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Home arrow Engineering arrow Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete: Proceedings of the International RILEM Workshop FRC-CREEP 2016

Selected Experimental Results

The results from the long term loading of group 3 and 4 are presented in terms of time-dependent: deflections and cracks width.

Time-Dependent Deflections

The beams from group 3 were first loaded with permanent load “g”. In order to induce cracks and activate the fibres, the beams were precracked with load “g + q” and than the load was returned to the level of permanent load which was acting in the period of 360 days. In Figs. 5 and 6, total and long term deflections are presented as an average value of two beams for each concrete type.

From the figures can be noticed that the instantaneous, total and long term deflection decreased with the addition of fibres.

Instantaneous deflection after precracking with the load “g + q”, at the level of permanent load “g”, for the concrete residual strength classes FL 1.5/1.5 and FL 2.5/2.0, decreased for 19.6 % and 32.5 %, respectively.

Total time-dependent deflection for the beams from group 3

Fig. 5 Total time-dependent deflection for the beams from group 3

Total deflection after being subjected to permanent sustained load “g” for 360 days, for the concrete residual strength classes FL 1.5/1.5 and FL 2.5/2.0 decreased for 17.8 % and 24.5 %, respectively.

Long term deflection, which is the total minus instantaneous deflection after precracking, at the level of permanent load “g”, for the concrete residual strength classes FL 1.5/1.5 and FL 2.5/2.0 decreased for 15.6 and 15.3 %, respectively. It can be noticed that both concretes with the addition of fibres decreased the deflections for about the same percentage.

The beams from group 4 were first loaded with permanent load “g” and after the measurements were performed they were loaded additionally with variable load “q”. The variable load “q” was kept for 8 h and removed in the next 16 h. This was repeated every day in the period of 360 days. Before and after each application or removal of the variable load, which means four times each day, all the necessary measurements were performed.

In Figs. 7 and 8, total and long term deflections are presented as an average value of two beams for each concrete type.

From the previous figures, it can be noticed that the instantaneous, total and long term deflection decreased with the addition of fibres.

Instantaneous deflection at the level of service load “g + q”, for the concrete residual strength classes FL 1.5/1.5 and FL 2.5/2.0 decreased for 7.6 and 22.8 %, respectively.

Total deflection after being subjected to permanent sustained and repeated variable load “g ± q” for 360 days, decreased for 14.4 and 22.5 % at the level of permanent load, respectively for residual class FL 1.5/1.5 and FL 2.5/2.0.

Long term deflection after 360 days under load, at the level of permanent load “g”, which is the total deflection minus instantaneous deflection at the level of service load “g + q”, also decreased for 19.2 and 22.2 %, respectively. It can be noticed that both concretes decreased the deflections for about the same percentage with the addition of fibres and increasing the residual strength.

The comparison between the deflections of the beams from group 3 and 4 (Table 3) with a resulting ratio, which were subjected to different load histories, is

Long term deflection for the beams from group 4

Fig. 8 Long term deflection for the beams from group 4

Table 3 Comparison between deflections of the beams from group 3 & 4 and creep ratios

no

Concrete type deflection (mm)

C30/37

C30/37 FL 1.5/1.5

C30/37 FL 2.5/2.0

1

a0 (inst.) g—group 3

0.845

0.83

0.815

2

a0 (inst.) g—group 4

0.795

0.975

0.80

3

a (long-term)g—group 3

1.695

1.43

1.435

4

a (long-term)g—group 4

2.655

2.145

2.065

5

ratio: no 4/no 3

1.57

1.50

1.44

6

Creep ratio no 3/no 1

2.00

1.72

1.76

7

Creep ratio no 4/no 2

3.34

2.20

2.58

very important in order to find out the influence of the repeated variable load on the long term deflections. In the same table, the creep ratios for the beams from group 3 and 4 are presented separately. It is obvious that the addition of fibres reduced the creep effect.

 
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