"Uso de Hormigón con Fibras para sostenimiento de túneles" Giovanni Plizzari - Università degli Stud

Uso de HormigĂłn con Fibras para sostenimiento de tĂşneles G. Plizzari University of Brescia, Italy giovanni.plizzari@unibs.it

August 27th, 2020, Santiago, Chile

Fiber Reinforced Concrete (FRC) “Il calcestruzzo fibrorinforzato è un materiale composito caratterizzato da una matrice cementizia e da fibre discrete (discontinue). La matrice è costituita da calcestruzzi o da malte, normali o ad alte prestazioni. Le fibre possono essere di acciaio, di materiale polimerico, di carbonio, di vetro o di materiale naturale.”

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General aspects FRC Bending in FRCon Beams

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Fiber effects in concrete

Fibre content Vf  1%

res(w) plain

Fibre effects • durability (cracking control)

• minimum reinforcements (N, M,V)

• anchorage lengths

• fatigue

• deformability (tension stiffening)

• shrinkage

• stress limits in P/C elements

•D regions (spalling, bursting, splitting)

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Fibers for concrete

• Steel fibers

• Aluminum fibers

• Carbon fibers

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• Glass fibers

•Polypropylene fibers

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Parameters influencing FRC toughness – fiber content – fiber length (aspect ratio) – fiber geometry

– fiber distribution – mechanical properties of the matrix – fiber-matrix bond August 27th,2020, Santiago, Chile

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Structural design of FRC elements Bending in FRC Beams

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fib Model Code 2010

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Main goal of the fib Model Code To provide guidance to engineers to properly (and safely) design FRC structural elements both at serviceability and ultimate limit states, based on the state-of-the-art knowledge

CLASSIFICATION

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Base requirement for structural design

Engineers can design structures with new materials only if they are performance based!

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Structural design of concrete in tension

Concrete class C40/50 August 27th,2020, Santiago, Chile

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FRC classification • A performance approach is chosen: the material has to be tested as composite, because the mechanical response cannot be properly identified by knowing the mix design and the mechanical characteristics of each component UNIAXIAL TENSION TEST

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BENDING TEST

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FRC classification (3PBT)

EN 14651 hsp = 125 mm b = 150 mm

Linear stress distribution

August 27th,2020, Santiago, Chile

fR , j 

3 Fj l 2 b h 2sp

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FRC performance classes (New fib Model Code) Post-cracking residual strength can be classified by using two parameters, namely fR1k (representing the strength interval) and a letter a, b, c, d or e (representing the ratio fR3k/fR1k).

The strength interval is defined by two subsequent numbers in the series: 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 [MPa]

while the letters a, b, c, d and e correspond to the ratios: a if 0.5 ≤ fR3k/fR1k ≤ 0.7 b if 0.7 ≤ fR3k/fR1k ≤ 0.9 c if 0.9 ≤ fR3k/fR1k ≤ 1.1 d if 1.1 ≤ fR3k/fR1k ≤ 1.3 e if 1.3 ≤ fR3k/fR1k SLS

ULS

The designer has to specify the class, the residual strength ratio and the material of the fibre August 27th,2020, Santiago, Chile

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Performance classes fR1k =2.2 MPa

fR3k /fR1k = 0.82 ----- 2b

fR3k =1.8 MPa

4

e

2

d c b a

1

fR3k

CMOD 2

CMOD 1

fR1k

CMOD 3

3

CMOD 4

ĎƒN [MPa]

5

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

CMOD [mm]

Minimum requirements for structural applications: Fibres can substitute conventional reinforcement (rebars) only if the following relationship is fulfilled: August 27th,2020, Santiago, Chile

fR1k/fLk > 0.4 fR3k/fR1k >0.5 15/116

Constitutive law in uniaxial tension: sw • Experimental result: N – CMOD 

fFt=fct

–w

 hardening f Ftu fFts

fFts

Simplified constitutive law -w

fFtu

softening

fFtu

wu

w

 w



f Fts  0.45 f R1 f Ftu  f Fts

wu  ( f Fts  0.5 f R 3  0.2 f R1 )  0 CMOD 3

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fFtu

rigid-plastic

fFtu wu

w 16/116

Stress-strain relationship

ε1 = εSLS = CMOD1/lcs ε2 = εULS = wu/lcs (=2% or 1%)

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Optimized reinforcement: definition

Place the best performing reinforcement (fibers and/or rebars) where required by tensile stresses in the structural elements

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Reinforcement use in structural elements • 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 August 27th,2020, Santiago, Chile

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Hybrid systems fibers Bending in FRCofBeams

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Fiber effects in concrete

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Optimization of mechanical properties of HyFRC Improve composite strength by bridging micro-cracks

MICRO-FIBRES

MACRO-FIBRES Improve post-peak toughness by bridging macro-cracks

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Early experimental results: Bending tests

18 16 14

Load F [kN]

12 10 8 6 4 2 0 0,0

0,5

1,0

1,5 CMOD [mm]

2,0

2,5

3,0

Combinations of micro and macro-fibers show synergistic effect August 27th,2020, Santiago, Chile

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FRC for segmental tunnel lining Bending in FRC Beams

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Segmental lining Lining Tunneling machine

Segments Main lining features: • ground support • tunnel watertightness • longitudinal thrust resistance to the tunnelling machine Fonte dell’immagine: www.skf.com/it/index.html

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Precast tunnel segments  The lining is made by rings. Each ring is made by precast segments Shield

Hydraulic jacks

Cutter Head

 The tunnel is excavated by means of the TBM (Tunnel Boring Machine) August 27th,2020, Santiago, Chile

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Typical loading phases

Produzione e transitorie TBM LOAD

Montaggio TBM LOAD

Finale Fase di spinta complessa distribuzione di sforzi all’interno del concio, influenzata della dimensione dell’elemento stesso e delle condizioni al contorno

rischio di fessurazioni indotte dai carichi August 27th,2020, Santiago, Chile

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Typical loading phases

Produzione e transitorie

Montaggio

Finale

HOOPING FORCE

TBM LOADS

Introduzione di carichi concentrati su area limitata HOOPING FORCE

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Precast tunnel segments De-moulding

