Issue 63

M. Khalaf et alii, Frattura ed Integrità Strutturale, 63 (2023) 206-233; DOI: 10.3221/IGF-ESIS.63.17

loading increased, the diagonal tension (shear) cracks initiated and propagated around the rectangular opening corners of the model SR26 and within the vicinity to the periphery of the circular opening of the model SC26 after which the flexural cracks within the span middle third of the beams SR26 and SC26 are intended to become wider and wider. Consequently, they are seemed to be fail in flexure at which CFRP sheets resisted the diagonal tension and the shear stresses generated within the openings regions of the strengthened models. The flexure cracks propagated towards up the extreme compression fibers of the beam resulting in reducing of the compression zone area depth which is followed by the crushing of the extreme top surface of the beam which occurs at the maximum failure load of 87% and 88%Pu for the beam models SR26 and SC26 respectively simultaneous with yielding of the reinforcement at the span middle third for both. The crack patterns in the case of circular opening is the same as the rectangular, but the cracks around the circular opening are distributed around the periphery of the circular opening unlike the rectangular where the cracks are concentrated at the opening corners.

(a) Patterns of initial cracking and cracking at failure S26 models.

(b) Patterns of initial cracking and cracking at failure for S40 models.

The cracking patterns and propagation features of the strengthened models with rectangular and circular opening (SR40 and SC40) are similar to the cracks propagation of the models SR26 and SC26 as can be noticed from Fig. 21-b except that they occurred at relatively little lower applied loading levels of 85% and 87%Pu respectively. Also, the cracks (c) Patterns of initial cracking and cracking at failure for S55 models. Figure 21: Cracking status for the strengthened rectangular and circular openings drilled under service loads levels up to 55%Pu.

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