No abstract

This study aims to investigate experimentally the behavior of self-compacting reinforced concrete beams with in-plane loaded openings strengthened with different techniques in the opening zone. The experimental program consists of testing five specimens with a rectangular opening at the midspan, one of the beams serves as a control beam (without strengthening), and four beams are strengthened at the opening zone with several methods including steel fibers, semi-rhombus crossed bars, jacketing with steel plates, and utilizing the composite section technique. The response has been discussed in terms of the first cracking load, ultimate load, maximum deflection, failure modes, loading history, crack patterns, toughness value, ductility index, and crack width to recognize the best strengthening proposal opening. Test results indicate that the technique of strengthening the WT-rolled steel recorded an increase in the ultimate load capacity, toughness, and ductility of about 21%, 91%, 44 %, respectively, relative to the control beam. However, the beam strengthened by steel fiber reinforced concrete around the opening yielded an increase in the cracking and the load-carrying capacity of about 33.3%, 10.95%, respectively. Concerning the specimen strengthened by the crossed steel bar making a semi-rhombus shape around the opening yields a slight enhancement in the loading capacity of about 8.5%. Furthermore, strengthening the opening with steel plates increases the beam’s load-carrying capacity by about 11.23% compared to the control beam.

In precast building construction, some beams are designed to support one or several concentrated loads resulting from the reactions of the attached cross beams. Consequently, the pocket beams without or with dapped ends may represent one of the innovative solutions to constitute the joints between the two attached members. In the present research work, the behaviour of dapped end beams that included rectangular opening loaded with in-plane force, have been investigated. Several detailing have been proposed, in addition the vertical stirrups, to improve the strength of the opening region including the use of steel fibre concrete (SFC),Configuration of the inclined crossed bars, jacketing with steel plates and the composite section technique with two arrangements of the reinforcement of the dapped end . Ten specimens have been tested under gradually increased vertical static loading. The tested specimens are categorized into two sets based on the configuration of dapped end reinforcement. Two variable have been considered which are the strengthening configuration of the opening region and the configuration of the dapped end reinforcement. The response has been discussed in terms several indicators including, the cracking and failure loads, maximum deflection, mode of failure, load-deflection curves, crack patterns, crack width, to recognize the optimum strengthening proposal of the opening. Results revealed that using the inclined steel bars (modified arrangement) yield better response than the conventional (standard) reinforcement (vertical stirrups) within the dapped end. For beams with pockets strengthened with crossed inclined bars, failure load enhanced in range of (8.5-11%) whereas the enhancement was in ranged in (8-10%) for the steel SFC method. Moreover, an improvement by about (11-13%) in load capacity increased when the jacketing with steel plates was applied. The maximum improvement was obtained when using the embedded rolled section within the opening with values of (21-23%).