Storage of segments

wood blocks arms of picking system

Kďƒ—dead weight

adhesion forces

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Precast tunnel segments Transportation and positioning of the segment (the segments need to be transported around the segment plant, to the project site, down to the tunnel)

Pin shear erector

Positioning of the segment by means of erector system

Kďƒ—dead weight

(pin shear erector or vacuuming system)

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Precast tunnel segments TUNNEL SEGMENT

TBM shield hydraulic jacks

direction of excavation

concrete tunnel segments

cutting wheel

Test of in-plane action (thrust phase, global behaviour)

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Critical stage

Splitting Test (thrust phase, local behaviour)

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Precast tunnel segments Final stage: Ground support

- Favorable loading condition: lining under compression and bending: limited flexural demand - Shear forces due to bending are small (minimum shear reinforcement generally sufficient): stirrups can be substituted by fibers;

Ground/ water pressure

- Possible improvement of crack control of fibers

Lining

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Main advantages of using FRC  Enhanced toughness  Smaller crack opening (durability) and fiber corrosion resistant (durability)  Higher resistance to impact loading

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Main advantages of using FRC  No detachment of cracked concrete blocks in tunnels  Improved industrial process  Reduction of storage areas for reinforcement  Reinforcement spread everywhere in the segment (corners)

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Development of FRC tunnel linings Growing use of FRC for precast tunnel segments: from ’80s → 78 tunnels FRC & RC/FRC (Hybrid) precast tunnel segments: case studies over the years 2011-2017

2006-2010

2000-2005

'90s

'80s

Hybrid RC/FRC

0

5

10

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15

20

25

30

35

FRC

40

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Fiber Reinforced Concrete, FRC

 ITA report n. 16 (2016), “Twenty years of FRC tunnel segments practice: lessons learnt and proposed design principles”, April 2016, ISBN 978-2-970-1013-5-2, 71 p.  ACI Committee 544 (2016). “Report on Design and Construction of Fiber Reinforced Precast Concrete Tunnel Segments”, ACI 544.7R-16, American Concrete Institute, Farmington Hills, MI, 36 p.  fib Working Party 1.4.1. (2017) “Tunnels in fiber reinforced concrete”, fib Bulletin 83, “Precast tunnel segments in fibre-reinforced concrete”, ISSN 1562-3610, ISBN 978-2-88394-123-6, 168 p.

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Reinforcement optimization in precast segments There is NOT a unique solution but it is fundamental to know and to be able to quantify in a comprehensive design procedure the benefits due FRC Final stage:

Thrust phase:

Grouting process:

Mechanism

Ground support

Ground/ water pressure

Method of investigation

Lining

-Experimental tests on local splitting behavior on small specimens;

-Plane strain model-2D½ bedded ring model (parametric study);

-3D Non linear finite analyses (unfavorable conditions);

-Analytical procedure for the evaluation of lining behavior at SLS;

-Small scale/full scale tests

-Analytical procedure for the evaluation of lining behavior at ULS

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TBM in thrust Bending FRCload Beams

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TBM thrust phase Possible approaches for taking into account FRCs properties during this stage:  Full scale experimental tests

Conforti, Tiberti, Plizzari, Caratelli, Meda, TUST, 2017

 Small scale experimental tests

 Non linear numerical simulations August 27th,2020, Santiago, Chile

Conforti, Tiberti, Plizzari, TUST, 2015

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TBM thrust phase: local splitting phenomena

Thrust phase: high compressive stresses on a small area

Force exerted by jack

Proper specimens dimensions and configurations were adopted in order to study this local behavior

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Partially loaded area & FRC

FRC

Partially loaded area

The theoretical solution was proposed by K. T. S. R. Iyengar (1962)

+

Splitting stress

Hypothesis: 1. elastic material 2. plane stress state 3. infinitely extended element (h>2d) 4. no friction under the loading plate

Short fibers, having straight or deformed shape, are uniformly dispersed in the concrete matrix.

Fibers activate after cracking by bridging the crack. The concrete is able to transmit higher forces between the crack planes.

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TBM thrust phase: local splitting phenomena Experimental campaign on SFRC prismatic specimens Hooked-end-steel fibers 60/65 BATCHES The 60/65 steel fibers are characterized by a length of 60 mm, a diameter of 0.90 mm 60/65-25 (aspect ratio of 65) and tensile strength of 2300 MPa. 60/65-40 Concrete

60/65-25

60/65-40/40H

Sand 0-4 [kg/m3]

889.6

889.6

Coarse aggregate 0-10 [kg/m3]

332.2

332.2

RC BATCHES

Coarse aggregate 10-20 [kg/m3]

583.6

583.6

RC-0.6

Cement content [kg/m3]*

390

390

RC-1.0

Water-cement ratio

0.48

0.48

Super-plasticizer [L]

1.56

2.16

60/65 fibers [kg/m3]

25

40

60/65 fibers volume fraction [%]

0.32

0.51

Concrete slump [mm]

170

140

60/65-40H

Traditional reinforcement Ď•8

* CEM II/A-LL 42.5R

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Splitting test: experimental program

h=3d 750mm

h/d=3

Fibre types: 30/80

steel

steel

double hooked end

hooked end

0.90

0.38

Length [mm]

60

30

Aspect ratio [-]

65

80

Dosage [kg/m3]

25-40-60

25-40-60

Material Shape Diameter [mm]

August 27th,2020, Santiago, Chile

d=250mm

a=100mm

a/d=0.40 d=250mm

Load configuration

60/65

Sample geometry

Experimental campaign: • prismatic samples • line load configuration • reinforcement solutions:  fibres only  rebars only • two casting directions

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Splitting test: experimental program Horizontal casting

Vertical casting Loading direction

Casting direction perpendicular to loading direction

Unfavourable fibres orientation

Favourable fibres orientation

Casting direction identical to loading direction

Casting direction Form-work

k

Casting direction

Form-work

Loading direction

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Loading direction

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Experimental campaign on FRC prismatic specimens

Two different casting directions:

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Line load configuration:

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Splitting test: test set-up FRONT VIEW

Reacting frame Columns: HE 400 B; Beams: HE 450 B

Electro-mechanical actuator

Load cell HE 180 B Steel plate 100x250x40 mm Specimen Steel plate 400x400x30 mm High strength mortar

Displacement controlled loading procedure August 27th,2020, Santiago, Chile

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Splitting test: test set-up FRONT VIEW

