reinforcement optimization for structural frc elements · reinforcement optimization for structural...

Reinforcement optimization

for structural FRC elements

University of Brescia (Italy),

Department of Civil Engineering,

Architecture, Environment, Land

and of Mathematics (DICATAM)

[email protected]

Giovanni Plizzari

Madrid – October 13th, 2016

Reinforcement optimization for structural FRC elements 2/72Madrid, October 13th, 2016

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fib Model Code 2010


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Place the best performing reinforcement

(fibers and/or rebars) where required by

tensile stresses in the structural elements

Optimized reinforcement: definition


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• In structural elements both distributed and localized

stresses are generally present

• Conventional rebars represent the best

reinforcement for localized stresses

• Fibers represent the best reinforcement for diffused

stresses

• Structural optimization generally requires the use of

a combination of rebars and fibers

• Structural ductility is generally enhanced

Reinforcement use in structural elements


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FRC and degree of redundancy of structures

1- Structural elements with low degree of redundancy

Fibers can not generally replace the main flexural reinforcement but they can used to substitute the secondary reinforcement or the shear reinforcement

Conventional reinforcement

Example: Box culverts

Optimized reinforcement


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1- Structural elements with low degree of redundancy

Fibers can not generally replace the main flexural reinforcement but they can used to substitute the shear reinforcement

Example: Linear elements (beams)

RC spandrel

wide-shallow

beam

Lightweight ribbed

one-way reinforced

concrete slab

RC central

wide-shallow

beam

Topping concrete layerTypical Concrete Floor used in

Southern Europe

Conventional Reinforcement for Wide Shallow Beams

Floor section

Wide Shallow Beams with Optimized Reinforcement

FRC (Vf=25kg/m3)



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Shear in beams without stirrups

V = Vc + Vf

In FRC elements there is an additional contribution to shear resistance provided by fiber reinforcement:

Vc represents the concrete contribution.Vf represents the fiber contribution (post cracking strength).


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W750 PC

Wide Shallow Beams with b=750 mm

W750 FRC25


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W1000 MSR

Wide Shallow Beams with b=1000 mm

W1000 FRC35


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Example of Application for Shear

2Ø24 Bars

500

mm

p = 35 kN/m

d

6 m

2Ø24 Deformed Bars

500

200

35 / ( )

500 ; 460

30 ; 500

1.5; 1.15

30 50020 ; 435

1.5 1.5

2 ( 2)

u

ck yk

c s

cd yk

ctk

p kN m ULS

h mm d mm

f MPa f MPa

f MPa f MPa

f MPa EC

2 2

max

max

2

1 135 6 157.5

8 8

1 135 6 105

2 2

9040.98%

200 460

161

sl

w

u

M p l kN m

V p l kN

A mm

b d mm mm

M kN m


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13

, 1

0.18(100 ) 0.15 49

WRd ct ck CP

c

V k f b d kN

1.6 1.4

Minimum Shear Reinforcement

3.2 meters requiring design shear reinforcement; 2.8 meters requiring

minimum shear reinforcement.

Design Shear Reinforcement:

, , 56

321

2 8@300

swR ds yd Rd Rd ct

AV z f V V kN

s

s mm

mm

,min

0.75 345

0.08 0.0009

2 6 @300

ck

w

yk

s d mm

f

f

mm

Minimum Shear Reinforcement:


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dbff

fkV

WCPck

ctk

uFtk

c

FRd

15.0))5.71(100(

18.03

1,

1,

13

,

0.18 200 0.901 (100 0.0098 (1 7.5 ) 20) 200 460 81

1.5 460 2Rd FV kN

Minimum Shear Reinforcement

2.30.7

ck

Ftuk

300 27

20 20

ff . MPa

, , 242 6@300

420

swR ds yd Rd Rd ct

AV z f V V kN

mms

s mm

Assume 30 kg/m3 of steel fibers having l/f =67 and fFtk,u=0.90 MPa (tested at the

University of Brescia)

Minimum shear reinforcement

OK

Design Shear Reinforcement


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Example of optimized shear reinforcement

2Ø8@300mm 2Ø6@300mm

2Ø6@300mm

Plain concrete

FRC


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Salò, 15-16 October, 2010


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2- Structural elements with a high degree of redundancy

Fibers can partially replace the main flexural reinforcement. Conventional rebars are placed only in the areas of the structures with subjected to localized stresses.

