Flexural Performance of Composite Prestressed UHPC-NC T-Girders

Abstract

Ultrahigh-performance concrete (UHPC) is increasingly recognized as being a better material in girders, and a composite prestressed UHPC-normal concrete (NC) girder is a better choice to be used for strengthening existing members and precast concrete constructions. In this study, 10 composite girders and 1 pure NC girder were fabricated and tested to investigate the effect of UHPC heights, prestress levels, and NC compressive strengths on the flexural properties of composite girders. The test results show that increasing the prestress level and UHPC height both delayed the formation and propagation of cracks. Compared with the pure NC girder, the mean crack spacing of composite girders decreased, and the number of cracks was considerably higher for the incorporation of UHPC. Adding UHPC into girders can considerably increase the stiffness and ductility of members. An analytical model based on the finite strip method was developed by considering the constitutive models of materials. The agreement between the predicted results and the experimental data is sufficient, indicating that the analytical model is suitable for analyzing composite girders. Additionally, the influencing factors of composite UHPC-NC girders were comprehensively investigated using the theoretical model. Finally, the reasonable range of the UHPC height is determined by the analytical results. The experimental results revealed the flexural behavior of large-scale composite prestressed UHPC-NC girders, including the failure modes, the load–deflection relationship, the concrete strain, and the crack pattern. The analytical model provides a powerful tool for the prediction of flexural behavior of composite girders, which would be helpful for the design analysis of composite girders.