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

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1 Università degli Studi di Roma Tor Vergata CIVIL ENGINEERING AND COMPUTER SCIENCE DEPARTMENT 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

2 INDEX 1 INTRODUCTION SEGMENT GEOMETRY MATERIAL SEGMENT TESTING PROCEDURES Bending test Point load test BENDING TEST RESULTS POINT LOAD TEST RESULTS CONCLUSIONS University of Rome Tor Vergata 2

3 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/m 3. The adopted fiber are Dramix 4D 80/60BG with a length of 60 mm. University of Rome Tor Vergata 3

4 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 University of Rome Tor Vergata 4

5 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 MPa. University of Rome Tor Vergata 5

6 Table 3.1. Results of the compressive test ID Sample fc,cube [MPa] C C C C C C f cm,cube [MPa] The tensile behaviour was characterized through bending tests on three 150x150x600 mm notched specimens (Fig. 3.3) according to the EN (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. A Section A-A 150 hsp=125 A b= L= Figure 3.3. Tensile behaviour: bending test set-up (EN 14651). University of Rome Tor Vergata 6

7 Nominal stress [MPa] f R1 f R2 f R3 f R4 CMOD 1 CMOD 2 CMOD 3 CMOD CMOD [mm] 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/m 3 ] [kn] [MPa] B kg/m 3 B B Average University of Rome Tor Vergata 7

8 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 University of Rome Tor Vergata 8

9 Left side Right side 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). University of Rome Tor Vergata 9

10 Furthermore, the crack pattern was recorded at different step, with the help of a grid plotted on the intrados surface (100x100mm). LVDT left LVDT right Wire transducer w1 (left) Wire transducer w3 (right) Wire transducer w2 (middle) Figure 4.4. Bending test instrumentation University of Rome Tor Vergata 10

11 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 University of Rome Tor Vergata 11

12 LVDT1 Transducer LVDT2 Transducer Transducer P5 Transducer P1 Transducer P3 Figure 4.6. Test set up for segments subjected to compression: intrados Transducer P6 Transducer P2 Transducer P4 Figure 4.7. Test set up for segments subjected to compression: extrados University of Rome Tor Vergata 12

13 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. University of Rome Tor Vergata 13

14 w2 Load [kn] w1 w Displacement [mm] 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 University of Rome Tor Vergata 14

15 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) Figure 5.4. Bending test. Load level 180 kn; a) left face; b) right face; c) intrados, d) maximum crack width c) 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). University of Rome Tor Vergata 15

16 a) b) Figure 5.5. Bending test. Load level: 222 kn; a) left face; b) right face; c) intrados. c) 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. University of Rome Tor Vergata 16

17 Figure 5.6. Bending test. End of the test. University of Rome Tor Vergata 17

18 Right side Left side 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. University of Rome Tor Vergata 18

19 LVDT-Left LVDT-Right Load [kn] Displacement (By LVDT) [mm] 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 BT-SFRC Loading Load [kn] Crack colour P max Crack n. Crack width [mm] 1 < < < n/a University of Rome Tor Vergata 19

20 6 POINT LOAD TEST RESULTS The segment under the point load test is reported in Figure 6.1. F 1 F 2 F 3 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. University of Rome Tor Vergata 20

21 Load [kn] st Cycle F 1 =F 2 =F 3 2 nd Cycle Time [s] 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 Load [kn] Green pad Red pad Blue pad Displacement (By Potentiometer) [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. University of Rome Tor Vergata 21

22 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. University of Rome Tor Vergata 22

23 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. University of Rome Tor Vergata 23

24 a) Figure 6.7. Point load test: load level 2500 kn; a) intrados side; b) extrados side b) a) b) Figure 6.8. Point load test: load level 2670 kn; a) top side; b) maximum crack width University of Rome Tor Vergata 24

25 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 University of Rome Tor Vergata 25

26 Table 6.1. Crack width Phase Cycle I Loading Unloading Load [kn] Crack color Crack n. Crack width - cycle I [mm] closed closed Phase Cycle II Loading Unloading Load [kn] Crack color after 2 hours Crack n. Crack width - cycle II [mm] 1 closed < closed closed closed closed closed <0.05 closed closed closed 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 LVDT-1 LVDT-2 Load [kn] Displacement (By LVDTs) [mm] Figure Point load test; Load-displacement (by LVDTs) curves University of Rome Tor Vergata 26

27 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, Prof. Alberto Meda Prof. Zila Rinaldi University of Rome Tor Vergata 27