Benefits of high strength reduced modulus (HSRM) concrete railroad ties under center binding support conditions

Abstract

Concrete ties, also referred to as sleepers or crossties, have become a promising alternative to timber ties for freight lines in demanding territories with high curvature, high grade, and high axle loads. Concrete ties have also become popular in rail transit systems. High strength (HS) concrete is the material of choice in the fabrication of prestressed concrete railroad ties. The higher strength of the concrete is directly related to higher values of the elastic modulus, thus increasing the rigidity of the material. The combination of increased strength, rigidity, and the material brittleness may lead to premature cracking and deterioration which has raised major concerns within the rail industry. With experience in frontier concrete material research, researchers at the University of South Carolina (USC) have developed a High Strength Reduced Modulus (HSRM) concrete by introducing weathered granite aggregates into concrete mix designs. A comprehensive study has been conducted at USC to quantify the benefits of using HSRM concrete in railroad ties. Both laboratory experiments and computer simulations at the material, component, and structural levels were performed. HSRM can improve the cracking resistance and fatigue performance and extend the service life of the concrete ties. This paper presents the details of the computer simulations used to quantify the benefits of using the HSRM material in ties subjected to center binding conditions. Three-dimensional nonlinear Finite Element (FE) models have been developed for the HSRM and the “Standard” concrete ties. Nonlinear material models based on concrete damaged plasticity are implemented. The concrete-steel bond interface is also modeled. The numerical models are first validated through comparisons with laboratory testing results of prestressed concrete prisms and commercial prestressed ties, which showed excellent agreement. Results from a parametric study simulating the center binding conditions in a tangent track have shown that the HSRM concrete tie outperforms the Standard concrete tie by: (i) showing smoother stress distribution, (ii) delaying the initiation of cracks, and (iii) failing at higher ultimate loads.