Verification of the bursting and spalling formulas in the FIB model code by finite element analyses of anchorage zones of pretensioned girders

In order to predict the stress and possible crack distribution in the anchorage zones of pretensioned girders several models have been developed as can be found in the fib Model Code, the ASHTOO code or Eurocode 2. In this paper, the bursting and spalling formulas from the fib Model Code are evaluated by finite element calculations since some issues could be raised when applying the proposed formulas for industrial applications, especially for beams of limited dimensions. The effect of the upper strands, the assumed stress distribution at the opposite side of the equivalent symmetric prism, the stress transfer diagram along the strands and the effects of the strand position relative to the simplified resultant forces remain unclear. Accordingly two-dimensional finite element models were developed to gain insight into the bursting and spalling formulations from the fib Model Code. The numerical models render stresses and the stress flow results, which allow a more clear coupling to well-known strut-and-tie models. The results indicate that for various strand configurations, especially for small beams, the fib formulations may be too conservative

Nonlinear analysis of the end zones of prestressed concrete girders

Pretensioned concrete girders have been used for many years in construction. Nevertheless, optimization is still possible, especially regarding the anchorage zones. These are typically subjected to different types of stresses due to the local transmission of the prestressing force. By using a 3D nonlinear finite element model, the stresses and cracks in the anchorage zone due to the prestressing forces can be predicted in a more reliable manner. In this paper two 3D FE models are developed by using the concrete damage plasticity model in Abaqus. In the first model, the load transfer is defined by creating a shear force around each strand. In the second model, the interaction between the strands and the concrete is created by using surface-to-surface contact elements with friction. Finally, to validate the models, the results are compared with strain measurements on a precast beam during production at a precast concrete plant

Non-linear 3D finite element analysis of the anchorage zones of pretensioned concrete girders and experimental verification

This paper focuses on the modelling of the anchorage zone of a pretensioned girder. The finite element software Abaqus was used to create a 3D non-linear finite element model (FEM). This analysis was performed on a full-scale pretensioned girder with end blocks and with various types of strand modelling, where accurate contact properties between prestressing steel and concrete are essential. The model has been validated by comparing the numerical strain results with the strain measurements on a full-scale girder with end blocks, which was produced in a precast concrete plant. At the same time, a parametric study was executed to determine the value of the coefficient of friction between the strands and the concrete and to examine the sensitivity of the input parameters of the model. The results have indicated that an accurate determination of the concrete properties at the time of release is very important. Furthermore, the Hoyer effect is analysed. It is found that the radial expansion of the strand in the finite element model is in good agreement with the theoretically calculated expansion of the strand which demonstrates the accuracy of the finite element model. In addition, it is shown that the Hoyer effect influences the force transfer of two adjacent strands. The aim of this research is to investigate the potential of an alternative FE model of a pretensioned girder based on strand to concrete frictional behaviour, rather than the commonly used models based on an assumed shear stress distribution along the transfer length

Numerical and experimental analysis of the transfer length and its influence on the anchorage zone design of pretensioned concrete members

In order to optimize the end block of a prestressed girder, nonlinear finite element models are frequently used. This way the stresses and possible cracks in the anchorage zones can be predicted in a more reliable manner. However, a preliminary parametric study of nonlinear finite element models has shown that the transfer length has a major influence on the stresses in the concrete and in the reinforcement, and on the crack formation. In this paper this transfer length is examined, firstly by performing a parametric study of the formulations found in literature, secondly by measurements on beams produced at a precast concrete plant. The aim of this parametric study and the experimental research is to get further insight into the transfer length function as required for further numerical analysis of the end zones