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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

Results and Discussion

Services Conditions

3.1.1 Load-Deflection Responses

Figure 3a presents the load-deflection responses of the two beams, one in drying condition (P07-D) and one in sealed conditions (P07-S) cracked to a maximal crack opening ws of 0.1 mm and then subjected to a sustained load level corresponding to 60 % of the load Ps during 4 weeks (Table 2). The results show that the load-deflection responses are comparable in terms of the initial stiffness and the residual deflection prior to sustained loading. The loads Ps of beams P07-D and P07-S measured at ws are respectively 31.1 and 35.4 kN. Although the load Ps of beam P07-S is about 10 % greater than the load Ps of beam P07-D, the loads are also comparable as they are within the expected variability of the material.

Mechanical behavior in service conditions

Fig. 3 Mechanical behavior in service conditions

3.1.2 Deflection-Time and CMOD-Time Responses

Figure 4 presents respectively the deflection-time and the crack opening-time responses of the beams. The results show that the amplitude of the elastic deflection and the elastic crack opening of beam P07-S are slightly greater than beam P07-D. The elastic deflection and crack opening correspond to the deflection and crack opening due to the application of the sustained loading. This difference in amplitude is coherent to the fact that the load Ps of beam P07-S is greater than beam P07-D. Within the first 7 days of sustained loading, the deflection of beams P07-D and P07-S increases by approximately 4 and 7 % respectively, whereas the crack opening increases by approximately 9 and 17 % respectively. The deflection and crack opening, thus creep, of both beams stabilises toward an asymptote after 7 days of sustained loading.

Deformation in service conditions

Fig. 4 Deformation in service conditions

3.1.3 Compliance Response

Figure 3b presents the compliance evolution of the beams. As expected, the compliance of beam P07-S at the time of application of the sustained loading is greater than the corresponding compliance of beam P07-D. This is due to the fact that the pre-cracking cycle of beam P07-S led to a greater deflection, thus a greater global damage state. Figure 3b also shows that the compliance evolution of both beams tends to be constant over the first 21 days. The compliance increase of beam P07-D observed between the 21st and 28th days of the test may be explained by the lack of precision in the compliance measurement. Indeed, the evolution of the deflection and CMOD, presented in Fig. 4, may not explain such a compliance increase within that time period.

3.1.4 Significance

The results show that the evolution of the creep behaviour of both beams, sealed (P07-S) and not sealed (P07-D), is comparable. Therefore, the influence of the moisture conditions on the evolution of the creep may be considered negligible for that condition.

Besides, the crack opening of the beams quickly stabilize to an average opening of 0.065 mm under sustained load representing 60 % of the load required to create opening of 0.1 mm. According to the Canadian Highway Bridge Design Code [8], the allowable crack opening is 0.25 mm in reinforced concrete. In addition, dead loads on bridge slabs associated to the sustained load represent around 10-30 % of the total service loads. Therefore, the results indicate that the use of SFRC in a bridge deck could be adequate to satisfy the crack opening limits defined by the code under sustained loading corresponding to its dead load. However, the impact of live loads (rapid cyclic loads) should be investigated.

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