Reacting frame

Specimen

H4 H5

Steel plate 400x400x30 mm

[x d] 0.5 0.5 0.30.3 0.4

125 125 75 75 100

Load cell HE 180 B Steel plate 100x250x40 mm

H1 H2 H3

250

Electro-mechanical actuator

[mm]

1.0

Columns: HE 400 B; Beams: HE 450 B

High strength mortar

d=250mm

Displacement controlled loading procedure August 27th,2020, Santiago, Chile

Instrumentation 47/116

TBM thrust phase: local splitting phenomena Two failure mechanisms were observed: SPLITTING FAILURE

I: Linear elastic phase of concrete II: Crack formation and propagation III: Concrete wedge formation and failure August 27th,2020, Santiago, Chile

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TBM thrust phase: local splitting phenomena Two failure mechanisms were observed: CRUSHING FAILURE

I: Linear elastic phase of concrete II: Crack formation and propagation III: Multi-cracking in compressed zone and failure August 27th,2020, Santiago, Chile

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TBM thrust phase: local splitting phenomena Comparison between different fiber contents: 1800 Load 1600 [kN]

25 kg/m3 of steel fibers significantly enhance the splitting behavior and the bearing capacity of a concrete prism (up to +54%), as well as the specimen ductility.

LL: Mean Experimental Curves H1 LVDT 60/65-25 fcm=37.9 MPa; 60/65-40 fcm= 41.0 MPa

1400

1200 60/65-40

1000 60/65-25

60/65-40H

800

40 kg/m3 of steel fibers are able to change the failure mode from splitting to crushing in elements under LL configuration.

600

A higher fiber content determines a greater stiffness in the post-cracking phase

400 200

0 0.00

wH1 [mm] 0.50

1.00

1.50

2.00

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2.50

Casting direction influences fiber orientation, thus the resistance and postcracking behaviour of specimens 50/116

TBM thrust phase: local splitting phenomena Comparison between different SFRC and RC solutions: 1800 Load 1600 [kN]

LL: Mean Experimental Curves

All RC samples showed a crushing failure at a load level of about 1200 kN

H1 LVDT 60/65-25 fcm=37.9 MPa; 60/65-40 fcm= 41.0 MPa RC-0.6 fcm =36.9 MPa; RC-1.0 fcm= 38.4 MPa

1400

RC-1.0

1200 60/65-40

1000 60/65-25

60/65-40H

As expected, an increment of splitting reinforcement led to a better control of the splitting crack

800 RC-0.6

600 400 200

0 0.00

wH1 [mm] 0.50

1.00

1.50

2.00

August 27th,2020, Santiago, Chile

2.50

RC samples showed similar performance to 40kg/m3 of fibers, coherently with the failure mechanism (the different crushing load is in accordance to the difference compressive strength fcm).

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Splitting test: database

18 prismatic samples subjected to splitting failure

August 27th,2020, Santiago, Chile

ID

Failure

Psplitting [kN]

Pmax [kN]

Lmax [mm]

LL-PC-1

splitting

1152

1152

750

LL-PC-2

splitting

1011

1011

750

LL-PC-3

splitting

970

970

750

LL-PFRC-1

splitting

1020

1439

560

LL-PFRC-2

splitting

840

1271

510

LL-PFRC-3

splitting

885

1160

590

SFRC33/55-1

splitting

795

1001

600

SFRC33/55-2

splitting

750

955

460

SFRC33/55-3

splitting

840

1072

560

SFRC60/75-1

splitting

800

1042

620

SFRC60/75-2

splitting

760

1006

650

SFRC60/75-3

splitting

795

1064

670

60/65-25-1

splitting

765

1072

460

60/65-25-2

splitting

670

1121

600

60/65-25-3

splitting

710

1093

400

30/80-25-1

splitting

767

1163

425

30/80-25-2

splitting

810

1207

410

30/80-25-3

splitting

770

1174

375

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TBM thrust phase: FRC tunnel segments (II) Ratio governing local splitting behavior

(I) Force on thrust shoe - ground conditions - tunnel overburden - number of shoes

TBM THRUST PHASE (III) Segment configuration

(IV) Irregularities

(V) FRC performance

- eccentric placement of thrust shoes - un-even support

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Tunnel segment geometry

MAIN CHARACTERISTICS: • Tunnel overburden 30 ÷ 70 m; • internal diameter 10.90 m; • external diameter 11.60 m.

SEGMENT GEOMETRY: • Length (Li) 4.70 m; • depth (b) 1.80 m; Li

August 27th,2020, Santiago, Chile

b

• thickness (t) 0.35 m.

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(I) Force on thrust shoes

• 30 hydraulic jacks: 4 jacks/segment; • service load applied by each jack: 3 MN; • service load applied on each segment:12 MN;

• nominal maximum load by each jack: 4.7 MN; • nominal maximum load on each segment: 18.8 MN.

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(II) Ratio governing local splitting behavior

Radial direction

Tangential direction

arad= 225 mm

atan= 1235 mm

drad= 350 mm

dtan= 2350 mm

arad/drad= 0.64

August 27th,2020, Santiago, Chile

atan/dtan= 0.53

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(III) Segment configuration

Configuration A

Configuration B

• Two pairs of thrust jack;

• Two pairs of thrust jack;

• four bearing pads.

• two bearing pads.

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(IV) Irregularities

Perfect placement of thrust shoes → NORMAL LOADING CONDITION

Eccentric placement of thrust shoes → OUTWARD ECCENTRICITY

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(V) FRC performance FRC Post-cracking properties determined according to: EN-14651 SFRC 6c

SFRC 2b

9.0

9.0

Experimental mean curve

8.0

8.0

Characteristic curve

Nominal Stress σN [MPa]

10.0

Nominal Stress σN [MPa]

10.0

7.0 6.0 5.0

4.0 3.0 Experimental mean curve

2.0

Characteristic curve

1.0

7.0 6.0 5.0

4.0 3.0 2.0 1.0

0.0

0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0

0.5

1.0

1.5

CMOD[mm]

2.0

2.5

3.0

3.5

CMOD [mm]

Series ID

Fiber ID

Ec [GPa]

fcm,cube [MPa]

fctm [MPa]

fLk [MPa]

fR1k [MPa]

fR2k [MPa]

fR3k [MPa]

fR4k [MPa]