Example: Elevated slabs Slab with Optimized Reinforcement

Loading set-up

FRC (Vf=30kg/m3)Localized

reinforcement


Aim of the optimization: to find a best combination between rebar contend and FRC toughness (volume fraction of FRC)


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FRC slabs


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Slab on piles

Example: Slab on piles

Pressure

Maximum principal stresses acting on the top surface

Minimum principal stresses acting on the top surfaceOptimized reinforcement

FRC

Local rebars


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Slab on grade: stresses along the borders

Slabs on grade can be made with FRC without conventional reinforcement. However, some areas of the structures can be subjected to high local stresses (borders, corners)

and thus fibers could not be enough.

High stresses due to concentrated loads

along the slab border


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Slab on grade: cracking at SLS

The optimized reinforcement may consist in a combination of fibers and conventional reinforcement placed only along the borders.

FRC

Conventional

reinforcement

(wire mesh)


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Case study

Geometry

Elevated slab made with Steel Fiber Reinforced Concrete

Loads

1. Dead weight (G1)

2. Overload (Q)Overload (Q)


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Reinforcement optimization

Optimized reinforcement: combination of steel fibers and rebars placed in the

most stressed areas of the slab

Proposal of an optimal reinforcement layout

Hypothesis: top and bottom

reinforcement have the

same effective area

Reinforcement placed within

diagonal and longitudinal chords


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Parametric study

Parameters investigated by numerical simulations:

1. longitudinal reinforcement ratio;

2. diagonal reinforcement ratio;

3. steel fiber content.

3D f.e. model implemented in the program Diana 9.6

1/4 of the whole slab Rebars layout


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Parametric study

Mechanical properties according MC2010

Tensile properties of SFRC

fct =2MPa

Fiber content fR1,k fR3,k

[kg/m3] [MPa] [MPa]

30 2.3 2.6

50 3.0 2.8

70 3.7 3.1


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Parametric study

Mechanical properties according MC2010

Compression properties of SFRC

fck=30MPafck

Tensile properties of conventional reinforcement

t

et

[MPa]

617519

13%210GPa


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Results of the parametric study

Typical Overload (Q) – Deflection (d) curve obtained from the simulations

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

Overl

oad

(Q

) [k

g/m

2]

Maximum deflection (d) [mm]

Maximum deflection (d)

Qmax = maximum overload


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Summary of the analysis program

Diagonal reinforcement ratio (d)

Longitudinal reinforcement ratio (l)

As

B d = ·100

B=400mm ; d=170mm


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0

400

800

1200

1600

2000

2400

2800

0 20 40 60 80 100 120 140 160 180 200 220

Maxim

um

Overlo

ad

(Q

max)

[kg/m

2]

Total Rebars Content (TRC) [kg/m3]

Fiber Content = 30kg/m^3


Fiber Content =70kg/m^3

Q = 606+(5965·TRC)0.53

R2 = 0.97

Q = 330+(5965·TRC)0.53

R2 = 0.98

Q = 850+(5965·TRC)0.53

R2 = 0.94


Effect of the total rebars content (longitudinal+diagonal) on the slab capacity (Qmax)

The diagram may be used to

design the optimal Hybrid

Reinforcement for the slab


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0

10

20

30

40

50

60

70

80

90

100

110

0 500 1000 1500 2000 2500

To

tal

Reb

ars

Co

nte

nt

red

ucti

on

(D

TR

C)

[kg

/m3]

Maximum Overload (Qmax) [kg/m2]

TRC30 - TRC50

TRC30 - TRC70

0

400

800

1200

1600

2000

2400

2800

0 20 40 60 80 100 120 140 160 180 200 220

Maxim

um

Overlo

ad

(Q

max)

[kg/m

2]

Total Rebars Content (TRC) [kg/m3]




Q = 606+(5965·TRC)0.53

R2 = 0.97

Q = 330+(5965·TRC)0.53

R2 = 0.98

Q = 850+(5965·TRC)0.53

R2 = 0.94


Increment of the Total Rebars Content (TRC) at a fixed loading level

The diagram highlights the

additional rebars content (DTRC)

that has to be employed with respect

to the slab with 30kg/m3 of fibres to

ensure the same maximum overload

level.


