Dynamic Winkler Modulus for Axially Loaded End-Bearing Piles

The problem of dynamic pile-soil interaction and its modeling through the concept of a Dynamic Winkler Foundation are revisited. It is shown that depth-dependent Winkler springs and dashpots, obtained by dividing the complex-valued soil shear tractions and the corresponding displacements along the pile, may faithfully describe pile-soil interaction, contrary to common perception that the Winkler model is always approximate. A theoretical wave model is then derived for analyzing the response of axially loaded endbearing piles embedded in a homogeneous viscoelastic soil medium. Closed-form solutions are obtained for: (i) the displacement field in the soil and along the pile; (ii) the impedance coefficients (stiffness and damping) at the pile head; (iii) the depth-dependent Winkler moduli along the pile; (iv) the average, depth-independent, Winkler moduli to match the impedance coefficient at the pile head. Results are presented in terms of dimensionless graphs and charts that highlight the salient features of the problem. The predictions of the model compare favorably with established solutions from the literature, while new results are presented

A simple method for N-M interaction diagrams of circular reinforced concrete cross sections

A novel analytical method is derived for the ultimate capacity interaction diagram (i.e., axial compression, N - bending moment resistance, M) of reinforced concrete (RC) columns with circular cross section. To this aim, the longitudinal rebar arrangement is replaced with a thin steel ring equivalent to the total steel area; moreover, according to modern design approaches, simplified stress–strain relationships for concrete and reinforcing steel are used. Illustrative applications demonstrate that the ultimate capacity computed by the proposed analytical approach agrees well with the results obtained by rigorous methods based on consolidated numerical algorithms. The new solution allows for a rapid, accurate assessment of circular cross section capacity by means of hand calculations; this is especially useful at the conceptual design stage of various structural and geotechnical systems. The method can be easily extended to more general configurations, such as multiple steel rings and composite concrete-steel sections

Stability Analysis of a 70m-High Cut at an Ancient Landslide Area in Patras, Greece

A 70m-high slope is currently under construction near the entrance of a cut-and-cover tunnel in the inner loop highway of City of Patras – a seismically active area in Western Greece (PGA = 0.24g). The slope consists of marl layers dipping inwards and exhibiting distinct sets of joints. The landscape provides evidence that the site has been subjected to a major landslide at an unknown time in the past. Geotechnical investigation detected a sheared zone at about 15m below ground surface, and a water table a few meters below the planned toe of the slope. The angle and position of the slope surface together with the estimated position of the sheared zone provide a chair-like potentially unstable volume with convex plan view. In addition to the general stability problem, surface instabilities due to the aforementioned sets of joints create the potential of smaller wedge-type failures near the surface of the slope. Following a detailed geotechnical investigation, nonlinear stress finite-element analyses considering both gravitational and earthquake loads were performed. The analyses encompassed a number of different assumptions about: (a) depth to water table, (b) soil strength and (c) geometry of slope and soil layer interfaces. Results show that adequate safety can be achieved using a combination of piles and passive anchors. The effects of various factors/assumptions on the safety of the slope are discussed

On soil-structure interaction in large non-slender partially buried structures

This paper addresses the seismic analysis of a deeply embedded non-slender structure hosting the pumping unit of a reservoir. The dynamic response in this type of problems is usually studied under the assumption of a perfectly rigid structure using a sub-structuring procedure (three-step solution) proposed specifically for this hypothesis. Such an approach enables a relatively simple assessment of the importance of some key factors influencing the structural response. In this work, the problem is also solved in a single step using a direct approach in which the structure and surrounding soil are modelled as a coupled system with its actual geometry and flexibility. Results indicate that, quite surprisingly, there are significant differences among prediction using both methods. Furthermore, neglecting the flexibility of the structure leads to a significant underestimation of the spectral accelerations at certain points of the structure