Three alternative procedures for computing the transient kinematic pile bending in two-layer soil

Stefania Sica, Armando Lucio Simonelli

Dipartimento di Ingegneria, Università degli Studi del Sannio, P.za Roma 21 -  82100 Benevento

George Mylonakis

University of Patras, University Campus, Rio 26500, Greece

Results from an extensive parametric analysis will be reported, carried out on single vertical elastic solid piles in layered soil, accounting for different material properties, geometric factors and earthquake excitations. The analyses were performed using a numerical tool developed by Mylonakis et al. [1997] based on a properly calibrated Beam-on-Dynamic-Winkler-Foundation (BDWF) model.

The paper accounts for a comprehensive parametric study on a two-layer soil profile as function of: (i) stiffness contrast between upper and lower layer, (ii) depth of upper layer, (iii) waveform of input motion and (iv) soil damping adopted in the free-field site response analysis.

On the basis of the above results, new regression analyses were carried out for computing the transient pile bending moments at the soil layer interface, revisiting existing predictive equations [Nikolaou et al., 2001; Mylonakis, 2001].

A synthesis of findings in terms of a set of simple equations is provided. Three alternative procedures were outlined to solve the problem in the realm of routine engineering calculations. Specifically:

a)     An approach based on a variable F₁, which does not require any free-field site response analysis to be carried out. The parameter F₁ is function of the ratio (f_input / f₁) between the dominant frequency of the input motion and the fundamental frequency of the subsoil.

b)     An approach based on a parameter F₂ (which is a constant), where the dynamic effects due to frequency content of the input-motion are incorporated into the parameter (γ₁)_dyn which is the shear strain at the interface, computed by a free-field site response analysis.

c)     An approach based on a variable h, which requires knowledge of M_resonance. As in the case with parameter F₁, h is sensitive to variations of the frequency ratio (f_input / f₁).

The use of these equations will be discussed through examples.

* corresponding Author: Stefania Sica

E-mail: stefsica@unisannio.it, Tel. 0824-305512, Fax 0824-325246.