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Total reinforcement (fibres + rebars) vs. Maximum overload

30

50

70

90

110

130

150

170

190

210

230

250

500 1000 1500 2000

Tota

l R

ebars

Con

ten

t (T

RC

) +

Fib

re c

on

ten

t

[kg/m

3]

Maximum Overload (Qmax) [kg/m2]




Qmax,1 Qmax,2

Optimal reinforcement

for the load level Qmax,1

Optimal reinforcement

for the load level Qmax,2


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Elementi con fibre e armatura convenzionale

La verifica di elementi di calcestruzzo fibrorinforzato con armatura

convenzionale può essere eseguita con i metodi tradizionalmente

adottati per il calcestruzzo armato; il contributo delle fibre può essere

considerato adottando metodi di analisi non lineare (analisi limite,

analisi non lineare evolutiva).


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Tunnel linings


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Segmental lining


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Design features in tunnel segments

Modelling the loading/boundary conditions generally adopted by designers

Ring joint

Longitudinal joint

Bearing pad

Ring joint

Longitudinal joint

Bearing pad

Modelling the loading/boundary conditions representing possible

irregularities

Irregular supportsOuter/Inner eccentricities

Eccentricity

Inside tunnel

Outside tunnel Outside tunnel

Inside tunnel

Outside tunnel

Inside tunnel

Eccentricity inside Eccentricity

outside

Design of an optimized reinforcement

50/1,0-Vf=0,57%45 kg/m3

50/0,75-Vf=0,32%25 kg/m3 RC97 kg/m3

350mm

350mm

2 chords

Stiirups6@200mm

14 =0,22%

350mm

350mm

2 chords

Stiirups6@200mm

14 =0,22%

RCO+50/0,75-Vf=0,32%71 kg/m3

RC+50/0,75-Vf=0,32%122 kg/m3


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Thrust jack actions

Spalling cracks

Splitting cracks

Relative displacement in the region between the thrust jacks [mm]

0

5

10

15

20

25

30

35

0,00 0,50 1,00 1,50 2,00 2,50

Normal loading condition

To

tal

Lo

ad

[M

N]

0

0,5

1

1,5

2

2,5

3

Lo

ad

/Se

rvic

e l

oa

d [

-]

50/1,0 - Vf=0,57%

50/0,75 - Vf=0,32%

RC

RC + 50/0,75 - Vf=0,32%

RCO + 50/0,75 - Vf=0,32%


0

5

10

15

20

25

30

35

0,00 0,50 1,00 1,50 2,00 2,50


To

tal

Lo

ad

[M

N]

0

0,5

1

1,5

2

2,5

3

Lo

ad

/Se

rvic

e l

oa

d [

-]

50/1,0 - Vf=0,57%

50/0,75 - Vf=0,32%

RC

RC + 50/0,75 - Vf=0,32%

RCO + 50/0,75 - Vf=0,32%

Relative displacement in radial direction under the thrust jacks [mm]

0

5

10

15

20

25

30

35

0,00 0,20 0,40 0,60 0,80 1,00 1,20


To

tal L

oad

[M

N]

0

0,5

1

1,5

2

2,5

3

Lo

ad

/Serv

ice lo

ad

[-]

50/1,0 - Vf=0,57% - Point 1

50/0,75 - Vf=0,32% - Point 1

RC - Point 1

RC + 50/0,75 - Vf=0,32% - Point 1

RCO + 50/0,75 - Vf=0,32% - Point 1

Relative displacement in radial direction under the thrust jacks [mm]

0

5

10

15

20

25

30

35

0,00 0,20 0,40 0,60 0,80 1,00 1,20


To

tal L

oad

[M

N]

