Calculated Load-Transfer Responses from a Tensile Static Load Test on an Internally Instrumented Concrete-Filled Steel Pipe Pile-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines how to convert measured strain into internal axial force in a concrete-filled pipe pile under tensile loading. Because force is calculated as \(F=EA\varepsilon\), interpretation depends on the pile’s axial rigidity, \(EA\), which may vary with location and strain.<br /><br />A case history describes a closed-ended, 12.75-inch-diameter steel pipe pile with a 49-foot embedded length, filled with concrete after driving and instrumented at six levels. The pile was pulled vertically by its steel shell. Internal force profiles were calculated using three assumptions for concrete modulus and an Incremental Rigidity (I.R.) method.<br /><br />The conventional calculations used either the ACI formula or a laboratory test to estimate concrete’s compressive elastic modulus. The presentation cautions that neither is appropriate for interpreting tensile response: cementitious materials may have different tensile and compressive moduli, and their properties can vary along the pile. Setting concrete’s tensile modulus to zero produced a fairly reasonable force profile in this case.<br /><br />The I.R. method estimates local \(EA\) from changes in applied load and measured strain after shaft resistance above a gauge level has been mobilized. It can account for strain-dependent and potentially bilinear behavior, without requiring separate estimates of material modulus and area. For this test, it produced a somewhat improved force-profile interpretation compared with assuming zero concrete modulus, though it requires additional analysis.<br /><br />The presenter concludes that the I.R. method may be worthwhile when greater accuracy is needed or when simpler assumptions cannot represent the pile’s response adequately.

Keywords

concrete-filled pipe pile

tensile loading

strain to axial force

axial rigidity

EA method

incremental rigidity

steel shell

concrete modulus

force profile

shaft resistance