SFRC 2b

33/0.75

40.2

75.7

4.53

5.11

2.30

1.94

1.73

1.59

SFRC 6c

50/0.75

40.1

74.1

4.50

5.21

6.49

7.14

6.77

6.10

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4.0

(V) FRC performance FRC classification according to Model Code 2010

Series ID

Fiber ID

fR1k [MPa]

fR3k/fR1k [-]

Classification

SFRC 2b

33/0.75

2.30

0.75

2b

SFRC 6c

50/0.75

6.49

1.04

6c

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Numerical Model: mesh discretization Configuration B

Configuration A Steel plates Interface under steel plates Segment

Interface on lateral surfaces

Interface on the bottom surface

Number of elements: Steel Plates: 192 Interface under steel plates: 96 Segment: 5184 Interface on the bottom surface: 96 Interface on lateral surfaces: 216 August 27th,2020, Santiago, Chile

Interface on lateral surfaces

Number of elements: Steel Plates: 192 Interface under steel plates: 96 Segment: 5184 Interface on the bottom surface: 128 Interface on lateral surfaces: 216 61/116

Numerical Model: modeling of material SFRC 6c

SFRC 2b

9.0

9.0

8.0

8.0

Nominal Stress ĎƒN [MPa]

10.0

Nominal Stress ĎƒN [MPa]

10.0

7.0 6.0 5.0

4.0 3.0 Experimental mean curve 2.0

Characteristic curve

1.0

Experimental mean curve Characteristic curve Inverse analysis

7.0 6.0 5.0

4.0 3.0 2.0 1.0

Inverse analysis

0.0

0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

CMOD[mm]

3.5

4.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

CMOD [mm]

Inverse analysis method: discrete crack approach August 27th,2020, Santiago, Chile

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Numerical Model: modeling of material  SFRCs uni-axial post cracking laws: characteristic values (applied in the model by means of a smeared crack approach): Series ID

SFRC 2b

Bi-linear tensile post-cracking law fctk

1

SFRC 6c

fck [MPa]

fctk [MPa]

w1 [mm]

σ1 [MPa]

wc [mm]

Gf,tot [N/mm]

54.17

3.16

0.075

0.67

6.0

2.13

54.17

3.16

0.020

2.25

15.0

16.91



Gf,tot

w w1

wc

 SFRCs uni-axial compressive law: Thorenfeldt  Steel conventional rebars: embedded reinforcement, fyk=500 MPa, fsk=575 MPa

August 27th,2020, Santiago, Chile

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Numerical Results Global behavior: bearing capacity & development of cracks Normal loading condition, configuration-B 45 3.5

35

3.0

30

2.5

25

2.0

20 1.5

(C)

15

(B)

1.0

10

(A)

5

Total load/Service load [-]

Total load [MN]

40

0.5 SFRC 6c

0.0

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Average displacement under the loading surfaces [mm]

August 27th,2020, Santiago, Chile

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Numerical Results Local behavior: influence of FRC performance on spalling crack Normal loading condition, configuration-B 45

Total load [MN]

35

3.0

30

2.5

25

2.0

20

1.5

15 1.0

10 SFRC 2b

5

0.14 mm

0.45 mm

Total load/Service load [-]

3.5

40

0.5

SFRC 6c 0.0

0 0

0.2

0.4

0.6

0.8

1

1.2

Crack opening in the region between the thrust jacks [mm]

SFRC 2b exhibits a crack opening of about three times of that shown by SFRC 6c at 1.5 times the service load August 27th,2020, Santiago, Chile

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Numerical Results Local behavior: influence of the adopted segment configuration Dotted-line = Configuration-AA

Normal loading condition 45 SFRC 2b, config-B SFRC 6c, config-B SFRC 2b, config-A SFRC 6c, config-A RC, config-A

Configuration-B

Total load [MN]

35 30

25

3.5

3.0 2.5

Total load/Service load [-]

40

2.0 Configuration-A

20

1.5

15 1.0

10

Solid-line = Configuration-BA

0.5

5

0. 35 mm 0.0

0 0.0

0.5

1.0

1.5

2.0

2.5

Crack opening in the region between the thrust jacks [mm]

Configuration-A leads to higher spalling crack opening with respect Configuration-B: SFRC 6c: from 0.14 mm to 0.35 mm at 1.5 times the service load August 27th,2020, Santiago, Chile

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Numerical Results Local behavior: influence of the eccentricity Configuration-AA

Outside eccentricity, configuration-A

Total load [MN]

25

2.0

20 1.5 15 1.0 10

SFRC 2b 5

0.5

Total load/Service load [-]

2.5

30

+ A Outward-EccentricityA

SFRC 6c RC 0.0

0 0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Crack opening in the region between the thrust jacks [mm]

Outward eccentricity leads to higher spalling crack opening: SFRC 6c: from 0.12 mm (normal loading condition) to 0.89 mm at service load SFRC 6c behaves like RC (reference solution) August 27th,2020, Santiago, Chile

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Optimized reinforcement

Traditional Reinforcement

Optimized Reinforcement

Steel content: 97 kg/m3

Steel content: 48 kg/m3 + SFRC 2b

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Optimized reinforcement

Longitudinal rebars (intrados surface)

These rebars (Ď s~0.2-0.3%) guarantee an adequate bearing capacity at ULS and Myielding > Mcracking The combination of these rebars with SFRC 2b: -enhances the flexural bearing capacity (demoulding, storage, handling) -noticeable improves crack control

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Optimized reinforcement

Longitudinal rebars (extrados surface)

These rebars (intrados and extrados) in combinations with SFRC 2b guarantee a noticeable better crack control for: spalling crack between the thrust jacks during the TBM thrust phase

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Optimized reinforcement

Stirrups (radial joints)

Minimum amount of stirrups in order to avoid:

- buckling phenomena longitudinal rebars

of

- spalling off of the cover due to radial stresses caused by curved shape of longitudinal rebars

+ A

practical issues: for placing the reinforcement cage

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Optimized reinforcement

Stirrups (longitudinal joints)

Local stirrups: These stirrups are mainly placed for practical reasons (handling and lifting the reinforcement cage)

+ A

SFRC 2b enhance the control of local effect in the longitudinal joints such as local splitting stress due to hooping force (normal force)