0

0,5

1

1,5

2

2,5

3

Lo

ad

/Serv

ice lo

ad

[-]

50/1,0 - Vf=0,57% - Point 1

50/0,75 - Vf=0,32% - Point 1

RC - Point 1

RC + 50/0,75 - Vf=0,32% - Point 1

RCO + 50/0,75 - Vf=0,32% - Point 1

Splitting cracks Spalling cracks


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9,3MN

12,6MN

Outer eccentricity:


0

5

10

15

20

25

-1,00 0,00 1,00 2,00 3,00 4,00 5,00 6,00

Eccentricity outside

To

tal

Lo

ad

[M

N]

0

0,5

1

1,5

2

Lo

ad

/Se

rvic

e l

oa

d [

-]

50/1,0 - Vf=0,57%

50/0,75 - Vf=0,32%

RC

RC + 50/0,75 - Vf=0,32%

RCO + 50/1,0 - Vf=0,32%


0

5

10

15

20

25

-1,00 0,00 1,00 2,00 3,00 4,00 5,00 6,00


To

tal

Lo

ad

[M

N]

0

0,5

1

1,5

2

Lo

ad

/Se

rvic

e l

oa

d [

-]

50/1,0 - Vf=0,57%

50/0,75 - Vf=0,32%

RC

RC + 50/0,75 - Vf=0,32%

RCO + 50/1,0 - Vf=0,32%

- Safety factor reduction

- Crack increase between loading areas;

Average displacement under the load surfaces [mm]

0

5

10

15

20

25

30

0,00 0,50 1,00 1,50 2,00 2,50 3,00


Tu

nn

el

Lo

ad

[M

N]

0

0,5

1

1,5

2

2,5

Lo

ad

/Se

rvic

e l

oa

d [

-]

50/1,0 - Vf=0,57%

50/0,75 - Vf=0,32%

RC

RC + 50/0,75 - Vf=0,32%

RCO + 50/0,75 - Vf=0,32%

0

5

10

15

20

25

30

0,00 0,50 1,00 1,50 2,00 2,50 3,00

0

0,5

1

1,5

2

2,5

Normal l.condition

Additional moments due to outer eccentricity

Eccentricity

Inside tunnel

Outside tunnel Outside tunnel

Inside tunnel

Outside tunnel

Inside tunnel

Eccentricity inside Eccentricity

outside


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Precast structural elements


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Floor slab for Electrical Equipment Shelters

Typical modular Self Compacting Concrete (SCC) Electrical Equipment Shelter reinforced with conventional steel bars

Properties of a typical the precast reinforced concrete floor:

- Reinforcing steel weight-to-concrete

volume ratio (RR) :

Steel Weight / Concrete Volume = 77kg/m3

- Dimensions: 2.5x4.2x0.08m

Typical rebars

layout for a

r.c. floor slab

- SCC class: C40/50 (EC2)

- Reinforcing steel: B450C (NTC2008)


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The research aim at testing full scale Steel Fiber Reinforced Self Compacting Concrete

(SFRSCC) slabs under Four Point Loads. No conventional reinforcement is used.

Conventional reinforced SCC Optimized reinforcement (SFRSCC+rebars)

Optimize the reinforcement typically used in the conventionally reinforced concrete slab


Geometry of the simply supported slab

Aim of the research:


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Optimized reinforcement (fibers + localized bars)

SFRSCC (Vf =0.32%)

Reinforced concrete

Conventional bar reinforcement layout

Reinforcing steel weight-to-concrete volume ratio (RR)

Total rebars weight (SW) = 65kg

Slab volume (V) = 0.84m3

RR=SW/V= 77 kg/m3

Total rebars weight (SW) = 15 kg

Slab volume (V) = 0.84 m3

RR=(SW+FW)/V= 47kg/m3

Total Steel Fiber weight (FW) = 25 kg/m3


Proposal of an optimized reinforcement for the tested slabs


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Conventional RC tank

Section B-B

Section A-A

Tank with optimized reinforcement

Numerical

simulation

Conventional

steel wire mesh

FRC (Vf=30Kg/m3)

