Issue 63

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

Deflection The applied loading is incremented gradually and the deflections are recorded then the corresponding load-deflection curves are plotted. Load versus mid-span defection curves for un-strengthened and strengthened beams with rectangular and circular openings drilled under different service loads levels as percentages of ultimate failure load Pu of reference model without opening (R) are presented in the following figures.

The appropriate load deflection relation for the control un-strengthened rectangular (UR00) and circular (UC00) openings models in addition to the reference beam without any openings (R) are shown in Fig. 10. Drilling a rectangular opening of equivalent area as a circular one under no service loads within the shear zone seriously reduced the maximum mid-span deflection of the beam at failure to be only of 26% for (UR00) and 41% for (UC00) of that for the beam (R). In other words, this action reduced the maximum recorded mid-span deflection by about 74% and 59% for (UR00) and (UC00) respectively as can be deduced from Fig. 10. These results enhanced the undesired structural brittle behavior or the abrupt collapsing at failure although the opening drilling is assumed to be achieved under no service loads. Therefore, it is of serious importance to take care of the service loads application levels when it is required to drill the openings within the RC beams shear zones which has forced the authors to prepare the current research program to meet the practical conditions as possible as could. Strengthening the openings in the models (SR00 and SC00) seriously increases the mid span deflection at failure to be up to 2.4 and 1.7 times that recorded for the un-strengthened opening models (UR00) and (UR00) respectively as can be deduced from Fig. 11. However, openings CFRP strengthening enhances the models desired structural ductile behavior. Figure 10: Influence of the openings drilling under no service loads on the beams models deflection compared to the (R) beam model.

Figure 11: Influence of the openings drilling and strengthening under no service loads on the main control beams models mid-span deflection.

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