PSI - Issue 66

Bineet Kumar et al. / Procedia Structural Integrity 66 (2024) 337–343 Author name / Structural Integrity Procedia 00 (2025) 000–000

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specimen depth ratios set at 2.5 and 0.2, respectively. The current research details the results from crack mouth opening displacement (CMOD) controlled monotonic loading tests, carried out on notched concrete beams using a 500 kN servo-hydraulic testing system. UHPFRC beam specimens with consistent geometry have been subjected to three-point bending, applying a gradually increasing load, with a CMOD increment rate of 0.0005 mm/sec. Vertical displacement at the center of the beam has been recorded using a linear variable displacement transducer (LVDT), while the load–CMOD response has been monitored throughout the tests. Additionally, the digital image correlation (DIC) technique has been used throughout the testing period to observe and characterize the fracture behavior under monotonic loading.

Table 1. Geometric detailing of specimens

Fibre percentage

Notation

Span length (mm)

Thickness (mm)

Notch length (mm)

Width (mm)

No of Specimen

S

187.5

75

15 30 60 15 30 60

75 75 75 75 75 75

3 3 3 3 3 3

1.5 %

M

375 750

150 300

L S

187.5

75

2.5 %

M

375 750

150 300

L

Fig 1. Load-CMOD behaviour of all the specimen sizes for both the fibre content

The analysis of load–CMOD plots for small, medium, and large specimens, as illustrated in Fig.1, revealed differences based on fiber content. In beams with 1.5% fiber content, there is a noticeable drop in load-carrying capacity beyond the peak load, followed by a slight recovery, leading to a plateau. Conversely, beams containing 2.5% fiber content shows a more gradual decline in load capacity after the peak. The fracture behavior can be predicted through these Load–CMOD plots. Initially, the specimens demonstrated elastic deformation as CMOD increased. With further loading, micro-cracks along with matrix cracking may take place, leading to a sudden drop in load-bearing capacity. Matrix cracking refers to the fractures that form within the concrete matrix due to a lack of sufficient steel fibers, thereby reducing the overall strength, especially in the 1.5% fiber specimens. However, in specimens with 2.5% fiber content, a higher volume of fibers effectively bridged the cracks, mitigating matrix