PSI - Issue 64

Asad-ur-Rehman Khan et al. / Procedia Structural Integrity 64 (2024) 1065–1072 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1070

6

and placed for testing, with more hairline cracks appearing. The shear crack appeared, and the beam continued to take the load until the concrete at the compression face reaches crushing. The crack width at failure was found to be 2.0 mm. A possible reason for a wider crack in a strengthened beam is the presence of cracks before the beam was put to testing again. However, it can be observed that in the case of strengthened beam, the cracks are closely spaced and evenly distributed and do not extend towards the far end as much as they did in the case of the control beam CT1.

Figure 5: Spacing and patterns of crack for control and corresponding strengthened specimen at failure

Beam CT2 followed the same sequence as beam CT1 with the appearance of hairline flexural cracks, followed by a crack in the shear region, which was then halted by the shear reinforcement present in the region, and the beam continued to take the load as the flexural cracks widened and resulted in flexural failure with very minor crushing in the compression zone. At the time of failure, width of the flexural crack causing the failure, was found to be 2.5 mm. Another crack right next to the flexural crack of almost the same thickness may be observed in the case of the control beam. For beam TRM2, a delay in initial cracking in terms of loads was observed. The cracks in this case were closely spaced. The shear crack appeared as the loading continued, and the beam continued to take loads until it resulted in flexural failure. The primary crack in flexure was noted to be around 2.5 mm wide, while the other cracks were narrower and more closely spaced, showing the effect of TRM in this regard. Beam CT2.5 shows a hairline shear crack, after which the beam continued to take loads until it reached flexural failure. A wider shear-flexure crack exists beside the primary crack in flexure, which had a crack width of 4 mm. The cracks near the major cracks were widely spaced and wider in spacing. The cracking extended towards the far end, with crack width and thickness decreasing as it moved towards the far end. For beam TRM2.5, the shear-flexure crack appears to be a hairline. The beam failed in flexure, and the flexural crack at failure was 1.5 mm wide. Cracks, especially on the far side of the beam, were observed to be hairline and closely spaced, which was again a reflection of efficacy of TRM in terms of controlling crack propagation. 3.3 Load-Deflection Curves Figure 6 presents the load-deflection curves for a/d ratios 1 to 2.5 for control and strengthened beams. The beam TRM1 had inherent hairline cracks due to the slicing of support during a prior attempt at testing. The beams CT1 and TRM1 showed similar behaviour in terms of stiffness. The yielding of the control beam took place at a load of 441.86 kN with a deflection value of 14.95 mm. The corresponding TRM1 specimen yielded a corresponding deflection of 14.28 mm at a load of 410.26 kN. The ultimate loads of control and TRM strengthened beams at failure were found to be 445.13 kN and 420 kN at deflections of 15.24 mm and 16.2 mm, respectively. The pre-existing cracks led to not only a decrease in load-carrying capacity but also reduced stiffness of TRM1. The TRM2 beam reflected increased post-cracking stiffness in comparison with the control beam. The yield load of the control beam was 248 kN with a deflection of 18.06 mm, whereas the yield load of the TRM2 beam was 267