TECHNICAL REPORT TESTS ON PRECAST TUNNEL SEGMENT IN … · 2018-02-27 · Figure 4.2 Segments under...

Università degli Studi di Roma “Tor Vergata” CIVIL ENGINEERING AND COMPUTER SCIENCE DEPARTMENT TERC – TUNNELLING ENGINEERING RESEARCH CENTRE

TECHNICAL REPORT

TESTS ON PRECAST TUNNEL SEGMENT IN CONCRETE REINFORCED WITH STEEL FIBERS (DRAMIX 4D 80/60BG)

CUSTOMER:

BMUS

September 2017

Prof. Alberto Meda Prof. Zila Rinaldi

TERC – TUNNELLING ENGINEERING RESEARCH CENTRE University of Rome Tor Vergata 2

INDEX

1 INTRODUCTION ............................................................................................................. 3

2 SEGMENT GEOMETRY ................................................................................................. 4

3 MATERIAL ...................................................................................................................... 5

4 SEGMENT TESTING PROCEDURES ............................................................................. 8

4.1. Bending test ..................................................................................................................... 8

4.2. Point load test ................................................................................................................. 11

5 BENDING TEST RESULTS ........................................................................................... 13

6 POINT LOAD TEST RESULTS ..................................................................................... 20

7 CONCLUSIONS ............................................................................................................. 27


1 INTRODUCTION

The loading tests, object of the present report, are carried out on precast tunnel segments in fiber reinforced concrete produced in the Laboratory of Materials and Structures of the Civil Engineering Department of the University of Rome Tor Vergata. The segments were cast by using segment moulds typically used in metro tunnels.

The tests were conducted by the Laboratory of Materials and Structures of the Civil Engineering Department of the University of Rome Tor Vergata. Responsible of the tests are Prof. Alberto Meda and Prof. Zila Rinaldi.

Two different kinds of tests were performed, as described in the following: a flexural test simulating the behaviour of the segments when loaded under bending, and a test simulating the point loads effects on the segments, produced by the TBM machine during the digging phase.

The tests were performed on two elements made in concrete without traditional reinforcement, with a fiber content equal to 40 kg/m3. The adopted fiber are Dramix 4D 80/60BG with a length of 60 mm.


2 SEGMENT GEOMETRY

The tests have been carried out on precast segments characterized by a thickness of 300 mm, a length of about 2000 mm and a width of about 1400 mm (Fig. 1.1).

Figure 1.1. Segment geometry


3 MATERIAL

The segments were cast in moulds available at the laboratory of the University of Rome Tor Vergata (Fig. 3.1). The concrete was prepared in a track mixer. The adopted moulds have electrical vibrators in order to compact the concrete. Both the segments were made from the same batch, as well as beams and cubes for the material characterization.

Steel fibers Bekaert Dramix 4D 80/60BG were added to the concrete mix, with a content of 40 Kg/m3.

The casting and curing phase is shown in Figure 3.1., while the specimens for the material characterization are shown in Figure 3.2.

Figure 3.1. Segment cast and curing

Figure 3.2. Specimens for FRC material characterization

The results of the compressive tests performed, on 6 cubes having 150 mm side are reported in Table 3.1. The average compressive strength of the fiber reinforced material, measured was equal to 55.10 MPa.


Table 3.1. Results of the compressive test

ID Sample fc,cube

[MPa]

C1 52.84

C2 56.01

C3 56.25

C4 55.42

C5 56.31

C6 53.75

fcm,cube [MPa] 55.10

The tensile behaviour was characterized through bending tests on three 150x150x600 mm notched specimens (Fig. 3.3) according to the EN 14651 (Fig. 3.4). The diagrams of the nominal stress versus the crack mouth opening displacements (CMOD) are plotted in Figure 3.3. Furthermore, in Table 3.3 are summarised the values of the stress related to the proportionality limit (fL) and the residual nominal strengths related to four different crack openings - CMOD (0.5, 1.5, 2.5 and 3.5 mm), named fR1, fR2, fR3, fR4.

250

150

b=150

A

A

Section A-A

250

hsp=

125

L=500

Figure 3.3. Tensile behaviour: bending test set-up (EN 14651).


