Transfer Length Measurements in Pretensioned Concrete Railroad Ties Under Rail Loads

Abstract

During January 2013, concrete railroad ties were cast at a tie manufacturing plant with fifteen different reinforcement types that are widely employed in manufacturing of railroad ties worldwide. Among these reinforcements; there were 12 different 5.32 mm diameter wires with various surface indent geometries, two different 7-wire strands with 3/8-inch diameter, and one 3-wire strand with 5/16-inch diameter. Four concrete ties were cast for each reinforcement type for a total of 60 concrete ties. Among the four ties for each reinforcement type, two ties were installed in track and subjected to a cumulative in-track loading of 85 million gross tons (MGT). Before being subjected to this loading, special surface preparation was done on the ties to protect the strain measuring points on the bottom surface of the ties from surface abrasion during loading. The other two ties, which are companion ties for each reinforcement type, were not subjected to any loading. Surface strains of concrete railroad ties were measured at three different stages after prestress transfer: immediately after prestress transfer, one year after prestress before ties subjected to loading (January 2014), and after half of the ties were subjected to 85 million gross tons loading (August 2014). Transfer lengths were calculated at all these stages from the measured surface strain values and are presented here. Transfer length results are compared between the ties subjected to loading and the ties not subjected to loading, along with detailed explanation of results.