The shear capacity of reinforced concrete members with plain bars

Assessment of the capacity of the existing infrastructures has become more relevant in the recent years. With regard to the concrete bridges, the shear capacity of a large amount of existing concrete slab bridges reinforced with plain (smooth) bars are of concern. However, it was argued that the shear formula that is currently adapted in the design codes are not fully calibrated by experiments on members with plain bars. The arguments are based on several experimental results found in literature from the 60s. At that time, the size effect on shear capacity of members without shear reinforcement was not widely recognized yet. Thus, the specimens applied in these experiments were mostly of small depth (d = 300 mm). In those experiments a significant improvement of the shear capacity was obtained in members reinforced by plain bars. The conclusions derived in those tests have to be further evaluated with specimens that represent realistic dimensions and other configurations of the slab bridge of concern. To serve that purpose, a series of shear tests have been carried out at the Stevin Lab in Delft University of Technology recently. A number of shear tests have been carried out on specimens reinforced by plain bars with low yielding strength. The heights of the specimens are 300 mm, 500 mm and 800 mm. The test results are compared with results of peer specimens with normal deformed bars with the same configurations (dimensions, concrete strength and reinforcement ratio). The experimental results are reported in this paper.