Lubao Luan

This paper presents an analytical study on the lateral kinematic response of offshore pipe piles subjected to vertically propagating S‐wave seismic excitation. Both the kinematic interaction of the pipe pile with the soil and seawater are considered. The lateral resistances of the outer and inner soil are obtained based on the confined viscoelastic dynamic continuum models, while the hydrodynamic pressures of the seawater are based on the inviscid incompressible fluid theory. The pile response is then obtained by utilizing the continuity condition at the soil‐pile and seawater‐pile interfaces along the pile shaft. The derived solution is employed to investigate the sensitivity of the seismic response of pipe piles to certain key problem parameters, such as length of pile segment embedded in seawater, the relative stiffness of the pile and soil and the pile radius ratio. We demonstrate that the partially embedded piles are much more flexible compared with fully embedded piles when subjected to S‐wave excitation, resulting more strong motion transferred to the superstructures and the existence of seawater will amplify the seismic responses of offshore pipe piles.

This paper presents a mathematical model for the elastic analysis of single floating piles subjected to axial dynamic loads, that is based on treating the soil surrounding the pile as a Tajimi‐type viscoelastic continuum. The pile and the soil column underlying the pile tip are modelled using one‐dimensional rod theory, and this allows obtaining an elegant solution that requires solving a system of linear equations, instead of complicated integral equations. Closed‐form expressions are derived for the dynamic stiffness at the pile head, and the frictional resistance along the pile shaft. The presentation concludes with a discussion on the main mechanisms that govern the inertial response of floating piles, and an investigation on the sensitivity of the dynamic stiffness and of the frictional resistance to the main geometrical and material problem parameters.

This paper presents a method for the seismic analysis of open‐ended pipe piles subjected to vertically propagating S‐waves, that considers kinematic interaction between the pipe pile and its external and internal soil. Following the presentation of the elastodynamic continuum model, which is based on the assumptions of linear elastic soil response and uniform soil conditions, we employ the derived solution to investigate the sensitivity of the seismic response of pipe piles to certain key problem parameters, such as pile slenderness or the relative stiffness of the pipe pile compared to its surrounding soil. We demonstrate that the bending stiffness of pipe piles is governing their seismic response, and that thin‐walled pipe piles offer the best material usage versus seismic performance ratio. The presented solution offers a low‐cost alternative to complex numerical simulations for preliminary seismic design purposes, such as the selection of optimal pipe pile section geometry.

This paper presented an analytical method for determining the response of a rigid strip foundation resting on the surface of a viscoelastic half‐space to horizontal dynamic loads, and the associated transient soil displacements resulting from the vibration of the footing. This mixed boundary value problem was solved by means of Jacobi orthogonal polynomials, a more efficient method compared to transforming the dual integral equations resulting from the boundary conditions to Fredholm integral equations. Displacements and stresses of the soil‐footing system were accordingly obtained by applying the inverse Fourier transform. Finally, we used the proposed solution to investigate the effects of material damping and Poisson's ratio of soil on the dynamic response of the strip footing, and the resulting soil displacements.

Summary: This paper presents an analytical method for modeling the dynamic response of a rigid strip footing subjected to vertical‐only loads. The footing is assumed to rest on the surface of a viscoelastic half‐space; therefore, effects of hysteretic soil damping on the impedance of the foundation and the generated ground vibrations are considered in the solution. To solve the mixed boundary value problem, we use the Fourier transform to cast a pair of dual integral equations providing contact stresses, which are solved by means of Jacobi orthogonal polynomials. The resulting soil and footing displacements and stresses are obtained by means of the Fourier inverse transform. The solution provides more realistic estimates of footing impedance, compared to existing solutions for elastic soil, as well as of the attenuation of ground vibrations with distance of the footing. The latter is important for the estimation of machine vibration effects on nearby structures and installations.

An analytical solution is presented for evaluating the dynamic responses of pile groups subjected to vertical harmonic loads. The solution allows us to consider the effects of pile geometry on the pile head impedance of the vertically loaded pile groups by the use of a new dynamic interaction factor. To this end, the stress distributions of the soil surrounding the vertically vibrating pile is first determined for calculating the pile–pile interaction factor, instead of the classical interaction factor based on two-pile displacements in past studies. Accordingly, the impedances of the pile group are derived using the proposed pile–pile interaction factor and the superposition principle. Some selected examples are presented to demonstrate the proposed refined technique for evaluating the dynamic characteristics of the pile group.