The effect of the ratio of Λ-shaped shear connectors on the flexural behavior of a reinforced concrete frame

Abstract

Failure in a structural system can appear because of different types of pathologies and can cause a large number of problems during seismic action. Among these pathologies are design and execution flaws, underestimation of the required capacity of cross-section or seismic demand, and use of low quality of materials. The jacketing technique for a frame element is the most common use strengthening method in the practice to remove such disadvantages in a structural system. Then, the shear stress transferability at the concrete-to-concrete interface surface is the main objective. Shear connectors application is a solution for that consideration, but the investigation in the literature focusing this point is not adequate. The effect of the ratio of steel shear connectors on the interfaces of a reinforced concrete frame constructed using reinforced concrete formworks on its flexural behavior is numerically evaluated. Initially, the same ratio of Π-shaped and Λ-shaped shear connectors, 0.312%, is applied to determine the more effective shape. It should be clear that the ratio of shear connectors on any separate surface is calculated as the fraction of the total area of the cross-section of shear connectors placed perpendicularly (Π-shaped) at the surface and the area of that surface. The same ratio is understood as after evaluating the Π-shaped shear links, each of them is replaced by a Λ-shaped link at the same location. As a result, compared to the bending capacity of the frame whose surfaces are smooth, Λ-shaped connectors enhance the bending capacity of the frame up to 9.67% while the amount of improvement brought by Π-shaped ones is modest, about 2.172%. After that, a wide variety of the ratio of Λ-shaped connectors, 9 values, are placed on concrete-to-concrete interfaces. Tremendously, due to clamping stress brought by Λ-shaped shear connectors at the concrete substrates, the nonlinear behavior is improved and the amount of enhancement rises as the number of applied connectors is augmented but not linearly. The most important observation is that the amount of improvement is insignificant after the ratio of shear connectors reaches the percentage of between 0.3% and 0.4%. On the other hand, compared with the frame whose interfaces are smooth, the displacement ductility factor of the frame strengthened using 0.4% decreases an amount of about 30%.