Model Derivation and Validation of Spalling-Force Calculations for Prestressed Concrete Bridge Girder Ends Based on a Modified G-S Model

Abstract

Horizontal cracks occur at the web of prestressed bridge girder ends during prestress release due to the spalling force, which is produced by the transfer of the prestressing force to the concrete. To avoid using a trial-and-error method to determine the maximum moment section and unify the methods to determine the arm length of the maximum moment in the conventional Gergely-Sozen (G-S) model, a modified G-S model is proposed to calculate the spalling force in a pretensioned anchorage zone. A compression dispersion model (CDM) is developed and formulated for the pretensioned anchorage zone, and the extreme edge of isostatic lines is visualized mathematically with its geometric and physical boundary conditions, which can be used to accurately predict the arm length and spalling force of the horizontal moment at any horizontal section. Based on experimental and field observations and previous finite-element method (FEM) analysis results, the junction section between the bottom flange and the web, instead of the maximum moment section, is recommended as a critical control section to calculate the spalling force in the web. Compared with the numerical and experimental results, a good agreement was obtained confirming that the modified G-S model method not only can predict the arm length of the horizontal moment, but can also evaluate the magnitude of the spalling force. A case study illustrates how to apply the proposed method to calculate the spalling force at the junction section, and the results explain why horizontal cracks often occur at the junction section.