Figure 3.4. Results of the beam bending tests

Table 3.3 Results of the beam bending tests

Residual flexural tensile strength

Dosage Specimen ID First-Peak

Load fR1 fR2 fR3 fR4

[kg/m3] [kN] [MPa]

40kg/m3 B1 13.16 4.52 6.97 8.11 8.28 B2 15.61 5.37 8.26 9.40 9.23 B3 12.38 5.73 9.06 7.81 7.92 Average 13.72 5.21 8.10 8.44 8.48

0

1

2

3

4

5

6

7

8

9

10

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

No

min

al s

tre

ss

[MP

a]

CMOD [mm]

CM

OD

1

CM

OD

2

CM

OD

3

CM

OD

4

fR1

fR2fR3 fR4


4 SEGMENT TESTING PROCEDURES

One flexural and one point load test were carried out, as discussed in detail in the following

4.1. Bending test

The bending test was performed with the loading set-up illustrated in Figures 4.1 and 4.2, in displacement control, by adopting a 1000kN electromechanical jacket, with a PID control and by imposing a stroke speed of 10 µm/sec.

The segment was placed on cylindrical support with a span of 2000 mm and the load, applied at midspan, was transversally distributed be adopting a steel beam as shown in Figure 4.2 and 4.3.

Figure 4.1: Bending test set-up


Figure 4.2 Segments under bending test

Figure 4.3 Loading distribution system

During the test, the following measures were continuously registered:

the load F, measured by means of a 1000kN load cell with a precision of 0.2%;

the midspan displacement measured by means of three potentiometer wire transducers placed along the transverse line (Fig. 4.4);

the crack opening at midspan, measured by means of two LVDTs (Fig. 4.4).

Right side

Left side


Furthermore, the crack pattern was recorded at different step, with the help of a grid plotted on the intrados surface (100x100mm).

Figure 4.4. Bending test instrumentation

Wire transducer w3 (right)

Wire transducer w2 (middle)

LVDT right

LVDT left

Wire transducer w1 (left)


4.2. Point load test

The point load test was performed by applying three point loads at the segment, by adopting the same steel plates used by the TBM machine (Fig. 4.5). A uniform support is considered, as the segment is placed on a stiff beam suitably designed. Every jack, having a loading capacity of 2000 kN, is inserted in a close ring frame made with HEM 360 steel beams and 50 mm diameter Dywidag bars (Fig. 4.5).

The load was continuously measured by pressure transducers. Six potentiometer transducers (three located at the intrados and three at the extrados) measure the vertical displacements, while two LVDTs transducers are applied between the load pads, in order to measure the crack widths (Figs. 4.6 and 4.7).

Figure 4.5. Point load test


Figure 4.6. Test set up for segments subjected to compression: intrados

Figure 4.7. Test set up for segments subjected to compression: extrados

Transducer P6

Transducer P2

LVDT2 Transducer

Transducer P1

LVDT1 Transducer

Transducer P5

Transducer P3

Transducer P4


5 BENDING TEST RESULTS

The test set up for the steel fiber reinforced segment subjected to bending test is shown in Figure 5.1.

Figure 5.1. Bending test set up

It is worth remarking that the test is carried out in displacement control, with an electromechanical jack, up to the collapse. The cracking phase is highlighted during the test.

The displacements measured by the three wire transducers (Fig. 4.4) are plotted versus the load in Figure 5.2. No appreciable torsion was found, as the three wire transducers measured almost coincident displacements.

The maximum load was about 225 kN.


