Research on DNLC element for HPC beams strengthened with high performance prestressed HFRP sheet

The calculative double nonlinear layered combinative(DNLC) element of high performance concrete(HPC) beams strengthened with prestressed hybrid fiber(HFRP) sheet were established for different kinds of mixture ratios. The prestress effect of HFRP sheet was effectively simulated by isoperimetric layer element with initial stress. After considering the material nonlinearity of the HPC beams and the geometry nonlinearity of the structures, the analytical model based on DNLC element was validated, and then the mechanical behaviors including the cracking loads, the stress development of the steel and the stress redistribution of HFRP sheet of the strengthened beams were studied. By comparing with the experimental results, the results of this method are in good agreement with the experimental results, which proves that the prestress of HFRP is efficiently modeled by isoperimetric layer element and the DNLC element is reliable. The characteristic loads of prestressed CFRP sheet are higher than those of prestressed GFRP sheet. However, the degree of increase of the cracking loads of prestressed CFRP sheet is smaller compared with hybrid fiber sheet and the residual strength of CFRP sheet is more than other hybrid fiber sheets. Before cracking loads, the stress redistribution of the hybrid fiber sheet changes a little and then after yielding loads, it increases fast until the structure fails.