OasisLMS

Abstract: Instrumented static loading tests are performed on deep foundation elements to characterize pile load-transfer response with depth. Appropriately calculating internal forces from measured pile strains is critical to the success of any instrumented static load test, and knowing the pile’ s axial rigidity (composite-section Young’ s Modulus (E) times total cross-sectional area (A), or EA) is required. In recent years, the Incremental Rigidity (I.R.) method [Komurka & Moghaddam, 2020] has proven to be a robust tool for converting static load test strain-gauge data for piles with cementitious content, as the I.R. method provides a direct relationship between strain and internal force without requiring knowledge of E or A. The method also accounts for inherent uncertainty and variability in E, A, and strain-gauge measurements themselves at specific strain-gauge locations along the pile. It may be commonly assumed that the I.R. method need not be applied to all-steel piles due to presumably uniform axial rigidity values along the pile and the strain-independent response of such piles. Instead, a constant EA factor is usually used. This paper provides a brief overview of the I.R. method, shows results from applying the I.R. method to numerous static load tests performed on all-steel piles (H-piles and pipe), and reveals that conventional strain-to-internal-force conversion methods may have greater degrees of uncertainty and variability than is typically assumed. The I.R. results presented reveal potential impacts of pile material and geometry variability, strain-gauge calibration error, strain-gauge measurement noise, and instrumentation procedures on load-transfer results. Interpreted internal-force values derived from the I.R. method are compared to conventionally interpreted static and dynamic load testing results. Additional results are shown using the I.R. method to salvage erroneous strain-gauge readings to produce reasonable internal force profiles. The benefits, limitations, and recommended best practices of applying the I.R. method to all-steel piles are discussed.

Mr. Joseph Mulcahey; Mr. Brett Belzer

Annual Conference Proceedings