Jesse L. Beaver
Papers # 2014 Chicago
The design of corrugated wall thermoplastic pipes requires evaluation of loads applied to the pipe upon installation and those applied to the pipe throughout its service life. For loadings that are characterized as dead loads, the thermoplastic pipe will experience creep and/or relaxation for the duration of the applied load. This well-known phenomenon is typically captured for design by the use of creep testing on the base materials or relaxation testing on the pipe sections to determine the apparent modulus due to long-term loadings. Existing design specifications, such as the AASHTO LRFD Bridge Design Specifications Section 12.12 provide guidance on a load level for creep testing, but provide no basis for determination of the load.
This presentation describes the basis for selection of the load level for testing to determine the creep modulus of thermoplastic corrugated wall pipe for design in accordance with the AASHTO LRFD specification. This basis includes evaluation of the specific design checks that use the creep modulus. The presentation will also provide an explanation of the linear viscoelastic material behavior assumed in the design process. Finally, this presentation will describe the test methods currently used to evaluate the long-term behavior, including conventional creep testing, use of the Boltzman Superposition Principle to account for loading history, and testing using the stepped isothermal method (SIM). SIM testing utilizes time-temperature superposition (TTS) to simulate very long-term loading. Applications that rely on SIM testing use data from a one-day test to estimate material properties for loads that are applied to 100 years and beyond.