Strengthening the Self Compacting Reinforced Concrete Dapped Ends with Near Surface Mounted (NSM) Steel Bar Technique

Qasim M. Shakir, Ruqyia Alliwe


An experimental study has been conducted to explore the response of reinforced self-compacting concrete dapped ends retrofitted with NSM steel bars. Eleven specimens are tested with two shear slenderness ratio values (a/d), namely (1.0 and 1.5). Deficiencies in reinforcement in the nib and hanger zone are considered. The response is studied in terms of loading history, cracking and failure load, failure mode, cracking pattern, toughness, stiffness, and ductility. It is observed that retrofitting the nib region with horizontal bars improved the capacity by 29% and 20% for the two shears span/depth (a/d) values, respectively. The maximum enhancement in the capacity for upgraded hanger regions with a/d= 1 is about 21%. Regarding toughness, this research indicated that for reduced nib steel specimens with a/d=1.0 and 1.5, a reduction by 17% and 27%, respectively, were obtained. Whereas reducing the hanger steel by 30% led to a drop by 29%. Strengthening of deficient nib reinforced specimens with a/d =1.0 and 1.5 led to an improvement in toughness by 43% and 62%, respectively. For specimens with deficient hanger steel (a/d=1.0), the strengthening led to toughness enhancement by 87%. Strengthening of deficiently reinforced nib end with the two a/d values resulted in improving stiffness by 18% and 24%, whereas when strengthening the hanger zone, an enhancement of 9% is obtained. For ductility, it is concluded that the prediction of ductility ratio using the displacement ratio method is more efficient than the toughness ratio method because it is considered the premature failure cases. Also, it is obtained that increasing the a/d value resulted in reducing the ductility ratio.


High strength; self-compacting; NSM steel bar; strengthening; dapped end beam; fictitious hinge.

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