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Optimized reinforcement NOTE THAT: - Local radial splitting cracking phenomena:

- Local tangential splitting cracking phenomena:

are mainly controlled by Fiber Reinforcement only August 27th,2020, Santiago, Chile

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Numerical Results Local behavior: influence of the eccentricity Outside eccentricity, configuration-A

Configuration-AA 2.5

Total load [MN]

25

2.0

20

1.5 15

1.0 10 SFRC 2b 2b SFRC SFRC 6c SFRC 6c RC RC RCO+SFRC 2b

5

0.5

0

Total load/Service load [-]

30

+ A Outward-EccentricityA

0.0 0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Crack opening in the region between the thrust jacks [mm]

Outward eccentricity leads to higher spalling crack opening: SFRC 6c, RCO+SFRC 2b and RC (reference solution) exhibit a similar behavior August 27th,2020, Santiago, Chile

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A case study with polymeric Bending in FRC Beamsfibers

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Full scale tests: segment geometry CASE STUDY: Scilla tunnel    

internal diameter: 3.50 m thickness: 0.20 m width: 1.10 m N° of segments (per ring): 4

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Precast tunnel lining The precast tunnel lining considered corresponds to the Scilla tunnel, which is one of the main structures of a new power line between Sicilia and Calabria (Italy)

This tunnel has an internal diameter (Di) of 3500 mm, a thickness (t) of 200 mm and a width of 1100 mm→ the segment C1 was investigated August 27th,2020, Santiago, Chile

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Research program Macro synthetic

Four steps: 1. Mechanical characterization of four Polypropylene Fibre Reinforced Concretes (PFRCs)

Material Shape Diameter [mm] Length [mm]

2. Reinforcement design  RC segment – traditional reinforcement solution Aspect ratio [-]  PFRC segment – fibre only solution  SFRC segment – fibre only solution  RCO+PFRC segment – hybrid solution

polypropylene embossed

0.70 48

68

3. Transient stage: flexural test 4. Construction stage: point load test August 27th,2020, Santiago, Chile

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Material properties Summary of results from Three Points Bending Tests (3PBTs) according to European Standard, EN 14651: 8.0 Nominal stress [MPa] 7.0

EN14651

6.0 3e

5.0

2.5 e

4.0

2e

3.0 PFRC4 PFRC6 PFRC8 PFRC10

2.0 1.0 0.0 0.0

0.5

1.0

1.5

August 27th,2020, Santiago, Chile

2.0

1.5 d

PFRC8 was selected for casting segments

CMOD [mm] 2.5

3.0

3.5

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Reinforcement solutions The following reinforcement solutions were adopted for the segment under investigation: RC: traditional reference solution (steel rebars only) RCO+PFRC8: optimized reinforcement (low amount of steel rebars) and 8 kg/m3 of PP fibers PFRC8: solution based on fiber reinforcement only The reinforcement solutions were delivered based on preliminary design considerations regarding the possibility of PP fibers of controlling splitting local phenomena (TBM thrust phase) or spalling phenomena in combination with traditional reinforcement (hybrid configuration). With regard to flexural behaviour, the hybrid solution was expected to exploit the mutual combination of fibers and rebars. Hence, the longitudinal steel rebar ratio adopted for RCO+PFRC8 solution was reduced to 0.11%

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Precast tunnel lining Two steel molds of segment are available. The mold of segment “C1� was used for casting segments by using the planetary mixer

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Precast tunnel lining After de-molding, the segments were stored in the laboratory

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Reinforcement solutions RC precast tunnel segment Concrete Class: C50/60 Longitudinal reinforcement: Curved steel rebars 8+8 8 Reinforcement ratio, s=0.23% Shear reinforcement: Stirrups 8 @ 12 cm, 4 legs Reinforcement ratio, w =0.15% Splitting reinforcement: Local stirrups 8 @ 12 cm, 2 legs Total reinforcement: Steel rebar content=110 kg/m3

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Reinforcement solutions RCO+PFRC8 precast tunnel segment Concrete Class: C50/60 Longitudinal reinforcement: Curved steel rebars 4+4 ď Ś8 Reinforcement ratio, ď ˛s=0.11% Fibers: 8 kg/m3 Shear reinforcement: Fibers: 8 kg/m3 Splitting reinforcement: Fibers: 8 kg/m3 Total reinforcement: Fibers 8 kg/m3 + steel rebar content of 35 kg/m3 August 27th,2020, Santiago, Chile

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Reinforcement solutions Steel reinforcement cage of RC vs. RCO+PFRC8 precast tunnel segment

Steel rebar content = 110 kg/m3 (RC) vs. 35 kg/m3 (RCO+PFRC8): reduction of 68% August 27th,2020, Santiago, Chile

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Flexural tests: experimental set-up A three points bending test configuration was adopted, characterized by a net span of 1600 mm. The two supports were continuous on the entire segment width, while the load was applied at segment extrados by means of two steel plates (150x200 mm) placed on a layer of high-strength mortar

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Flexural tests: instrumentation Three Linear Variable Differential Transducers (LVDTs) were placed on segment intrados to measure the mid-span deflection; The flexural crack opening at the maximum bending moment was measured by means of Potentiometric Transducers (PTs)

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Flexural test: results

140

Load [kN]

Load [kN]

Instrumentation

RC segment Load vs. Deflection

120

Pcr Ppeak

Flexural cracking load Flexural initial peak load

Pmax

Flexural maximum load

PULS

Ultimate load [handling]

140

RC segment Load vs. Net Deflection

120

100

100

80

80

60

60

Pmax = 105.6 kN

Ppeak = 46.9 kN 40

40

20

0

10

20

30

40

50

60

Mean curve

0 70

Deflection [mm]

August 27th,2020, Santiago, Chile

PULS = 29.7 kN

20

D1 (front) D2 (back) D3 (centre)

0

Pcr = 35.1 kN

0

5

10

15

20

25

30

35

40

45

50

Net deflection [mm]

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Load [kN]

Flexural test: results PFRC8 segment: minimum flexural performance according to MC2010 § 7 and fib Bulletin 83 § 3 (Ppeak ≈ Pmax)

