Interpretation of laboratory creep testing for reliability-based analysis and load and resistance factor design (LRFD) calibration

ABSTRACT: Load and resistance factor design (LRFD) is now recommended in North American design codes for reinforced-soil structures, including internal stability limit states. The selection of load and resistance factors that appear in limit state equations is best carried out using reliability-based analysis. In this paper the conventional approach to compute the limit state for geosynthetic reinforcement tensile rupture is reviewed, and is then recast in a reliability-based analysis framework suitable for LRFD calibration using bias statistics. The paper describes how to compute bias statistics from product-specific laboratory creep tests for the reinforcement rupture limit state. A database of results from creep tests on 94 different geosynthetic products was collected from 21 different sources. A total of 1086 in-air tensile test results and 540 creep-rupture data points were examined. This database is used to compute virgin and creep-reduced strength bias statistics for three different geosynthetic product categories. The results of analysis show that variability in the prediction of creep-reduced strength is very low, and is probably captured by the magnitude of variance in the original tensile strength of the test specimens. This greatly simplifies future LRFD calibration for the geosynthetic rupture limit state. An important implication of this study for LRFD design is that creep strength reduction factors can be taken as deterministic. The paper also provides a summary of computed creep-reduction factors that is a useful reference for future estimates of this factor from laboratory creep testing, and for preliminary design purposes using allowable stress design or LRFD approaches.