The Effect of Higher Prestress on Concrete Railroad Tie Behavior

Prestressed concrete crossties are used extensively by North American railroads because they offer improved service life and consistent performance. Recent industry trends have encouraged manufacturers to effectively increase concrete ties’ prestressing force to improve their structural performance in flexure and shear. This paper presents the results of linear and nonlinear three-dimensional finite element analyses of typical concrete crossties to study the stress state of crossties at prestress transfer and to identify potential negative consequences of increasing effective prestressing force. The analyses utilize finite-sliding contact with Coulomb friction to model interaction between prestressing strands and adjacent concrete. Variation of several parameters that affect stress state at prestress transfer are considered, including magnitude of prestressing force, stiffness of concrete, crosstie geometry, and strand configuration. The analyses indicate that tensile stresses develop near the ends of the crossties at prestress transfer and their magnitudes increase with decreasing transfer length and increasing prestress force. These tensile stresses may account for widespread longitudinal cracking that has been observed in premature failure of concrete crossties in the last ten years.