Issue 59

ZB. Xia et alii, Frattura ed Integrità Strutturale, 59 (2022) 49-61; DOI: 10.3221/IGF-ESIS.59.04

and the main cracks that penetrated the surface of the specimen began to appear. When the load rose to the limit, the specimen suddenly cracked, the load dropped sharply, the slip values of the free end and the loading end no longer increased, the steel bar completely separated from the main body of the concrete specimen, the specimen split into two or three pieces, and it was seen from the split surface that the concrete was sheared by the steel bar rib. Splitting pull-out failure mainly occurred in the pull-out specimen with a low content of steel fibers. The failure behavior is shown in Fig. 3(b). There was no obvious slip at the free end of the specimen at the beginning of loading. With the further increase of the load, when the bonding stress reached the split bond strength of the specimen, the internal cracks of the specimen developed slowly because of the cracking resistance effect of steel fibers. When the cracks further increased, the relative slip between the steel bar and the concrete gradually expanded to the free end, and the concrete on the surface of the steel bar was sheared by the ribs. After the failure, there were obvious transverse cracks on the surface of the test specimen, and the steel bar and the concrete were partially separated, but the test specimen was not completely split; there was a friction resistance and mechanical interaction between the steel bar and the concrete.

The slip value S ui of the free end/mm

The slip value S uz of the loading end/mm

Ultimate load P u /kN)

Ultimate strength  u /MPa

Average slip value S u /mm

No. of test specimen

Failure behavior

N-0-0 DC-30 DC-50 DC-70 DC-100 SFC-0.4 SFC-0.8 SFC-1.2 SFC-.16

112.85 109.05 108.97 96.08 86.87 117.18 117.90 121.28 117.32 109.43 111.05 113.17 116.45 108.95 109.33 112.28 113.13

22.19 21.41 21.40 18.87 17.08 23.01 23.15 23.84 23.05 21.50 21.81 22.23 22.87 21.40 21.49 22.05 22.23 19.31

1.95 1.38 1.39 1.50 1.25 1.26 1.45 1.54 1.91 1.58 1.26 0.94 1.16 1.42 1.08 1.21 1.28 1.48

3.39 2.36 2.11 1.92 2.23 3.40 2.69 2.92 2.99 2.18 2.70 3.12 3.50 1.50 2.68 2.33 2.90 1.66

2.67 1.87 1.75 1.71 3.48 2.33 2.07 2.43 2.45 1.88 3.96 2.03 2.33 1.46 1.88 1.77 2.09 1.57

Splitting failure Splitting failure Splitting failure Splitting failure Splitting failure Splitting pull-out failure Splitting pull-out failure Pull-out failure Pull-out failure Splitting pull-out failure Splitting pull-out failure Pull-out failure Pull-out failure Splitting pull-out failure Splitting pull-out failure Pull-out failure Pull-out failure Splitting pull-out failure Splitting pull-out failure Splitting pull-out failure Pull-out failure Splitting pull-out failure Splitting pull-out failure Splitting pull-out failure Pull-out failure

SFDC-30-0.4

SFDC-30-0.8 SFDC-30-1.2 SFDC-30-1.6 SFDC-50-0.4 SFDC-50-0.8 SFDC-50-1.2 SFDC-50-1.6 SFDC-70-0.4

98.36

SFDC-70-0.8

102.75

20.20

1.63

1.75

1.69

SFDC-70-1.2 SFDC-70-1.6 SFDC-100-0.4

101.18 101.43

19.88 19.92 19.13

1.62 2.04 1.50

1.84 2.86 2.10

1.73 2.45 1.80

97.30

SFDC-100-0.8

102.41

20.11

0.78

3.02

1.90

SFDC-100-1.2 SFDC-100-1.6

106.33 101.22

20.89 19.88

1.55 0.73

2.49 4.95

2.02 2.84

Table 5: The results of the pull-out test

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