Influence of Indirect Loads on Shear-Critical RC Deep Beams with Secondary Beams of Unequal Depth

초록

This study evaluates the reduction in the shear strength of reinforced concrete (RC) deep beams subjected to indirect loads from intersecting secondary beams. The effectiveness of the hanger reinforcement recommended by current structural design codes for shear-critical RC deep beams is verified in this study. To experimentally evaluate the shear performance of RC deep beams under indirect loads, directly supported deep beams with secondary beams crossing at right angles were designed as test specimens. The experimental variables included the loading type, the location of the secondary beam, and the presence or absence of hanger reinforcement. The loading type refers to the manner in which the load is transmitted to the main beam and is divided into direct and indirect loads. The locations where the secondary beams carrying indirect loads were designated as the upper and lower portions of the sides of the supporting main beam. The hanger reinforcement was placed within the reinforcement zone proposed in the current design codes for cross beams. The experimental results showed that the shear strength of specimens subjected to indirect loading was influenced by the position of the secondary beams, and it decreased by up to 76.2% compared to the specimen subjected to direct loading. Additionally, the specimen with secondary beams at the lower portion, despite having hanger reinforcement as recommended by the CSA design method, showed only a 55% increase in shear strength compared to the performance of the hanger reinforcement. This work demonstrates that CSA code provisions for hanger reinforcement are unsafe for lower-positioned secondary beams, necessitating revised design guidelines. This study proposes finite element (FE) analysis modeling methods that can effectively reflect the shear strength reduction of RC deep beams subjected to indirect loads, and from the comparison with experimental results, relatively reasonable prediction results were obtained with an average of 1.02 and a coefficient of variation of 8.4%.

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