Issue 46

S.Y. Jiang et alii, Frattura ed Integrità Strutturale, 46 (2018) 275-284; DOI: 10.3221/IGF-ESIS.46.25 279 cracks. Besides, the reinforcement both enhances the sectional stiffness and restrains the cracks after the CFRP enhancement. This partially offsets the negative effect of cracking on sectional stiffness. At the moment of loading, most tensile load was borne by the reinforced part, which further limits the crack development. That is why the pre-loading has an unobvious effect on sectional stiffness of reinforced beams in the short time. Of course, the initial stiffness of the test beams might not be exactly the same due to the discrete nature of the experiment (e.g. the casting quality of the beams). Under the above factors, there is no significant difference in instantaneous deflection among the four beams. Fig. 4 shows the crack pattern of each beam at the moment of final loading. The red lines stand for pre-cracks, and black lines for the new cracked induced by the final load. It is clear that the instantaneous cracks under final load are all affected by the pre-cracks. The cracks on B-1 and B-2, which are intact beams, were all newly formed cracks, while no new crack was observed on B-3 and B-4, which are pre-cracked. The absence of new cracks on the pre-cracked beams is attributable to the near homogeneity of the pre-cracks. Furthermore, B-1 and B-2 had lower degree of instantaneous cracking and smaller crack spacing than B-3 and B-4. Under the action of pre-cracking and final loading, the four beams can be ranked as B-4> B-3> B-2 (B-1) according to the degree of cracking at final loading. Long-term deflection and cracks Temperature and humidity variation The long-term test was conducted in lab at the mean temperature of 21.5°C and the mean humidity of 73%. During the test, the temperature and humidity varied over time. Figure 5 : Test temperature and Relative humidity during the sustain-loading time Long-term deflection All the beams were subjected to a sustained and constant load for 300 days. During the period, the midspan deflection and crack development of each beam were recorded regularly (Figs. 6~8; Tab. 3). B-1 B-2 B-3 B-4 Immediate deflection(mm) 3.570 2.857 3.443 3.205 Total deflection(mm) 5.636 4.771 5.140 4.578 Additional deflection(mm) 2.066 1.914 1.697 1.373 Additional/Immediate (mm) 0.579 0.670 0.493 0.428 Table 3 : Deflection under sustain-loading time. Tab. 3 lists the instantaneous midspan deflection of each beam (excluding the residual deflection after pre-loading and unloading), the total deflection and the additional deflection in the test period. As shown in the table, all reinforced beams underwent varied degrees of increase in deflection under sustained loading. After 300 days, the additional deflection of most beams reached almost half of the instantaneous deflection. That of B-2 even reached 67% of the instantaneous deflection. The additional deflection of B-2, B-3 and B-4 was respectively 7.3%, 17.9% and 33.5% lower than that of B-1. In the other