Kinematic bending of piles: analysis vs. code provisions

Recent seismic codes prescribe that piles have to be designed for “soil deformations arising from the passage of seismic waves which impose curvatures and thereby lateral strains on the piles along their whole length”(EC-8). Accepting these lines, recent seismic Italian normatives (OPCM 3274/2003 and more recent ones) specify that kinematic effects should be taken into account when seismicity of the area is moderate or high, subsoil type is C or worse, and consecutive soil layers with sharply different shear moduli are present. The final aim of the study is to evaluate, from a practical viewpoint, to what extent kinematic pile bending is worth considering in typical subsoil conditions, namely soil types C and D according to EC8. The analysis method is that proposed by Mylonakis et al. (1997) based on a numerical Beam-on-Dynamic-Winkler-Foundation (BDWF) model. In this paper analysis results for two-layered soil profiles are illustrated. Italian acceleration recordings are used as input motions. Results indicate that in the high seismicity zones of the Italian zonation (OPCM 3274/2003 and OPCM 3519/2006) and for subsoil types D and C, kinematic bending moments may be very high and well above the yielding level of typical RC piles, the latter being dependent on the magnitude of the normal load acting in the pile.