Varvara Zania

Friction Effects on Lateral Loading Behavior of Rigid Piles

The adequacy of the p-y curves used in the current practice for the design of rigid pile foundations with large diameter, like in the case of monopile foundations of offshore wind turbines, has been widely questioned. The current study aims at analyzing the lateral behavior of rigid piles, while taking into account the shear frictional resistance along the pile. For this purpose efficient three dimensional finite element models of different diameter have been developed. The increase of the side friction and of the diameter of the pile is shown to alter the failure pattern and increase the lateral capacity of the pile. The obtained p-y curves demonstrate the importance of the aforementioned parameters in the design of rigid piles, as the reduction of friction along the interface reduces not only the ultimate load but also the stiffness of the soil-pile response.

Analyzing Track Responses to Train Braking

The objective of this study was to suggest a response analysis framework for railway tracks that are subjected to braking. An analytical formulation was developed, in which the rail–track system was modeled as an infinite beam supported by an orthogonal Winkler foundation consisting of linear springs in perpendicular directions. The spring constants were varied over a wide range in order to represent different track types. Braking loads were simulated as representative sets of vertical and longitudinal forces, either concentrated or distributed. Considering a realistic set of model parameters, the approach was demonstrated by evaluating the track responses for a single axle and for a full train. The computations included determination of axial rail stresses, forces at the base of a sleeper, and the associated friction demand required to resist longitudinal slippage. Based on these analyses, it is concluded that longitudinal track responses have a much longer influence zone compared to vertical track responses. This implies that calculations involving a full train must be done on a case-by-case basis, i.e. they cannot be deduced from a single axle analysis. It is also found that high values of friction demand may develop at the sleeper bases indicating possible slippage. Overall, the proposed formulation provides a highly adaptable and easily implementable first-order mechanistic tool for the analysis of track responses to decelerating vehicular loads.