Investigation of Bursting Forces in Anchorage Zones: Compression-Dispersion Models and Unified Design Equation

Anchorage zones of posttensioned structures are prone to splitting cracks, necessitating rational reinforcement design methods for anticracking in such regions. This paper presents a generalized method to calculate bursting forces in posttensioned anchorage zones. Compression-dispersion models are individually formulated for anchorage zones with single concentric, eccentric, and inclined tendons, and a unified equation for calculating bursting forces is developed accordingly. In these models, the load paths of the anchor force are mathematically visualized by infinite isostatic lines with their own geometric and physical boundary conditions. The models are demonstrated to be capable of reflecting the nature of anchorage zones with regard to the distribution of bursting stresses. Finite-element evaluation and experimental verification show that the proposed equation provides accurate and safe predictions for different loading conditions, while the AASHTO equation is found to be overly conservative in most cases. For this reason, a suggested revision to the AASHTO-LRFD Bridge Design Specifications is presented.