Local rebars

Local rebars

Water tanks


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Properties of the tank

Typical loading conditions

Plan view (dimensions in mm)

Section Y-Y (dimensions in mm)

Ground pressure acting on the outer surface Water pressure acting on the inner surface

Water tanks


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ULS non-linear analysis for reinforcement optimization


Inner surface

Outer surfaceInner surface

Outer surface

Inner surfaceOuter surface

Localized stresses along the vertical corner Localized stresses along the vertical corner

Localized stresses along the long wall Localized stresses along long wall

Water tanks


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Optimized reinforcement and behavior at SLS


Optimized reinforcement:

- SFRC (V f=30kg/m3)

- 8/30cm steel rebars

Crack pattern at service loadCrack pattern at service load

Optimized reinforcement:

- SFRC (V f=30kg/m3)

-8/30cm steel rebars

-16 rebars

Water tanks


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Structural elements that transfer to the main structure:

Self weight Wind pressure

Geometrical classificazion:Panels with horizontal axis

Panels with vertical axis

Precast facade panels


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00

200

20

0

200

Substitution of conventional reinforcement (welded mesh)

with fibers

Industrialisation of the production

process

Reduction of the structural thickness

Weight reduction of the elements

Enhanced thermal insulation

Lower transportation costs

Structural optimisation


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Moment vs. Displacement

Mid-Span Section - RC Panels

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250 300

Displacement [mm]

Mo

me

nt

[kN

m]

Mes

PT1

PT2 5

Ø5/2

0/2

5

5 10

Ø5/2

0/2

5

125 3

Experimental results 1/2

RC Panels

SFRC Panels

(Vf=0.45%)


Mid-Span Section - SFRC Panels (Vf=0.45%)

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250 300 350

Displacement [mm]

Mo

men

t [k

Nm

]

Mes

PT1

PF3

PF4

PF1

PF2

PF5

2.54.5 13

5 12 3

3125


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Mid-Span Section - SFRC Panels (Vf=0.38%)

0

15

30

45

60

75

90

0 50 100 150 200 250 300

Displacement [mm]

Mo

me

nt

[kN

m]

Mes

PT1

PF6

PF7

PF8Self weight reductions

~20%

Experimental results 2/2

Consistent experimental results

L/400


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Durability of FRCFibers for durability of RC beams


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Classi di esposizione Corrosione da cloruri Nessun

rischio di corrosione o attacco

Corrosione da carbonatazione Acqua marina

Altri cloruri (diversi dall’acqua

di mare)

Attacco gelo/disgelo Ambienti chimici

aggressivi

X0 XC1 XC2 XC3 XC4 XS1 XS2 XS3 XD1 XD2 XD3 XF1 XF2 XF3 XF4 XA1 XA2 XA3 Rapporto massimo a/c

- 0.65 0.60 0.55 0.50 0.50 0.45 0.45 0.55 0.55 0.45 0.55 0.55 0.50 0.45 0.55 0.50 0.45

Classe di resistenza minima

C12/15 C20/25 C25/30 C30/37 C30/37 C30/37 C35/45 C35/45 C30/37 C30/37 C35/45 C30/37 C25/30 C30/37 C30/37 C30/37 C30/37 C35/45

Contenuto minimo di cemento [kg/m

3]

- 260 280 280 300 300 320 340 300 300 320 300 300 320 340 300 320 360

Contenuto minimo di aria [%]

- - - - - - - - - - - - 4.0a) 4.0a) 4.0a) - - -

Altri requisiti

Aggregati conformi al prEN12620:2000 con

sufficiente resistenza al gelo/disgelo

Cemento

resistente ai solfati b)

a) Quando il calcestruzzo non contiene aria aggiunta, le sue prestazioni dovrebbero essere verificate conformemente ad un metodo di prova appropriato rispetto ad un calcestruzzo per il quale è provata la resistenza al gelo/disgelo per la relativa classe di esposizione.

b) Qualora la presenza di SO42- comporti le classi di esposizione XA2 e XA3, è essenziale utilizzare un cemento resistente ai solfati.

