This paper presented an extensive study about the strengthening of RC square short columns with high strength concrete jackets reinforced with steel fiber. The aim of this study is to investigate the effect of confinement by fibrous jacket on the behavior of RC column. A comparative study is performed on 23 square columns (six of them were unconfined columns where the remaining seventeen were confined columns) with varied parameters such as steel fibers ratio and type, jacket thickness, partial and full strengthening, type of confining jacket (hoop and composite), use of epoxy as bond material between the concrete column and strengthening jacket, and length parameter. The test results showed that the strengthened columns showed a significant improvement in the ultimate stress, load-carrying capacity, maximum strain, ductility, and energy absorption. Increase the steel fibers ratio (1, 1.5 and 2%) increased the ultimate stress by (22.5, 12.3 and 12.5%) respectively. The use of epoxy as bond material enhanced the ultimate stress by an average improvement by (55%). Composite case in the strengthening enhanced the load-carrying capacity larger than hoop case by (28.7 and 42%) for FRC jackets with hooked and straight fibers respectively but in case of stress capacity, hoop jacket carries stresses more than composite according to the stressed cross-sectional area. Increase jacket thickness (25 and 35 mm) enhanced the ultimate stress by (28.7 and 15.5%) respectively. Partial strengthening has a good enhancement in the ultimate load but was less than full strengthening. Increase the length by (25 cm) decreased the enhancement in load capacity of the column with hoop jacket by (45.3%). Concrete jackets enhanced Energy absorption and ductility which improved the deformation capacity. The compressive behavior of stub concrete columns was also modeled, simulated, and analyzed numerically by a 3D nonlinear finite element model. The verification process was performed against the reported data of the experimental test which proved the results of experimental results and showed a good agreement between experimental and numerical outcomes.
This research presented a wide study about the structural behavior and strength of RC circular short columns when strengthened with concrete jackets strengthened with steel fiber. A total of 17 circular columns were designed, fabricated, and tested experimentally under monotonic load. An experimental investigation was carried out to assess the efficiency of the fibrous jacket in the retrofitting of RC column. The parametric study was conducted which included using four columns as control specimens with different cross-section dimensions. The remaining 13 column specimens included strengthening the column by different parameters such as steel fibers ratio and type, jacket thickness, bond by epoxy, and full and limited jacket height. The ultimate stress and strain, crack pattern, failure modes, ductility, and toughness capacity of the specimens were studied. The experimental outcomes exhibited that the fibrous jacket enhanced the ultimate strength capacity, ductility, and changed the failure mode of columns. The increase in the steel fibers ratio (1%, 1.5%, and 2%) enhanced the ultimate load capacity by (194%, 71%, and 126%) respectively. Strengthened columns by FRC jacket with thicknesses (25, 35, and 45) showed enhancement in the stress carrying capacity by (126%, 242%, and 171%) respectively. Using epoxy appeared a different behavior in comparison with square columns. The use of epoxy showed lower stress capacity by (21% and 24%) for (1% and 2%) hooked steel fibers ratio respectively. Use of hoop jacket case enhanced the ultimate stress capacity better than composite case. straight fibers were better than hooked ones in the improvement of ductility and energy absorption.
This study introduces an experimental program to investigate the performance of concrete wrapping jackets reinforced by steel fibers used for retrofitting of the square and circular RC columns under axial loads. Ten columns divided into two groups; the first group included seven square columns while the second group involved three circular columns. The experimental study included testing the columns with varied parameters such as cross-section shape, type and aspect ratio of steel fibres, jacket thickness, and using several techniques for retrofitting the column such as strengthening by plain and reinforced concrete jackets. The selected parameters affected the compressive behavior of confined columns high strength concrete jackets. The obtained results revealed that all strengthened columns with square cross-section appeared maximum strength greater than a circular one. Using several types of concrete jacketing promotes the load-capacity of the column with a clear improvement in the ductility. Increasing thickness appeared increasing in the load-carrying capacity in comparison with the reference column. Using the straight fibres showed better enhancement in the load capacity than the hooked ones. The main result was the failure mode was different from unstrengthen columns which showed more crushing in the concrete core with an increase in thickness.
In this paper, a new masonry construction is proposed based on honey beehive cell internal geometry as a unique structure and hydrostatic pressure principle. The considered experimental program involved suggestion, manufacturing, testing and analysis of masonry specimens of honey beehive units’ arrangement as well as corresponding specimens of custom arrangement, two classes of cementations bonding mortars are used. Plan strain concept and Saint Venant’s principle are adopted to model and assign proper boundary conditions of testing specimens. The significant improvement of masonry construction bearing capacity is confirmed by the obtained results and could be related to the presence of internal or self-confining pressure, which is produced due to the specific internal geometry of proposed honey beehive units’ arrangement of hexagonal construction units. The obtained results show that, the masonry specimens of proposed honey beehive arrangement Mode II exhibited higher bearing capacity in term of ultimate and service loads besides stiffness improvement in comparison with the customary arrangement Mode I.
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