Effect of member depth and concrete strength on shear strength of RC deep beams without transverse reinforcement

Abstract Eight reinforced concrete deep beams without shear reinforcement were constructed and tested. The test parameters were the effective depth (ranged from 180 to 1440 mm) and the concrete compressive strength (ranged from 35 to 50 MPa). The results revealed that after the formation of diagonal cracks, the stress field redistributed and the tied-arch action formed. The normalized shear strength decreased 32.3% and 27.3% by increasing the depth from 180 to 1440 mm for the beams with the concrete strength of 35 and 50 MPa, respectively, which indicated an obvious size effect. On the other hand, an average reduction of 7.5% in normalized shear strength was obtained by increasing the concrete strength from 35 to 50 MPa. Based on the test results, the strut coefficient βs = 0.4 in ACI 318-19 was evaluated, indicating that the safety margin decreased with the increase of effective depth. Therefore, a fracture mechanics based coefficient considering the size effect for strut coefficient, which can be easily applied to existing strut-and-tie models, was proposed based on the 38 specimens tested in this study and collected from other studies. Additionally, the test results of the 38 specimens were also compared to predictions by three design shear models and five mechanics based shear models. The results indicated that a refined strut-and-tie model previously proposed by the authors provided the best prediction, and the average value and coefficient of variation of the tested-to-predicted shear strength ratio are 1.00 and 17.8%, respectively.