Se il cemento è classificato a moderata o ad alta resistenza ai solfati, il cemento dovrebbe essere utilizzato in classe di esposizione XA2 (e in classe di esposizione XA1 se applicabile) e il cemento ad alta resistenza ai solfati dovrebbe essere utilizzato in classe di esposizione XA3.

Durability in EN 206

I valori si riferiscono all’uso di cemento CEM I 32.5 R e aggregato con 20 < Dmax < 32 mm


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Cracks in a beam


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Cracking and durability


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Durability of FRCCrack development in RC elements


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Four point bending tests on a beam

Constant Moment:

reinforcement and

surrounding concrete like a

tension tie

Beam Cross-Section Sample

Experimental Program


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Experimental Program II

Two fiber typologies:

Macro (M): Hook ended, 30 mm long, 0.62 mm

diameter

Micro (m): Straight, 13 mm long, 0.2 mm

diameter mm

950

Reinforcement

b

LVDT

900

Base of measurement 4 LVDTs, one for each side

of the specimen

b

b


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vIl

f Vf b

[mm]

As

[mm2]

Ac,eff

[mm2]

Reinf.

Ratio (%)

Clean

cover

[mm]

Denomination # of

specimens

f 10

0*

50 79 2421 3,24 20

N 50/10 - 0 3

0,5%* N 50/10 - 0,5/M 3

1,0 %* N 50/10 - 1/M 3

0,5%+0,5%* N 50/10 - 1/M+m 3

1%+1% N 50/10 - 2/M+m 3

f 10

0*

80 79 6321 1,24 35

N 80/10 - 0 2

0,5%* N 80/10 - 0,5/M 3

1,0 %* N 80/10 - 1/M 3

0,5%+0,5%* N 80/10 - 1/M+m 3

1%+1% N 80/10 - 2/M+m 3

f 20

0*

100 314 9686 3,24 40

N 100/20 - 0 3

0,5%* N 100/20 - 0,5/M 3

1,0 %* N 100/20 - 1/M 3

0,5%+0,5%* N 100/20 - 1/M+m 3

1%+1% N 100/20 - 2/M+m 3

f 20

0*

150 314 22186 1,41 65

N 150/20 - 0 3

0,5%* N 150/20 - 0,5/M 3

1,0 %* N 150/20 - 1/M 3

0,5%+0,5%* N 150/20 - 1/M+m 3

1%+1% N 150/20 - 2/M+m 3

f 30

0*

150 707 21793 3,24 60

N 150/30 - 0 3

0,5% N 150/30 - 0,5/M 3

1,0 % N 150/30 - 1/M 3

0,5%+0,5% N 150/30 - 1/M+m 3

1%+1% N 150/30 - 2/M+m 3

f 30

0*

200 707 39293 1,80 85

N 200/30 - 0 2

0,5% N 200/30 - 0,5/M 3

1,0 % N 200/30 - 1/M 3

0,5%+0,5% N 200/30 - 1/M+m 3

1%+1% N 200/30 - 2/M+m 3

Bar diameter f=10 mm



50

50

80

80

150

15

0

95

0

11

50

100

10

0

150 200

15

0

20

0

Reinforcement

b

Varia

tion o

f the re

bar d

iam

ete

rVariation of the specimen

size, b

Variation of the longitudinal

steel ratio, ρ=3,24% to 1,24%

Varia

tion o

f the re

bar d

iam

ete

r

Experimental Program III


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Experimental Results

Comparison specimens N 50/10 - 10 - =

3,24%

0

10

20

30

40

50

60

0 1 2 3 4 5

Average strain [‰]

Axia

l lo

ad

, N

[kN

]

