Strain Rates in Prestressed Concrete Sleepers and Effects on Cracking Loads

摘要

Prestressed concrete sleepers (PCSs) play an essential role in structural response and performanceof ballasted railway tracks. Due to defects in track or train components, high magnitude dynamic loads maygenerate at the rail head and transfer to the PCSs which can generate cracks in PCSs. Cracking from dynamicloads have been reported as the most critical problem of PCSs around the world and impose an earlyreplacement of sleepers which is a financial burden to the rail industry. This paper investigates the effects ofstrain rates on the strength enhancement of PCS. By using available measurements, the strain rates arecalculated at two critical points of the PCSs, the rail seat and midspan. Considering the dynamic increase factor(DIF) of concrete, the cracking loads of a PCS are calculated and are compared with commonly occurringdynamic loads. Results show that the maximum strain rates at both rail seat and midspan are about 0.08 and0.016 1/s, respectively. The increase of cracking wheel load due to the strain rate effects is about 5 to 26 percent.The results are also shown to be able to demonstrate the level cracking from dynamic loads with very shortreturn periods.