140

Flexural Tests Load vs. Net deflection

120 100

-19%

80 60 40

PULS 20

0 0

5

10

15

20

25

30

35

RC RCRC PFRC8-I PFRC8-II RCO+PFRC8-I RCPFRC8-I SFRC40 RCO+PFRC8-I RCO+PFRC8-II RCO+PFRC8-II PFRC8-II SFRC40 40

45

50

SFRC40 segment: flexural bearing capacity comparable to RC solution (10%) RCO+PFRC8 segment: satisfactory flexural behaviour

Net deflection [mm]

Pcr [kN]

δcr [mm]

Ppeak [kN]

δpeak [mm]

Pmax [kN]

δmax [mm]

δmax /δpeak

RC

35.1

0.18

46.9

0.38

105.6

36.6

96.3

PFRC8-I

47.8

0.28

51.4

0.46

48.6

4.9

10.6

PFRC8-II

43.5

0.23

52.4

0.58

53.9

8.0

13.8

RCO+PFRC8-I

50.6

0.18

69.4

0.40

94.5

12.7

31.8

RCO+PFRC8II

41.6

0.21

59.6

0.38

76.3

14.9

39.4

SFRC40

39.0

0.21

66.1

0.59

95.4

3.87

6.6

August 27th,2020, Santiago, Chile

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Flexural test: results Crack patterns & fibre counting RCO+PFRC8-I

RCO+PFRC8-II

-14% N° of Fibre [-]

Fibre density [fibre/cm2]

N° of Fibre [-]

Fibre density [fibre/cm2]

2085

0.98

1802

0.83

August 27th,2020, Santiago, Chile

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Flexural tests: experimental results The better flexural behavior (in terms of bearing capacity and ductility) of segment PFRC8-II with respect to PFRC8 I can be qualitatively explained by analyzing the final crack patterns.

In fact, the segment PFRC8-II has exhibited a more distributed crack pattern as compared to PFRC8-I Both segments reinforced with a hybrid solution (RCO+PFRC8 I and RCO+PFRC8 II) were able to provide a significant and similar ductility after cracking, as proven by measurement of mid-span deflection

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Point load tests: experimental set-up The force exerted by the TBM thrust shoes on tunnel segments during the excavation process were simulated through a steel&concrete reacting frame

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Point load tests: experimental set-up Two steel reacting frames with two correspondent hydraulic jacks are able to transfer the point loads on the upper-part of the segment at TBM thrust shoes locations.

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Point load tests: instrumentation Several displacement transducers were used for monitoring crack developments and displacements of tunnel segments

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Loading procedure & instrumentation Loading procedure

Top

700 kN

Digital microscope Service load

1000 kN Exceptional load

Instrumentation

Intrados

Extrados

1600 kN Emergency load 2750 kN Maximum load of thrust system

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Point load tests: crack pattern First cracks occurred between TBM thrust shoes.

The latter are defined as spalling cracks.

All the segments were uncracked at service load and also at exceptional load

Spalling Cracks

Splitting Cracks

Secondary cracks occurred under the TBM thrust shoes.

The latter are defined as splitting cracks

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Point load tests: experimental results Load vs. average vertical displacements (average values of intrados and 3500 extrados) are herein reported: Vertical displacement

Intrados and Extrados average values

3000

Load [kN]

2500 2000 1500 RCO+PFRC8-I-V

1000

RCO+PFRC8-II-V

PFRC8-I-V

500

PFRC8-II-V

0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Vertical displacement [mm]

Note that the average displacement of RC sample are not reported for faulty readings of extrados disp. transducers, even though vertical intrados displacement (left TBM jack) was similar to those retrieved from other segments August 27th,2020, Santiago, Chile

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Point load tests: experimental results The preliminary diagrams of load (for each TBM shoes) vs. spalling are herein reported (spalling were first cracks occurring in all segments) 3500

Spalling intrados Middle Level 1 3000

Load [kN]

2500 2000 1500 RC

RCO+PFRC8-I

1000

RCO+PFRC8-II 500

PFRC8-I

PFRC8-II 0 0.00

0.20

0.40

0.60

0.80

1.00

1.20

Realative displacement [mm]

Segments RCO+PFRC8s (hybrid solution) were able to exhibit the same spalling local crack behavior of RC segment August 27th,2020, Santiago, Chile

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Point load tests of tunnel segments: results All precast tunnel segments (according to the different reinforcement solutions previously described) were loaded up to approximately the maximum bearing capacity of hydraulic jacks.

Hence, all segments were loaded by a maximum load of about 2750 kN for each TBM shoe. The latter load level corresponds to about 3.93 times the nominal service load (service load=700 kN for each TBM shoes) By considering spalling cracks development (intrados middle transducer, level 1), all the segments, including PFRCs, exhibited a satisfactory behavior (very small relative displacement, less than about 0.1 mm) up to 1500 kN (2.14 times the service load) August 27th,2020, Santiago, Chile

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Point load tests: experimental results By considering spalling cracks development, for all load levels investigated the RCO+PFRC8 segments present equal or lower relative displacements (and expected crack widths) than reference RC segment The mutual collaboration of local longitudinal steel rebars and PP fibers in possible cracked region between the TBM thrust shoes is particularly effective in controlling spalling crack phenomena, as proven for RCO+PFRC8 segments In hybrid segments, the residual splitting crack at the end of second load cycle (1600 kN, 2.28 s.l.) is equal to the one presented by RC segment. On the other hand, for spalling crack, at the end of the second load cycle, it was possible to observe how the combination of bars and fibers allows the hybrid solution to guarantee a lower residual opening August 27th,2020, Santiago, Chile

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FRC forin crack Bending FRCcontrol Beams

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FRC performance in combination with rebars (SLS) Four point bending tests on a beam

Beam Cross-Section

Sample

Constant/low gradient of bending moment: reinforcement and surrounding concrete can be

assumed as a tension tie August 27th,2020, Santiago, Chile

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1st phase (NSC and HSC): tie 950/1000 mm long tested in by means of a hydraulic servo-controlled (closed-loop) testing machine with MTS control 2nd phase (only NSC): tie 1000 mm and 1500 long tested in by means of a available steel reacting frame conveniently modified Typical instrumented specimen (2nd phase):

300

FRC performance in combination with rebars (SLS)

b

b

Reinforcement

August 27th,2020, Santiago, Chile

* for ď Ś10 bar

L=1500 (1000*) 300

Base of measurement

LVDT

1400 (900*)

