Semi-analytical study of defective pile-beam systems under transient excitation: Implications for low-strain testing

This paper establishes a theoretical model of defective pile-beam system. The soil around the pile is modeled as a continuous three-dimensional model. The pile is modeled as a Rayleigh-Love rod model that considers its transversal inertia effect. The defect of the pile is simulated by a pile segment with a different radius from the normal pile segment. The impedance function recursion method, along with RSPT and AIFTM, is utilized to derive the impedance of the pile top. The beam is modeled as a Timoshenko beam and the transient excitation is applied at the connection between the pile and the beam. Analytical solution for the dynamic response of the system in the frequency domain is derived, and the discrete Fourier transform is used to obtain a semi-analytical solution for the time-domain response. The velocity at the connection between the pile and beam and the pile body can be measured to assess defects. The semi-analytical solution presented in this paper was validated through comparison with FEM results. Reflection from necked segment is more pronounced at pile-beam connection than at pile body. Both velocity curves at these two points should be measured when beam cross-section height is large to determine pile integrity. The peak value and arrival time of characteristic waves are influenced by burial depth, necking section parameters, beam cross-section height, cantilever length, and soil parameters. These findings can provide guidance for the application of low strain integrity testing in pile-beam systems.