Simplified discontinuous field model for RC beams with a medium shear span ratio: Experimental study and shear strength formula

It is generally believed that the shear span ratio is one of critical factors governing the shear failure of reinforced concrete beams. For a certain shear span scenario, the shear transfer mechanism is often attributed to one of the two typical categories: 'beam-action' for slender beams with a large shear span ratio, and 'arch-action' in deep beams with a small shear span ratio. However, in the medium shear span ratio range, neither the beam action nor the arch action dominates. In this study, an alternative model based on the notion of discontinuous fields is established under the framework of limit analysis. A shear strength formula for medium shear spans is derived subsequently by solving a combined action of the smeared-arch subfield and the vertical stirrups linking the fan subfield. After that, the least shear strength is obtained via the kinematic analysis of these discontinuous fields. To examine the proposed model, an experimental study is conducted through two T-beam specimens with artificially preset cracks and two benchmark specimens. In comparison with existing approaches and test results collected from this study and other twenty-two specimens in the literature, the proposed discontinues field model has a fairly good agreement in the shear strength predictions. A further discussion on the advantages and limitations of the simplified discontinuous field model also demonstrates that it provides a better transition of the shear strength verifications between slender beams and deep beams.