Figure 5.2. Bending test: load-mean displacement

The first cracks appeared for a load value of about 125 kN, at the lateral surfaces close to the midspan of the segment and propagated on the intrados. The crack pattern is shown in Figure 5.3. The maximum crack width was lower than 0.05 mm (Fig. 5.3d).

a) b)

c) d)

Figure 5.3. Bending test: Crack pattern: load level 125 kN; a) left lateral surface, b) right lateral surface, c) intrados surface, d) maximum crack width

0

50

100

150

200

250

0 5 10 15 20 25 30

Loa

d [k

N]

Displacement [mm]

w2

w3

w1


New cracks formed for a load level of 160 kN at both the lateral surfaces and at the intrados surface (Fig. 5.4), furthermore a widening and lengthening of the already formed crack takes place (Fig. 5.4 and Tab. 5.1). The crack pattern for a load level of 180 kN is shown in Figure 5.4a, b, c. The maximum crack width is about 0.35 mm (Fig. 5.4d).

a) b)

c)

Figure 5.4. Bending test. Load level 180 kN; a) left face; b) right face; c) intrados, d) maximum crack width

The crack pattern for a load level of 222 kN is highlighted in Figure 5.5. New cracks formed at the lateral and intrados surfaces, and a lengthening and/or widening of the already formed cracks took place (Figs. 5.5a, b, c).


a) b)

c)

Figure 5.5. Bending test. Load level: 222 kN; a) left face; b) right face; c) intrados.

Finally, the segment at the end of the tests is shown in Figure 5.6, and the detected crack pattern is summarised in Figure 5.7.


Figure 5.6. Bending test. End of the test.


Figure 5.7. Bending test. Crack pattern

The crack width on the intrados is evaluated on the basis of the two LVDTs measures. In Figure 5.8, the LVDTs displacements are plotted versus the load. It is worth noting that two cracks pass through the instruments lengths (Fig. 5.7), and then the measure is related to the sum of their crack widths.

Left side

Right side


Figure 5.8. Bending test. LVDTs measures

Finally, with reference to the crack numbering of Figure 5.7, the measured crack widths, for each load step, are summarised in Table 5.1.

Table 5.1. Measured crack widths

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8 9 10

Loa

d [k

N]

Displacement (By LVDT) [mm]

LVDT-Left

LVDT-Right

Load [kN] 125 160 180 210 222 225

Crack colour Pmax

Crack n.1 <0.05 0.05-0.10 0.10 0.30 0.402 <0.05 0.25 0.35 0.35-0.40 0.703 - 0.20 0.35 0.60 1.004 - 0.10-0.15 0.30-0.35 0.45 0.705 - 0.05 0.10 0.15 0.35-0.406 - 0.10-0.15 0.20-0.25 0.30 0.307 - <0.05 0.15 0.15 0.158 - - 0.15 0.30 0.409 - - 0.10-0.15 0.40 0.9010 - - - 0.20 0.3011 - - - 0.40 0.6012 - - - 0.20 0.2013 - - - 0.05 0.2014 - - - 0.15 0.1515 - - - - 0.6016 - - - - 0.0517 - - - - 0.40

BT-SFRCLoading

Crack width [mm]

n/a


6 POINT LOAD TEST RESULTS

The segment under the point load test is reported in Figure 6.1.

Figure 6.1. Set up of the point load test

The loading process is summarised in Figure 6.2 through the load – time diagram.

It is worth remarking that, in this report, the term load will refer to the single pad.

F1 F2 F3


Figure 6.2. Point load test: Load on the single pad vs Time

The displacements under the three pads, expressed as average value of the couple of the potentiometer transducers, (Figs. 4.6, 4.7) are plotted in Figure 6.3, versus the load (of each pad). The maximum measured displacement is about 0.43 mm.

Figure 6.3. Point load test: Load – displacement curves

The first cracks appeared for a load level of 1250 kN (for each steel pad) between two pads at the top and lateral surfaces (Fig. 6.4). The crack width was lower than 0.05 mm. This crack propagated in the following step (1580 kN) at the intrados surfaces, as highlighted in Figure 6.5a. The maximum crack width was about 0.1 mm.

0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

0 900 1800 2700 3600 4500 5400 6300 7200 8100 9000 9900

Loa

d [k

N]

Time [s]

1st Cycle

2nd Cycle

0

500

1000

1500

2000

2500

3000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Loa

d [k

N]

Displacement (By Potentiometer) [mm]

Green pad

Red pad

Blue pad

F1=F2=F3


According to the adopted loading history (Fig. 6.2), the complete unloading followed and the cracks appeared completely reclosed.

a)

b) c) d)

Figure 6.4. Point load tests: a) First crack formation (F1=F2= F2= 1250 kN); b) top and intrados surfaces; c) extrados faces; d) maximum crack width

a) b) Figure 6.5. Point load test: Load level 1580 kN; a) crack evolution; b) maximum crack width.


