Issue 46

S.Y. Jiang et alii, Frattura ed Integrità Strutturale, 46 (2018) 275-284; DOI: 10.3221/IGF-ESIS.46.25 278 2 is similar to that of B-1. After the pre-loading and unloading, the four test beams can be ranked as B-4> B-3> B-2 (B-1) by the cracking degree. Then, all the beams were reinforced as per the said plan. Figure 3 : Cracks induced by pre-loading. B-2 B-3 B-4 Pre-load(kN) 23.54 70.63 102.02 Deflection(mm) 0.490 2.365 6.394 Residue Deflection(mm) 0.003 0.171 2.051 Table 1 : Midspan deflections of pre-loaded beams. Short-term deflection and cracks Tab. 2 records the midspan deflections of all beams under 75% Fu (117.68kN). The crack development under this load is presented in Fig. 4. B-1 B-2 B-3 B-4 Deflection(mm) 3.570 2.857 3.443 3.205 Table 2 : Deflection of static loading. Figure 4 : Cracks at the moment of final-loading. As shown in Tab. 2, all four beams share similar instantaneous midspan deflections. The similarity can be explained as follows. The sectional stiffness of the test beams underwent similar amount of decrease despite the different degrees of