Rail anchor slip strength: Effect of anchor wear, rail wear, load rate, and reaction position

Rail anchors contribute significantly to longitudinal track resistance and rail neutral temperature management, yet their slip behavior under realistic wear and loading conditions remains poorly quantified. This study presents a laboratory program to characterize the slip strength of drive-on rail anchors as a function of anchor and rail wear, loading rate, and reaction location. A force-controlled slip test, adapted from current recommended practice, was implemented using a 245 kN actuator, a 136RE rail segment, and adjustable reaction blocks to simulate tie plate and crosstie loading while measuring rail–anchor relative displacement with high-resolution laser sensors. Results show that repeated anchor installation reduces ultimate slip strength by approximately 10%, 20%, and 45% after two, three, and ten applications, respectively, due to progressive plastic deformation of the anchor head and reduced steel-on-steel friction. Worn rail has limited influence on first installations, but worn anchors on worn rail exhibit additional strength loss. Impact loading produces slip strengths roughly 30% lower than quasi-static loading, consistent with rate-dependent stick–slip mechanics, while larger reaction gaps promote anchor rotation and walking, complicating replication and interpretation of peak strength. These findings indicate that anchor slip strength is strongly condition-dependent, and that use of a single characteristic value is inadequate for mechanistic rail stress management, longitudinal resistance modeling, and anchor design optimization.