Shear Behaviors Of Reinforced Ultrahigh Toughness Cementitious Composite Beams With Large Shear-span Ratio

Ultrahigh toughness cementitious composite (UHTCC), as a new kind of high performance cementitious composite reinforced with short fibers, shows apparent strain-hardening under uniaxial tension load, exhibiting outstanding crack controlling capacity and high tensile strength under high deformation. The use of UHTCC in engineering structures has great potential as it can greatly improve concrete structure members’durability and ductility. Far from now, some investigations on basic mechanical properties and practical use of UHTCC have been performed, but few experimental investigations are about UHTCC bending beams. Based on this, the following investigations on shear performance of RUHTCC beams with large shear-span ratio were carried out:(1)The shear properties of RUHTCC beams without stirrups and RC beams with stirrup ratios of 0,0.226%,0.316% and 0.395% were investigated through the shearing experiment under a concentrated loading at mid-point. Test results indicated that the use of UHTCC could greatly improve the shear performance, crack controlling capacity and energy-dissipating capacity of beams. Compared with RC beams, it also showed the feasibility of replacing the stirrups by UHTCC. As to beams in present experimental investigation, the stirrups with a ratio of 0.395% in RC beams could be replaced by UHTCC.(2)The influences of stirrup ratio, shear-span ratio and volume percentage on the shear behaviors of RUHTCC beams with large shear-span ratio, under a concentrated loading at mid-point, were reported in terms of the failure mode, the crack propagation, shear cracking load, ultimate shear capacity, load-deformation curves as well as the shear ductility. The tested results showed that the ultimate shear capacity of the RUHTCC beams is above 1.4 times that of the RC comparison beams. Stirrup ratio, shear-span ratio and volume percentage had no effect on the shear cracking load and the diagonal crack width of RUHTCC beams while the ultimate shear capacity of beams with lower shear-span ratio, larger stirrup ratio or larger volume percentage of fibers are higher. As the shear resistance of UTHCC couldn’t be exerted totally due to the constraint of stirrups, the improvement of ultimate shear capacity was not so significant when the stirrup ratio increased. All the RUHTCC beams presented the stable propagation of multiple fine diagonal cracks with the maximum crack width below 0.2mm under the ultimate service condition. The shear ductility of beams improved as stirrups were used or the shear-span ratio increased. But the shear ductility was not always improved as the volume percentage of fibers increased.(3)Based on the experimental results and related references, using the discrete model to separately calculate the shear contribution of cement composite, stirrups and fibers, and then taking into account the combined effect between UHTCC and stirrups, the empirical formulas for predicting the ultimate shear strength of RUHTCC beams with stirrups and lager shear-span ratio was proposed through the regression analysis, and the predicted value based on such formulas was in good agreement with the tested values in present experiment and related references.