An experimental investigation conducted with studying the behavior high strength self-compacting reinforced concrete corbels strengthened with NSM steel bars. The experimental work involved testing ten corbel specimens. They are categorized into two groups with two values of shear span/depth ratio (a/d). Each group consists of five specimens, one considered as a control; others were strengthened with four different configurations of NSM steel bars. The load-deflection curves were traced, cracking and ultimate loads were recorded, crack width was measured and crack propagation up to failure was trucked. This research found that strengthening RC corbel with NSM steel bar system improved the failure load significantly by 57% and 41% for a/d of 0.85 and 1.25 respectively. The strengthening system named as "Upside down V-shaped" is more efficient for small values of a/d (a/d <1). The horizontal bars configuration is more convenient for large a/d values (a/d >1); with a/d greater than one, the general mode of failure is of Bond type. Also, it is found that the strengthening of specimens results in some elimination in ductility with a value depending on the strengthening configuration.

An experimental study has been conducted to scrutinize the response of reinforced self-compacting concrete half joints upgraded with CFRP strips. Fourteen RC half joints have been tested. Two values of shear slenderness ratio were considered, namely 1.5 and 1.0. Two beams have been treated as reference specimens (with the design steel), and the twelve other beams were casted with deficiency in steel of the hanger and the extended end regions relative to the control beams. Eight of these beams have been strengthened with different arrangements to discuss the influence of shear slenderness ratio and strengthening arrangement on the overall performance of such joint elements. It is found that the reduction in nib-main steel by about 50% results in decreasing load capacity by about 36% and 15% for shear slenderness ratio of 1.5 and 1.0 respectively. Also, it is found that the orthogonal arrangement combined with inclined strips yielded the best results in terms of preventing the diagonal shear failure at the re-entrant corner with maximum enhancement in load capacity by 18%. In addition, the maximum improvement in failure load when strengthening hanger region by such alignment was about 23%. Results also revealed that the effective stiffness and ductility ratio enhanced with reducing shear span of a half joint and may be adopted as a good indicator to evaluate the suitable strengthening scheme. Moreover, it is concluded that the relative displacement method for predicting the ductility ratio is more applicable than that based on the dissipated energy.

This paper represents a historical review, on the experimental studies carried out to investigate the behavior of non-prestressed dapped end beams. The specimens discussed are made of normal, high-strength and self-compacting concrete and subjected to several systems of loading setup. Different values of the (shear span-to-effective depth) ratio that were adopted by researchers are discussed. Some specimens are full scale other are prototypes. Different methods and suggestions by previous studies to strengthen the dapped end. Different failure modes that have been recognized based on detailing, dimension and material properties of the dapped end beams. Several parameters that may affect the behavior of dapped end beams are reported. Many shown also, the conclusions that have been drawn from various studies. In addition, some suggestion for future work are proposed and to extend studies about the behavior of the dapped end beams. Finally, a comprehensive list of references is provided.

This paper presented a new modified arrangement (inclined) for corbel shear reinforcement. Moreover, the performance of composite corbels including WF- and Tapered WT- section with the usual and proposed alignment is investigated. Shear span/depth ratio (av/d of 0.70 and 1.0 are considered. Results revealed that the proposed configuration improves ductility and toughness by 16% and 38% respectively for av/d of 0.70, and 55% and 64% respectively for av/d of 1.0. Furthermore, It is found that using the composite corbels with the proposed alignment improved ductility and toughness by (35-80) % and (45-173) % respectively for av/d=0.70. The respective values for corbels with av/d=1.0, are (38-101) % and (67-88) %. Moreover, relative enhancements in cracking and failure loads, ductility, and toughness for the composite WF-steel corbel with diagonal stirrups of 82%, 98%, 105%, and 273% respectively for av/d=0.7. The respective values are 111%, 115%, 138% and 188% respectively for av/d=1.0.

This paper represents a historical review of the theoretical and experimental studies carried out previously to study the behavior of reinforced concrete dapped end beams. Prestressing is one of the techniques that have been adopted to enhance the performance of such members. Furthermore, a dapped end needs to be strengthened due to various reasons to improve its performance. Consequently, the review has been extended to include studied such aspects. It was concluded that the ultimate capacity enhanced by reducing the shear-slenderness ratio and horizontal tension reaction and increasing the strength of concrete and fiber content. In addition, nib main reinforcement affects significantly the mode of failure, cracking and ultimate load. However, it was observed that the inclined hanger stirrups or bent performed better than that of vertical alignment and that the prestressing level and strand profile affect the shear capacity and performance significantly. On the other hand, it was found that the external bonding CFRP is the most adopted strengthening material and that the STM (Strut-and-Tie Model) approach results in better predictions of the ultimate load than the shear-friction method. Moreover, directions for future work are proposed, several conclusions have been drawn and a comprehensive list of references is provided.