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

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5

The beam TRM1 experienced a support failure because of the offset placement of the flexural and shear reinforcement during casting. The support sheared off at a load of 245 kN. The beam TRM 1 was set for testing again by placing it a bit further from the intended support location. For the same reason, beam TRM1 showed no improvement in load-carrying capacity. Beams TRM2 and TRM2.5, however, showed a considerable increase in failure loads, i.e., 11 and 9%, respectively, showing almost consistent results for basalt fibre TRM for strengthening in the shear acute region.

Table 3: Failure loads of beams with corresponding modes of failure Shear Span to-depth ratio Control Beam Failure Load

Strengthened Beam

% Increase

Theoretical Failure Load

Failure Mode

Failure Load

Mode of Failure Flexure Flexure Flexure

1 2

365 183 146

445 258 215

Flexure Flexure Flexure

420 287 234

0

11

2.5

9

3.2 Crack Patterns Table 4 presents the noted experimental values of load against the first crack for flexure and shear for corresponding control and strengthened flexural specimens and the rise in the percentage of the corresponding load after the application of TRM. The first flexural cracks for every control beam appeared immediately under the load, the point of maximum moment. During the continual increase in load application, more cracks became visible in the region of the higher flexural stress zone, near the primary crack in the flexure, exhibiting textbook flexural failure. For TRM-strengthened beams, primary cracks in flexure popped up at the point of maximum moment, subsequently showing nearly spaced, well-spread hairline cracking. The TRM-strengthened beams showed textbook flexural failure with the improved crack distribution.

Table 4: Loads at the initiation of flexural and shear cracks in the beams Shear span-to depth ratio Flexural Cracks Control Specimen TRM Specimen % Increase

Shear Cracks

Control Specimen

TRM Specimen

% Increase

1 2

72 kN 61 kN 48 kN

86 kN 74 kN 61 kN

19.4 21.3 27.1

222kN 126 kN 103 kN

245 kN 149 kN 124 kN

10.4 18.3 20.4

2.5

The TRM applied for flexure strengthening purposes significantly increased the cracking load. The influence of strength enhancement on the initial flexural cracking load of beams for shear span-to-depth ratios in the 1 to 2.5 ranges yielded around 20 – 30% improvement, depicting the usefulness of TRM in the control of flexural cracks within shear-critical regions. For shear cracks, an increase of 10 – 20% was observed in TRM strengthened beams for a/d ratios 1 to 2.5, which is pretty much consistent when studied in terms of load increased for a single layer, i.e., 21 – 23 kN. It may be deduced that the use of TRM also played an active role in the delay of shear cracking. Figure 5 shows the spacing and patterns of cracks for all control and strengthened specimens at failure, which are discussed in the sections to follow. It might appear from Figure 6 that the failure modes are not flexure, but the beams failed in flexure as the shear-flexure cracks were hairline cracks and the major crack was flexural crack, directly under the applied load. Presence of stirrups and U-shape TRM wraps also helped in avoiding the shear failures. For beam CT1, the flexural crack at the location of the maximum moment appeared, which was followed by the generation of very fine flexural cracks widely spread out. With the increment in load, a very fine shear crack was observed, which was halted by the shear reinforcement in the shear span, and the beam continued sustaining the load until flexure as a mode of failure was attained. The cracks in flexure propagated in width with the increment of load. The specimen achieved load at failure in flexure with the eventual crushing of concrete in the vicinity of the applied load. The major flexural crack was around 2.5 mm near failure, while the other major cracks in the flexural region were mostly around 2mm wide. For beam TRM1, there is a pre-existing flexural crack along with closely spaced and well-distributed hairline cracks due to the slicing of support, as discussed earlier. The beam was again repositioned