1,721,021 research outputs found
Discussion of "kinematic framework for evaluating seismic earth pressures on retaining walls" by Scott J. Brandenberg, George Mylonakis, and Jonathan P. Stewart
Get PDFKinematic bending of fixed-head piles in nonhomogeneous soil
No full textAbstractKinematic bending of elastic single fixed-head piles in continuously inhomogeneous soil is explored in both static and dynamic regime. A generalized parabolic function is employed to describe the variable shear modulus in the inhomogeneous stratum, which can simulate both cohesive and cohesionless soil deposits. The problem is treated numerically by means of rigorous elastodynamic finite-element analyses and simplified beam-on-dynamic-Winkler-foundation (BDWF) formulations. A novel expression is proposed for the active length of a pile in inhomogeneous soil, by means of kinematic interaction considerations. This allows an alternative interpretation of kinematic soil-pile interaction along an effective depth, contrary to existing definitions in which soil response is evaluated at a specific location. Following this interpretation, a design formula for kinematic pile-head moments is derived for both static and dynamic loading. A new dimensionless parameter is identified to govern dynamic pile bending, which allows a straightforward assessment of frequency effects in pile design
Piles-induced filtering effect on the Foundation Input Motion
No full textThe inertial interaction analysis of a structure founded on piles is conventionally performed by imposing that the Foundation Input Motion is merely that of the free field, thus neglecting the kinematic interaction between piles and soil generated by the passage of seismic waves. This would lead to unnecessary overconservatism in the design, as there is evidence that the free-field motion may be thoroughly filtered out by piles (generally reduced), especially in the case of soft soils, where piles are recurrently required to carry out the total load transmitted by the superstructure and/or to reduce foundation settlements. Results provided from analytical and numerical tools elucidate the crucial aspects controlling the mechanism of filtering effect. Reduced design spectra are also suggested to account for the beneficial effect coming from the piles when the inertial interaction analysis of the superstructure is being performed
Axial kinematic response of end-bearing piles to P waves
Get PDFKinematic pile-soil interaction under vertically impinging seismic P waves is revisited through a novel continuum elastodynamic solution of the Tajimi type. The proposed model simulates the steady-state kinematic response of a cylindrical end-bearing pile embedded in a homogeneous viscoelastic soil stratum over a rigid base, subjected to vertically propagating harmonic compressional waves. Closed-form solutions are obtained for the following: (i) the displacement field in the soil and along the pile; (ii) the kinematic Winkler moduli (i.e., distributed springs and dashpots) along the pile; (iii) equivalent, depth-independent, Winkler moduli to match the motion at the pile head. The solution for displacements is expressed in terms of dimensionless transfer functions relating the motion of the pile head to the free-field surface motion and the rock motion. It is shown that (i) a pile foundation may significantly alter (possibly amplify) the vertical seismic excitation transmitted to the base of a structure and (ii) Winkler moduli pertaining to kinematic loading differ from those for inertial loading. Simple approximate expressions for kinematic Winkler moduli are derived for use in applications. © 2013 John Wiley & Sons, Ltd
A method for designing the longitudinal spacing of slope-stabilising shafts
No full textThe work at hand deals with the design of the longitudinal spacing among rows of closely spaced large-diameter shafts used to stabilise a precarious slope. The problem under consideration is idealised through a conceptual framework where an unstable mass of an infinitely long slope pushes a stable portion of soil adjacent to shafts, leading to failure along a slip surface passing through the upper end of the reinforcement elements. By exploiting the upper bound theorem of plastic collapse, a closed-form solution is derived for the load required for the failure of the stable mass as a function of geometrical and mechanical parameters of the slope and the soil. Results are validated through physical model tests by means of geotechnical centrifuge. Given the satisfactory agreement between analytical and experimental results, the model is extended to evaluate the safety conditions of the reinforced slope
An Exponential Matrix Method for the Buckling Analysis of Underground Pipelines Subjected to Landslide Loads
No full textAbstractDue to their dimensions, long pipelines often cross areas that are highly susceptible to landslides. In Italy, this problem requires special attention, as many slow-moving landslides interact with buried pipelines. The paper analyzes such interaction problem with particular reference to buckling analysis, tackling the solution of the governing equations by an exponential matrix method. In the paper the basic equation, its computational aspects and numerical analysis options are outlined. Representative results of the proposed methodology and potential applications on buckling analysis of buried pipes are presented
Relevance of Dynamic Soil-Foundation-Structure Interaction Effects for Pile Supported Buildings
No full textThe paper examines the problem of the soil-structure interaction for buildings founded on piles throughout the comparative
6 analyses between the seismic demand in compliant base and fixed base models. The aim of the work is to introduce a simple approach
7 for evaluating the effects of soil-foundationstructure interaction (SFSI) for buildings founded on piles and, hence, to quantify the relevance
8 of SFSI effects for this kind of structure. Inertial interaction analyses are carried out by idealizing the complete system as a linear SDOF on a
9 deformable base represented by frequency dependent springs and dashpots. An application of the proposed methodology to a case study of a
10 nine-story building resting on two well-studied subsoils, a deep clay layer from Piana del Fucino (Italy) and a pyroclastic deposit from Napoli,
11 is presented and discussed. Reference is made to a complete seismic risk analysis in which the input signals are grouped into strips according
12 to the conditional spectrum method. As a further objective, the effect of wall infills on the seismic demand in the reference buildings is
13 investigated. The results show that for pyroclastic deposit the seismic demand in the compliant model is comparable with that for the fixed
14 base. By contrast, SFSI leads to a relevant reduction of the seismic demand for buildings on the clay profile. It is concluded that, contrary to
15 the common belief, SFSI may also be relevant for tall buildings if they rest on soft soil
Simple Approach to Static and Seismic Design of Piled Rafts
Get PDFCurrent design of piled rafts often neglects a number of aspects well known in
scientific literature, sometimes leading to increased costs without appreciable increase in
performance. This work makes an attempt to partially fill this lack between State of Art and State
of Practice; to this end, the paper briefly recalls available simple design methods regarding both
geotechnical and seismic issues and proposes a novel simple procedure to estimate the loadsettlement
curve of a piled raft as well as the load sharing between piles and raft for vertical
centered loads. The method has been validated through comparison with numerical and
experimental data and applied to a case history; it will be shown that the proposed procedure,
despite its simplicity, is able to account for the non-linearity in the soil behavior, the latter being
responsible of progressive variation of the load sharing with increasing applied top load. Further,
regarding seismic issues, simplified formulae from past works are recalled and discussed
Modifica del segnale sismico alla base di una struttura prodotta dalla presenza dei pali
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