Bare bar Ф 10

Average response plain

Average response Vf=0,5%

Average response Vf=0,5%+0,5%

Average response Vf=1%

ΔN Plain

ΔN SFRC Vf=0,5%

ΔN SFRC Vf=0,5%+0,5%

ΔN SFRC Vf=1%

Comparison specimens N 80/10 - 10 - =

1,24%

0

10

20

30

40

50

60

0 1 2 3 4 5

Average strain [‰]A

xia

l lo

ad

, N

[kN

] Bare bar Ф 10

Average response plain

Average response Vf=0,5%

Average response Vf=0,5%+0,5%

Average response Vf=1%

ΔN Plain

ΔN SFRC Vf=0,5%

ΔN SFRC Vf=0,5%+0,5%

ΔN SFRC Vf=1%

DN: combined effect of tension stiffening and

residual tensile stresses


G. Plizzari

Plain Concrete FRC

Results

w


G. Plizzari

Plain Concrete FRC

Tension stiffening in FRC

s c=fctm

t bm

concrete stress

bond stress

s c=0

lt lt

s c=fctm

t bm

s c= fFtsm

ltFRC lt

FRC

s c=0

s c=fctm

t bm

x s c=fFtsm

s c=fctm

t bm

x

s c=fctm

t bm

concrete stress

bond stress

s c=0

lt lt

s c=fctm

t bm

s c= fFtsm

ltFRC lt

FRC

s c=0

s c=fctm

t bm

x s c=fFtsm

s c=fctm

t bm

x

Average strain

Non-fibrous tie

Fibrous tie

N

esm esm Average strain

Non-fibrous tie

Fibrous tie

N

esm esm Average strain

Non-fibrous tie

Fibrous tie

N

esm esm


G. Plizzari

Average crack spacing: comparison with

standard formulations

0

50

100

150

200

250

300

350

400

0 300 600 900 1200 1500 1800f/r eff [mm]

Ave

rag

e c

rack

sp

ac

ing

[m

m]

Plain

SFRC Vf=0,5%

SFRC Vf=0,5%+0,5%

SFRC Vf=1%

CEB - FIP Model Code, 1978

Eurocodice 2, 1991

CEB - FIP Model Code, 1993

Eurocodice 2, 2003

Comparison against code provisions

eff

21b

mρ

kk10

sc2s

f

CEB, FIP Model Code 1978:

eff

mρ3.63

2s

f

CEB, FIP Model Code 1993:


G. Plizzari

Exposure in aggressive (marine) environment

10 beams has been exposed for more than 2 years in a coastal zone,

under a load equal to 50% of the ultimate load

Aim of the research: evaluate the influence of fibers on mechanical

behaviour of FRC in short and long term bending test


G. Plizzari

Materials

(UNI 11039)

3Ø14 18

2 Ø14

18

300

25

294

25

25

7 7

10

14 14

10

294

3

3

52

DiameterYield strength

(MPa)

Ultimate strength

(MPa)

Longitudinal

bars14mm 520 614

Stirrups 8mm 567 600


G. Plizzari

Tests for determining material properties

(UNI 11039)

0 500 1000 1500 2000

0

2

4

6

8

10

12

06S

09P

TQ065

LO

AD

(kN

)

CTOD (microns)

0.6% steel

0.9% polyester

Vf=0,6%

Vf=0,9%


G. Plizzari

Crack monitoring

Crack width, crack length and

crack position have been

measured during the exposure

period. The crack width has been

measured with a digital

microscope (200x magnification)


G. Plizzari

Cracking monitoring

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 50 100 150 200 250

pp1

pp2

st1

st2

tq

In FRC beams the crack widths were in the range of 0.1 to 0.2 mm, without overcome the

threshold of 0.2 mm. In plain beam the 93.3% of cracks had a crack width over 0.1 mm, while

the 60% over 0.2 mm.


G. Plizzari

Cracking monitoring

Average of crack widths between the loading points

Beams Dw /%

ST1-2_E 54%

POL1-2_E 53%

0.31

0.14 0.140.16

0.13

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

TQ1_E ST1_E ST2_E POL1_E POL2_E

Cra

ck w

idth

(m

m)

Crack width reduction of the FRC beams respect

to the plain beam (Dw /%).

steel polyester

PC


G. Plizzari

Cracking behavior at SLS

SLE

(50kN)

ST1-2 35%

POL1-2 28%

SHORT TERM

BEAMS

LONG TERM

BEAMS

SLE (50kN)

ST1-2_E 43%

POL1_E 37%

POL2_E 43%

Crack width reduction of the FRC beams respect to the plain beam.