The same cracks re-opened in the second cycle for a load level of about 1000 kN (maximum crack width 0.05 mm). The maximum crack width was equal to about 0.1 mm for a load level of 1750 kN (see Table 6.1).

For a load level of 2250 kN, new cracks appeared at the intrados side and a lengthening of the already formed crack took place. The maximum crack width was equal to 0.3 mm (Fig. 6.6c).

a) b)

c) d)

Figure 6.6. Point load test: Load level 2250 kN; a) crack evolution; b) new cracks; c) extrados side; d) maximum crack width.

For a load level of about 2500 kN a bursting crack opened under the point load named F2 (see Figure 6.1), at both the intrados and extrados sides (Fig. 6.7). Further small cracks formed at the top surface for the last value of load equal to 2670 kN. (in pink in Figure 6.8a). The maximum crack width measured with a crack gauge was equal to about 0.4 mm (Fig. 6.8b). The maximum crack width at the end of the test, after the complete unloading, was about 0.05 mm.


a)

b)

Figure 6.7. Point load test: load level 2500 kN; a) intrados side; b) extrados side

a) b)

Figure 6.8. Point load test: load level 2670 kN; a) top side; b) maximum crack width


During the unloading phase, the crack width were measured for load level of 1500 kN and at the end of the test (complete unloading), and are reported in Table 6.1.

The final crack pattern is summarised in Figure 6.9 and the crack widths measured during the test are reported in Table 6.1.

Figure 6.9. Point load test; Crack pattern


Table 6.1. Crack width

Finally, the crack width, measured by the LVDT placed between the steel pads (Fig. 4.6) is plotted versus the load (of the single pad) in Figure 6.10.

Figure 6.10. Point load test; Load-displacement (by LVDTs) curves

UnloadingLoad [kN] 500 750 1000 1250 1580 0

Crack color Crack n.

1 - - - 0.05 0.05÷0.10 closed2 - - - 0.05 0.10 closed3 - - - - - -4 - - - - - -5 - - - - - -6 - - - - - -7 - - - - - -8 - - - - - -

Crack width - cycle I [mm]

PhaseCycle I

Loading

Load [kN] 500 1000 1500 1750 2000 2250 2500 2670 1580 0 0Crack color after 2 hours

Crack n.1 closed 0.05 0.05 0.10 0.10 0.15 0.20 0.25 0.25 0.05 <0.052 closed 0.05 0.10 0.10 0.10÷0.15 0.30 0.35 0.40 0.40 0.15 0.10÷0.153 - - - - - 0.10 0.10 0.10 0.10 closed closed4 - - - - - 0.05÷0.10 0.05 0.10 0.10 closed closed5 - - - - - 0.25 0.25 0.20 0.2 0.10÷0.15 0.05÷0.106 - - - - - - 0.1 0.10÷0.15 0.10÷0.15 0.05 0.057 - - - - - - 0.25 0.25 0.25 0.1 0.18 - - - - - - - <0.05 closed closed closed

Loading Unloading

Crack width - cycle II [mm]

Cycle IIPhase

0

500

1000

1500

2000

2500

3000

0 0.1 0.2 0.3 0.4 0.5

Loa

d [k

N]

Displacement (By LVDTs) [mm]

LVDT-1

LVDT-2


7 CONCLUSIONS

The technical report shows the results of bending and point load tests carried out in the Laboratory of the University of Rome Tor Vergata on precast fiber reinforced concrete segments.

The load –displacement diagrams, the load – crack opening and the evolution of the crack pattern are highlighted and pictures related to each test are summarised in this report.

Roma, 14.09.2017

Prof. Alberto Meda

Prof. Zila Rinaldi

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TECHNICAL REPORT TESTS ON PRECAST TUNNEL SEGMENT IN … · 2018-02-27 · Figure 4.2 Segments under...

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