Abstract:
A valuable objective of statically load testing deep foundations is to determine load-transfer response. Integral to this objective is determining internal forces at various elevations within the deep-foundation element. These internal forces are often calculated from strain measurements. Strain measurements do not determine internal forces directly. One approach to converting measured strains to calculated internal forces requires estimating the foundation’s composite-section elastic modulus, ECOMPOSITE, and total cross-sectional area, ACROSS. For tensile tests of deep foundations with a cementitious constituent (i.e., concrete or grout), composite-section elastic modulus determination or estimation can be problematic since cementitious material is generally considered unable to develop significant tensile force and strain, if any. This presentation briefly discusses fundamental differences between metallic (steel) and ceramic (cementitious) materials’ mechanical properties in varying loading configurations to aid in interpreting composite-section tensile strain data. A case history of a tensile test on a concrete-filled steel pipe pile instrumented with strainmeters embedded in the concrete fill is presented. The strain data and resulting load-transfer responses are evaluated by 1) using a concrete compressive modulus determined from laboratory testing, 2) assuming that the concrete tensile modulus is equal to zero, and 3) by the Incremental Rigidity (I.R.) method which determines a foundation’s axial rigidity at individual strain-gauge levels. The resulting load-transfer responses are compared, and the I.R. method is shown to provide the most reasonable interpretation.