Abstract
An analysis model of the shear capacity of prestressed ultrahigh performance concrete (UHPC) beams under the combined action of bending and shearing was established in this paper based on the modified compression field theory and by considering the unique material constitutive relation of UHPC. Shear tests were performed using three prestressed UHPC-T beams with different shear-span ratios to verify the correctness of the model. The results showed that the shear-span ratio greatly influenced the shear capacity and failure modes of UHPC-T beams. Upon increasing the shear-span ratio, the failure modes of the three beams were inclined compression failure, shear compression failure, and diagonal tension failure, successively. When the shear-span ratio changed from 1.04 to 2.12, the shear bearing capacity decreased greatly; however, when the shear-span ratio changed from 2.12 to 3.19, the decrease of the shear bearing capacity was very small. In addition, the MCFT analysis model was used to analyze the experimental data, and the predicted results were in good agreement, which proved the applicability of the model. Finally, according to the existing shear test results of UHPC beams and based on the main influencing factors, a simplified formula for predicting the shear capacity of UHPC beams was obtained by fitting. Comparing the MCFT model with the results of other pieces of literature, this formula accurately predicted the shear capacity of UHPC beams. The MCFT model and the simplified formula presented in this paper provide a powerful tool for predicting the shear performance of UHPC-T beams, which will contribute to the design and analysis of UHPC-T beams.
Highlights
Ultrahigh performance concrete (UHPC) is a new type of steel fiber-reinforced cement-based composite material with many excellent properties [1,2,3], including superhigh strength, high ductility, good durability, and resistance to environmental degradation [4,5,6,7]
The softening coefficient was corrected to establish the truss model, and the shear performance of RPC beams was predicted. e above calculation methods of UHPC shear capacity used different theories to explain the shear failure mechanism of the structure from different perspectives [20,21,22,23]; the shear-span ratio is not fully considered by the limit equilibrium theory. e analysis accuracy of specimens with a shear-span ratio of 2 that undergo shear-pressure failure is relatively high, while it is relatively low for specimens with a small shear span. e plasticity theory primarily considers the influence of compressive strength and horizontal projected length of the main diagonal crack, but it does not consider the influence of stirrups, longitudinal reinforcement, or prestress on the shear capacity
When the shear-span ratio increased from 1.06 to 2.12, the bearing capacity of the beam decreased by 39.64%, and when the shear-span ratio increased from 2.12 to 3.19, the bearing capacity decreased by 4.58%, indicating that the shear-span ratio greatly influences the shear performance of UHPC beams, and its influence degree decreases upon increasing the shear-span ratio. e reason is that vertical compressive stress is generated at the support reaction and concentrated load, which reduces the main tensile stress of concrete, which improves the shear capacity of the beam
Summary
Ultrahigh performance concrete (UHPC) is a new type of steel fiber-reinforced cement-based composite material with many excellent properties [1,2,3], including superhigh strength, high ductility, good durability, and resistance to environmental degradation [4,5,6,7]. 2. Calculation Model Based on MCFT e modified compression field theory was used to establish the strain compatibility equation and stress balance equation based on material mechanics and combined with the UHPC constitutive relations to obtain the calculation method of the shear bearing capacity according to three convergence conditions. In the section analysis of bending-shearing composite action, the test beam is analyzed separately according to pure bending and pure shear stress forms, and the corresponding UHPC constitutive models are used in the calculation.
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