4 LVDTs, one for each side of the specimen

Steel plate 103/116

FRC performance in combination with rebars (SLS) The typical response terms of axial load vs. average tensile strain of RC and FRC for NSC and HSC series 200

- ρ = 2.23% Specimens 120x120 - Φ20

180

180

160

160

140

140

Axial force [kN]

Axial force [kN]

200

120

-

100 80

Specimens 150x150 - 20M - ρ= 1.35%

120

-

100 80

60

Bare bar Φ20

40

N 120/20 - 0/2

40

20

N 120/20 - 0.5M/1

20

60 Bare bar 20M H 150/20 - 0/2 H 150/20 - FRC1/1

0

0 0

1

2

3

NSC

4

5

Average strain [‰]

August 27th,2020, Santiago, Chile

0

1

2

3

HSC

4

5

Average strain [‰]

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FRC performance in combination with rebars (SLS) Plain Concrete (NSC)

FRC (NSC)

w

Fibre addition determines a reduction of the mean crack spacing August 27th,2020, Santiago, Chile

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FRC performance in combination with rebars (SLS) Mean crack spacing srm (NSC) Crack spacing reduction with respect to plain samples [%] Average reduction fiber Vf=0,5% - 27,1% -18% -27% Average reduction fiber Vf=1,0% - 38,7% -28% -65%

-14% -36%

-24% -22%

-42% -49%

-13% -26%

-31% -40% -28% -30% -46% -54%

August 27th,2020, Santiago, Chile

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FRC performance in combination with rebars (SLS) Prismatic FRC element with central rebar: recent experimental results 250

500

Specimens 120x120 - Ф20 - ρ = 2.23%

Specimens 200x200 - Ф30 - ρ = 1.80 %

450 400

200

Axial force [kN]

Axial force [kN]

350 150

100

Bare bar - Ф20

300 250 200 Bare bar Ф30

150 N120/20 - 0

N200/30 - 0 100

50

N200/30 - 0.5MH

N120/20 - 0.5MH 50

N200/30 - 0.75MH

N120/20 - 0.75MH 0

0 0

1

2

3

Average member strain, sm [‰]

4

5

0

1

2

3

4

5

Average member strain, sm [‰]

 Tiberti, G., Trabucchi, I., AlHamaydeh, M., Minelli F., Plizzari, G.A., “Crack control in concrete members reinforced by conventional rebars and steel fibers”, In: Proceedings of the 9th international conference, Fibre Concrete 2017, Prague (Czech Republic), 13-16 September, full paper on usb-stick, 10 p.  Tiberti, G., Trabucchi, I., AlHamaydeh, M., Minelli F., Plizzari, G.A., “Crack development in steel-fibre-reinforced concrete members with conventional rebars”, Magazine of Concrete Research, https://doi.org/10.1680/jmacr.17.00361.

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Workshop proceedings

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Workshop proceedings

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Published papers  Plizzari G.A., Cominoli, L., 2005. “Numerical simulations of SFRC precast tunnel segments. In: World Tunnel Congress ITA-AITES 2005, Istanbul, Turkey, May 7-12, pp. 1105-1111.

 Plizzari G.A., Tiberti G. 2006. “Steel Fibers as reinforcement for precast tunnel segments”. In: -.

Proceedings of the ITA-AITES 2006 World Tunnel Congress, “Tunnelling and Underground Space Technology - Safety in the Underground Space”, Seoul, Corea, April 22-27, 2006, vol. 21, p. 438-439, Amsterdam: Elsevier, ISSN: 0886-7798.  Plizzari G.A., Tiberti G., 2007. Structural behaviour of SFRC tunnel segments. In: Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCos 2007), vol. 3, Editors: Carpinteri A., Gambarova P., Ferro G., Plizzari G.A., Catania, Italy, June 17-22, 2007, p.1577-1584, ISBN 9780415440660.  Burgers R., Walraven J., Plizzari G.A., Tiberti G., 2007. Structural behaviour of SFRC tunnel segments during TBM operations. In: Proceedings of the ITA-AITES World Tunnel Congress 2007 “Underground space-the 4th dimension of metropolises”, vol.3, p. 1461-1467, Praga, Czech Republic, May 5-10, 2007, London: Taylor & Francis Group, ISBN: 9780415408073.

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Published papers  Tiberti, G., and Plizzari, G.A., 2008, “Tunnel linings of fiber reinforced concrete combined with traditional reinforcement”. In: Proceedings of Seventh International RILEM Symposium (BEFIB 2008), “Fibre Reinforced Concrete: Design and Applications”, Editor: Gettu, R., RILEM publications S.A.R.L., Chennai (India), 17-19 September, 2008, pp. 617-629, ISBN: 978-2-35158-064-6.  Plizzari, G.A., and Tiberti, G. 2008, “Final concrete linings with optimized reinforcement”. In: Proceedings of ITA-AITES World Tunnel Congress, “Underground Facilities for Better Environment & Safety”, Editors: Kanjlia V.K., Ramamurthy T., Wahi P.P., Gupta A.C., Agra (India), 22-24 September, 2008, Vol. 2, pp. 922-932, Central Board of Irrigation&Power.  Tiberti, G., Plizzari, G., Blom, C.B.M., and Walraven, J.C. 2008, “Concrete tunnel segments with combined traditional and fiber reinforcement”. In: International fib symposium “Tailor Made Concrete Structures”, Editors: Walraven, J.C., and Stoelhorst, D., Taylor & Francis Group (CRC Press), 19-22 May, 2008, Amsterdam (the Netherlands), extended abstract on p. 66; full paper on CD, pp. 199-205, ISBN: 978-0-415-47535-8, doi: 10.1201/9781439828410.ch37.  Plizzari, G.A., Tiberti, G., and Winterberg, R., 2008. “Design aspects of SFRC tunnel segments”. In: Mechanised Tunnelling and Segmental Lining, Published by German-Czech Scientific Foundation (WSDTI), pp. 266-274, ISBN 978-3-00-025435-2.

