10 20 30 40 50 60Bar diameter ds [mm]

Coe

ffic

ient

3

[-]

MC 90

Stuttgart

JC

MC 90:

Stuttgart:

JC:

s

3 ss

1.0 for d 32mm132 d for d 32mm

100

s3

50 d1100

0.2

3s

20 1.2d

Influence of bar diameter


MC90 COEFFICIENT 1

0,00

0,25

0,50

0,75

1,00

1,25

1,50

1,75

Form of bars

Coe

ffic

ient

1/

1 [-

]bent

straight

bent straight

MC 90: ! = 0.7 for bent bars

1 = 1.0 for straight bars

Influence of form of reinforcing bars


MC90 COEFFICIENT 3

0,0

0,5

1,0

1,5

2,0

2,5

3,0

0 10 20 30 40 50 60Confining cover cd [mm]

Coe

ffic

ient

1/

3 [-

]

MC 90

Stuttgartd3

s

c1 0.15 1d

12

d3

s

c1d

MC 90:

Stuttgart:

d 1c min a 2, c , c acc. to MC90

Influence of confinement by concrete


MC90 COEFFICIENT 4

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0 100 200 300 400 500 600Reinforcement area Ast [mm2]

Coe

ffic

ient

1/

4 [-

]K=0.10

K=0.05

K=0

MC 90:

St St,min4

S

A A1 K

A

K values acc. to MC90

Influence of confinement by transverse reinforcement


MC90 COEFFICIENT 5

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0,0 1,5 3,0 4,5 6,0 7,5 9,0Transverse pressure [N/mm2]

Coe

ffic

ient

1/

5 [-

]MC 90

MC 90:

5 1 0.04 p

Influence of confinement by transverse pressure


MC90 COEFFICIENT 6

MC 90:

6 = 1.2 for ≤ 20 %

6 = 1.4 for 25 %

6 = 1.6 for 33 %

6 = 1.8 for 50 %

6 = 2.0 for > 50%

of lapped bars relative

to total cross-section

0,00

0,25

0,50

0,75

1,00

0 20 40 60 80 100Percentage of lapped bars [%]

Coe

ffic

ient

1/

6 [-

]<20%

25%

33%

50%

>50%

Influence of percentage of the reinforcement lapped


s

3 ss

1.0 for d 32mm132 d

for d 32mm100

EVALUATION OF MC90 APPLICATION RULES

2

3s ck d

sm 3ss

l f c9 1.4 1 1 0.15 1dd 10

0

200

400

600

800

1000

0 200 400 600 800 1000Predicted Steel Stress s [N/mm2]

Mea

sure

d St

eel S

tres

s s [

N/m

m2 ]

Test Database

Linear (Test Database)

Number of tests 363 Average 1,35 Maximum 3,02 Minimum e 0,31 Stand.Deviation 0,52 CoV 0,38 0.05 Fractile 0,50 0.95-Fractile 2,20


14

s ck sd ssm

s ss

l f 50 dc 7 d9 2.3 1 1 0.15 1 1 1 0.3d ld 10 100

REVISED VERSION OF JC

0

200

400

600

800

1000


Mea

sure

d St

eel S

tres

s s [

N/m

m2 ]

Database

Linear (Database)



12 13 4 2s ck sd

smss

l f 50 dc9 2.3 1 1dd 10 100

REVISED VERSION COMB. OF JC & STUTTGART

0

200

400

600

800

1000


Mea

sure

d St

eel S

tres

s s [

N/m

m2 ]

Test database

Linear (Test database)



REVISED VERSION OF STUTTGART

0

200

400

600

800

1000


Mea

sure

d St

eel S

tres

s

s [N

/mm

2 ]

Test database



12 1 0.23 4 2s ck d

smss s

l f 20c9 2.3 1dd 10 d


0

200

400

600

800

1000


Mea

sure

d St

eel S

tres

s s [

N/m

m2 ]

Test database



12 1 0.23 4 2s ck d

smss s

l f 20c13.5 2.3 1dd 10 d

FINAL REVISED VERSION OF STUTTGART


FUTURE WORK

Further investigations needed to clarify

the influence and the treatment of:

▫Confinement by transverse reinforcement

▫Confinement by transverse pressure

▫Anchorages/Laps with (ribbed) headed bars

▫Lapping all bars in a section

▫Anchorages/Laps under moderate bond cond.(„top cast effect“)

evaluation of mc90 application rules against bond test database

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