G. Plizzari

Cracking behavior at ULS

SLU

(100kN)

ST1-2_E 56%

POL1_E 25%

POL2_E 54%

SLU

(100kN)

ST1-2 41%

POL1-2 39%

Crack width reduction of the FRC beams respect to the plain beam.

SHORT TERM

BEAMS

LONG TERM

BEAMS


G. Plizzari

Carbonation depth

CARBONATION DEPTHCHLORIDE CONTENT


G. Plizzari

Carbonation depth between the cracks


G. Plizzari

Carbonation depth at cracks

K

(mm/anni

^0.5)

t

armature

(anni)

TQ_E 19.4 2.4

ST1_E 12.7 5.6

ST2_E 13.4 5.0

POL1_E 12.5 5.8

POL2_E 14.7 4.2


G. Plizzari

Workshop proceedings


G. Plizzari

Thank you for your kind attention!

University of Brescia, Italy


G. Plizzari

FRC Roof ElementsFRC Roof Elements


G. Plizzari

Tests on Full-Scale Roof Elements

F1

F2

F3

F4

F5


G. Plizzari

Set up and Testing

HEB 550

HEB 260

UPN 300

HEB 160


G. Plizzari


Moment vs. Wing Displacement

0

100

200

300

400

500

600

0 50 100 150 200 250 300

Displacement [mm]

Mo

me

nt

[kN

m]

S45

S80

SWM

Elastic limit

SWM

S45

S80


G. Plizzari

Transverse Flexure Failure

Longitudinal flexural failure at the two bottom chords



G. Plizzari

Comparison specimens : average crack spacing

0

25

50

75

100

125

150

175

200

225

250

275

300

Φ=10,

ρeff=3,24%

Φ=10,

ρeff=1,24%

Φ=20,

ρeff=3,24%

Φ=20,

ρeff=1,41%

Φ=30,

ρeff=3,24%

Φ=30,

ρeff=1,80%

Ave

rag

e c

rack

sp

ac

ing

[m

m]

Plain

SFRC Vf=0,5%

SFRC Vf=0,5%+0,5%

SFRC Vf=1%

SFRC Vf=1%+1%

ratiogreinforcin

diameterBar

ρeff

f

Crack Spacing Comparison

-51% -69%

-27% -45% -24%-46%

-51% -25%


G. Plizzari

Crack Spacing and Experimental Residual Stress

Comparison specimens: average crack

spacing

050100150200250300

Φ=10, ρeff=3,24%

Φ=10, ρeff=1,24%

Φ=20, ρeff=3,24%

Φ=20, ρeff=1,41%

Average crack spacing [mm]

SFRC Vf=1%

SFRC Vf=0,5%+0,5%

SFRC Vf=0,5%

Plain

Comparison specimens: estimated residual

post-cracking strength fres

0,0 0,5 1,0 1,5 2,0 2,5

Φ=10, ρeff=3,24%

Φ=10, ρeff=1,24%

Φ=20, ρeff=3,24%

Φ=20, ρeff=1,41%

fres [MPa]

Comparison specimens: average crack spacing and

estimated residual post-cracking strength fres

Comparison specimens: average crack

spacing

050100150200250300

Φ=10, ρeff=3,24%

Φ=10, ρeff=1,24%

Φ=20, ρeff=3,24%

Φ=20, ρeff=1,41%

Average crack spacing [mm]

SFRC Vf=1%

SFRC Vf=0,5%+0,5%

SFRC Vf=0,5%

Plain

Comparison specimens: estimated residual

post-cracking strength fres

0,0 0,5 1,0 1,5 2,0 2,5

Φ=10, ρeff=3,24%

Φ=10, ρeff=1,24%

Φ=20, ρeff=3,24%

Φ=20, ρeff=1,41%

fres [MPa]

Comparison specimens: average crack spacing and

estimated residual post-cracking strength fres

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