1,721,046 research outputs found
Pile design in seismic areas: Small or large diameter?
No full textThis work investigates the role of pile diameter in resisting seismic actions, with reference to two example subsoils, namely a dry sand and a fully saturated NC clay. After a ground response analysis in free-field conditions for different values of peak rock acceleration, mobilized soil stiffness and surface acceleration are used as ingredients for assessing the kinematic and inertial moment in a concrete pile. An optimum pile diameter is identified as the one that, while guaranteeing safety, corresponds to the minimum cost. It is also proven that, with a constant value of reinforcement area and length, increasing pile diameter (i.e. increasing safety factor and cost) leads rapidly to failure. Likewise, if pile reinforcement is designed only for inertial action, increasing pile diameter is severely detrimental
Kinematic bending of piles in made ground
No full textThis work explores earthquake-induced kinematic bending in the so far unresolved case of a pile embedded in a two-layer soil with a thin surface layer. The problem is treated analytically by means of a generalized Winkler model which additionally considers the effect of boundary conditions at the pile-head over earlier contributions on the subject. Novel analytical closed-form expressions of the kinematic bending moment at the pile-head and at the interface between the two soil layers are provided for both fixed- and free-head piles. The analytical solutions are validated through a rigorous Finite Element model, which proves a remarkable accuracy in static regime. While for interface bending past literature indications for the dynamic coefficient make the proposed formula accurate for both shallow and deep interface, a novel dynamic interaction factor, describing dynamic effects for pile head bending, is introduced. A numerical example provides guidance on application of the formulae in real design scenarios
Design of Axially-loaded Piles: Experimental evidence from 400 field tests
No full textThis work is aimed at furnishing an experimental support to the design of axially-loaded piles, taking advantage of an extensive database of pile load tests carried out in different sites nearby Napoli, in South Italy. Experimental data consist of nearly 400 full-scale pile load tests, some of them reaching large values of settlement. Different construction methods, including Non-Displacement, CFA and Displacement piles, have been used. The main results of the work consist in furnishing experimentally-derived rules and indications for pile design. With regards to failure loads, mobilization curves relating properly normalized values of load and settlement are proposed as function of the installation technique; indications on the bearing capacity of piles as function of geometry and technology are also provided. Initial stiffness of piles is investigated, identifying a rule of thumb for a rapid assessment, function solely of pile diameter and valid regardless of length and specific properties of pile and soil material
Some aspects of the design of pile foundations under seismic motion
No full textThe design of piles under seismic loads is conventionally carried out with reference to the inertial forces arising from structural vibrations and, hence, neglecting kinematic interaction between pile and soil. Even if in the last years several research efforts gave particular attention to kinematic effects, they focused on bending moments at the interface between two soil layers with different stiffness, while few contributions investigated kinematic effects at pile head. The paper presents the results (both in the frequency and time domain) of extensive parametric studies, leading to a simplified formula for predicting kinematic bending moments at pile head. The paper gives some indications about their relative importance with respect to the inertial ones and provides simply rules to combine inertial and kinematic maximum effects taking into account their phase lag
An analytical solution for the filtering effect of piles in two-layer soil
No full textThe aim of this work is to investigate the kinematic response of a floating pile (either free- or fixed-head) embedded in a two-layer soil subjected to upward-propagating seismic waves. Closed form analytical solutions are provided for the kinematic interaction factors, based on a Beam-on-Dynamic-Winkler-foundation (BDWF) model properly adjusted for the problem at hand. For the fixed-head pile case, a simplified solution to assess the pile-to-soil acceleration ratio is provided adopting the concept of average soil motion over an effective pile length. The proposed solutions compare well with rigorous elastodynamic Finite-Element analysis. Insight is given into the interpretation of the mechanisms regulating the reduction of design spectra as function of structural period. Finally, as an outcome of a wide parametric study, ready-to-use formulae are proposed for a rapid assessment of the pile-induced spectral reduction
Substructure Method Revisited for Analyzing the Dynamic Interaction of Structures with Embedded Massive Foundations
No full textThis paper proposes a new simple approach for assessing dynamic soil-structure interaction effects on structures supported by embedded massive foundations. The classical substructure method was revisited by proposing an exact decomposition approach which allows performing the inertial interaction analysis of the superstructure without modeling foundation and soil, which are replaced by properly defined impedances. The proposed approach requires redefinition of simplified formulas for both the dynamic stiffnesses and the kinematic interaction factors, which are referred to the top of the massive foundation. Accurate expressions for the complex impedances were derived based on rigorous finite-element results. The same formulas were used to calibrate a four-spring model for the analysis of the kinematic interaction problem, resulting in different expressions for the kinematic interaction factors depending on the adopted assumptions. The proposed approach, in conjunction with the novel formulas for impedances and kinematic factors, was applied to the case of bridge piers on caisson foundations, and the results were more accurate than those of the existing simplified procedures
Some remarks about Eurocode and Italian Code about piled foundations in seismic area
No full textIn 2008 a new Building Code (Norme Tecniche per le Costruzioni, D.M. 14/01/2008) was introduced in Italy following the in-troduction of Eurocodes 7 (part 1) and 8 (part 5). Apart from some changes due to the need of adapting the content of the Eurocodes to local practice, the main structure of the latter was held.
In the paper some comments are reported reference to the design of piled foundations in seismic areas. Some specific topics are developed, with particular reference to kinematic and inertial interaction, with the aim of pointing out questions which may be worthy of discussion in light of a possible re-examination and updating of Codes
Momento cinematico alla testa di un palo in terreno a rigidezza variabile con la profondità
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