RESUMO
According to the shear capacity test results of six steel-fiber-reinforced high-strength concrete (SFHSC) corbels with welded-anchorage longitudinal reinforcement under concentrated load, the effects of shear span ratio and steel fiber volume fraction on the failure mode, cracking load and ultimate load of corbel specimens were analyzed. On the basis of experimental research, the shear transfer mechanism of corbel structure was discussed. Then, a modified softened strut-and-tie model (MSSTM), composed of the diagonal and horizontal mechanisms, was proposed, for steel-fiber-reinforced high-strength concrete corbels. The contributions of concrete, steel fiber and horizontal stirrups to the shear bearing capacity of the corbels were clarified. A calculation method for the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels was established and was simplified on this basis. The calculation results of the model were compared with the test values and calculation results of the GB50010-2010 code, the ACI318-19 code, the EN 1992-1-1 code and the CSA A23.3-19 code. The results showed that the concrete corbel with small shear span ratio mainly has two typical failure modes: shear failure and diagonal compression failure. With the increase in shear span ratio, the shear capacity of corbels decreases. Steel fiber can improve the ductility of a reinforced concrete corbel, but has little effect on the failure mode of the diagonal section. The calculated values of the national codes were lower than the experimental values, and the results were conservative. The theoretical calculation values of the shear capacity calculation model of the corbels were close to the experimental results. In addition, the model has a clear mechanical concept considering the tensile properties of steel-fiber-reinforced high-strength concrete and the influence of horizontal stirrups, which can reasonably reflect the shear transfer mechanism of corbels.
RESUMO
As short cantilever members, corbels are mainly used to transfer eccentric loads to columns. Because of the discontinuity of load and geometric structure, corbels cannot be analyzed and designed using the method based on beam theory. Nine steel-fiber-reinforced high-strength concrete (SFRHSC) corbels were tested. The width of the corbels was 200 mm, the cross-section height of the corbel column was 450 mm, and the cantilever end height was 200 mm. The shear span/depth ratios considered were 0.2, 0.3, and 0.4; the longitudinal reinforcement ratios were 0.55%, 0.75%, and 0.98%; the stirrup reinforcement ratios were 0.39%, 0.52%, and 0.785%; and the steel fiber volume ratios were 0, 0.75%, and 1.5%. According to the test results, this paper discusses the failure process and failure mode of corbel specimens with a small shear span/depth ratio and analyzes the effects of variables such as shear span/depth ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, and steel fiber volume content on the shear capacity of corbels. The shear capacity of corbels is significantly affected by the shear span/depth ratio, followed by the longitudinal reinforcement ratio and the stirrup reinforcement ratio. Moreover, it is shown that steel fibers have little impact on the failure mode and ultimate load of corbels, but can enhance the crack resistance of corbels. In addition, the bearing capacities of these corbels were calculated by Chinese code GB 50010-2010 and further compared with ACI 318-19 code, EN 1992-1-1:2004 code, and CSA A23.3-19 code, which adopt the strut-and-tie model. The results indicate that the calculation results by the empirical formula in the Chinese code are close to the corresponding test results, while the calculation method based on the strut-and-tie model of a clear mechanical concept yields conservative results, and hence the related parameter values must be further modified.