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Published papers  Tiberti G., and Plizzari, G.A. 2009. “Parametric study on tunnel linings in fiber reinforced concrete combined with traditional reinforcement.” In: Proceedings of the ITA-AITES World Tunnel Congress, “Safe Tunnelling for the City and for the Environment”, Editor: P.Kocsonya, Budapest (Hungary), May 23-28, 2009, extended abstract on pp. 238-240; full paper on CD, 9 p., Hungarian Tunneling Association, ISBN: 978-963-06-7239-9.  Plizzari, G., Tiberti, G. 2009. “Tunnel linings made by precast concrete segments”. In: Construction Methodologies and Structural Performance of Tunnel Linings, pp. 136-131. Editor: G.A. Plizzari, Vol. unico, ISBN/ISSN: 978-88-96225-31-8, Starrylink, Brescia, Italy, 226 p.  Gambarova, P.G., Chiaia, B., Fantilli, A.P., Oggeri, C., Ronco, C., Minelli, F., Plizzari, G.A., Tiberti, G., Aiello, M., and Vasanelli, E. 2009. “Innovative Materials for Tunnel Linings”. In: Construction Methodologies and Structural Performance of Tunnel Linings, pp. 19-56. Editor: G.A. Plizzari, Vol. unico, ISBN/ISSN: 978-88-96225-31-8, Starrylink, Brescia, Italy, 226 p.  Plizzari, G.A., and Tiberti, G. 2010. “Fiber Reinforced Concrete for tunnel linings”. In: Proceedings of the World Tunnel Congress 2010 “Tunnel vision towards 2020”, Vancouver (Canada), 15-20 May, 2010, full-paper available on CD, 8 p.

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Published papers  Tiberti, G., Minelli, F., and Plizzari, G.A. 2011. “Crack control in FRC tunnel linings”. In: Proceedings of the ITA-AITES World Tunnel Congress and 37th General Assembly, “Underground spaces in the service of sustainable society”, Helsinki (Finland), May 20-26, 2011, extended abstract on pp. 234-235; full paper on CD, pp. 1036-1047, ISBN 978-951-758-531-6, ISSN 0356-9403.  Minelli, F., Plizzari, G.A., and Tiberti, G. 2012. “FRC tunnel linings: new design perspective”. In: Proceedings of the World Tunnel Congress 2012, “Tunnelling and Underground Space for a Global Society”, Editors: Phienwej, N., Boonyatee, T., published by Engineering Institute of Thailand (EIT), Bangkok (Thailand), 21-23 May, 2012, extended abstract on pp. 334-335; full-paper on CD, 8 p., ISBN: 978-974-7197-78-5.  Tiberti, G., Plizzari, G.A., and Cominoli, L. 2013. “Fiber reinforced concrete for tunnel linings”. In: Proceedings of international fib symposium “Engineering a concrete future: technology, modelling and construction”, Editor: A. N. Dancygier, Tel Aviv, 22-24 April, 2013, pp. 702-707, ISBN: 978-965-92039-01.  Tiberti, G., Minelli, F., and Plizzari, G.A. 2013. “Reinforcement optimization of fiber reinforced concrete linings for conventional tunnels”, Composites Part B: Engineering, ISSN 1359-8368, doi: http://dx.doi.org/10.1016/j.compositesb.2013.10.012.

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Published papers  Tiberti, G. and Plizzari, G.A. 2014. “Structural behavior of precast tunnel segments under TBM thrust actions”. In: Proceedings of the World Tunnel Congress 2014, “Tunnels for a better life”, Editors: Negro, A., Cecilio Jr., M.O., Bilfinger, W., Foz do Iguaçu (Brazil), 9-15 May, 2014, extended abstract on pp. 232, full-paper available on CD, 10 p., ISBN: 978-85-67950-00-6.  Tiberti, G., Conforti A., Plizzari, G.A., and Moro, S. 2015. “Experimental investigation on the local splitting behavior under TBM hydraulic jacks”. In: Proceedings of the World Tunnel Congress 2015, “See tunnel”, Editor: Kolić, D., Dubrovnik (Croatia), 22-28 May, 2015, extended abstract on pp. 268-269, fullpaper available on CD, 10 p., ISBN: 978-953-55728-5-5.  Tiberti, G., Conforti, A., Plizzari, G.A. 2015. “Precast segments under TBM hydraulic jacks: Experimental investigation on the local splitting behavior”, Tunnelling and Underground Space Technology, ISSN 0886-7798, 50, pp. 438-450 doi: http://dx.doi.org/10.1016/j.tust.2015.08.013.  Conforti, A., Tiberti, G., and Plizzari, G.A. (2016), “Combined effect of high concentrated loads exerted

by TBM hydraulic jacks”, Magazine of Concrete Research, http://dx.doi.org/10.1680/jmacr.15.00430.

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Published papers  Conforti, A., Tiberti, G., Plizzari, G.A. and Moro, S. (2016),“Experimental Study on the Effects of HighConcentrated Loads Exerted by TBM Hydraulic Jacks”, In: Proceedings of the World Tunnel Congress 2016, “The World Tunnel Congress”, San Francisco (USA), 23-28 April, 2016, full-paper available on CD, 10 p.  Conforti, A., Tiberti, G., Plizzari, G.A. (2016). “Splitting and crushing failure in FRC elements subjected to a high concentrated load”, Composites Part B: Engineering, Vol. 105, November 2016, ISSN: 13598368, pp. 82-92, doi: http:// dx.doi.org/10.1016/j.compositesb.2016.08.032.  Tiberti, G., Chiriotti, E., and Plizzari, G.A. (2016), “Twenty years of FRC tunnel segments practice: lessons learnt and proposed design principles”, ITA report n. 16, April 2016, ISBN 978-2-970-1013-5-2, 71 p.  Conforti, A., Tiberti, G., Plizzari, G.A., Caratelli, A., Meda, A. (2017). “Precast tunnel segments reinforced by macro-synthetic fibers”, Tunnelling and Underground Space Technology, Vol. 63, March 2017, ISSN 0886-7798, pp. 1-11, doi: http://dx.doi.org/10.1016/j.tust.2016.12.005.  Tiberti, G., Trabucchi, I, and Plizzari, G.A. (2017). “Numerical study on the effects of TBM highconcentrated loads applied to precast tunnel segments”, EURO:TUN 2017, Innsbruck University, Austria.

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Thank you for you kind attention!

August 27th,2020, Santiago, Chile

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