السلوك الانشائي للأعتاب الصندوقيه الخرسانيه ذاتية الرص الحاوية على فتحات موقعية

Structural Behaviour of Self-Compacted Concrete Box Girders with In-Place Openings

    This research aims to investigate the structural behaviour of a reinforced self-compacted concrete hollow beam with in-place openings that are non-strengthened or externally strengthened by CFRP strips. The aim is achieved by implementing experimental and numerical work by ABAQUS 2019.

    The experimental program comprised casting fourteen reinforced self-compacting concrete hollow beams, which are tested under two concentrated and symmetrical loading. The beams have identical properties (i.e. dimensions, flexural reinforcement, concrete compressive strength, and opening size). The specimens are categorized into three groups, in addition, to two additional beams without openings as control beams. The first group includes six beams with an opening in the front or the front and rear of the web, while the second group contains three beams with openings in the bottom flange of the beam. Besides, the third group comprises three beams with an opening in the front and rear of the web and strengthened with CFRP laminates. The studied parameters were the number and locations of openings.

   The experimental results for the first group of specimens revealed that creating openings in the flexure or shear zone or both can cause reductions in the ultimate failure loads by about (5% to 16 %). Furthermore, increase in the deflections of the specimens were observed by about (20% to 70%) owing to the reductions in their stiffness from (16% to 41%) when compared with the hollow control beam. The second group specimens, on the other hand, suffered from reductions’ ratios in the ultimate failure loads within the ranged (5% to 9 %). Furthermore, all beams in the second group suffered from higher deflections ranged from (28% to 63 %) owing to the reductions in the stiffness of these beams from (22% to 39%) if compared to control beam. In contrast, the reductions’ ratios in the ultimate failure loads for the third group of beams were nearly (2% to 8 %), while the increases in the deflections ratios were (22% to 43 %) due to the reductions in the beams’ stiffness from (18% to 23%) if compared with the control beam.

    Moreover, the strengthening by CFRP laminates enhanced the post-cracking behavior of specimens and delayed the appearing of the cracks compared with the unstrengthened beams in the first group. Regarding the first group of beams, the values of the ductility indices ranged from (1.5 to 2.8) if compared with the control beam, while the values for the second group were ranged from (2.2 to 2.5) if compared with the control beam. On the other hand, higher values for the ductility indices were recorded for the third group of beams (2.4 to 3.2) compared with the unstrengthened beams in the first group.

   Non-linear finite element analysis was performed using ABAQUS (2019) to conduct a numerical investigation for the reinforced self-compacting concrete hollow beams with or without openings and strengthened or unstrengthened by CFRP laminates. New parametric study of various variables was also numerically examined. Full bond was assumed between the concrete and steel reinforcement and between the concrete surface and CFRP. There was a good convergence between the experimental and numerical results in terms of the ultimate load, maximum deflection, load-deflection curves, and mode of failure. The average difference in the ultimate load and the maximum deflection found to be equalled to 1.8 and 9.2 %, respectively that ensure the veracity of numerical results.

    Furthermore, numerical results obtained from the analyzed beams revealed that the ultimate failure loads for hollow beams with openings decreased with the increase in the opening’s diameter from nearly 4 to 18.2 % for opening located at the middle web and from about 2 to 27 % for openings located near the supports in comparison with the control beam. The increase in the number of opening with the same diameter caused a decrease in the ultimate failure loads by 10 to 36 % if compared with the control beam. Furthermore, the ultimate hollow beam load with an opening (s) of identical diameter near the supports increased with the increase in the compressive strength of concrete. The bottom flange-strengthening scheme by CFRP was the best in terms of the ultimate strength viewpoint for hollow beams with a near supports’ openings or mid-span’s openings, in which the increases were 29 and 37 % for both beams respectively if compared with the unstrengthened beams.